Guidelines for Non-destructive Inspection by Phased Array Ultrasonic Testing

Guidelines for Non-destructive Inspection by Phased Array Ultrasonic Testing

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The shipping Classification Society, ClassNK, has released its “Guidelines for Non-destructive Inspection by Phased Array Ultrasonic Testing”.

Phased array ultrasonic testing is an advanced non-destructive inspection technology that enables the visualising of flaw detection results and the digitising of the record-keeping process. It has higher detection performance for defects in materials and welded joints compared to conventional ultrasonic testing.

In recent years, the application of phased array ultrasonic testing in various industrial fields has been increasing, and it has also been gradually spreading in the shipbuilding field, taking advantage of the above features.

Based on the knowledge acquired from its R&D, ClassNK has comprehensively summarised the requirements for non-destructive inspection by phased array ultrasonic testing and specific flaw detection procedures for butt welded joints of carbon steels in the shipbuilding field into its guidelines.

These guidelines are available to download free of charge via ClassNK’s website www.classnk.com for those who have registered for the ClassNK “My Page” service. To register for the “My Page” service free of charge, go to the ClassNK website www.classnk.com and click on the “My Page Login” button.

Members of NACE International and SSPC overwhelmingly vote in favour of merging the two Organisations

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During the two-week voting period, thousands of members of the two associations cast votes, with an overwhelming 89% of NACE members and 88.3% of SSPC members in favour of the merger.

Several steps are required before completion of the combination and most changes will not be immediate. Initial efforts will be focused on determining the new governance and membership structure by January 1, 2021. Member volunteers will drive discussions and decision-making to ensure the final combined organisation represents the best interests of the membership.  McKinley Advisors will continue to serve as a third party, independent advisor to assist both organisations with combining resources, knowledge, and cultures.

NACE International CEO, Bob Chalker and SSPC Executive Director, Bill Worms issued the following joint statement, “From the time each of us began working for our organisations we have believed our members can be stronger together. We are devoted to providing our members with the best services, education, and products possible and we know this combined organisation will accomplish that and more. We are pleased to see this come together and look forward to a bright future ahead for the members of NACE and SSPC.”

ISO 12944 – Steel structure design and corrosion

ISO 12944 – Steel structure design and corrosion

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Corrosion must be considered early in the design of steel structures

If left unprotected in corrosive environments, steel structures are liable to corrosion that can be both costly and put lives in danger. One way to control corrosion is to use paints and coatings. ISO 12944 is the internationally recognised standard that provides instruction and guidance to those working with steel structure design, including planners, painters, inspectors, maintenance, and manufacturers of coatings.

The third part of the standard provides guidance to those designing steel structures that are to be coated with protective paint systems, setting the criteria for design to avoid premature corrosion of the asset.

Why is steel structure design important?

How a steel structure is designed has a real bearing on the ability to protect it against corrosion. Poorly designed structures may have corrosion traps which are difficult to protect and from which corrosion can spread rapidly. To help prevent this, designers should consult with corrosion experts as early as possible in the design phase to consider the following elements of design that may affect corrosion:

  • The shape of the structure
  • The use of the structure
  • Structural elements such as method of joining
  • Environmental factors

Effective design of steel structures

The basic steel structure design criteria that may be exposed to corrosive environments include keeping the design simple and minimising surfaces that may be exposed to corrosive pressures. The designer will need to ensure that maintenance and inspection work is facilitated by the design, that appropriate joins are made, and that they consider how the structure will be transported and erected.

Here are the primary areas of concern that this section of ISO 12944 covers (but is not limited to):

·         Accessibility

Those who are applying, inspecting and maintaining coatings need access to the areas to be protected for their work to be effective. Design should allow this; for example, by providing for fixed walkways and the fitting of maintenance equipment (such as anchorages for scaffolding).

Safety of all operators should also be considered when designing for accessibility. For example, the surfaces to be coated and maintained should not only be accessible, they should also be within safe, easy reach and with plenty of space to work in.

In box members and tanks, openings should be large enough to allow easy access, and ventilation holes should be included.

·         Prevention of trapped water

Designers should incorporate design elements to prevent water being trapped and where foreign matter may combine to increase the potential for corrosion. Design features that might be considered include inclined surfaces, drainage systems, and chamfered edges.

