VFK
Mechanical
- Aug 13, 2023
- 16
What additional design requirement needs to be specified to a fully-threaded, stud-bolt, ASTM F468M UNS N06625 Gr1 with ISO metric coarse thread so that its design is suitable for use as bolting for a pressure containing flange? Reason is F468(M)’s title is “General Purpose” fasteners and for comparison, BS 4882 title is “Bolting for pressure containing flanges”, which suggests to me the latter includes some specific design requirements not covered in the former std. For example, BS4882 appears to mandate the design of the “point”. I know the definition of the stud-bolt nominal length is not a consideration, because BS 4882 specifies a different derivation for metric sizes compared to inch-sizes.
Context follows:
Client, who is an oil & gas major, has requested for a brownfields minor project modification these changes:
• The heat exchanger has been upgraded from SS316L to titanium-2 due to chloride cracking risks.
• heat exchangers and piping fasteners to inconel 625 (UNS N06625) from SS316 due to chloride cracking risks.
• CNAF gskts are being upgraded to kammprofiles due to maintenance issues (long story).
• Service is LP steam, seawater, up to 200degC and up to 3 barg max operating pressure.
• The existing piping connected to the heat exchanger is a mixture of EN1092-1 PN16 flanges and JSA-JIS-10K flanges sizes ranging up to DN100.
• The new Ti-2 heat exchangers
o nozzle flanges have been spec’d to match the existing piping flanges and were designed for temperature/pressure using ASME VIII-1 App2 and WRC538 equations.
o will be workshop hydrotested using the service bolting and service gaskets as required by IOGP. And service leak-tested once installed offshore.
• The above-mentioned piping flanges use M16 stud-bolts.
Summary of stds:
• N06625 only appears in ASME II-D table 3 bolting materials table as SB-446, which is a standard for forged bar.
• Issue is SB-446 contains no requirements for design, manufacturing, finishing, or mechanical testing of fasteners.
• ASTM F468 on the other hand does list N06625 with the same mech properties as SB-446 plus includes all the necessary fastener design, mech testing, etc. requirements. Trouble is the application is for a pressure containing flange, while F468 is for “general purpose”.
• BS 4882 is for pressure containing flanges but does not list N06625. BS4882 is referenced in the Client's bolting specs for a couple of nickel alloy fasteners.
• EN1092-1 refers to EN1515-* for bolting materials but N06625 is not listed.
Context follows:
Client, who is an oil & gas major, has requested for a brownfields minor project modification these changes:
• The heat exchanger has been upgraded from SS316L to titanium-2 due to chloride cracking risks.
• heat exchangers and piping fasteners to inconel 625 (UNS N06625) from SS316 due to chloride cracking risks.
• CNAF gskts are being upgraded to kammprofiles due to maintenance issues (long story).
• Service is LP steam, seawater, up to 200degC and up to 3 barg max operating pressure.
• The existing piping connected to the heat exchanger is a mixture of EN1092-1 PN16 flanges and JSA-JIS-10K flanges sizes ranging up to DN100.
• The new Ti-2 heat exchangers
o nozzle flanges have been spec’d to match the existing piping flanges and were designed for temperature/pressure using ASME VIII-1 App2 and WRC538 equations.
o will be workshop hydrotested using the service bolting and service gaskets as required by IOGP. And service leak-tested once installed offshore.
• The above-mentioned piping flanges use M16 stud-bolts.
Summary of stds:
• N06625 only appears in ASME II-D table 3 bolting materials table as SB-446, which is a standard for forged bar.
• Issue is SB-446 contains no requirements for design, manufacturing, finishing, or mechanical testing of fasteners.
• ASTM F468 on the other hand does list N06625 with the same mech properties as SB-446 plus includes all the necessary fastener design, mech testing, etc. requirements. Trouble is the application is for a pressure containing flange, while F468 is for “general purpose”.
• BS 4882 is for pressure containing flanges but does not list N06625. BS4882 is referenced in the Client's bolting specs for a couple of nickel alloy fasteners.
• EN1092-1 refers to EN1515-* for bolting materials but N06625 is not listed.
