17-7PH CH900 in mild H2S atmosphere 2

[dgallup]

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?

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[WKTaylor]

Not 100% topic specific, but closely related...

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]

 

[dgallup]

Thanks but not looking for alternate materials, already have a great deal of testing completed on the 17-7PH CH900 with great results. Just looking for corrosion test date in mild sulfur environment. We do call out the wire to ASTM A 313 Type 631 Condition CH900 on the drawing but most people are more familiar with the 17-7PH designation.

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[EdStainless]

I doubt that 17-7 in that condition will like H2S.
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

 

[dgallup]

I DO NOT WANT ALTERNATE MATERIALS. I'm looking for DATA on 17-7PH CH900 in a very 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)

Any DATA to back up this claim by McGuire that 17-7PH is approved for petroleum industry applications:

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[EdStainless]

Have you read MRO175?
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

 

[dgallup]

I only have the first edition MR0175, searching it does not return any hits for 17-7, CH900 or 631.

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[WKTaylor]

dgallup... more info, similar vein...

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/titleDetail/AD732365.xhtml

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

http://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]

 

[SJones]

Since you are below 65 psia, MR0175 gives you a get-out-of-jail-card-free anyway, whether the alloy is listed or not. MR0175 only deals with sulphide stress cracking which won't help you too much with your fatigue assessment of the material.

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.