Effect of Tin Content and Heat Treatment on the Efficiency of Galvalum III Commercial Aluminium Anodes

Effect of Tin Content and Heat Treatment on the Efficiency of Galvalum III Commercial Aluminium Anodes

Technical Articles

Amr E. Saleh, Corrosion Engineer, Al-Masaood Oil & Gas Company, ADNOC Offshore, Abu Dhabi, UAE, Galal M Attia and Hany Ammar, Metallurgical and Materials engineering Dept., Faculty of Petroleum and Mining Engineering, Suez University, Suez, Egypt

Aluminum Galvalum III anodes are widely used in the Oil and Gas industry to protect carbon steel structures such as water tanks, vessels, pipelines and other onshore and offshore structures. These anodes need to be replaced after consumption, requiring the equipment to be taken out of service (shut down) to replace them, at high cost and time. Pure aluminum cannot function as
a galvanic anode as the formation of stable oxide films causes the electrochemical potential to shift to a very noble potential
(passivation).

However, the addition of activator elements can disrupt the oxide film formation and maintain the active electrochemical potential for the aluminum alloy. Therefore, by proper alloying, aluminum anodes can be used to supply cathodic protection current. [1]It has been reported that, alloying, grain refining, fabrication and anode material processing procedures, strongly affect the efficiency of sacrificial anodes. [2]
Research was carried out to investigate the effect of tin (Sn) addition at different concentrations to Galvalum III anodes, and the effect of heat treatment on aluminum anode efficiency.

(The efficiency of a galvanic anode depends on the alloy of the anode and the environment in which it is installed. The consumption of any metal is directly proportional to the amount of current discharged from its surface. For galvanic anodes, part of this current discharge is due to the cathodic protection current provided to the structure and part is caused by local corrosion cells on its surface).
Anode efficiency is defined as the ratio of metal consumed producing useful cathodic protection current to the total metal consumed. The efficiency of Galvalum III anodes, is around
85 %. [3].

This article reports the results of a study of four aluminum anode specimens (galvalium III) produced with different tin (Sn) concentrations (0%, 0.01%, 0.05% and 0.1%). Heat treatment was carried out by heating to a homogenisation temberature of 5100C for 5 hours, and after this, some samples were annealed by slow cooling in the furnace and other samples were quenched by rapid cooling to room temperature in a water bath.

Experimental procedures

Material and sample preparation
Aluminum Galvalum III anodes which had already been used for the cathodic protection of water tanks at a gas processing plant in Egypt, were used in the study and their composition is given in Table 1. Approximately, 1.2kg of the anode material was cut into small pieces for melting and preparation of the alloys used in the present work.

Table 1: Chemical composition of (Galvalum III) anode (wt.%)

Four alloy compositions were prepared by melting this anode material using a graphite crucible in an electrical resistance furnace. The alloying element (commercially pure tin) was added after melting of anode material. The nominal chemical composition of all produced alloys is given in Table 2. It should be noted that, during the melting process, an average of 1.5% of the input material is added to compensate for the losses due to oxidation and evaporation of alloying elements.

Table 2: Concentrations of each heat

Samples were cast in an electric furnace at 5000C for 1 hour to increase the fluidity of aluminum alloy inside the mold. Each mold was divided to three sections, one for ‘as cast’ condition, and two sections for different heat treatments, homogenising and annealing.
Chemical composition analysis for all samples was verified by X-Ray Fluorescence (XRF). [7]

Heat treatment

The aim of the homogenising heat treatment process was to redistribute the alloying element evenly through the specimens. The homogenising temperature was 510°C, which was selected to be just under aluminum melting point (670 °C) to help the diffusion process. Once the whole part reached the homogenising temperature it was allowed to cool rapidly by water quenching, resulting in a homogenous super saturated alloy.
For the annealing heat treatment process, once the whole part reached the homogenising temperature it was allowed to cool slowly inside the furnace, resulting in a part that had a uniform internal structure.

Electrochemical testing

Electrochemical testing was carried out for all specimens (different concentrations and different heat treatment) to assess the most important characteristics for galvanic anodes. The testing was carried out according to NACE Standard TM0190-2012 Impressed Current Laboratory Testing of Aluminum and Zinc Alloy Anodes. [4]
This standard test method describes a laboratory procedure for determining the potential and current capacity characteristics of aluminum alloy anodes used for cathodic protection. It provides a mean for screening various batches of anodes to determine performance consistency on a regular basis from lot to lot.
A 16-cm3 sample of the aluminum alloy anode material was immersed
in synthetic seawater, at ambient temperature for two weeks (336 h).
See ASTM D1141-98 (Reapproved 2013) [5]. Potentials were measured periodically and current capacity determined. Anode potentials were measured with a standard Ag/AgCl reference electrode.

Anode current capacity was determined by the mass loss method. The total current passing through the system was measured by multi-meter.
Anode mass loss was determined at the end of the two-week test when the samples were removed, cleaned, and weighed.
Mass loss current capacities were determined from knowledge of the total charge passed through the system and the mass loss of the anode samples.

Calculation of Efficiency

Mass Loss Method: Anode current capacity was calculated for each sample as shown in the equation below

 

E: Current capacity (amperes. hours/gram)
I: current (amperes) averaged over 14 days
Wi: initial sample weight (grams)
Wf: final sample weight (grams)
Polarization Resistance testing (Tafel slope) was carried out for 1C, 4C, 4A and 4Q (see definition below) according to ASTM G59-97 Standard Test Method for Conducting Potentio-dynamic Polarization Resistance Measurements. [6]
The specimens tested were
1C: Galvalum III + 0 % Sn (As cast condition)
4C: Galvalum III + 0.1 % Sn (As cast condition)
4A: Galvalum III + 0.1 % Sn (Annealed condition)
4Q: Galvalum III + 0.1 % Sn (Quenched condition)
These specimens were selected for this test to differentiate corrosion behaviour between 1C without tin, and 4C with 0.1% tin addition. 4C, 4A and 4Q were selected to assess the effect of heat treatment on corrosion rate.

Microstructure analysis (SEM and EDX)

Specimens (detailed below) were mounted, ground, polished and etched (using HF 40%, HNO370%, HCL 38% and distilled water) to reveal the original microstructures of the alloys and observe the distribution of phases and alloying elements.
1C: Galvalum III + 0 % Sn (As cast condition)
1A: Galvalum III + 0 % Sn (Annealed condition)
1Q: Galvalum III + 0 % Sn (Quenched condition)
4C: Galvalum III + 0.1 % Sn (As cast condition)
4A: Galvalum III + 0.1 % Sn (Annealed condition)
4Q: Galvalum III + 0.1 % Sn (Quenched condition)
Observations were made visually and by SEM.
Specimens 1C, 4C, 4A and 4Q were also analysed using EDX to identify the phases which were formed.

Results and discussion

Current capacity results
As cast condition
The electrochemical test results show that adding tin enhances the current capacity of Galvalum III anodes as shown in Table 3
The increase in current capacity may be attributed to the effect of tin addition as a depassivating element in neutral sea water. The presence of tin as alloying element will reduce the ionic resistance of the oxide film on the investigated alloys.

