The November meeting was a joint session with IOM3 and there were two topics presented - “Managing Marine Corrosion on Offshore Wells - Avoiding Structural Failure” by Ian Taylor of Shell, and “Cormorant Alpha Leg C4 Leaks – Cause, Response and Lessons Learned” by Fraser Selfridge (TAQA).
Ian gave an explanation of surface casing corrosion, where issues have been seen in practice, what was done, how inspections are performed and examples of repairs carried out. Photographs and diagrams were used to demonstrate subsea well components, how wells were built and typical corrosion issues experienced. Wells must be structurally self-sufficient and that the key was to prevent structural collapse, in particular the effect of corrosion on surface casing loading. He explained measurement techniques used to quantify wall thickness especially the use of Pulsed Eddy Current (PEC) with results later combined with structural modelling to improve predictions on failure. The mitigation approaches, such as loading redistribution, installation of supports, grouting and replacement, were discussed, and he emphasised the importance of an initially good design such as using good grade steels, appropriate centralising, and consideration of the effects of corrosion, among others. Ian concluded with a project example of how corrosion was identified and how a repair was performed using collars and load transfer techniques.
Fraser discussed leaks experienced on leg C4 of Cormorant Alpha. The platform was similar in design to a number of North Sea concrete structures – topsides steel process area on concrete legs, with a vast area of concrete storage cells below the legs. There were particular problems and a high risk area below the GTF (Gas Tight Floor) of leg C4, with limited isolation possibilities to control leaks. Follow-up inspections (for remaining life) are challenging, expensive and difficult to implement. The root cause of the failure was considered to be Corrosion Under Insulation (CUI) which was missed during the Risk Based Inspection (RBI) process. He explained that there were limitations on the pre-inspection techniques as in some cases, pre-inspection results showed no indications even when significant degradation was present after passive fire protection removal. He went on to discuss the project to implement suitable clamping repairs which were challenging due to the location. Also surface preparation and the presence of a lot of fully welded lengths poses extra challenges. Fraser concluded his talk by explaining that RBIs may not necessarily identify issues indicating technology limitations and lack of access issues may introduce gaps in the process.
The next meeting will be held on 28th February, when Gary Wallace of Permasense will discuss “Monitoring High Temperature Corrosion Attack: correlation between Crude Corrosiveness and results from online Corrosion Monitoring” Online monitoring of corrosion is fast becoming industry best-practice over traditional periodic manual inspection as a means of gathering an up-to-date and more thorough picture of asset integrity. This talk will demonstrate how data delivered by an online corrosion monitoring system correlated with micro-changes in the measured corrosion influencing variables during a period of high temperature corrosion attack. This will be held at the usual venue, the Palm Court Hotel, 81 Seafield Rd, Aberdeen AB15 7YX, with the evening starting at 18.00 and the presentation at 18.30.
On 28th March there is a visit to Cosasco at Bridge of Don, where the topic discussed will be, “Latest Advances in Real-Time Monitoring and Safe Retrieval”. The event starts at 18:00 and full details will be advised later.
A calendar of local events of interest to corrosion professionals in the Aberdeen area and the opportunity to sign up to the branch mailing list is available at https://sites.google.com/site/icorrabz/home