StressGuy
Mechanical
- Apr 4, 2002
- 484
This is a code question, but I’m specifically concerned about piping systems, so I’m addressing it in this forum first.
A36 Carbon Steel is commonly used for fabricating pipe support shoes either from structural shapes or from plate. No doubt every company has these shoes in there standards.
Now, on some recent projects, I’ve run into issues with it on some relief/flare applications. The lines are normally ambient, but due to some auto-refrigeration cases, can see temperatures down to -20°F. The lines are typically not insulated, but are installed with welded shoes as we would do with hot pipe.
Now, in looking at MSS SP-58 2002, it says that A36 can be used for pipe supports down to -20F with an allowable stress of 16,600 psi.
However, B31.3 Tables 323.2.2 and 323.2.2A say that A36 can’t be used below the temperatures indicated by curve A. Note 1 of table 323.2.2 specifically mentions A36 as a material that cannot be used below the minimum temperature curve.
Effectively, this means that shoes made from A36 can’t be used in B31.3 service below 15°F for material up to 3/8” thick and if using ½” plate, you can’t use A36 shoes below 30°F! Even in Houston, you can get temperatures that low in the winter, much less in the rest of the country. Now, even if I have a typical hot process line, it’s still going to be cold at the bottom of the shoe where an axial line stop (directional anchor) could be welded to the bottom of the shoe. The way B31.3 is written, we’d better hope that the steel for the shoe and stop is less that ½” thick and we don’t see temperatures below 30°F.
Can anyone explain why there is such a disconnect between MSS and ASME? If I were to order a spring hanger assembly with a pipe clamp, the vendor would no doubt give me a clamp made from A36 flat bar and be in compliance with MSS SP-58. Would I need to over ride this to get an alloy clamp to be in compliance with B31.3?
To further muddy the waters, MSS SP-58 is listed as a reference standard in Appendix E of B31.3.
Edward L. Klein
Pipe Stress Engineer
Houston, Texas
"All the world is a Spring"
All opinions expressed here are my own and not my company's.
A36 Carbon Steel is commonly used for fabricating pipe support shoes either from structural shapes or from plate. No doubt every company has these shoes in there standards.
Now, on some recent projects, I’ve run into issues with it on some relief/flare applications. The lines are normally ambient, but due to some auto-refrigeration cases, can see temperatures down to -20°F. The lines are typically not insulated, but are installed with welded shoes as we would do with hot pipe.
Now, in looking at MSS SP-58 2002, it says that A36 can be used for pipe supports down to -20F with an allowable stress of 16,600 psi.
However, B31.3 Tables 323.2.2 and 323.2.2A say that A36 can’t be used below the temperatures indicated by curve A. Note 1 of table 323.2.2 specifically mentions A36 as a material that cannot be used below the minimum temperature curve.
Effectively, this means that shoes made from A36 can’t be used in B31.3 service below 15°F for material up to 3/8” thick and if using ½” plate, you can’t use A36 shoes below 30°F! Even in Houston, you can get temperatures that low in the winter, much less in the rest of the country. Now, even if I have a typical hot process line, it’s still going to be cold at the bottom of the shoe where an axial line stop (directional anchor) could be welded to the bottom of the shoe. The way B31.3 is written, we’d better hope that the steel for the shoe and stop is less that ½” thick and we don’t see temperatures below 30°F.
Can anyone explain why there is such a disconnect between MSS and ASME? If I were to order a spring hanger assembly with a pipe clamp, the vendor would no doubt give me a clamp made from A36 flat bar and be in compliance with MSS SP-58. Would I need to over ride this to get an alloy clamp to be in compliance with B31.3?
To further muddy the waters, MSS SP-58 is listed as a reference standard in Appendix E of B31.3.
Edward L. Klein
Pipe Stress Engineer
Houston, Texas
"All the world is a Spring"
All opinions expressed here are my own and not my company's.
