PWHT of CRO

[normankiddie]

I have a project where I have to perform 3 mm of GMAW CRO (ErNiCrMo-3) onto a Vessel that had previously had 3 mm of 316L CRO applied by SAW to a SA516 Gr 70 Vessel. The vessel is ASME VIII Div 2 and also has to conform to NACE for Sour Service. The vessel is in Sour Service and is 2" thick.

Does one have to perform PWHT?

There are 2 questions,

1) What are ASME VIII requirements with the application of CRO onto CRO?
2) Which direction does one take onthe NACE requirements.

Any ideas as to which direction to head would be appreciated.

Thanks

 

[metengr]

normankiddie;
If you are depositing CRO on top of an existing CRO to build-up the surface, my initial response would be no PWHT is required because you are not contacting the base material directly. If this is the case, I would use elevated preheat.

If you completely remove the original CRO and deposit the overlay directly on the base material, PWHT would be required as per the original weld overlay.

 

[normankiddie]

I am of the same opinion. We will not be removing the existing cladding.

The problem with an elevated Pre-heat is that this work would be done in the field where conditions are difficult as is, adding a pre-heat always complicates matters......

We have in the past done a preheat of 100C on some of our other procedures, whats your thoughts on this?

 

[metengr]

Here is the reason why I suggested elevated preheat. One - using elevated preheat will reduce the rate of cooling of the base material and result in less harmful thermal gradients and thermal stresses. I would use resistance heaters to control preheat. My thought was to preheat to 150 deg C min.

 

[blacksmith37]

I also would reccomend a preheat; With the 3mm thickness of the original CRO, the HAZ in the A516 from the additional CRO, could possible be hot enough to austenitize it ( > 1330 F). So the preheat will slow the cooling rate to "prevent" hardness from exceeding HRC 22. If hydrogen diffuses through your CRO layers, you don't want crack suseptible (high hardness) areas in the A516.