·         Welding and bolting

The standard also makes it clear that welding should be clear from imperfections that make it difficult to protect effectively. Bolts, nuts and washers should be protected against corrosion, and to the same protection durability as the structure itself.

 

·         Treating gaps

Narrow gaps and blind crevices are particularly prone to potential corrosion, as they tend to retain moisture, foreign bodies and soluble salts. Very narrow crevices such as the enclosed spaces between two back-to-back flat surfaces can take up moisture by capillary action. The oxygen-deficient conditions within the crevice can set up an aggressive accelerated electrochemical concentration cell, leading to rapid pitting within the crevice. This type of corrosion is particularly dangerous as it is not visible (possibly until a structural failure), and the lack of access makes it very difficult to detect and repair.

Either filling or sealing will be needed to prevent corrosion in these gaps, with welding also used. Where steel transitions to concrete, the designer will need to pay specific attention to ensuring that gaps are treated.

Treating Sharp Edges

Liquid coatings in common with other liquids display surface tension. The surface tension of an applied coating film can cause the coating to pull away from a sharp edge (e.g. the edge of a splice plate or the flange toe of an I-section girder), resulting in a reduced film thickness along the sharp edge compared to the same system applied on a surrounding flat area. Sharp edges can therefore be vulnerable to premature breakdown unless they are given a supplementary coat(s) of protective coating (so-called ‘stripe coat’), or the design of the structure incorporates the provision for grinding of sharp edges, to provide a radiused edge profile which will allow the coating to follow the edge without a reduction in film thickness.

·         Preventing galvanic corrosion

Galvanic corrosion is possible should an electrically conducting joint exist between two dissimilar metals, with the less noble of the two metals corroding subsequently. The standard provides instruction on the type of joints that should be used to avoid this, but where it cannot be avoided then the surfaces should be electrically isolated by painting of both surfaces. However, cathodic protection may also be employed to protect against electrochemical corrosion.

·         Transportation and erection

Design of a structure should also consider how it will be transported and erected, as there will be potential for damage to occur to the corrosion protection used. The designer should include lifting points and fixings that may be needed to transport and erect the structure.

Summary

In summary, corrosion must be considered during steel structure design. The designer should enlist the advice of a corrosion expert, and deliver a structure whose design does not hinder the correct application and inspection of the specified corrosion protection coating system, coupled with subsequent inspection and maintenance of the corrosion protection measures.

In providing guidance and instruction for the design of steel structures liable to corrosion across a range of applications and in a range of corrosive environments, ISO 12944 provides recommended minimum dimensions for:

  • Accessibility
  • Openings for access to confined areas
  • Narrow spaces between surfaces
  • Treatment of gaps

It also provides detailed examples for design features to avoid retention of water and deposits, avoidance of sharp edges, and stiffener design.

If design considerations for corrosion protection are not implemented early enough in the design process, there is a greater chance that the structure will be adversely affected by corrosion. This will certainly result in greater expense in the long term, while increasing the potential for avoidable human cost.

It is far more cost-effective to implement corrosion protection on a ‘right first time’ principle rather than having to implement costly maintenance procedures later in the life of the asset. It must be borne in mind that maintenance does not just mean the cost of labour and materials for repainting the asset. Factors such as installing scaffolding and shutting down areas of a working asset could significantly multiply the cost of a maintenance project. In our next article in this series covering ISO 12944, we discuss part 4 of ISO 12944: types of surface and surface preparation. In the meantime, to learn about the Institute of Corrosion Coating and Inspection Training Courses – presented by IMechE Argyll Ruane and Corrodere – contact us today.

Outstanding Achievement Awards in Corrosion Science

Outstanding Achievement Awards in Corrosion Science

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Recognising Past, Present and Future Talent

Each year, the Institute of Corrosion presents several internationally recognised Outstanding Achievement awards in corrosion science. These are presented to individuals to recognise their contribution to furthering knowledge, learning and research in this specialised field. The awards range from cash to a sword of which King Arthur would have been proud.

Here’s a summary of the prestigious awards that are coordinated by the Corrosion Science Division, and presented to past, present, and potential pioneers in corrosion science.