There are different views on the role of tin, but it is generally accepted that the creation of additional cation vacancies by including tin as quadrivalent Sn4+ is responsible for improving the cathodic protection properties. It was clearly shown that the decrease in surface free energy with the addition of tin to Galvalum III anode alloy (Al + 5% Zn) is the principal reason for the increase in the cathodic protection properties of these cast alloys.

Table 3: Current capacity for as cast condition specimens

Annealed condition

The electrochemical test results showed that the 2A (Al-5%Zn – 0.01 % Sn) sample had the highest current capacity of all the annealed samples, as shown in Table 4. It is clear that the presence of 0.01 % tin gives the highest current capacity of all the measured annealed specimens.

Table 4: Current capacity for annealed condition specimens

Quenched condition

The electrochemical test results also showed that the 2Q (Al-5%Zn – 0.01 % Sn) sample had the highest current capacity of the four quenched samples as shown Table 5. Also, the alloy 2Q, with 0.01% tin addition hds the highest current capacity of all the investigated alloys.
The 3Q current capacity was low so the electrochemical test was repeated for this specimen, and the result was also relatively low in the second trial (1850 A.H/Kg).

Table 5: Current capacity for Quenched condition specimens

Effect of no tin addition at different heat treatments

Table 6 shows the results of the current capacity measurements for zero percent tin alloys, in the as cast, annealed, and homogenised conditions (viz alloys 1C, 1A and 1Q respectively). It is obvious that, heat treatments in general improve the distribution of alloying elements, the distribution of second phase precipitates, and also eliminate the casting defects such as macro and micro segregation. It is clear that quenched condition (1Q) gives the highest current capacity.

Table 6: Current capacity for original specimens

Effect of 0.01% in addition at different heat treatment

Table 7 summarises the effect of 0.01% tin addition on the current capacity. The current capacity increased by about 15% after annealing and by about 24 % after homogenising heat treatment, relative to the as cast conditions. Such an increase in in current capacity could be attributed to the effect of heat treatment which eliminate the segregation and inhomogeneity in the distribution of alloying elements in the as cast condition, in addition to the increase in solid solubility of alloying elements after quenching from solution treatment temperature.

Table 7: Current capacity for 0.01% tin specimens

Effect of 0.05% tin addition at different heat treatment

Table 8 shows the results of the current capacity measurements for 0.05% tin alloys in as cast (3C), in annealed (3A) and in as quenched conditions (3Q). There is no drastic change in the measured values, in contrast to the results obtained from the current capacity measurements for the alloy groups (1) and (2) where the current capacity increased by heat treatment. The explanation for such behavior was not found in the available literature. The results of repeated electrochemical measurements for this alloy group gave approximately the same results.

Table 8: Current capacity for 0.05% tin specimens

Effect of 0.1% tin addition at different heat treatment

Table 9 summarizes the effects of 0.1% tin addition on the value of current capacity. The measured values are 2343 for as cast (4C), 2121 for as annealed (4A) and 2455 A.H/Kg for as Quenched (4Q). Again there is no drastic change in the measured values, in contrast to the results obtained from the current capacity measurements for the alloy group (1) and (2) where the current capacity increased by heat treatment. It must be notice that, quenched condition (4Q) gives relatively higher current capacity than as cast and annealed conditions.

Table 9: Current capacity for 0.1% tin specimens

Current capacities of all specimens compared with Galvalum III

Table 10 shows the electrochemical test results for all specimens. It is clear that quenched alloy (2Q), which contains 0.01% tin addition, has the highest measured value of current capacity, with about 22 % increase over that measured for Galvalum III. In general quenching heat treatment drastically improves the current capacity of investigated alloys

Table 10: Current capacity for All Specimens compared to Galvalum III Current Capacity 2232 A.hr/Kg

Mean value of closed circuit potential of all specimens

Table 11 shows the mean value of the closed circuit potential for all specimens connected to carbon steel coupons, and as shown they all achieved the cathodic protection criteria according to NACE SP0169, which states that protection potential should be more negative than -760 mV regarding to Ag/AgCl reference electrode.
The highest negative potential mean value was achieved with specimen 4Q, with a value of – 1115 mV.

Table 11: Mean measured closed circuit potential for All Specimens

Microstructure analyses (SEM and EDX)

As cast condition microstructure Analysis:

Figures 1 and 2 represent the microstructures of Galvalum III without tin addition (1C as cast condition) and of Galvalum III with 0.1 % tin addition (4C as cast condition) respectively. The microstructures developed after casting of both alloys are distinctly different in grain morphology, distribution, and nature of second phase precipitates.

The microstructure morphology of Galvalum III alloy 1C appears to be cellular-dendritic structure and that of 4C appears to be dendritic. The difference in microstructure morphology may be due to the presence of 0.1% tin in alloy 4C, which may affect the surface properties of solidified aluminum solid solution primary phase. Both alloys (1C and 4C) are composed from aluminum – solid-solution matrix and second-phase dispersed precipitates. Table 1 gives the chemical composition of Galvalum III alloy. Iron and silicon are the most common impurities found in aluminum. The solubility of iron and silicon in the solid state are very low and therefore, most of the iron and silicon which are present in Galvalum III appear as an intermetallic second phase in combination with aluminum and often other elements. The presence of indium in both alloys, which is not soluble in aluminum, may be responsible for the presence of the white colored second phase precipitates at inter dendritic spaces as it seen in Figures 1 and 2, while the presence of tin in alloy 4C (figure 2) could be responsible for the presence of other precipitates which are dispersed inside grains and between the dendritic arm spacing.

The precipitates morphology appears to be spheroidal shaped particles, rode like particles and agglomerated spheroidal particles.

The results of energy dispersive X-Ray (EDX) phase analysis for the as cast structure of Galvalum III alloys 1C and galvalum III + 0.1 % tin alloy 4C are given in Figures 3 and 4 respectively.

The matrix point analysis of points 1 and 4 in alloy 1C figure 3 and points 1 and 3 in alloy 4C figure 4 showed identical chemical composition of aluminum zinc solid solution for both alloys. It clear that all tin additions in alloy 4C are presented only in the precipitated particles inside primary aluminum solid solution, and at the grain boundaries of the primary phase. The EDX analysis of the precipitates at points 2 and 3 which are present in microstructure of alloy 1C (the as cast structure of Galvalum III) in Figure 3 are not completely identical.

The precipitates present at point 3 may be considered as agglomeration of insoluble iron and silicon elements combined with matrix alloying elements of aluminum and zinc forming intermetallic compounds, while the precipitates present at point 2 have spheroidal shape, which is not similar to point 3 in shape and composition.

 

The results of energy dispersive X-Ray (EDX) phase analysis for the as cast structure of Galvalum III alloys 1C and galvalum III + 0.1 % tin alloy 4C are given in Figures 3 and 4 respectively.

The matrix point analysis of points 1 and 4 in alloy 1C figure 3 and points 1 and 3 in alloy 4C figure 4 showed identical chemical composition of aluminum zinc solid solution for both alloys. It clear that all tin additions in alloy 4C are presented only in the precipitated particles inside primary aluminum solid solution, and at the grain boundaries of the primary phase. The EDX analysis of the precipitates at points 2 and 3 which are present in microstructure of alloy 1C (the as cast structure of Galvalum III) in Figure 3 are not completely identical.

