Threaded fittings to join a threaded pipe of different material
Threaded fittings to join a threaded pipe of different material
(OP)
Hi,
I am planning to Use alloy 800HT pipe (NPS is 1" and Sch. 160) for a high temp process application (35 bar pre and 650 C temp). However, the pipe threaded fittings (union, tee, elbow etc) that I am planning to use for joining different pipe lengths are of SS316L material. Will it be thermally compatible ? What factors should I take into consideration before I decide it to be safe to use SS316L fittings with pipe of alloy 800HT. Has it got to do something with the coefficients of thermal expansion. Pls let me know. Thanks in advance
I am planning to Use alloy 800HT pipe (NPS is 1" and Sch. 160) for a high temp process application (35 bar pre and 650 C temp). However, the pipe threaded fittings (union, tee, elbow etc) that I am planning to use for joining different pipe lengths are of SS316L material. Will it be thermally compatible ? What factors should I take into consideration before I decide it to be safe to use SS316L fittings with pipe of alloy 800HT. Has it got to do something with the coefficients of thermal expansion. Pls let me know. Thanks in advance





RE: Threaded fittings to join a threaded pipe of different material
RE: Threaded fittings to join a threaded pipe of different material
Silver goop is a thread sealant that can work up to 815 C. I guess that should take care of that. Pls let me know the compatibility of SS316L fittings with Alloy 800HT pipe. Thanks in advance
RE: Threaded fittings to join a threaded pipe of different material
RE: Threaded fittings to join a threaded pipe of different material
Yes, you joints will loosen slightly at high temp., but that isn't my biggest concern.
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Still trying to help you stop corrosion.
formerly Trent Tube, now Plymouth Tube
eblessman@plymouth.com
or edstainless@earthlink.net
RE: Threaded fittings to join a threaded pipe of different material
The traditional way to do a transition between materials in piping is by means of flanges. Lap-joint flanges will allow you to use a cheaper high-temperature material than 800H for the backing flanges. And there are several gasket options for the temperatures you're thinking of.
Another option is to use a straight thread joint design like ISO parallel with a metal gasket. Then your silver Goop can do what it's designed to do and the gasket will do what it's designed to do. But you should expect to need to re-tighten the joint after a number of thermal cycles.
RE: Threaded fittings to join a threaded pipe of different material
Thanks everyone for sharing your valuable comments.
Since I don't need to disassemble, I guess welding would be the best option. Also as the working fluid is He gas and is a very small molecule, probably I should avoid flanges in order to have a leakproof joint.
The reason for choosing SS316L fittings is that they are cheap in comparison to Alloy 800HT fittings(around $500 each). As one of you pointed out that SS316L has lower strength at temps of 650 C, can anyone pls suggest me a much better and cheaper option than SS316L. I will appreciate that. Thanks
RE: Threaded fittings to join a threaded pipe of different material
If your service is helium, forget about threaded joints. You're best off welding. Ring-type joint (RTJ) flanges are also an option, as they work well for high pressure/temperature hydrogen services.
RE: Threaded fittings to join a threaded pipe of different material
= = = = = = = = = = = = = = = = = = = =
Still trying to help you stop corrosion.
formerly Trent Tube, now Plymouth Tube
eblessman@plymouth.com
or edstainless@earthlink.net