Lionel Shreir Award

Presented at the Corrosion Science Symposium, the Lionel Shreir Award is presented to the student judged to have given the best presentation at the symposium. A sub-committee of the Corrosion Science Division selects the recipient from all those who present at the event. This year, the symposium will be an online event for the first time, which brings in a whole new dimension to presenting skills. The criteria for selection for the award are:

  • Originality and creativity of research
  • Knowledge of corrosion science and practice
  • Clarity of presentation and rapport with audience
  • Clarity when answering questions

Submissions of 200-word abstracts detailing a 10-minute talk that students would like to give are being accepted from students around the world. These abstracts will be reviewed, and those selected will be contacted and asked to provide an extended abstract by Friday 28th August 2020.

For the opportunity to be awarded the highly sought-after certificate and cash prize, send your abstract to j.a.wharton@soton.ac.uk by Friday 17th July 2020.

Galloway Award

We have begun to receive nominations from overseas already for this award, which consists of a certificate and a cash sum.

The Galloway Award is presented to the student author of what the judging committee decide is the best published paper that describes original research in corrosion science and engineering during the last year.

In addition to the certificate and cash sum, a summary of the winner’s paper will be published in the Corrosion Magazine. (Don’t worry, if you’re the winner, you retain copyright of your work – allowing you to publish in other scientific journals.) The international reach of this magazine gives the student even more exposure to the global corrosion community.

Submissions of papers that have either been published in the last 12 months or are in draft form should be sent to the Corrosion Science Division Chair Julian Wharton, by email to j.a.wharton@soton.ac.uk.

T.P. Hoar Award

This award is reserved for those authors who have papers published in Corrosion Science and recognises the best paper from the previous year. A sub-committee of the Corrosion Science Division selects the winning paper, which is announced by the end of the year. The winning authors receive a certificate and a cash sum.

U.R. Evans Award

The U.R. Evans Award is the premier award of the Institute of Corrosion. An annual award, it is presented by the President of ICorr to an eminent researcher, corrosion scientist, academic, or industrialist. The recipient is selected by a Corrosion Science Division panel, and invited to give the plenary talk at the Corrosion Science Symposium. (The picture at the head of this article is Dr. Peter Andresen with the U.R. Evans award that was presented to him in 2014.)

It is usually at this event that the recipient is presented with their award and they are also granted Honorary Life Fellowship of the Institute. The award itself is a broadsword, and one that takes an edge – which has proved somewhat problematic in previous years.

Dr Julian Wharton recalls some trials and tribulations a previous winner of the award had in getting the sword home. “The sword had to go down to New Zealand in 2015, and the recipient had to try to get the ceremonial sword through customs. The winner, Professor David Williams, had real difficulties.

“Then you take it to university, and they say, ‘You want to hang a sword in your office?’ ”

The sword’s design has been modified slightly over time, and is no longer made from stainless steel. While a proper sword, if kept in non-ideal conditions they can corrode slightly. “But clearly, the recipient should be able to deal with any corrosion, given their background,” says Dr Wharton.

Robert Cottis – this year’s winner of the U.R. Evans Award

Professor Robert Cottis was appointed Professor Emeritus in Corrosion Science and Engineering on his retirement in 2011 after an exceptional career in the field of corrosion science. Here’s a potted history of his life in corrosion science:

  • Graduated in Natural Science, specialising in Metallurgy in 1967
  • Awarded a PhD in 1973 for work on electrodeposition in the fluidized electrode at the Department of Metallurgy and Materials Science at Cambridge
  • Appointed as a Project Manager, then Research Manager at the Fulmer Research Institute
  • Worked on long-term research in the general area of corrosion, especially on corrosion fatigue
  • Undertook many short-term failure investigations and other consultancy work
  • Joined the Corrosion and Protection Centre, UMIST in 1979, initially as a lecturer, then senior lecturer, reader, and professor

Active in the development of teaching in the field of corrosion, Professor Cottis was responsible for the development of a distance learning approach to the MSc in Corrosion Control Engineering.

He was the Director of the TLTP Consortium – which developed the Ecorr courseware to support corrosion teaching – and the founding editor of the open-access online Journal of Corrosion Science and Engineering.

In 2005 he was awarded the T.J. Hull Award of NACE International for services to NACE in the field of publications, and he is a NACE Fellow.

With the experience he has, you can expect the talk by Professor Cottis to light up this year’s Corrosion Science Symposium. To find out more, email Dr Julian Wharton at j.a.wharton@soton.ac.uk.