The precipitates present at point 3 may be considered as agglomeration of insoluble iron and silicon elements combined with matrix alloying elements of aluminum and zinc forming intermetallic compounds, while the precipitates present at point 2 have spheroidal shape, which is not similar to point 3 in shape and composition.

Annealed condition microstructure Analysis

Figures 5 and figure 6 represent microstructure of annealed Galvalum III alloy no. 1A and the annealed Galvalum III + 0.1% Tin alloy no. 4A respectively. Annealing process for both alloys was carried out at 510 οC for 5 hours followed by furnace cooling. The microstructures developed after annealing of both alloys are approximately similar. The microstructure morphology consists mainly from equi-axed grains of primary aluminum solid solution and massive precipitates located inside grains and at grain boundaries.

The high annealing temperature and relatively long annealing time give the driving force for equi-axed grain formation.

Figure 7 represents the energy dispersive X-Ray (EDX) phase analysis of annealed alloy no. 4A. EDX analysis revels that, the matrix phase analysis, point 1, composed from aluminum – zinc solid solution while the second phase precipitates in point 2, 3 and 4 are intermetallic compounds formed as result of interaction between the base metal alloying elements of aluminum and zinc mainly with other segregated insoluble elements of indium, tin, iron and silicon.

Solution treated (Water Quenched) microstructure analysis

When Galvalum III, alloy no.1, and Galvalum III + 0.1 Tin, alloy no. 4, are heated to 510 οC temperature which is selected to be just above the solvus line, only one single phase is thermodynamically stable. After 5 hours holding time at such homogenizing temperature all alloying elements must be dissolved in solid solution. When a solid-solutionized sample is rapidly cooled to room temperature below solvus line two phases are thermodynamically stable (alpha and beta). At room temperature in equilibrium conditions, the solubility of Zn in Al amounts 0.85 at%, and the one of Al in Zn is smaller than 0.5 %.

The rapid cooling process will produce non-equilibrium condition which gives thermodynamically unstable structure. The rapidly cooled microstructures of specimen no. 1Q and 4Q reveal thermodynamically unstable microstructures. The rapidly cooled microstructures of both alloys are composed mainly from super saturated solid solution and fine dispersed precipitates.

The microstructure of Galvalum III after rapid quenching as given in figure 8 (1Q) is clearly different in details comparing to the microstructure of Galvalum III + 0.1% Tin after same treatment as given in figure 9 (4Q). The main difference lies in the shape and distribution as well as the chemical composition of precipitates.

Figure 10 represents the energy dispersive X-Ray (EDX) phase analysis of the as quenched alloy no. 4Q. The EDX analysis revels that, the matrix phase analysis, point 1, composed from aluminum – zinc solid solution while the second phase precipitates in point 2, 3 and 4 are intermetallic compounds formed during rapid cooling as result of interaction between the base metal alloying elements of aluminum and zinc mainly with other segregated insoluble elements of indium, tin, iron and silicon.

The precipitate particle which is present at point 3 contains iron in addition to Silicon and base metal alloying elements Aluminum and Zinc and don’t contain Tin or Indium while the precipitate analysis of point 2 and 4 contain Tin and Indium and don’t contain iron or silicon.

The details mechanism which may explain the reasons for the presence of such different precipitate is not found in available literatures.

Conclusion

The addition of tin increases the activation of Galvalum III (Al-Zn-In) alloy, and the extent of activation increases with increasing tin content. Results confirm that the current capacity and efficiency of aluminum Galvalum III anodes increases by 16 % with the addition of 0.1 % tin without heat treatment.

Homogenisation heat treatment gives higher current capacity and efficiency than ‘as cast’ and annealed (in most investigated alloys).

The highest current capacity is 2729 A.hr/kg and it was achieved after homogenisation treatment of the alloy containing 0.01 % tin. After quenching of the alloy containing 0.01% Sn, the current capacity increased by 23.6 % compared with the ‘as cast’ condition for the same alloy and 22% compared with the as received Galvalum III.

Corrosion rate decreased from 0.21 mm/year in case of Galvalum III without tin addition (cast condition) to 0.15 mm/year in case of Galvalum III with 0.1% tin, which reflects the benefit of tin addition on decreasing self-corrosion of the anode and enhancement of the efficiency.

Corrosion rate of heat treated anodes (annealed and quenched) is decreased significantly from 0.15 mm/year for cast condition to 0.005 mm/year, and 0.003 mm/year for quenched and annealed respectively, reflecting also the benefit of heat treatment in decreasing self-corrosion of anodes and enhancement the efficiency.

The increase in current capacity of heat treated alloys could be attributed to the homogenised distribution of second phase precipitates and the super saturation of aluminum solid solution matrix by the alloying elements, and the beneficial elimination of the internal defects resulting from the casting process like voids and dislocations in the alloy, therefore improving the current capacity of the alloy.

References

[1] NACE International, CP 3- Cathodic protection technologist Course Manual, Houston, TX: NACE International,2008
[2] DNV Recommended Practice RP B401 (2010). Cathodic Protection Design, Det Norske Veritas Industry AS, Hovik 2010.
[3] NACE International, CP 2 – Cathodic Protection Technician. Houston, TX: NACE International, 2012.
[4] NACE International, NACE Standard TM0190-2012 Impressed Current Laboratory Testing of Aluminum and Zinc Alloy Anodes. Houston, TX: NACE International, 2012.
[5] ASTM International, ASTM D1141-98 (Reapproved 2013) Standard Practice for the Preparation of Substitute Ocean Water. West Conshohocken, PA: ASTM International, 2013.
[6] ASTM International G59 (Reapproved 2003) Standard Test Method for conducting potentiodynamic Polarization Resistance Measurements.
[7] Handheld XRF Analyzers MET7000 Series User Manual, Oxford Instruments.
[8] ASM Metal Handbook 2004 ASM International, Vol. 9, Metallography and Microstructure.

Development of Glassflake Coatings for In-Service Protection of Hot Substrates

Development of Glassflake Coatings for In-Service Protection of Hot Substrates

Technical Articles

Rob Allan, Emre Karapinar, Malcolm Morris, Neil Wilds and Sarah Vasey, Sherwin-Williams Protective & Marine Coatings.

Glass Flake Epoxy (GFE) technology has been a main stay of the Oil &Gas (O&G) offshore market for many years, particularly for highly aggressive splash zone areas, despite other technologies for similar end uses having been investigated. This, consequently, resulted in the opportunity of assessing the performance of these materials in real life conditions and enabled coating suppliers to optimize their GFE formulations for wider end uses and longer service life times.

The versatility of glass flake epoxy technology allows it to be used not only for O&G offshore applications but for buried steel in O&G downstream applications, subsea pipelines and equipment, and even for bridges & highways where local authorities – such as Network Rail and Highways Agency in the UK – dictate the use of such a technology due to its superior anti-corrosion properties and longer service life times.

Use of glass flakes in combination with other functional pigments (for example, aluminium) or more advanced epoxy polymers (such as surface tolerant epoxies, epoxy novolacs, amine cured epoxy linings…etc) delivers effective long term protection of water, fuel, and chemical tanks, vessels and pipelines, as well as maintenance and repair of such steelwork whether it’s immersed or atmospheric.

