Ask the Expert

Ask the Expert

The questions in this issue feature insulated stainless steel pipework, and transporting CO2

Question:
Should 304 stainless steel pipework be coated prior to insulation? CM

Answer:
Corrosion under insulation in austenitic stainless steel manifests itself in the form of chloride-induced stress corrosion cracking (CISCC), also referred to as external stress corrosion cracking (ESCC), as the source of chlorides is external to the process environment.
The mechanism of stress corrosion cracking (SCC) is well known in industry and can be found in lots of publications which are in the public domain. The mode of cracking failure is typically trans granular. There are a number of conditions that are in play when it comes SCC, as detailed below:
1. A susceptible 300 series austenitic stainless steel, in this case 304
2. Residual or applied surface tensile stresses
3. The presence of halides from either the environment of the insulation itself
4. Process temperatures leading to metal temperature in the range 50° to 150°C
5. An electrolyte (water)

All of the above are ever present, and hence the need to use specific coatings on stainless steel. The types of coating that can be employed are varied depending on the operating temperature, typically:
• Organic epoxy chemistry is capable of resisting cryogenic temperatures and up to 120/150C, depending on formula
• Epoxy phenolics/novolacs are suitable from cryogenic temperatures and up to 200/230C, again depending upon formula
• Inorganic coatings such as Inert Multipolymer Matrix, are also capable from cryogenic temperatures and up to 600C

These coatings when formulated correctly, using barrier pigmentation such as Micaeous Iron Oxide (MIO), aluminium flake or glassflake, will create a barrier to the ingress of chlorides to the stainless steel substrate.
There is also the matter of the insulation to consider when it is being used. It is well documented that with traditional insulation, and mineral based insulation with a metal jacket, that water will penetrate into the insulation system. The water will find a way through breakages in the metallic jacket or joints edges, and then it will soak through the insulation giving rise to CUI/CISCC conditions. Under certain operating conditions up to 177C, the traditional insulation could be replaced with a thermal insulation coating system (TIC) especially in the case where personal protection is required. This will remove the conditions which are required for CUI, and reduce the risk on CISCC, as no electrolyte is being held at the surface.

Therefore, a combination of a good barrier coating with high temperature resistance and a thermal insulation coating could be a very good choice in combatting both CUI and CISCC.

Neil Wilds, Global Product Director –
CUI/Testing, Sherwin-Williams, Protective & Marine Coatings.

Question:
Carbon capture and pipelines/storage – what are the limits of impurities when transporting CO2? PF
Answer:
Like many ‘Ask the Expert’ questions, there is no simple answer to this! Although general industry guidance on impurity limits is available from a number of sources [1-4], there are no internationally agreed specifications for CO2 composition during pipeline transport. Under current regulations, the responsibility lies with the pipeline operator to carry out their own assessment and specify impurity limits during the design phase of a given CO2 pipeline project. These limits can vary significantly depending on the composition of the CO2 stream, the economics of the purification technologies used and the operating conditions of the pipeline.

From a corrosion perspective, the most important impurity to consider is obviously water. When the water concentration is below its solubility limit in dense phase CO2 (~ 2500 ppm under typical pipeline operating conditions in the absence of other impurities) no corrosion will occur. However, the presence of other impurities can increase the likelihood of corrosive phases forming, either by reducing the water solubility or via chemical reactions between different impurities. Acid dropout is the most significant concern for pipeline operators, whereby highly corrosive aqueous phases, such as nitric and sulphuric acid, can form as a result of reactions between water, NOx, SOx, O2 and H2S impurities.

Assessment of the risk of water and acid dropout in CO2 pipelines due to the presence of multiple impurities is a complex process, which requires an understanding of the thermodynamics of fluid composition, the impact of operating temperature and pressure variations (including potential upset conditions) and interactions between impurities. The requirements for ship transport are typically more stringent than those for pipelines [5], with lowest temperatures representing the worst-case scenario.

Published corrosion rate data in the open literature should be treated with caution due to challenges in control of test parameters and the high degree of uncertainty around the correlation between laboratory test data and real world application. Combined with the relative lack of service experience in transport of CO2 captured from a range of industrial sources, this often leads to a degree of over-conservatism in materials selection. For CO2 specifications, thresholds in relation to acid drop out are set based on limited available data (often not lower than 25oC) and are therefore likely not conservative enough. The development of reliable standard test methods that are more representative of service conditions will go a long way towards addressing these issues.

