PWHT of Entire heat exchanger-NEN 3

[deepu78]

For NEN type Heat exchanger as per client specification Shell side PWHT is Mandatory-Due to service requirements.
Shell SA516-GA70 Thk 38mm, I.5 meter dia,10 meter long
Tubes SA-179 Dia 19.05, 2.11mm thk,9150 mm long(approx 3000 tubes)
Tube sheets(fixed): SA765 Gr.II

Which is the preferred PWHT option in the above case? and also why?

A.PWHT of the entire heat exchanger( with tubes assembled in tube sheet)after fabrication.
B.PWHT of shell welds completed first.Then after all the fabrication is completed, local PWHT at the circumferential seam closing welds .
C.IS there any other options?

Is there a industry practice which is recommended.Is PWHT of the entire vessel after fabrication recommended?

Thx,
DV

 

[deepu78]

1.Does entire HX(with bundle inserted, TS & TTS welded) in furnace has any advantage? Does any case study /experience available showing risks?

2.Slow heating and cooling < 10° C /hour
Fabricator(they said had experience) stated that "The slow rate of heating and cooling < 10° C /hour can reduce ΔT between the shell and the tubes and therefore can prevent thermal stresses on components in these phases."At this very slow rate they found no distortion when PWHT the entire HX.
Any one has experience with very slow rate of heating and cooling for eg.< 10° C /hour during PWHT?

3.How spheroidization (440° C -760° C) can be avoided during PWHT? especially during very slow rate of heating and cooling for eg. < 10° C /hour

4. What is the normal rate of heating and cooling during PWHT?

5.Does tubes expanded in grooves and TTS weld will have adverse impact during PWHT of entire HX?Is there some case study/reference available as a proof?

DV