Traditionally, glassflake coatings were based on relatively large particle size glass flake pigments (nominal width 0.4mm). These coatings typically required approx. 500µm to achieve a full film and an overall specification could be in excess of 1mm dry film thickness. However extensive research and development using significantly smaller glass flakes has enabled the production of formulations which could deliver equivalent performance at much lower film thickness, and with a vastly superior aesthetic appearance.

In this respect various tests have been conducted to understand the effect of glass flake pigmentation on the overall performance of epoxy coating systems. It is commonly accepted in the coatings industry that glass flake pigmentation increases barrier properties of the dry film and enhances mechanical properties, making it an ideal choice for immersed and buried steel. Table 1 clearly displays the benefit of using glass flake in a 500 microns thick dry epoxy film, which was loaded with 20% w/w glass flake at an average particle size of 0.4mm.

Benefits of incorporating glass flake in modern coating specifications

The current criteria for selection of coating specifications includes, reduced VOC and elimination of toxic components to comply with ever more stringent environmental legislation; fewer coats to reduce application costs; improved performance to give longer life to first maintenance compared to traditional multi-coat systems; and proven performance with external independent test evidence – NORSOK, Oil Company, Highway, Network Rail, specifications and ISO 12944.

Glass flake pigmentation is a primary weapon in the formulator’s armoury, which can be incorporated in a range of high performance binder systems to produce coatings with the following benefits;

• Very low VOC content.
• User friendly – easily applied over a wide range of specified  film thickness.
• Superior resistance to water ingress.
• Good mechanical properties – adhesion, abrasion resistance,  flexibility.
• Compatible with cathodically protected steel on immersed structures.
• Capable of withstanding a wide range of chemical resistance and high temperature conditions, depending on the binder
system used.

Glass flake

Borosilicate glass (c – glass), with a thickness  of 1 – 7 microns, and various nominal particle width grades, viz,

3.2mm – used for trowelling compounds
0.4mm – used in high build spray applied coating
micronised – used in spray applied coatings – low and high (typical 45 micron) build.

Binder types

The main properties of a coating are dependent upon the resin system employed.  These may be enhanced, or even detracted from, by the pigments and other ingredients included.

Epoxy

The properties of epoxy resins enable them to be formulated into coatings to provide protection over a wide range of specification requirements, including, excellent corrosion protection for subsea, splash zone and atmospheric environments, excellent resistance to cathodic disbondment, toughness and  abrasion resistant.  They have a long track record, and there are no catalyst storage problems.  The disadvantages however are, maximum immersion temperature typically 60C, maximum dry heat resistance typically 120C, chalking/colour retention problems on  atmospheric exposure, and generally poor acid resistance.

Polyester

These consist of isophthalic or bisphenyl polyester resins, cured with organic peroxide catalysts.  They offer improvement in performance over epoxy in terms of mechanical properties and temperature resistance, with maximum immersion temperaturetypically 80C and maximum dry heat resistance typically 140C.   The isophthalic polyesters are more resistant to chalking and offer superior colour retention on atmospheric exposure compared against epoxy. Polyesters can also offer faster curing rates than high solids epoxies, although applicators need to be sufficiently aware of the relatively short pot life, and safety aspects of the catalyst.  In order to minimise potential problems with the relatively short pot life of these products, twin component application equipment is used.

Vinyl Esters

These have the ultimate performance in terms of chemical and temperature resistance, with maximum immersion resistance typically 120C and maximum dry heat resistance typically 220C.  (in sea water immersed structures, the cooling effect of the water  allows application onto substrates operating at much higher temperature, e.g. pipelines with an internal temperature of 180C).

Specification philosophy – film thickness

Traditionally glass flake coatings have needed to be specified at dry film thicknesses in the order of 500 – 1000 microns, due to constraints caused by their application characteristics.  These thicknesses are required for performance under some, but not all, environments.  For atmospheric anticorrosive protection of structural steel, for example, such thicknesses can be over-engineered, and uneconomical.  A range of glass flake coatings which can be applied at different film thickness, ie to give the required protection without the need to apply more paint than is necessary is now available.  Extensive laboratory testing, and track record in the field, have proved the validity of such specifications which can be devised in conjunction with the ISO 12944 standard, plus testing to NORSOK or oil company performance testing.

Formulation Aspects

Given the available raw materials, how can they be combined to achieve the required performance?

The theory of glass flake pigment particles aligning within an applied paint film to give an extended diffusion pathway through the film is well documented, as is the reinforcing nature of the lamellar pigment. There are, however possibilities where particles of glass can end up misaligned in the film and if these particles have a length greater than the film thickness, they can create a potential fault within the coating leading to accelerated permeation through the film.  This effect can lead to the necessity of applying very thick films or multi coat application to compensate for these defects, and pass high voltage pinhole detection testing.

Micronised glass “Controversy”

The incorporation of micronised glass flake into high build epoxy coatings has been a cause for debate.   It is accepted that the lower aspect ratio of the micronised flake does not give the same potential diffusion pathway as the larger flake sizes, and indeed a straight A versus B comparison of 0.4 mm flake against micronised flake at constant loading in the same resin system will show that the micronised flake pigmented system has higher rates of water absorption and vapour permeability compared with the larger flake (tables 1 and 2).

Research has shown however that in epoxy systems, combination of the micronised flake with other lamellar fillers and zinc phosphate, gives a synergistic effect which offers similar permeability characteristics to large flake systems (tables  1 and 2),  coupled with a closed, defect free film which offers, ease of application using smaller spray tips than standard glass flakes allow, film thickness variable from 200 microns to 1000 microns depending on end requirements, retention of mechanical properties, abrasion resistance, cathodic disbondment, coupled with outstanding corrosion resistance (tables  3 – 5).

Glass flake levels

There are no official standards governing glass flake levels compared with the criteria laid down for  zinc phosphate for example in BS 5493.  The factors to be considered include:

1. Steric effects of glass flake – overloading will cause physical interference between flakes which may in turn give rise to film defects.
2. Viscosity increase – Higher levels of glass flake cause increased viscosity which will eventually affect application characteristics,

and that actual test data shows that more is not necessarily better.   In short, there is no such thing as a universal optimum for glass flake loading.  This is a case of “horses for courses” with the type of glass flake and its level of incorporation having to be thoroughly researched with the particular end use in mind. An epoxy based formulation intended for anticorrosive protection of structural or immersed steelwork will be quite different in terms of glass type and content to a vinyl ester for chemical resistant vessel linings.

Primer requirements

In the case of glassflake epoxy materials formulated on a blend of glassflake and zinc phosphate, a separate primer coat is not necessary from the viewpoint of anticorrosive performance, although in practice they are often used in conjunction with a proprietary epoxy blast primer or epoxy zinc phosphate primer.

In the case of polyester or vinyl ester specifications, a vinyl ester based holding primer is available to maintain the integrity of grit blasted substrates prior to application of the glassflake coating.  For non-immersed systems it is permissible to apply specially formulated glassflake polyester over epoxy primer.  Work is ongoing to confirm whether epoxy primers may be used under immersed polyester/vinyl ester systems.  However until results are confirmed, the vinyl ester primer should be used under any immersion system.

There is a synergistic effect of incorporation of zinc phosphate with micronised glass flake with gives similar results to larger flakes.

Increasing glass flake size reduces permeability of vinyl ester systems. In this case, zinc phosphate cannot be incorporated due to its effects on the curing mechanism of the resin system.

