Investigations into the Fatigue Strength of CRA Lined Pipe

Pipes that experience sour service need to resist that corrosive environment. One method for achieving corrosion resistance is by lining the inside of the pipe with a corrosion resistant alloy (CRA), such as stainless steel or a nickel based alloy. This has the advantage of being much cheaper than either making the pipe from the CRA or metallurgically bonding CRA to the pipe (ie clad pipe). Lined pipe is gaining popularity, and has so far been used successfully in applications where applied strain levels are low, however more data is needed on its fatigue strength and its behavior when subjected to high levels of applied strain. A Joint Industry Project (JIP), funded by Petrobras, BG Group, Saipem, Tenaris, Technip, Cladtek and HMC, was run by TWI Ltd and INTECSEA to investigate and generate data on CRA lined pipe. The JIP included full scale resonance fatigue testing, allowing the failure location of lined pipes to be investigated, development of an ultrasonic inspection procedure for lined pipe, small scale mechanical tests to generate materials data and calculation of stress intensity factors specific to the lined pipe geometry. This paper presents a summary of the work carried out. The significance of the paper is that it describes a body of work carried out in the field of CRA lined pipe, helping operators and those at the front-end engineering design (FEED) stage to choose lined pipe, with the resulting cost savings.