Q&A with George Winning on corrosion testing
Natalie Daniels talks to George Winning about his work in corrosion testing from the common causes and testing methodologies through to prevention and material selection.
Tell me about your background and career to date.
I studied applied chemistry at the University of Portsmouth, UK in the 1980s. I moved into the oil chemical industry through a company called International Drilling Fluids and then onto TR Oil Services, which later became part of Clariant, UK. I have worked in the oil industry for around 27 years at various places around the world including the Middle East, Far East and the USA. My focus was looking at the development of chemicals such as corrosion inhibitors. I worked for a number of other UK-based companies including Capcis Intertek Group and Premier Oil before moving to Element in 2015 as a global corrosion specialist, covering all aspects of corrosion testing.
What does your day-to-day work at Element involve?
My work is primarily as an internal consultant. At Element, we have three centres of excellence for corrosion in the oil and gas sector based in Aberdeen, the Netherlands and USA. The oil and gas testing industry covers many areas with routine testing focused on qualification of materials to NACE standards. This means that the materials and welding procedures used in oil and gas projects are qualified for sour service and conform to MR0175 (ISO 15156) standards. This involves testing materials in methodologies such as NACE MR0177, tensile tests in a sour gas environment and MR0316 four-point beam tests. My role is to support the routine testing as well as looking at other non-routine projects. As part of this, I develop new areas and test methodologies such as electrochemical testing, as well as assisting our business development group.
What materials do you test for corrosion?
We work predominately on metals for the oil and gas industry. The routine work we do, as mentioned before, is sour service in qualification of materials and welding procedures to standards such as NACE TM0177 or 0316 testing. We test the material under sour conditions to determine whether it is going to undergo sulphide stress cracking or not. From this, we are able to assess whether the weld is going to work for that system and can issue an accredited certificate based on our laboratory tests.
What are the most common causes of corrosion and cracking?
It is the misuse of materials in the environment and misunderstanding what a materials limit is. People who normally use carbon steel think that if they choose a corrosion-resistant alloy then it won’t corrode, but that isn't the case – they just corrode and crack in different ways. It becomes a bigger issue with sulphide stress cracking or stress corrosion cracking where failure is catastrophic rather than a gradual process as seen by corrosion. The correct selection of the materials carbon – low-alloy steels and corrosion-resistant alloys – is critical and the correct testing to confirm the suitability of the material is key to this selection process.
How do you test the material to determine the cause?
Our failure investigation groups in all the laboratories look into this. I get involved if anything is out of the ordinary rather than any standard failure mechanism. The testing technologies include scanning electron microscopy, microscopic analysis and positive materials identification.
What is the process from testing the material to its application in industry?
The routine process involves a front end engineering development stage, which provides a basic recommendation of a material and the design. From there, we would start looking at the materials and at welding them together. All the welding procedures also need to be approved to NACE standards, but with any welding procedure, issues arise as to whether you are doing the weld properly and whether it is covered by the recommended standards. At this stage you would start using a testing programme to qualify
the materials and welds for the project. You may then look at a number of weld procedures and only get three-to-four approved procedures at the end of the testing. If we observe cracking then we would avoid those procedures.
How can the effects of corrosion on metals be prevented?
The easiest way to prevent metal corroding is by correct material selection at the design stage. Once built, one of the main external corrosion prevention method is to coat the material. The important thing is choosing the right material including the coating for the right environment. Another area of testing which is required to prevent corrosion is the use of inhibitors to prevent internal corrosion of carbon steel tests. We are looking at testing to find the most efficient inhibitors to mitigate corrosion.
What specific coatings are used on these steels?
On the outside, subsea requires coatings such as polypropylene or polyethylene coatings, which are tested to determine their suitability. When you get to splash zone area then you would start to look at thermally sprayed aluminium (TSA) coating for the riser sections, as there is no cathodic protection to assist it.
Is it difficult to approve these materials in line with industry standards?
The methodologies are there – it is just a matter of going through the right process. Standards including Norsok M001 will list what metallic materials to use, it is then important to understand how to mitigate corrosion that may still occur. For coating, a separate standard is available to qualify the coating.
How have the testing procedures for corrosion developed during your time in the industry?
They are becoming better. For instance, when I first started in the industry, testing inhibitors was a basic test performed using CO2 in bubble (kettle tests) and wheel tests. Since then, the industry has advanced to make sure when testing is performed that field conditions are matched as closely as possible, for example, using H2S and CO2 and high pressure and/or high temperature testing. We are now testing to match the application environment as closely as possible.
What are the plans going forward for the Aberdeen facility?
We are looking at high pressure testing with electrochemical methodologies, specifically focusing on system pressures and temperatures – not just settling for low temperature testing. We are also assessing the fracture mechanics in different environments to determine the effect of corrosion on the behaviour of materials.
George Winning is an expert in corrosion science with a background in chemicals and metallic testing. He has over 25 years' experience in the fields of production chemicals, corrosion testing and integrity and corrosion management. George is also on the council of the Institute of Corrosion, UK, and director of the NACE Institute, USA.