Abrasion resistance is improved with increasing 0.4 mm glass content up to 20%, however further increases actually cause an increase in loss of coating.

Coating
Applied at
500 microns dft

Water Vapour Permeability
g/m²/day
ASTM E96

Water Absorption %
to Equilibrium
ASTM 570-81

Control. 
No Glassflake or

Zinc Phosphate

5.9

6.54

Epoxy, 0.4 m
Glassflake

1.05

1.18

Epoxy, Micronised Glassflake. No Zinc Phosphate

3.5

2.8

Epoxy Micronised
Glassflake & Zinc Phosphate

1.26

1.21

Table 2 – Water Absorption/Permeability Vinyl Ester.

Coating
Applied at
500 microns dft

Water Vapour Permeability
g/m²/day
ASTM E96

Water Absorption %
to Equilibrium
ASTM 570-81

Control. 
Unpigmented Vinyl Ester

8.24

7.3

Vinyl Ester Micronised Glass

2.24

3.56

Vinyl Ester
0.4 mm Glass

1.04

0.25

Vinyl Ester
3.2 mm Glass

0.59

0.15

Table 3 – Abrasion Resistance Comparison – Taber Abrador
Weight Loss Per 1000 Revolutions, 1000 gm Load H22 Wheel

Resin
Type

Glass
Type

Glass
Loading

Wt Loss

Epoxy at 500 microns dft

  

0%

0.703g
 

0.4 mm

5%

0.692g
   

10%

0.499g
   

15%

0.463g
   

20%

0.120g
   

25%

0.806g

Epoxy at 500 microns dft

  

0%

0.612 g
 

Micronised & Zn Phos

10%

0.403g
   

25%

0.392g

Vinyl Ester at 500 microns dft

  

0%

0.725 g
 

0.4 mm

5%

0.621g
   

10%

0.306 g
   

20%

0.300g
   

25%

0.378g

Increasing glass flake levels improve cathodic disabondment performance (CD).  However zinc phosphate content would appear to be a major contributory factor in CD of epoxy glass flakes.

Micronised glass flake does not perform well in polyester (or vinyl ester) resin systems on CD testing, and a glass flake loading of approx 20% of 0.4 mm flake is necessary for acceptable performance.  Dft is also a crucial factor in the performance of these systems.

Accelerated laboratory tests further confirm the superior performance of micronized glass flake epoxies (MGFE) over non-glass flake or ceramic filled epoxies. Figure 1 highlights this superior performance by carrying out salt spray (ISO 9227) tests for up to 6,000 hours, which is well over typical test durations in O&G, Power, Mining and Minerals and other industrial end uses.

Figure 1 – Micronised glass flakes epoxy versus ceramic filled epoxy.
micronised glass flake

Micronised Glassflake Epoxy @ 200µm                       Ceramic filled epoxy

Table 4 – Cathodic Disbondment Testing – Epoxy Formulations
28 Days at -1.50 Volts wrt Silver/Silver Chloride Electrode

Resin
Type

Glass
Type

Glass Loading
% Wt on Pigments

Temp

mm Disbondment

500 µm Epoxy

0.4 mm

0

23°C

28mm
   

5

  

25mm
   

10

  

16mm
   

15

  

17mm
   

20

  

13mm
   

25

  

7mm

1000 µm Epoxy

  

0

  

14mm
   

5

  

10mm
   

15

  

5mm
   

20

  

4mm
   

25

  

5mm

400 µm Epoxy

Micronised & Zn Phos

0

  

10mm
   

10

  

7mm
   

25

  

6mm

800 µm Epoxy

  

0

  

4mm
   

10

  

1-2mm
   

25

  

1mm

Table 5 – Cathodic Disbondment Testing – Vinyl Ester/Polyester
28 Days at -1.50 Volts wrt Silver/Silver Chloride Electrode

Resin Type/
Glass Type

Glass
Loading

Temp

mm Disbondment

500 µm Micronised Polyester

25%

23°C

Film degraded at holiday Polyester

500 µm 0.4 m Polyester

10%

23°C

20 mm    Some degredation

500 µm 0.4 m Polyester

20%

23°C

4-5 mm

1000 µm 0.4 mm Polyester

20%

23°C

0 mm

500 µm 0.4 mm Vinyl Ester

20%

23°C

2 mm

1000 µm 0.4 mm Vinyl Ester

20%

23°C

0 mm

1000 µm 0.4 mm Vinyl Ester

20%

60°C

0.5 – 1.0 mm

Table 6 – Hot CD Testing – 28 Days at -1.50 Volts wrt
Silver/Silver Chloride Electrode

Internal Wall
Temp

1mm dft

2mm dft

3mm dft

100°C

4mm

9mm

  

120°C

5mm

5mm

  

140°C

  

5mm

4mm

160°C

    

5mm

The micronized glass flake epoxy technology has delivered excellent performance over a 25 year track record. Relying on experiences gained from this success, the technology has been extended for end uses where properties such as surface tolerance, high film build in one layer by brush application, ability to go over damp surfaces, suitability to be applied over hot substrates are amongst the key requirements sought by asset owners, engineering contractors and paint applicators.  This makes the micronized GFE technology, which is capable of building up to 400µm in a single brush coat and able to go over hot substrates up to 120C, ideal for challenging maintenance and repair scenarios typically observed in O&G offshore and other similar heavy industries. It allows for maintenance painting on hot process steel (up to 120C) without the need to take the asset or process unit out of service, saving time and cost for the asset operator.

A proprietary product, which was formulated on the basis of micronised glass flake epoxy technology, has been evaluated to determine the effect of prolonged high temperatures on it after being applied to Sa2.5 blasted, and St2 and St3 hand prepared steel, at high temperatures (110C and 120C) and then stored at 150C, in comparison to when applied and kept at ambient temperature.   In summary, the testing on heat aged samples showed that there was very little change on cross cut adhesion (ASTM D3359) over 1-6 months (see Figures 2 and 3); no or other deterioration of the film was observed after 6 months heat ageing, and Thermogravimetric Analysis (TGA) showed no weight loss in the samples test up to 6 months in test area i.e. 150C (Figure 4).

These results show that the formula is thermally stable at 150C and has good adhesion to a range of substrates with good film integrity.   

 

Conclusions

 

Coatings specifications based on micronised glass flake epoxy technology have been developed which will allow paint application onto hand prepared steel at elevated substrate temperatures up to 120C, and with a maximum operating temperature of 150 C,  without the necessity of shutting down high temperature industrial processes. Such coatings will allow straightforward maintenance solutions under challenging conditions, typically found in O&G offshore and other Energy operations, where extensive surface preparation is not possible. Other differentiated value propositions of the technology deliver time and cost savings through up to 400µm dry film thickness build in a single brush coat, suitability for application with airless spray as well as brush and roller and aesthetically pleasing appearance in comparison to conventional epoxy glass flake epoxies. All of these operational and application benefits are complemented with an outstanding long term anti-corrosion performance through micronised glass flake epoxy technology.

