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Downhole injection tubing material selection (inconel /super duplex)
2

Downhole injection tubing material selection (inconel /super duplex)

Downhole injection tubing material selection (inconel /super duplex)

(OP)
Hello,

I have a question regarding choice of material for downhole gas production well, used for capillary or injection tubing. Normally the spec used for a scenario like this is Inconel 625 (0.5", 0.083" wall). However material is not readily available, lead time to long to wait. I was given the following alternatives available:
Inconel 825
A 2205
A 2507.
Environment is downhole, BHT 122C (252F), pressure 8.5-9MPa (1233-1885psi), 20% H2S, 6% CO2, elemental sulfur present, no or trace chlorides.
Internal tube service won't be much of an issue as it will essentially carry fresh water.
We error on the side of conservative, so normally use the inconel 625, we want to install and forget. Which of the above options would be best for corrosion/pitting/SSC/SCC resistance? To me it would seem the inconel 825, would perhaps be similar to 625, with slighlty less resistance due to less Ni, but still has relatively high concentration. It appears A 2507 generally better than A 2205, but we don't have to worry about chlorides here. Any comments on suitability of these materials to conditions or similar materials would be appreciated. Thank you.

RE: Downhole injection tubing material selection (inconel /super duplex)

If there is a policy that the material must also meet ISO 15156-3, then the duplex stainless steels are ruled out immediately with that gas composition and pressure.  For a possible alternative material, the issue will be the sulphur: is it remaining in the gas phase or is it precipitating onto the tubing?  If there is precipitating solid sulphur (or possibly liquid at that temperature), then 825 will probably be OK up to 2000 ppm Cl-. If you wish to move up for conservatism, then G-3 offers more resistance with C-276 probably offering best performance.

Steve Jones
Materials & Corrosion Engineer
http://www.oilandgaspeople.com/cv/11499664
http://www.linkedin.com/pub/8/83b/b04
 

RE: Downhole injection tubing material selection (inconel /super duplex)

I agree with SJones, Alloy 825 is the only grade to consider out of the three choices you were given.  Neither of the duplex stainless steels is appropriate for these conditions, based on ISO 15156-3 (NACE MR0175).  I'm not sure that G-3 or C-276 are any more available than Alloy 625...

RE: Downhole injection tubing material selection (inconel /super duplex)

(OP)
Thank you SJones and TVP. I was in the process of reviewing NACE MR0175 when I was writting this and came to the same conclusion. Elemental sulfur is precipitating onto tubing, which leads to other issues we have to deal with. I was also searching for material in field scenarios where material has shown resistance to elemental sulfur. I imagine C-276 is a bit expensive, I have never used it before...

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