Bolt material SA 193 B7M/ Nut material SA 194 Gr L7
Bolt material SA 193 B7M/ Nut material SA 194 Gr L7
(OP)
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
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





RE: Bolt material SA 193 B7M/ Nut material SA 194 Gr L7
Regards,
Cory
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RE: Bolt material SA 193 B7M/ Nut material SA 194 Gr L7
Thank you
RE: Bolt material SA 193 B7M/ Nut material SA 194 Gr L7
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
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RE: Bolt material SA 193 B7M/ Nut material SA 194 Gr L7
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