 

Technical Article: Applying Lean Manufacturing to Corrosion Protection Processes

Technical Article: Applying Lean Manufacturing to Corrosion Protection Processes

Technical Articles

Applying Lean Manufacturing to Corrosion Protection Processes
Lucia Fullalove – MSc, BSc, FICorr – Highways England – Lean Practitioner
Dr Algan Tezel – PhD Lecturer – Huddersfield University

Defects and failure of assets during service may often be traced back to corrosion deterioration, thus corrosion monitoring and corrosion protection become a vital and integral part of asset construction and maintenance. Corrosion protection is valuable in preventing unplanned production stoppages or safety risks as result of asset performance reduction.

Assets such as bridges, platforms and transportation equipment require corrosion protection or monitoring as an integral part of the maintenance programme throughout the life of the asset. Several corrosion protection and monitoring techniques have been developed and these are widely used in the industry with the objective of slowing down the inevitable corrosion degradation process. The techniques selected will vary depending on the material to be protected and the exposure environment. It is important to note that application and maintenance of corrosion protection such as painting, cathodic protection are time consuming, costly and have safety implications.

The construction industry has adopted Lean thinking in order to improve the effectiveness and efficiency of construction work. This new working practice requires the use of specialist tools and techniques.  Lean training is required to be undertaken so that Lean can be deployed throughout the supply chain. It is therefore essential for corrosion specialists to become acquainted with this new work practice and to have an understanding of its potential benefits.

In the construction environment corrosion protection and monitoring are often carried out, not as standalone activities, but alongside other work activities. This is more so during major maintenance works. For example, in road maintenance work several work activities compete for time and space in order to maximise traffic management.  This means that a variety of work activities will be carried out in parallel, often within a restricted space and adjacent to live traffic. Therefore, good planning, logistics and engagement with other work trades become even more crucial to ensure that the corrosion protection processes can be carried out and delivered within time, budget and at the desired quality standard.

Furthermore, as part of the Highways England supply chain, contractors are required to adopt the Lean approach. Quoting from the Capital Efficiency Delivery Plan from Highways England, “It is recognised within Highways England that Lean deployment substantially contributes to the efficiency savings as set by the UK Government Road Investment Strategy (RIS) which runs from 2015 to 2020.”

Also, quoting from the Lean Support to Highways England 2015-2020 plan (1), “Lean has a target contribution of £250m towards the total of £1.2bn efficiency target. The objective is only realised by developing the Lean capability of HE staff and those of our suppliers. The supply chain organisations are now required to adopt these principles and are assessed in their progress by the Highways England Maturity Assessment (HELMA). Furthermore the application of Lean tools and techniques direct supports Highways England to achieve the Organisation Strategic Outcomes and Key enablers as set out in the Highways England Delivery plan.”

The corrosion community is part of the civil construction supply chain and it will be expected to demonstrate adoption of Lean as part of their organisation objectives, which will be assessed regularly.

The corrosion protection/ monitoring methodology is essentially a process which includes and relies on elements such as: manpower, machinery and equipment, material, method and information and design. This can be compared to the process requirements of a production system, with the activities forming an essential pre-requisite to delivering an effective task planning and process control.  As a general rule, corrosion protection processes comprise of the following elements or activities (Figure 1).

corrosion

Fig.1. Simplified generic corrosion protection/ monitoring process

By mapping and analysing the process stages and identifying what activities are value added or non-value added (waste), the opportunities for improvement will be revealed. Removal of waste from the process will result in projects being delivered efficiently, safer, within budget, providing required performance, and at rate required  by the customer.

Background:

Over the past 40 years, many different industries, such as automotive, service, shipbuilding, healthcare, software and construction have adopted the principles and methodology of a renowned production system developed by the Toyota Motor Corporation to attain the same overarching operational targets of having a consistently effective production system and efficient processes. This production system is often called the Lean Production System (LPS), and will be referred to as Lean from now on. Lean has proven effective in contributing to a sustainable operational success on many occasions in different industries.

After the Latham report published in 1994, the UK Government set out to improve efficiency within the public sector. The Lean Production System (LPS) and its tools and techniques have been deployed since the late 2000s in large public organisations in the UK. For instance, Highways England has generated over £80M of benefits to date by applying the Lean tools and techniques to several of its schemes and projects within both the organisation’s internal processes, and across the supply chain (2).

This article will introduce some of the key principles and methods of Lean which, if deployed, are thought to be relevant to improving the effectiveness and efficiency of corrosion protection processes. The link between Lean and some common corrosion protection methods will also be discussed.

What is Lean?

Lean is a customer focused and structured production management system and process improvement methodology which aims to ensure the delivery of customer requirements at the required quality standards and rates. While delivering customer expectations, Lean utilises several tools and techniques to support the removal of waste within a process, thus ensuring a more efficient process.

An important aspect of Lean is the collection, understanding and analysis of the ‘as is’ state before the deployment of appropriate Lean tools and techniques. By achieving an in-depth understanding of the present state of the process, a Lean practitioner will be able to challenge the present process activities/practices.

There are five main Lean principles, which are described below and can be easily applied to corrosion protection:

  1. Specify value from the standpoint of the end customer (internal or external).
  2. Identify all the steps in the value stream for each corrosion protection activity and whenever possible, eliminate those steps that do not create value (the Lean wastes).
  3. Make the value-creating steps occur in a tight sequence so the work will flow smoothly toward the customer. In the meantime, standardise the system to minimize variability.
  4. As the flow is introduced, let the internal customer pull value from the next upstream activity.
  5. Continuously improve the system using the first four steps.

In Lean, work activities of the ‘end to end’ process are assessed and categorised into:

  • VA = Valued added. These are the activities which add value to the end product and for which the customers are prepared to pay.
  • ENVA = Essential Non-Value Added. In this category, are the legal, environmental, Health &Safety (H&S) and training requirements which are compulsory parts of the process, although the customer is not generally prepared to pay for these aspects.
  • NVA = Non- Value Added (WASTE). These are activities within the process which do not add any value to the end product and for which the customer has no appetite to pay.

A model of a Value Stream mapping analysis when all activities and links are shown and classified as VA, NVA and ENVA within a timeline, is shown in Figure 2. This provides a good visual representation of the activities that can and should be reviewed/ removed from the process, or to highlight where the main process improvement opportunities are.

corrosion protection

Fig. 2. Schematic example of value stream mapping for corrosion protection

In general, works across the construction industry are impacted by environmental and weather conditions and differ from those of controlled and repetitive processes found in the manufacturing industry. It is important to understand and adapt the fundamental Lean principles in order to effectively deploy these into one’s own work conditions. This needs to be done through customised applications.

In line with the five principles, Lean identifies process wastes that need to be eliminated in a production system.  In brief, the main wastes are those activities which the customer is not prepared to pay for, such as:

  • Transportation of goods during production.
  • Inventory which has to be managed, taking valuable space, time and resources.
  • Movement of workers during the delivery of work to get tools, equipment, and materials located away from their workstation.
  • Waiting for a product from the previous activity, or waiting for authorization or signatures to proceed
  • Overproduction – producing more than the customer or market can take
  • Over-processing –features which have not been required by customers and that add no value to the product’s purpose
  • Defects – defects waste time, resources for re-work, and can impact on customer satisfaction.
  • Skills misuse – performing work activities using staff without the appropriate training or competence

The use of untrained staff to perform specialised activities creates defects in the short, medium and long term and has direct impact on the protection and asset performance. Corrosion specialists are aware that the application of specialised corrosion protection and corrosion monitoring relies heavily on how they are executed. A lot of the times the execution of the protection is as important as the materials used. Therefore staff training is vital to the performance of the corrosion protection.

