Stainless Options for Part requiring 107 ksi MYS @ 350F... 2

[johnchrc]

Hi All,

I have a 3.11" OD Nut x 2" long with 2.5 SA box. It is a highly stressed part and I need suggestions for a SS or Non-Ferrous material with min requirements:

1) Commercially available
2) 107 ksi mys @ 350F (max temp)
3) Meet NACE MR0175 (Sulfide Stress Cracking)
4) Resistant to Chlorides

I would normally use Inconel 718, but it is mating to another 718 part and we have galling issues with matching connections (even with surface peened threads and an Electroless Nickel Plating with PTFE Codeposit in Box) so we use K500 Monel for mating parts to mitigate galling but K500 doesn't have the strength.

Cant use 17-4 because of H2S

Suggestions for commercially available bar or tube with 3-1/4" OD or > would be appreciated. (material will be machined in TX, LA area)

THANKS

 

[TVP]

Here is a list of alloys that are used for high strength fasteners for O&G applications:

Ni-base
Alloy 718
Alloy 725
Alloy 925
Alloy 625
Alloy 59
Rene 41

Co-base
MP35N
MP159

Ti-base
Ti-6246 (UNS R56260)
Ti-38644 (UNS R58640, also called Beta C or Grade 19)

I would expect good performance with one of the Co-based alloys, provided that the Alloy 718 box has the EN + PTFE coating.

 

[johnchrc]

Thanks TVP,

How would a Titanium based material perform on a thread with 2x the modulus? I'm not sure how the connection would behave or if it could create problems.

Also, in the case of bearing stress, shoulder vs. shoulder in compression, I have always used a "bearing stress factor" of 1.5 x YS. Is the compression stress or bearing factor available for the Titanium or do you know where I could find? I need to know the allowable stress on a 718/"Titanium or other" shoulder (90 degree) loaded in compression and I think 1.5 is a very conservative value.

Thanks again.

 

[TVP]

Internally threaded components are often less stiff than their externally threaded counterparts, e.g., steel bolts/studs into aluminum engine blocks. The joint just needs to be engineered such that the desired preload is achieved, and does not relax excessively, doesn't overload the threads, etc. If I understand your dimensions, the thread engagement is less than 1D? If so, thread stripping will certainly be a concern.

In terms of properties, there are a number of references for bearing and compressive strength, as well as limiting surface pressure (term used in the German standard VDI2230). The bearing yield strength is typically ~ 1.5 * tensile yield strength for metals according to data in MMPDS-05, assuming an edge margin e/D = 2. The tensile and compressive yield strengths are roughly the same. Based on your problem description, I would use the compressive yield strength as the design parameter. Here are some numbers:

p_G = 890 MPa for Ti-64 according to VDI2230 (YS = 820 MPa, UTS = 890 MPa)

Fcy = 889 MPa for Ti-64 bar according to MMPDS-05
Fty = 862 MPa for Ti-64 bar according to MMPDS-05
Fbry = 1480 MPa for Ti-64 bar according to MMPDS-05

Fcy ~ 1100 MPa for Ti-38644 bar (solution treated & aged condition) according to MPH - Ti
Fty ~ 1100 MPa for Ti-38644 bar (STA cond) according to MPH - Ti
Fbry ~ 1800 MPa for Ti-10-2-3 (STA cond, similar Fcy & Fty as Ti-38644) according to MMPDS-05


VDI 2230 Part 1 (Feb 2003) Systematic calculation of high duty bolted joints - Joints with one cylindrical bolt

http://www.beuth.de/en/technical-ru...sessionid=CDD94177A252A2C88A21CBA9AC026CFB.4?

Materials Properties Handbook - Titanium Alloys (edited by Rodney Boyer, Gerhard Welsch, & E Collings, ASM International, 1994)

http://www.asminternational.org/portal/site/

http://www/menuitem.2b9d1953d012ee1...e2b41ce0f8110VgnVCM100000701e010aRCRD&itemId=

DOT/FAA/AR-MMPDS-05 Metallic Materials Properties Development & Standardization
The older -01 revision can be freely downloaded, as can the predecessor MIL-HDBK-5J from the following website:

http://www.everyspec.com/FAA/FAA+-+General/DOT-FAA-AR-MMPDS-01-JAN2003_24102/

 

[johnchrc]

Thnaks TVP,

This is a 2.5"-16 TPI SA Box Connection threaded onto 718 mandrel with Pin thread under no load. The Nut holds the mandrel to a head via retainer coupling. See attached. There are no bolts. The nut would be Titanium or other High Strength CRA

 

[metengr]

The link above does not work for those that are not ASM members.

http://books.google.com/books/about/Materials_properties_handbook.html?id=x3rToHWOcD8C

 

[johnchrc]

Clarification - The nut is made up with no load but then transfers approx 400 kips across tool at up to 350F.

- CJ

 

[EdStainless]

An alloy like 725 (age hardening 625) would be my first pick.
Of course you don't need that great of corrosion resistance since 718 is not that fantastic.

Could you use 13-8PH in the overaged condition?

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