ASME B-31.1 Thermowell Stainless steel material in wet environment 1

[ATsampalas]

Thermowell Stainless steel material in wet environment according to ASME B-31.1 (up to 2010 Edition) .
Question 1 : Is Stainless steel material (A182-F316H) acceptable for use on Boiler External Piping at Temperatures of 316 °C max. ?

Remarks :
In my opinion, ASME B-31.1 does not mention this case.
The only information is given in § 123.2.2 (C) where ASME 1 + ASME 2D can be used...
In this case "Ferritic Material only can be used or S31803 (PG-5.5 + PG-9.1 + PG-9.7)
Question 2 : Does an alternative stainless steel exist for ASME B-31.1 ?

Sincerely,

 

[hacksaw]

instruments are not governed by B31.1, traditionally stainless steel components that tolerate the stress and suited to the fluid are fine, there is a new thermowell standard that gets into the B31 issue a bit more that previous versions

 

[Duwe6]

hacksaw, what is the "new thermowell standard" please? Sounds like something I need to read. Thanks.

 

[hacksaw]

was amazed that it did not just pop up on google, the code designation is PTC19.3TW

more that a few suppliers offer sizing codes

http://www.asme.org/products/codes---standards/thermowells

 

[ATsampalas]

Hello hacksaw,
Do not forget what the requirements are :
a) Governing Code = ASME B-31.1
b) Environment = Wet environment (see attachment)
c) Choice of the Base Material + Is Stainless steel material (A182-F316H) acceptable ?

Remark : 1) I have PTC 19.3 TW (2010 Edition) which is not giving any answer to my asking as can be seen in page 10 Materials - precautions to be taken with the base material to avoid stress corrosion cracking... (see attachment) .
2) One stainless alternative material given by ASME 1 is S31803...

Conclusion : Thank you for your answers but up-to-now I have no solution to my questions .
Sincerely,

 

[Duwe6]

ATsampalas: A thermowell is not "pipe", it is an instrument. Thus a s/s thermowell is acceptable in a B31.1 steam line. The typical material for TW's is 316L, but 304L will work also.

Due to a TW's small diameter to thickness ratio, if half of it was eroded off, it would still have a higher pressure rating than new pipe.

 

[hacksaw]

you can very well use non-stainless steel wells in B31 services, case in point: high pressure >150 bar, boiler and piping systems involving weld-in instrumentation components in the same materials as the adjacent piping/vessel. In those ases use of SS components as part of the primary pressure containment is simply not possible.

you are also right to be cautious about using any stainless steel in the steam drum where the thermowell is exposed to high temperatures and the various dissolved solids (salts) capable of causing SCC. In such cases go with the same material grade as the vessel, even if the thermowell is flange connected.