Intergranular Corrosion for AISI 316
Intergranular Corrosion for AISI 316
(OP)
Dear all I have had a conversation with one of my client about AISI 316 and it's resistance to pitting corrosion and intergranular attack.
My situation is the following, I have selected materials for an Emergency Shout Down valve sited near a well-head where the reservoir is constituted by gas, oil and associated water.
About associated water sampling says that Oxygen is not present and the PH is about 6.9-7.1, H2S is not present (no need of NACE requirements) and the molar percentage of CO2 is about 0.02%.
I have suggested the use of AISI 316 for valve trim because as I know as law no oxygen (cathodic process) no corrosion (in this case pitting). Now client says OK but what can you tell me about intergranular corrosion?
I know that a fundamental part in this type of corrosion is played by heat treatment done to make AISI material, agood treatment avoid the possibility of precipitation, at grane boundary, the intermetallic phase of chromium carbide which is the cause of intergranular attack.
Now, the environment in contact with metal is constituted by chlorinated water (120.000 ppm = 120mg/l), oil and gas phase (that represent the principal phase).
I suspect that chlorine ions could break the passivity film of AISI 316 but without oxygen no pitting is expected and intergranular attack could not be present if AISI 316 is treated in order to dissolve in the alloy matrix the intermetallic phase of chromium carbide (normally AISI 316 is made avoiding the intergranular corrosion including also teh use of alligant like Mo or Ti).
My question is am I right or have I, really, evaluate the intergranular attack of AISI 316?
Regards Vincenzo
My situation is the following, I have selected materials for an Emergency Shout Down valve sited near a well-head where the reservoir is constituted by gas, oil and associated water.
About associated water sampling says that Oxygen is not present and the PH is about 6.9-7.1, H2S is not present (no need of NACE requirements) and the molar percentage of CO2 is about 0.02%.
I have suggested the use of AISI 316 for valve trim because as I know as law no oxygen (cathodic process) no corrosion (in this case pitting). Now client says OK but what can you tell me about intergranular corrosion?
I know that a fundamental part in this type of corrosion is played by heat treatment done to make AISI material, agood treatment avoid the possibility of precipitation, at grane boundary, the intermetallic phase of chromium carbide which is the cause of intergranular attack.
Now, the environment in contact with metal is constituted by chlorinated water (120.000 ppm = 120mg/l), oil and gas phase (that represent the principal phase).
I suspect that chlorine ions could break the passivity film of AISI 316 but without oxygen no pitting is expected and intergranular attack could not be present if AISI 316 is treated in order to dissolve in the alloy matrix the intermetallic phase of chromium carbide (normally AISI 316 is made avoiding the intergranular corrosion including also teh use of alligant like Mo or Ti).
My question is am I right or have I, really, evaluate the intergranular attack of AISI 316?
Regards Vincenzo





RE: Intergranular Corrosion for AISI 316
RE: Intergranular Corrosion for AISI 316
Intergranular corrosion would be a corrosion threat for incorrectly processed material. It would be checked via an appropriate ASTM A262 test.
Steve Jones
Materials & Corrosion Engineer
http://www.linkedin.com/pub/8/83b/b04
RE: Intergranular Corrosion for AISI 316
You can't prevent all corrosion and these Cl levels can drive serious crevice corrosion. The risk of SCC is also a real concern.
Consult some of the references (NACE or API) for CRA wellhead construction.
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Plymouth Tube
RE: Intergranular Corrosion for AISI 316
RE: Intergranular Corrosion for AISI 316
Steve Jones
Materials & Corrosion Engineer
http://www.linkedin.com/pub/8/83b/b04
RE: Intergranular Corrosion for AISI 316
In addition, you may also have to consider the higher levels of the chloride contents in the future if there are. Absolutely a new evaluation for the material is required in this case.
Thomas Eun
RE: Intergranular Corrosion for AISI 316
thanks for your responses and evaluations.
About the possible corrosion mechanisms I want to underline the fact that I don't have Oxygen inside the Reservoir as indicated by Client with associated water analisys.
Valve is a GATE type and only trim is in AISI 316 while body is constructed with AISI 4130 (normal carbon steel with 1-1.5 % of Cr).
Obviously inox with high chloride concentration is subjected to depassivation, but without cathodic process how these mechanisms could take place?
Trim material is made without welds and all elements should be one piece and if the heat treatment is well done sensitization shall not take place (AISI 316 materials are constructed principally to avoid this problem trough a dedicated heat treatment).
In these conditions the use of AISI 316 permits a great cost saving instead of use superduplex of Nickel based materials like Hastelloy.
Anyway there is a non sense if Client had selected carbon steel materials for flowlines and pretends that valve trim shall be in superduplex or Hastelloy material. I say this only because I'm in the position to select a valve to be installed after a well while others have projected the entire system with carbon steel material.
Regards
Vincenzo
RE: Intergranular Corrosion for AISI 316
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Plymouth Tube
RE: Intergranular Corrosion for AISI 316
Steve Jones
Materials & Corrosion Engineer
http://www.linkedin.com/pub/8/83b/b04
RE: Intergranular Corrosion for AISI 316