ISO 12944 – The Corrosive Environment

ISO 12944 – The Corrosive Environment

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Categorising corrosivity by type of environment

In a recent article, we introduced you to ISO 12944, the internationally recognised standard that provides the guidelines for the use of paint and coatings to protect assets from corrosion. The second part of the standard discusses the corrosive environment. This article introduces you to this part of ISO 12944 and the changes that were introduced in the latest revision in 2018.

What is the corrosive environment?

The corrosive environment describes the environment in which the asset to be protected is situated. There are many variables within corrosive environments. Combined, these determine how corrosive the environment is, and therefore the types of protective paint systems that are needed to help prevent corrosion (covered in part 5 of the standard).

When discussing the corrosive environment, two terms are used:

  • The local environment, which describes the atmospheric conditions around a particular component
  • The micro-environment, which is the environment at the interface between an element of a structure and the local environment

The environmental factors that determine an environment’s corrosivity are:

  • Climate (the weather, which is established by reference to historical data)
  • Atmosphere (the gases – including aerosols and particles – that surround the asset to be protected against corrosion)

The classification of environments considers temperature, relative humidity, and the time of wetness (the length of time that the metal surface is likely to be covered in a film of electrolyte that can cause atmospheric corrosion). In brief, atmospheric corrosivity calculations are made by summing the hours when the relative humidity is above 80% and the temperature is above 0°C.

Corrosivity is dependent on the corrosive agents present in the environment, especially gases such as sulphur dioxide, and salts such as chlorides and sulphates.

Types of corrosive atmospheres

When specifying the protective coatings that should be used on assets, ISO 12944 considers the type of atmosphere in which the asset is located, and categorises these from rural (away from corrosive agents such as sulphur dioxide) through to marine (where airborne salts are present).

If the asset is indoors, the potential for corrosion is usually lower because atmospheric pollutants are usually reduced. However, if the indoor asset is poorly ventilated or suffers from high humidity, then this increases the potential for condensation and, therefore, corrosion.

The categories of corrosivity are taken from a separate standard, ISO 9223;2012 – “Corrosion of metals and alloys — Corrosivity of atmospheres — Classification, determination and estimation”.

The scientific method for determining corrosion rate is determined by calculating the rate of metal loss on sample coupons (mild steel or galvanized steel) that are placed in the given environment. In practice, this is rarely performed for the determination of corrosivity for a paint specification. The corrosivity is determined by an objective estimation of the general description of the environment based on the descriptions in the standard, and the professional assessment by all parties involved in drawing up the corrosion protection specification.

Location of asset and corrosivity

When protecting assets from corrosion, ISO 12944 also considers whether the asset is in soil or water. Where assets are only partially buried in soil or partly immersed in water, the corrosion is usually localised to where the rate of corrosion can be highest.

Corrosion of assets that are immersed in water depends upon the type of water (fresh, brackish, or salt), how much oxygen is present in the water, the water’s temperature, and the substances that are dissolved in the water. There are three different ‘zones’ for corrosion, transitioning from the splash zone (wetted by spray), through intermediate (where wetting is fluctuating), to fully immersed.

Corrosion of those assets that are buried in soil depends on factors that include the minerals present in the soil and its water and oxygen content. The type of protection coating needed for buried-in-soil assets may differ along the length of the asset, because it is more likely that they will be buried in different soils – in such cases, the rate and severity of corrosion will differ.

Changes to ISO 12944 in 2018

There are three major changes in environmental categorisation as described in ISO 12944. There are now five environmental categories for onshore assets, ranging from C1 (very low corrosivity, typically in a climate-controlled indoor environment) to C5 (very high corrosivity environments, such as a coastal refinery).

A new environmental category has been introduced – the CX category, which covers offshore environments. This category is now covered in detail in a new section of the standard – part 9.

The IM categories, covering immersed assets, now include a new category (IM4) that deals with immersed assets with cathodic protection.

Key takeaways

In summary, the environment in which an asset is sited has a significant effect on the potential for it to corrode, and therefore the design of corrosion prevention system used. Factors that determine corrosivity of the environment include temperature, humidity, condensation, and corrosive pollutants in the atmosphere.

In classifying corrosion environments, ISO provides a reliable guide for the design, implementation and maintenance of structures and corrosion prevention systems and the applicable characteristics of paints and coatings that may be used.

In our next article in this series covering ISO 12944, we examine the section of the standard that deals with steel structure design. In the meantime, to learn about the Institute of Corrosion Coating and Inspection Training Courses – presented by IMechE Argyll Ruane and Corrodere – contact us today.