mechglitch
Mechanical
- Nov 6, 2008
- 8
I have a 12 foot diameter penstock made of 3/8" thick plate. The penstock shell is exempted from PWHT since the plate thickness is less than 1.25" thick and carbon content is less than 0.3 per cent.
However, at the bifurcation where the pipe splits, a 2" thick stiffener (a T-shaped stiffener) is welded along the seam. The dimensions of the bifurcation (wye) piece are seemingly too big for furnace (65' long by 25' wide).
ASCE No.79 on Penstocks does seem to indicate PWHT might be required due to the stiffeners, however the companion guide to B&PV VIII (p.23) states the nominal thickness used to determine PWHT is the thickness of the weld, the pressure retaining material, or the thinner of the sections being welded, whichever is Least.
q1. Is PWHT required due to the thick stiffener or does the pressure plate thickness govern?
q2. How would such a large piece be PWHT if required?