A full description of the process for developing reliable CO2 impurity specifications for individual projects is clearly beyond the scope of this response but the interested reader is directed to the references below as a starting point.
References
1. DNV-RP-F104 – Design and operation of carbon dioxide pipelines, Recommended Practice, September 2021
2. Briefing on carbon dioxide specifications for transport, EU CCUS PROJECTS NETWORK, November 2019
3. DYNAMIS CO2 quality recommendations, EU DYNAMIS project D 3.1.3 report, June 2007
4. Materials challenges with CO2 transport and injection for carbon capture and storage, J. Sonke, W.M. Bos, S.J. Paterson, International Journal of Greenhouse Gas Control 114, 103601, 2022
5. Network Technology Guidance for CO2 transport by ship, ZEP/CCSA Report, March 2022
Gareth Hinds, NPL

Standards Up-date ISO

Industry News

The following documents have obtained substantial support during the past two months, and have been submitted to the ISO member bodies for voting, or formal approval.

ISO/DIS 4624 Paints and varnishes — Pull-off test for adhesion (Revision of ISO 4624:2016).
ISO/DIS 4628-10 Paints and varnishes — Evaluation of quantity and size of defects, and of intensity of uniform changes in appearance — Part 10: Assessment of degree of filiform corrosion (Revision of 2016 standard).
ISO/FDIS 4680 Corrosion of metals and alloys —Uniaxial constant-load test method for evaluating susceptibility of metals and alloys to stress corrosion cracking in high-purity water at high temperatures.
ISO/DIS 4773 Non-destructive testing — Ultrasonic guided wave testing using the phased array technique.
ISO/DIS 5668 Corrosion of metals and alloys —Guidelines for corrosion testing in simulated environment of deep-sea water.
ISO/DIS 7539-12 Corrosion of metals and alloys — Stress corrosion testing — Part 12: Requirements for atmospheric stress corrosion cracking testing.
ISO/FDIS 7784-1 Paints and varnishes — Determination of resistance to abrasion — Part 1: Method with abrasive-paper covered wheels and rotating test specimen (Revision of 2016 standard).
ISO/FDIS 7784-2 Paints and varnishes — Determination of resistance to abrasion— Part 2: Method with abrasive rubber wheels and rotating test specimen (Revision of 2016 standard).
New International standards published in the past two months.
ISO 4215:2022 Corrosion of metals and alloys — Test method for high-temperature corrosion testing of metallic materials by thermogravimetry under isothermal or cyclic conditions.
ISO 7784-3:2022 Paints and varnishes — Determination of resistance to abrasion — Part 3: Method with abrasive-paper covered wheel and linearly reciprocating test specimen.
ISO 11127-6:2022 Preparation of steel substrates before application of paints and related products — Test methods for non-metallic blast-cleaning abrasives — Part 6: Determination of water-soluble contaminants by conductivity measurement.

Online Learning: Courses for the Professional Development of the Corrosion Special

Online Learning: Courses for the Professional Development of the Corrosion Special

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World-Beating Virtual Learning in the Corrosion Industry

You’ve decided to continue your professional development as a corrosion specialist through online learning. This allows you to fulfil the requirements for your continuing professional development with corrosion courses specifically designed to be delivered virtually.

For many corrosion professionals, this is an excellent decision:

  • It means that you can fit your training around your professional and personal life
  • You won’t need to cancel other things or miss out on work to squeeze in your learning
  • You’re not bound by time or place, and you can work at a pace that is comfortable for you
  • You can learn while you’re commuting on a train, during the downtime in a hotel room while travelling for business, or at home after a full day’s work and when the children are in bed

Financially, online learning is generally cheaper than classroom learning – and there’s no added expense of accommodation and meals to consider. You won’t suffer a loss of earnings, plus you may have the opportunity to network with corrosion specialists from around the globe.

(If you’re still not certain if online learning or classroom learning is right for you, read our article, ‘Online Classes vs Classroom Learning: Which Is Best for Corrosion Professionals?’.)

Recognising the need for online learning for corrosion specialists, the Institute of Corrosion has partnered with corrosion training experts to design, develop, and deliver the quality of learning needed in the industry.

Online courses for corrosion specialists

Our online courses cover a range of specific subject areas. Below, you’ll find a summary of each of the current courses available for virtual learning. This includes the scope of each course, who should take it, the qualifications or accreditation you will receive upon successful completion, and a link to enquire about each course.

