These springs are for a critical downhole application. They are exposed to sour gas and CO2 (during production), and inhibited HCl during the initial phase of stimulation, following perforation. The springs are stressed at installation and used to control a flapper. We have experienced sevearl failures early on the project where the springs have broken at the turns. There is not much published information on any of these materials. Did anyone experience anything like this...any ideas, any papers? Are these materials susceptible to corrosion, pitting, cracking...or could it be a manufacturing & heat treating problem.

The reason we know it broke at the turns is due to running a downhole camera. Unfortunately the resolution will never be good enough to help us determine the mode of fracture. In addition, retrieving the spring (or the whole tool / assembly) means pulling out the whole completion, and as you can imagine is very costly, and not likley to occur. Even if we did retrieve it now, I believe the fracture surface would be damaged due to corrosion, or the two mating surfaces contacting one another. I think environmental testing on these two material is warranted. Thanks for your comments and help David!!