Lean Methods and Systems

At the operational level, the Lean principles are realised by implementing some Lean methodologies, tools and techniques. The selected tools and techniques outlined in this section have been chosen as their use seems to fit with the corrosion protection and monitoring activities, and where the corresponding benefits can easily be identified.

The Last Planner System or Pull Planning

Unlike highly structured and controlled work environments like factories and shop floors, corrosion protection of large structures/assets generally take place in dynamic and complex environments, such as, construction sites, motorways or oil platforms, where the tasks of trades are interconnected and dependent on many uncontrollable factors. In those complex work environments, alongside systematic coordination and constant planning and re-planning, proactively and collectively eliminating task constraints takes precedence. For those purposes, the Last Planner System (or Collaborative Planning as it is called in the UK) has been successfully used in project-based production systems for more than 25 years to provide a “pull-based” production planning and control mechanism that is executed by the very “doers” of tasks. (Plans are not pushed by “planners, schedulers or senior managers” who are detached from the actual production.) The Last Planner System goes beyond the Critical Path Method (CPM) by not only effectively controlling tasks themselves, but also controlling complex process flows and trade interactions (3).

The Last Planner System is essentially a collaborative planning process or method that involves the stakeholders such as, trade foremen and design team leaders (the last planners) in planning in detail the work to be done throughout the project. The discussions become more and more detailed as the work progress. This technique was created to enable more reliable and predictable production in projects. It also supports the flow of work through the project, building trust and collaboration within a project team and delivering safer projects faster. It brings together those who will execute the work (the team) to plan when and how work will be done through a series of conversational processes. It requires the group to remove constraints collaboratively as a team and to promise delivery of each task for the team.

The use of the Last Planner will promote engagement and discussions with stakeholders’ representatives at the beginning of the project, allowing for their understanding of the work interactions, any issues or any ideas they may have for improvements, and will lead to their consensus on the rate of work. The teams will actively work together and cooperate with other teams and trades to remove any process constraints to keep their planning promises on track. The 6 week look-ahead, with a review process every 2 weeks, has proven to be an effective approach to reduce project durations by up to 30%. Weekly meetings offer valuable learning and improvement opportunities for even more reliable planning in the future. It is also important to collect data on percentage planned completed (PPC) to measure performance against targets and review what went well and what didn’t go so well, to ensure lessons learned are understood and communicated to the team in order to drive Continuous Improvement.

These systematic processes increase the chances that the work flows reliably, and recognizes that personal relationships and peer pressure are critical to that process. The basic planning stages of the Last Planner include,

  1. Master scheduling; front-end planning to set the project milestones that incorporates the CPM logic to determine the overall project duration.
  2. Phase scheduling; a detailed schedule dividing the project into discrete phases. It specifies handoffs through reverse scheduling the project to understand how to meet the milestones identified in the master planning together with all teams and trades.
  3. Look-ahead planning; the pull planning phase covering two-six week periods. It is used to breakdown activities into detailed processes/operations, to regularly identify constraints, to assign responsibilities and to make assignments ready.
  4. Weekly work plans or commitments; the most detailed plan in the system showing interdependence between the work of various specialist organisations. It directly drives the production process. At the end of each plan period, assignments are reviewed to measure the reliability of planning and the production system. Analysing reasons for plan failures and acting on these reasons is used as the basis of learning and continuous improvement

The Last Planner System is highly applicable in corrosion protection planning and control. As there are several trades working together under complex project systems in corrosion protection, and sometimes within confined spaces and with limited time to complete the work, the Last Planner System would render an effective mechanism to engage the trades, and to ensure they all understand the impact of each of their activities on others. Such as, if the scaffolding is not in place in time, the blasting is delayed or the fact that the paint or the equipment is not in place, will impact on the delivery time and the process flow.

As the process progresses, a daily stand-up meeting around a Continuous Improvement cell or board should take place to check, in detail, what has gone well, what has not gone well, and why. This is known as the 3C’s tool (Concern, Cause and Countermeasure) and it makes certain that the day meeting is focused on these points. This practice also ensures that all raised concerns are discussed and addressed by those involved in doing the work, as resulting actions will promote improved work flow for the next day or shift.

corrosion protection

Caption : The daily meeting, credit Katie Jones, Graham construction

Visual Management and the 5S

Lean work places rely extensively on visual communication (i) to make deviations and non-compliances obvious, (ii) to increase coordination, (iii) to reduce complexities in the work environment, (iv) to help teams to understand the purpose of communication easily, (v) to facilitate process transparency to reduce the number of work-related questions people may pose, (vi) to guide people to work efficiently on their own (self-control), and (vii) to reduce human-related errors. This conscious information visualization, or work-facilitation strategy, is called Visual Management. For instance, daily team meetings are held around performance boards to review past performance and future constraints, which openly display the Key Performance Indicators (KPIs). Standard operating sheets and instructions (i.e. process, health and safety, quality etc.) are highly visual and integrated into the workplace, close to the operations, not in drawers or anywhere far from the operational area. Daily and look-ahead work plans are communicated to the teams on visual boards or sheets in an easy-to-understand fashion. Problems in the processes are immediately signaled by the workforce using ‘andon’ lights. (The term ‘andon’ most often refers to a signaling system used to call for help when an abnormal condition is recognized, or that some sort of action is required.) The pace of processes and material consumptions as per production plans can be regulated in a “pull” fashion by using simple cards called kanban. (Kanban is Japanese for “visual signal” or “card.” Toyota line-workers used a kanban, i.e., an actual card, to signal steps in their manufacturing process.)

In order to realise Visual Management, a systematic visual workplace framework should be followed (see Figure 3).

corrosion protection

Fig 3. Visual workplace framework (Adopted from Tezel and Aziz, 2015, reference 4)

A brief explanation of the framework elements is as follows:

  • Visual order (the 5S) which stands for Sort, Set in order, Shine, Standardise and Sustain: Creating a visual workplace should start with adopting the systematic 5S methodology to create better organised, tidier, and cleaner workplaces to increase productivity, reduce risks, better control materials and equipment, and to provide a better working environment. The 5S is an acronym for the 5 distinct steps (Figure 3), and are,
    • (i) sort for organising the workplace in an efficient way and eliminating unnecessary items,
    • (ii) set-in-order for standardising the location, quantity, responsibilities etc. of the remaining necessary items,
    • (iii) shine for implementing a systematic cleaning and inspection mechanism,
    • (iv) standardise for standardising the methods, procedures and responsibilities for the first 3S, and
    • (v) sustain for implementing some supporting activities like training, team building, incentives etc. to sustain the 5S
  • Visual standards: Work standards in terms of process procedures (i.e. the most efficient and safe way of completing a high-quality process with required durations) and process outcomes (i.e. high-quality outcome features) are visually demonstrated to work teams at their point of use, close to where the actual process is going to happen. Standards are effectively built into the workplace.
  • Visual measures: General and team level KPIs are regularly maintained and shared with work teams. KPIs are shown with their actual and target figures. Teams have their meetings around their KPI boards to review their past performance and to coordinate their future efforts, as per their team targets.
  • Visual controls: Visual controls are visual clues or small artefacts that are used to limit and guide human actions. For instance, in the pull-production system, production signals from succeeding workstations are given to preceding workstations through the exchange of simple cards called kanban. Without a kanban card, the preceding workstation does not start any production. By issuing a certain number of cards to workstations, the production pace and material consumption rates are controlled.
  • Visual guarantees: Humans are prone to making mistakes. The important thing is to prevent mistakes from becoming defects. Visual guarantees are devices, process design elements or product features designed to counter human failures by either warning people of mistakes, rendering making mistakes harder, or controlling the effects of their mistakes. They are also called poka-yoke systems. (Poka-yoke is a Japanese term that means “mistake-proofing” or “inadvertent error prevention”.) Visual guarantees are good for increasing process quality and safety, and reducing process set-up times. ‘Andon’ boards that give visual and auditory signals (warnings) in case of a mistake or deviation is a typical example of this.

