H2S and CO2 corrosion
H2S and CO2 corrosion
(OP)
Hi, all... I am currently doing a study on various materials and their properties under influence of H2S and CO2 for downhole equipment, e.g. tools for use in an oil well. So far I have found a general guideline which states that the listed materials are accepted, but the non-listed materials have to undergo a thorough analysis to be accepted under certain conditions. I have used standards such as ISO 15156 and NACE MR 0175 to check whether or not our material is accepted in various conditions, but the results are very confusing. The oil companies are still asking for certain temperatures and concentration levels, but to find these answers quickly is a matter to experts. So I am asking this knowledge base for answers...





RE: H2S and CO2 corrosion
several problems occur in CO2/H2S/H2O environments :
- generalized corrosion (loss of metal thickness) of carbon steel materials due to - pH lowered by dissolution of acid gas CO2 and H2S - and to scaling properties of the formed iron carbonate / sulfur scales. it exists models that describe with more or less success the corrosion rates in CO2/H2S/H2O environments : Dewaard / Nesic / ... Stainless steel and other corrosion resistant alloys (Ni-alloys) are very resistant to generalized corrosion and should be selected when corrosion rate of carbon steel goes above 0.1 to 0.25mm/y
- cracking mechanisms : wet H2S conditions lead to crack initiation and propagation (SCC : SSC, HIC, SOHIC, ...) particularly on carbon steel (refer to NACE MR0175 part 2 or to EFC 16) but stainless steel maybe sensitive in the presence of chloride ions (refer to part 3 of NACE MR0175). These mechanisms have to be anticipated as they can lead to rapid failure by thru-wall propagation of cracks.
selected material should have resistance to both types of potential failure mechanisms : generalized corrosion AND SCC
Depending on your operating conditions, carbon steel or Ni-alloy C-276 may be suitable.
regards
RE: H2S and CO2 corrosion
RE: H2S and CO2 corrosion
"material is NACE approved" means nothing to me
"material complies with NACE MR0175/ISO 15156" really means something
appart from that,
when a ferritic material (such as carbon steel or low alloy steel) complies to a NACE standard or another, it should mean that the material is resistant to CRACKING mechanism(s), i.e. SSC (sulfide stress corrosion cracking) of welded areas in the first place and not necessarily other cracking mechanisms (i.e. HIC of plate materials) and it does not proove at all that the corrosion rate is acceptable.
compliance with NACE MR0175 maybe necessary versus cracking in wet H2S service but this does not give any information on the suitability of the material regarding generalized corrosion.
the material may have an improved resistance to cracking (NACE compliance) but may still corrode within the first years of operation.
I don't work in E&P anymore and I don't know if the material you proposed (1%Cr) is suitable for the encountered operating conditions (vs. generalized corrosion)
regards
RE: H2S and CO2 corrosion
The issue is that you have to consider so many factors, SSC, CSCC, HIC, pitting, general corrosion, weldability, and a few more.
A single spec or test does not assure you that the material is suitable for an application
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P.E. Metallurgy, Plymouth Tube