17-7PH CH900 in mild H2S atmosphere
17-7PH CH900 in mild H2S atmosphere
(OP)
I have a helical compression spring in a natural gas atmosphere. The natural gas will be in compliance with ISO 15403-2 which has rather strict limits on the amount of sulfur:
⎯ Total sulfur 120 mg/m3 (short-term, 150 mg/m3)
⎯ Mercaptan sulfur 6 mg/m3
⎯ Hydrogen sulfide 5 mg/m3 (short-term, 16 mg/m3)
I'm assuming the pressure is ~1 ATM, I don't see it specified anywhere.
We have been using a 316 spring but it's fatigue life has been less than satisfactory. The 17-7PH CH900 spring has doubled the B10 life. However, I'm getting some opinions that it's corrosion resistance will be inferior to the 316 spring. We have had similar parts in the field for 6 years with a 302 spring with zero failures.
I've read NASA MSFC-SPEC-522B and it's replacement MSFC-STD-3029 but they only cover stress corrosion cracking in Sodium Chloride environments. I've read excerpts from MqGuire's book Stainless Steels for Design Engineers which lists 17-7PH in any condition as acceptable for petroleum industry applications. However, I have a copy of NACE MR0175:2003 and can't find any mention of 17-7 or S17700 anywhere in it.
Can someone point me something definitive on corrosion resistance between 304, 316 & 17-7PH CH900 in this kind of relatively mild atmosphere?
⎯ Total sulfur 120 mg/m3 (short-term, 150 mg/m3)
⎯ Mercaptan sulfur 6 mg/m3
⎯ Hydrogen sulfide 5 mg/m3 (short-term, 16 mg/m3)
I'm assuming the pressure is ~1 ATM, I don't see it specified anywhere.
We have been using a 316 spring but it's fatigue life has been less than satisfactory. The 17-7PH CH900 spring has doubled the B10 life. However, I'm getting some opinions that it's corrosion resistance will be inferior to the 316 spring. We have had similar parts in the field for 6 years with a 302 spring with zero failures.
I've read NASA MSFC-SPEC-522B and it's replacement MSFC-STD-3029 but they only cover stress corrosion cracking in Sodium Chloride environments. I've read excerpts from MqGuire's book Stainless Steels for Design Engineers which lists 17-7PH in any condition as acceptable for petroleum industry applications. However, I have a copy of NACE MR0175:2003 and can't find any mention of 17-7 or S17700 anywhere in it.
Can someone point me something definitive on corrosion resistance between 304, 316 & 17-7PH CH900 in this kind of relatively mild atmosphere?
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RE: 17-7PH CH900 in mild H2S atmosphere
SAE J217 Stainless Steel 17-7 PH Spring Wire and Springs
ASTM A313 Standard Specification for Stainless Steel Spring Wire [17-7PH = UNS S17700 = Type 631]
The wire shall conform to ASTM A 313 Type 631 Condition CH 900 and ASTM A 555/A 555M.
SAE HS-795 Manual on Design and Application of Helical and Spiral Springs
Perhaps Inconel X750 spring-wire would work best. Special Metals X-750 TDS...
http://www.specialmetals.com/alloys, click on the following tabs in-sequence TECH CENTER then click on ALLOYS
AMS5699 Nickel Alloy, Corrosion and Heat-Resistant, Wire 72Ni - 15.5Cr - 0.95Cb - 2.5Ti - 0.70Al - 7.0Fe Spring Temper, Precipitation Hardenable - UNS N07750
Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]
RE: 17-7PH CH900 in mild H2S atmosphere
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RE: 17-7PH CH900 in mild H2S atmosphere
If there is any moisture present you could be in trouble.
Any corrosion will result in hydrogen, and then EAC will be an issue.
What about Nitronic 50 if you don't want a Ni alloy.
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P.E. Metallurgy, Plymouth Tube
RE: 17-7PH CH900 in mild H2S atmosphere
⎯ Total sulfur 120 mg/m3 (short-term, 150 mg/m3)
⎯ Mercaptan sulfur 6 mg/m3
⎯ Hydrogen sulfide 5 mg/m3 (short-term, 16 mg/m3)
Any DATA to back up this claim by McGuire that 17-7PH is approved for petroleum industry applications:
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RE: 17-7PH CH900 in mild H2S atmosphere
17-7 is acceptable for some components (under the general PH SS use), springs not among them (those are usually Ni or Co alloys).
The field for 'sulfur resistant' all of the PH SS are marked 'no data supplied'.
And the strength level depends on the type of component, I don't believe that any of them allow the use of CH material.
In one copy that I have the only austenitic PH SS listed is A286, in another older copy 17-7 is listed in a catch-all paragraph.
If you don't want to infer the information then pay to do the testing.
As far as I know there no such data available.
If you can guarantee that this part will always be 100% dry then it might be a worthwhile risk.
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P.E. Metallurgy, Plymouth Tube
RE: 17-7PH CH900 in mild H2S atmosphere
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RE: 17-7PH CH900 in mild H2S atmosphere
Some seawater corrosion data for 17-7PH [search 631] for lower HT condition [H1025] material... not good...
AD732365 - CORROSION OF MATERIALS IN HYDROSPACE. PART IV. STAINLESS STEELS
https://ntrl.ntis.gov/NTRL/dashboard/searchResults...
also... for grins...
Some artificial seawater SCC data for 17-7PH [search 631] for lower HT condition [RH950] material... not good...
AD709044 - D6-25219? STRESS-CORROSION PROPERTIES OF HIGH-STRENGTH PRECIPITATION-HARDENING STAINLESS STEELS IN 3.5% AQUEOUS SODIUM CHLORIDE SOLUTION
www.dtic.mil/dtic/tr/fulltext/u2/709044.pdf
Field observation [only]. KC-135E TF33 Engine installation, aft cowling: aluminum skins/rivets with 17-7PH TH1050 sheet metal frames and stiffeners. The interior of the aft cowling [over the engine hot-section] runs 'warm-hot [+200F]' and were mostly coated with engine exhaust soot. The 17-7PH parts seemed to hold-up well: no corrosion; however many [annoying] cracks 'appear' to be from sonic-fatigue or thermal cycles... no info whether heavy soot-coating made any difference in cracking. Due to frequent engine-operation, it is likely that the inner cowl surfaces remained 'relatively dry' [moisture free] due to high-heating.
Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]
RE: 17-7PH CH900 in mild H2S atmosphere
Steve Jones
Corrosion Management Consultant
http://www.linkedin.com/pub/8/83b/b04
All answers are personal opinions only and are in no way connected with any employer.