Coating Inspector Courses

Coatings systems are a protective method used to eliminate or slow the corrosion of metallic structures, thereby increasing lifespan and reducing the need for and cost of maintenance and replacement.

The courses that the Institute have endorsed and that have been accredited by Lloyd’s Register and the Royal Society of Chemistry are:

  • Coating Inspector Level 1

The entry-level requirement for a career as a coating inspector, this course is designed for those with industrial coating experience but without coating inspection experience.

After passing the exam, you will be qualified to carry out coating inspections. Online learning includes 40 hours of flexible study and online practical workshops.

  • Coating Inspector Level 2

This course has been designed for those who have passed the ICorr Level 1 Coating Inspector course and have at least 12 months of Level 1 coating inspection experience.

Upon successful completion of the course and exam, you will be qualified to perform direct inspections and testing operations.

  • Coating Inspector Level 3

This is the most advanced Coating Inspector level, open to those with at least three years of experience of coating inspection.

When successfully completed, you will have demonstrated the ability to interpret and evaluate inspection or test results in terms of existing normative documents; that you have the scope and level of knowledge sufficient to enable the individual to select inspection methods and tests, and to assist in the establishment of inspection and test criteria where none are otherwise available; and that you possess a general familiarity with coating materials, fabrics and structures protected by painting and coating, application methods and associated areas.

To enquire about the coating inspector courses delivered online, please email the Institute of Corrosion.

Other online courses

As well as the cathodic protection and coating inspector courses, you may also be interested in:

  • Hot Dipped Galvanizing Inspector Level 2

Produced in collaboration with the Galvanizers Association, this course delivers the knowledge needed to prepare for the ICorr Hot Dip Galvanizing Inspector examination. The course includes:

  • HDG overview
  • Corrosion mechanisms
  • Surface preparation
  • Galvanizing chemistry
  • Inspection overview
  • Organic coating on galvanizing
  • Testing of galvanizing
  • Coating Faults
  • Handling and storage
  • Coating repair methods

You will need to sit the exam within 90 days of completing the course.

For more information, please email the Institute of Corrosion.

  • Coating Surveys Course

This world-first course has been compiled by industry experts and enables you to gain full certification as a professional coating surveyor. You’ll get an exceptional grounding in areas that include:

  • Coating surveys
  • Common defects
  • Marine fouling
  • Dry film thickness surveys
  • Passive fire protection
  • Adhesion testing
  • Sampling techniques
  • Standard test methods, field tests and laboratory analysis
  • Paint testing, paint constituents and paint chemistry
  • And more

If your daily job includes coating surveys, you are strongly recommended to take this course.

For more information, please email the Institute of Corrosion.

Accelerate your professional development with the Institute of Corrosion

The Institute of Corrosion is committed to ensuring that its members and the wider community of corrosion specialists have access to learning and development opportunities wherever they are in the world.

We also understand that the rigours of your job can make classroom learning not only inconvenient, but expensive. Therefore, in collaboration with our educational partners, we are continually expanding our range of learning and professional development opportunities via online learning.

To learn more about any of the above corrosion courses, or to enquire about professional development courses for corrosion professionals that are not included above, please email the Institute of Corrosion. We will be happy to help you in the development of a successful career in the corrosion industry.

Manipulating transport paths of inhibitor pigments

Industry News

The microstructure of an organic coating affects the leaching of inhibitor pigment, and this microstructure can be altered by the addition of other pigments.

The network of cavities and voids formed upon dissolution and removal of the soluble pigment introduces transport paths, and consequently, facilitates the leaching of the main inhibitor pigment.

Adequate leaching of active inhibitor pigments in organic coatings is essential for corrosion protection that relies on active inhibition of the metallic substrate. Therefore, it is important to obtain a comprehensive understanding of the factors that influence leaching kinetics and mechanisms. In the present study, model organic coatings were formulated to investigate the influence of additional pigmentation (i.e. pigments other than the main inhibitor) on the leaching of species released from the main inhibitor pigment.

In a recent article, It was found that addition of soluble/sparingly soluble pigments to the organic coating resulted in increased leaching rate. This was attributed to the formation of clusters comprised of both the main inhibitor pigment and the additional pigment. The network of cavities and voids formed upon dissolution and removal of the soluble pigment introduces transport paths in the organic coating, and consequently, facilitates the leaching of the main inhibitor pigment.

The study was published in Progress in Organic Coatings, Volume 172, November 2022.