The offshore oil and gas industry has seen a continual trend of conservatism in design for applications where a high level of strain is expected during the installation phase, leading to a tightening of the acceptable mechanical property performance of the linepipe. This is especially true with regards to longitudinal tensile properties in the strained and aged condition. Due to the expected change in data seen throughout previous projects, are the tightening expectations realistic for the manufacturers and cost effective for the client?
The current condition that is widely accepted for the release of pipes suitable for high strain events is straining and ageing. However is this appropriate given that pipes are coated (aged), installed (strained) then left over time (aged)? These questions will be investigated through a series of tests and data analysis. For this project a conventional ageing as per the standard and a coating simulation were used, with all test pieces having either 0% or 1% applied strain. The test pieces for this project were tested in one of seven conditions;
• As manufactured
• Aged (at 200°C/5min or 250°C/1hr)
• Strained and aged (1% strain applied then aged at 200°C/5min or 250°C/1hr)
• Aged and strained (aged at 200°C/5min or 250°C/1hr then 1% strain applied)
To ensure a direct comparison in the data the comparable test pieces were taken from the same circumferential position on the pipe. All testing for this project was carried out on material of a similar composition and future development of this work will comprise of documenting the effect on different microstructures, t/D ratios and levels of strain. It was clear from the project that changing the conditions used had an impact on the results. This could have implications for the industry in the future and has set up a scheme of development following on from this project to gain a greater understanding.
