Bolt material SA 193 B7M/ Nut material SA 194 Gr L7

[Peter113]

Hi,
the bolts material specified for assembly of WET SOUR process piping (non exposed to fluid) was SA 193 B7M. Due to a mistake in our material take-off software, SA 194 Gr L7 was specified for nuts instead of SA 194 Gr 2HM (22HRC). This material is qualified under a hardness (24-38 HRC). Because of this material is not in contact with fluid, it is in compliance with NACE MR0175 but we are not confident about a excessive wear may happen in the bolt material due to the difference in hardness.
Please advise.
Peter

 

[CoryPad]

Fasteners like these don't wear appreciably during assembly and use. Is either the bolt or nut coated? What is the environment? You may have a rust-in-place, non-serviceable joint, but that has nothing to do with hardness.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Peter113]

No coating is used. The plant is near the coast.
Thank you

 

[CoryPad]

There is no L7 designation in ASTM A 194. There are grades 7 and 7M.

Wear is not a concern for this application, unless you are disassembling and reassembling parts frequently.

Without a coating, and located near coastal salt water, these parts will corrode. That could cause binding, wear (if the corrosion products are ground into the thread surfaces), even fracture.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Cockroach]

You probably mean ASTM A193 B7M stud and ASTM A194 2HM nut, NACE bolting material for standard thermal service. But I would strongly suggest HRc<<22 since 22 is the limit under the specification and most technical types would argue successfully that microscopic sites of HRc>22 could exist and push you to test. My experience with valves!

I suggest HRc 18-20. It DOES NOT matter if the material is exposed to the wetted perimeter of the pressure containment envelope! The point of the specification is that you have potential for contact in a sour environment. You could for example, bleed off H2S gas from an aerated fluid leaked from a flange gasket. Now your bolting would potentially see the sour environment.

I couldn't caution you more strongly not to split grey hairs and put your interpretation into the specification. Many, many engineers get into problems and force unnecessary cost, time expenditure and grief to suppliers of equipment. One good example of this is ISO 15156 which calls out for no stainless steel above 65C applications. There must be a trillion valves in global usage inside plants exposed to 65C. They worked successfully historically. So should we change them all out?

Seems kind of crazy! So be careful!

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada