Welding on the cladding for an existing PWHT Vessel

[mech1925]

I'm working on an existing PD 5500 Cat.1 cladded(CS+316L) vessel that requires Weir Plate modification work on the inside.
The vessel is applied with PWHT due to thickness.
Planned weir plate modification work, will require additional welding on the the clad part for the weir plate support.

Question:
Since the new welding will be done on the cladding part, is PWHT required after welding?

 

[metengr]

As long as the welding does not create a weld heat affected zone in the vessel base material, you should not require PWHT.

 

[racookpe1978]

Seems to me it will be very hard to support a claim that the heat-affected zone will not be through the cladding and into the wall. How thick a wall? How thick is the cladding? What size weld? What length of weld?

 

[mech1925]

CS is 90mm, Cladding is 3mm

 

[mech1925]

@metengr, That is exactly what I was thinking. But, normally when vessel is PWHT'd it is generally marked in the vessel as "PWHT'd vessel, welding is not allowed". Now, this makes it complicated in terms on how I will convince the client because it generally says no welding. It did not say no welding on the HAZ.
So, can anybody give some code references that mentions about HAZ.

 

[metengr]

Most likely, you would need to use a weld coupon (flat plate) to demonstrate that based on remaining cladding thickness, that weld build-up does not result in a locally hardened heat affected zone in the vessel material. This can be easily done using flat plate of similar material as the vessel with cladding applied, PWHT and then locally removing some thickness of the cladding by grinding that you intend to weld overlay. This is the only way to demonstrate that PWHT would not be required.