Effect of Heat treatment on pressure vessel with seal welded trays

[kissjxp]

We have a pressure vessel which will be post weld heat treated. The vessel materials is SA516-70. Trays materials is 410S stainless steel. The trays are seal welded to the support ring (Carbon Steel).

We plan to perform the whole vessel PWHT after the seal weld of tray to support ring. But we worry about the distortion and warping of trays during PWHT due to the thin thickness of tray and different thermal coefficient of carbon steel and 410S.

Does anybody has the experience before? please advise. Thanks.

 

[metengr]

The difference in coefficient of expansion between 410 ss and carbon/low alloy steel is not significant.

 

[kissjxp]

metengr:

Do you means that the warping and distortion will not occur during the PWHT?

The vessel diameter is 4200mm. Tray thickness:3 mm.

 

[metengr]

kissjxp;

Do you means that the warping and distortion will not occur during the PWHT?

No. It can occur because of exposure to elevated temperature during PWHT. Why did you install the tray structure before PWHT? Normally, carbon steel pads are used during fabrication and PWHT to allow structural welding to these pads after PWHT of the main vessel.

If you already have welded the tray structures before PWHT, I would suggest you install some temporary supports for PWHT.

 

[kissjxp]

Our client do not accept the 410S welding without PWHT.

 

[kissjxp]

The vessel is in caustic service

 

[stanweld]

To reduce distortion during heat treatment monitor the trays during PWHT to assure that the temperature difference is less than 200F or so of the shell. Distortion occurs during heating or cooling due to high temperature gradients between the tray support ring and tray.