MATERIALS SELECTION FOR VALVES IN -Cl & O2 ENVIRONMENT 2

[valvesarefun]

Hello All,

I am trying to select an appropriate materal for the construction of flanged ball valves to be used under the following operating conditions:

Crude Oil & produced water
150 psig max pressure
0-130F temp range
120,000 - 180,000 ppm chlorides
Nil - 300 ppm H2S (hot spots up to 3000 ppm in areas)
<1% CO2
O2 range <5ppb to well into ppm range

A very authoritative materials engineer has reccomended to the end user that 316/CF8M is acceptable for the above conditions excepting that the temprature must stay below 75F. NACE MR0175, however places a constraint on using 316SS in environments with greater than 5000 ppm -Cl. I am confused as to wether or not 316SS is really an acceptable material for this environment,and I am looking for some clarification as to why it is or isnt acceptable.

The alternate reccomendation by the materials engineer was super duplex at tempratures below 175F. I believe it is clear that the super duplex will work, however it is going to be very expensive as compared to the 316.

I am also thinking that a superaustentitic grade of stainless would work. Particularly CN3MN, although I am not sure if it will be more or less expensive than the Super Duplex (6A material). If its more expensive than there is not really any advantage I can see to using it. If there is anything I am overlooking as to why this material might not be suitable, I would appreciate input here too.

Thanks in advance!

-VRF

 

[blacksmith37]

MR-01-75 was intended to address only sulfide SCC ; not Cl SCC.
If you are certain the temperature will never go above 75F,(like shut in the summer,in the sun) austenitic SS are a reasonable risk. Personally , I would not risk it in the USA.

 

[valvesarefun]

The valves are to be buried in N. Dakota somewhere, which means they will very likely stay pretty cool most of the time. However, with the temperature data the customer has supplied I don't think I have any other choice but to exclude the 316ss from my quote.

-VRF

 

[SJones]

What is the material of the connecting pipework because if there is that much oxygen around, the valves will be the least of the end user's worries?

As to the use of ISO 15156-3, you may wish to review Table A.2 again where you will note that, below 60 deg C (140 deg F) and 100 kPa partial pressure H2S, there is no limit on the chloride content of the environment when dealing with sulphide stress cracking/stress corrosion cracking. Get that much oxygen into a system with that much H2S and there is a high likelihood of generating elemental sulphur that will take you into a whole new ball park.

As an aside, please note that ISO 15156 places the onus of materials selection onto the end user, not the valve manufacturer.

As a further aside, 22Cr duplex stainless steel may not have such a price differential as to be unattractive; ask around. Using 22Cr requires that the partial pressure of H2S not exceed 10 kPa.

Steve Jones
Materials & Corrosion Engineer

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

 

[valvesarefun]

SJones,

Thank you for your reply!

The piping and storage tanks are all plastic, so there are no major issues there. There is a seperator being employed upstream of the valves, I'm not sure what materials it will be constructed from, but undoubtedly it will be metal.

I am confused about table A.2. Because it is common practice to consider CF8M & 316SS material to be equals, generally speaking, I would assume it is prudent to use the guidelines set out for S31600 in table A.2. That call out indicates that there is a limit on chlorides of 5000 mg/l max. Am I wrong in my thinking?

You bring up the point of Sulfur, and I believe its presence alone would disqualify the CF8M & the CN3MN. 15156 shows "NDS" regarding elemental sulphur for Duplex SS. Do you have any experience with Sulphur causing problems for Duplex?

Yeah that clause in 15156 is a life saver for manufacturers. However, I always do my best to offer only materials that I believe will be acceptable for the intended application. I wouldnt sell them a carbon steel valves in this scenario, and then expect it to be "not my problem" whenever it fails.

Regarding the 22Cr or 25Cr, I should have specified that we will be quoting 6A Super Duplex with a PREN greater than 40. Based on that I think it will be acceptable.

Best Regards,

VRF

 

[SJones]

It is a convenient time to point out that the Table A.2 in the 2009 version of ISO 15156-3 is a misprint and that there should not be a differentiation between S31600 and S31603. It is understood that some form of correction will take place in due course.

If you are following ISO 15156-3 (sorry, but to me it is ISO and not NACE) then there is only a restriction on chloride content if the designated equipment temperature exceeds 60 deg C with a chloride content of greater than 50 mg/l, i.e. the first two rows of the table There is then also further restrictions on liquid pH.

Elemental sulphur will cause problems for nickel alloys, let alone duplex!

Steve Jones
Materials & Corrosion Engineer

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

 

[valvesarefun]

SJones,

Just so I am clear, are you saying that the restrictive parameters set forth in A.2 for S31600 & S31603 are set to be retracted at some point in the future, leaving, esentially, lines 1 & 2 as a stand alone mandate for Austenitic grades, with the exception of the special restrictions for Nitronic 50(S20910)?

Best Regards,

VRF

 

[SJones]

No I am not. I am saying that I expect there to be no differentiation between S31600 and S31603 for the temperatures, H2S partial pressures, chloride contents and pHs shown.

Steve Jones
Materials & Corrosion Engineer

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

 

[valvesarefun]

SJones,

Thank you for clarifying that point, and thank you for your other input as well.

Best Regards,

-VRF

 

[SJones]

Anytime

Steve Jones
Materials & Corrosion Engineer

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