Continuous Improvement tools

Continuously improving process (i.e. methods, tools/equipment, and information systems) and workplace elements are an integral part of Lean. There are some frequently employed continuous improvement strategies, tools and techniques

  • PDCA cycle and time/motion studies. The PDCA cycle is a standardized continuous improvement approach that is an abbreviation for “Plan-Do-Check-Act”. Plan; recognize an opportunity and plan a change. Do; test the change. Carry out a small-scale study. Check; review the test, analyze the results and identify what you have learned. Act; take action based on what you learned in the study step. If the change did not work, go through the cycle again with a different plan. Often, processes are improved with time/motion studies through this cycle, in which processes are recorded on video and studied by their value-adding, non-value adding and necessary non-value adding activities. The aim is to eliminate the non-value adding activities while reducing the non-value adding necessary activities by making changes in the process elements.
  • Value stream mapping. Documenting the flow of material and information as a product or service makes its way through the value stream, from start to finish to classify the many activities as VA, NVA or ENVA and to check for wastes in the process and to identify improvement opportunities.
  • Root cause analysis and 5 whys. Root cause analysis is a popular technique that helps Lean practitioners to answer the question why the problem occurred in the first place. It seeks to identify the origin of a problem using a specific set of steps, with associated tools, to find the primary cause of the problem, so that one can, determine what happened, why it happened, and what to do to reduce the likelihood that it will happen again. Alongside Pareto and scatter diagrams, fishbone diagrams tracing the root causes of problems back to methods, machines (equipment), people (manpower), materials, measurement and environment, are popular root cause analysis tools. Also, it is believed that asking the why question five times (5 Whys) with respect to the problem, in an iterative manner is an effective tool to trace the problem’s root cause.
  • Continuous improvement circles
  • A3 sheets – This is a Lean summary report in an A3 page which captures the main elements of the Lean project.

 Corrosion Protection and Lean

The table below summarise’s the Lean tools and techniques that could be deployed in corrosion protection/monitoring processes, and identifies their potential benefits. It should be noted that this table highlights only some initially conceived connections that can, and will be expanded as the implementation progresses and matures.

 Table1. Conceptual link between corrosion protection methods and some Lean tools/ techniques

Corrosion protection   Lean tools/ techniques  Objective  Benefit/s
 Anti-corrosive painting The Last Planner System  Ensure all stakeholders/trades are aware of the various activities and their impact on the overall process & understand customer expectations at every stage of the process Check the opportunities for changes within the  work activities to minimise, effort, time, e.g. This can be as simple as leaving access ladders in place for the next work activity
 Painting Critical to quality (CTQ) analysis  Ensure that stakeholders understand what and how their work needs to be performed to the satisfaction of their customers. That should reduce time waste as result of re-work before the follow up activity can be performed.  Reduce constraints/ re-work
 Painting  5S  Ensure that materials and equipment are kept under controlled environments, ready to be handed at the start of the work and labelled and within up to date calibration dates  Prevent delays to the process, ensure PPE reducing H&S issues. Ensure paint material not exposed to temperature extremes which will result in material deterioration. Prevent wasted time trying to find the right equipment/ materials to perform the work.
 Painting  Use of kanban  Ensure that there is a flag raised at the end of each stage to ensure the next stage starts only once the previous is completed, thus preventing awaiting time and uncertainties  Maximize performance, managing workflow and ensure each stage is finalized and/or inspected before next one starts to prevent defects
 Painting/ Cathodic Protection  Skills checking  Ensure workmanship has necessary training and skills to perform the tasks  Maximise coating/ anti-corrosive performance thus prevent early failures increasing asset whole life costs. Prevent waste due to skills misuse.
 Cathodic protection The Last Planner System  Ensure all stakeholders/ sub-contractors are aware of the required access, tools, materials & skills necessary to allow for the implementation of the Cathodic protection  Prevent time waste, delay on the works, reduce performance of the system.

 Conclusion & Recommendations

Material deterioration as result of corrosion is often accepted as unavoidable and it has led to the lack of awareness of the economic aspects of corrosion. The estimated cost of corrosion as per Hoar committee findings is around 3.5% of the UK GDP (Hoar report – 1971, reference 5). For major asset owners, maintenance of the anti-corrosion technology is an integral part of the asset design and management to ensure asset integrity throughout its service life.

Maintenance intervention for corrosion protection is costly and the number of interventions will vary with asset design life, quality of the protective material, workmanship and service environment. Deployment of Lean is likely to improve the efficiency and effectiveness of corrosion protection/monitoring.  This can be achieved by using the Lean techniques described in the previous sections.

As examples:

  • Finding improvement opportunities by mapping the ‘as is’ process – the identifying and removing wastes.
  • By improving/ promoting staff engagement among the various trades involved in and around the corrosion protection/ monitoring, opportunities for improved work practices are identified
  • Preventing defects by continually training specialist staff who specify, and perform corrosion protection and corrosion monitoring, as well as those who perform inspection work.
  • Employing the Last Planner for improved task coordination.
  • Using VM techniques to increase the transparency and control in corrosion protection and corrosion monitoring processes

Deployment of the Lean tools and techniques will result in reduction of time, cost and H&S risks associated with corrosion protection and monitoring. Applying the Lean principles to corrosion protection and monitoring will also improve the quality and reduce the whole life cost of major assets, which will be of a direct benefit to asset owners and customers.

Raising awareness of Lean among corrosion protection professionals, and documenting some implementation cases, seem of critical importance for Lean to diffuse into the corrosion protection sector.

References

  • Document available from gov.uk/highways
  • HE Lean Knowledge Transfer Packs, and Lean tracker can be accessed on https://kol.withbc.com/HA-Lean/
  • Hamzeh, F., & Bergstrom, E. (2010, April). The lean transformation: A framework for successful implementation of the last planner system in construction. In International Proceedings of the 46th Annual Conference. Associated Schools of Construction
  • Tezel, A., & Aziz, Z. (2015). Visual controls at the workface of road construction and maintenance: Preliminary report, University of Salford, UK.
  • P. Hoar Report of the committee on Corrosion and Protection – Department of Trade and Industry – HMSO. London UK – 1971

  Acknowledgments

The authors would like to thank John Fletcher of Elcometer, and past President of the Institute of Corrosion, and Katie Jones – Lean Manager of Graham Construction, for their contributions to this article.