PWHT of BS 1501-151-28A

[johnnymist2003]

Hi all,

we have modifications to do on two Separator Vessels, and two Columns.The vessels and columns have been in service since 1967.They were constructed from BS 1501-151-28A material.All of them are in wet sour service.When constructed, none of them were post weld heat treated.Code data book information is sketchy, with very little in the way of test certificates for the plates.We will be welding onto the vessels, and PWHT will be required for the mods.We wish to get a confidence level on the risk of PWHT of the exiting plates and the effect the PWHT will have on the mechanical properties of the plate.We are unable to get a test specimen from the vessels as they are in service.To remove a test piece during the shutdown, PWHT and test and then have a decrease in mechanical strength which would result in de-rating the vessel constitutes too high a risk.Does anybody have any experience in this regard?Can anyone provide any literature references which will provide some guidance?
Any help would be much appreciated.
Thank you
John

 

[codeeng]

Your Gr 28A material (now Gr 430A) is similar to SA 285 Gr C and you should use the allowable stress from this grade for your modifications. After 38 years in service I wouldn't be too concerned about PWHT on the existing vessels but you may want to apply it to your mods. Typical vessel design life is 25 years so you should use this opportunity to perform a thorough inspection.