Header & Tube Temperature Measurement 1

[Guest102023]

Thanks to all the contributors on my 'T23' questions. I am designing a system that will capture tube and header temperatures over time on HRSG startup. Not sure yet if I can plug in directly to the plant's DCS, otherwise it will be stand-alone.

I have a specific question concerning TC attachment to the 2" T23 tubes and the thick P22 header. I have received conflicting opinions on the effectiveness of mechanical TC attachment compared with welding. Of course I prefer to avoid welding, and B31.1 does not appear to have anything to say on the subject.

What is 'accepted practice' for TC welding on the above materials, one of which (P22) normally requires PWHT? The thick header has leeway for grinding off the evidence after removal, but the 0.11" wall tube might be a bit trickier.

Any suggestions/opinions on mechanical vs. welded TC attachment?

 

[metengr]

I would recommend capacitor discharge welding or electric discharge welding for T/C attachment. This is addressed in Section I, PW-39. See below

Excerpt from ASME Section I, PW-39....

Postweld heat treatment is not mandatory for attaching bare wire thermocouples by capacitor discharge welding or electric resistance welding
provided the following requirements are met:

 

[Mr168]

I'll second Met's suggestion. The benefit is that when you remove the TC marks after removal, they're easy to file/buff down without removing any significant portion of the base material.

 

[Guest102023]

Thanks for the replies.
I dropped in on my local heat treater who told me pretty much the same thing; I expect to contract that part out to them. The folks at Omega outlined a very simple data aquisition system that plugs into a PC via USB. So I think I am good to go.

 

[Guest102023]

metengr: "Postweld heat treatment is not mandatory for attaching bare wire thermocouples by capacitor discharge welding or electric resistance welding
provided the following requirements are met: ..."
____________________________________________________

What are those requirements?

 

[metengr]

ASME Boiler and Pressure Vessel Code, Section I, Part PW, Table PW39, under Note exemptions for PWHT(see P-No 5A).