Cladding Disbonding at Tray Support Ring Attachment after PWHT

[doct9960]

Owner has requirements for new vessels with austenitic SS cladding to weld minor load-bearing internals (e.g. 1/2" thick x 3" wide tray support ring) after PWHT. According to our material engineer, the Owner requirement may be due to instances in the 1980's of clad disbonding after PWHT by the tensile stresses of the tray support ring acting on the cladding that occurred during PWHT cool down. I believe this is possible because of the difference in thermal expansion/contraction of the base metal and SS cladding.

1. What inspection technique is effective in detecting clad disbondment at the tray support ring area?

2. It has been industry standard to weld minor load-bearing internals on cladding before PWHT. Has there been reported incidents of clad disbonding after PWHT?

3. @TGS4, can FEA be done to simulate PWHT conditions and check cladding or weld overlay disbondment at the tray support ring?

I will be requesting for a technical deviation from the Owner requirement and would like to present some options to mitigate the deviation.

Thanks,
doc

 

[weldstan]

UT can detect disbondment.
Way in the past, we had a couple of cases of disbondment in roll and explosion clad items after PWHT but hard to confirm that welding and PWHT was the culprit since no checks were made in the as-welded condition.

 

[Guest102023]

UT.
Disbonding can also go wrong during the bonding process, so I would want to include fairly thorough inspection as a basis for acceptance of the material before beginning construction.


"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[r6155]

I suggest:
1) The fillet weld must have the minimum possible dimensions.
2) Preheat
3) Weld tray support ring after PWHT.
4) Increase inspections. An inspection plan is required.
5) UT, as said, is correct.
6) Acoustic Emission Test can be performed during pressure test.

Regards

 

[jtseng123]

I have the same situation many years ago that we ask vendor to weld a buffering layer of weld overlay, then after PWHT, weld the SS support ring to the buffering layer.
The buffering layer is welded to the base metal for major load bearing support.

 

[GD2]

Doct9960,
What is vessel base material, service and design parameters? Is the vessel exposed to hydrogen?

Hydrogen induced disbonding is common to cladding with PWHT.

GDD
Canada

 

[GD2]

Doct9960,
I am not sure if the Owners decision to weld the support rings after cladding PWHT is right or wrong. Cladding cracks and disbondment is still a continuing study.

Internal Attachment welds are stress risers. Coupled with the differential thermal expansion between the SS clad and the ferritic base metal makes it worse. Presence of hydrogen will even make it more complex.

In fact, study shows that susceptibility to cladding disbonding is reduced by second PWHT.

I don’t think there is so far a solution to avoid cracks and fissures in cladded vessels. Periodic inspection is definitely a necessity.

GDD
Canada

 

[r6155]

An alternative is "Strip cladding weld overlay".

Regards