Compressor shaft and impellers require NACE compliance? 1

[JasonLouie]

Hello,
I was wondering if the NACE MR0175 requirements are for pressure boundaries only or are internals applicable as well?

We are purchasing a compressor for a gas stream that contains CO2 and H2S. There will be no water drop out in the compressor, but NACE MR0175 requirements were requested as a precautionary measure. Now we are questioned about the applicability of the NACE standard on the shaft and impellers of the compressor. The shaft is 4340 and the impellers are F6NM. They do not meet the hardness limits indicated in NACE MR0175. Are the impellers and shaft usually made compliant for sour service, or is it only the casing?

I appreciate any advice you may have.

 

[SJones]

ISO 15156 requirements apply to all materials in the specified scope of application. You will note that Part 3, Table A1 has references to both non-pressure containing parts and to compressors.

If you specified ISO 15156 requirements then the shaft and impellers do not comply and simply trying to sidestep the specification is not an appropriate means of dealing with the non-conformance.

You have three things that you can proceed with:

1. Categoric proof of no liquid water even during settle out and shut in may be sufficient justification to waive ISO 15156 requirements

2. An impeller or shaft failure is unlikely to result in a loss of containment incident but it could be very costly in downtime if a spare is not immediately available (and even then, the spare will be the same material!)

3. Qualifying the non-conforming materials by testing (not an easy route to go down with compressor suppliers from bitter experience)

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[JasonLouie]

Steve,
Thank you very much for your advice. I will insist that the internal components comply with NACE.