PWHT Requirements 4

[FixedEquipment]

I am working on a project to add some nozzles to vertical drums. Both of them were built in 1975 and the shell material is SA-285-C.

I have some confusion regarding the Post Weld Heat Treatment of the vessels. One has a 1-9/16" thick shell and the other has a 1-5/8" thick shell. The manufacturers data reports indicate that neither vessel was heat treated. According to table UCS-56, SA-285-C should be heat treated if its thickness is greater that 1-1/2"

Does anyone know of a reason why these vessels would not have been heat treated.

Any advice is greatly appreciated.

 

[metengr]

FixedEquipment;
If what you are reporting is accurate, the vessels should have been subjected to a thermal treatment after long seam and girth welding. Was the heat treatment reported as a re-normalization heat treatment versus a subcritical PWHT?

 

[stanweld]

Does the Data reports state the shell thickness described or as 1 1/2"? In 1975, the requirements for PWHT were for T > 1 1/4" unless a 200F preheat was applied and the max nominal thickness was raised to 1 1/2".

Maybe somebody got paid under the table to look the other way or sheer incompetense by all parties involved.

 

[vesselfab]

you have to look at data report U-1a

if it shows 1 1/2" thick....it could have been preheated to skip the PWHT.

you only pwht ""greater"" than 1 1/2" thick

that is if they were code stamped

 

[chaulklate]

Could also be the difference between the nominal thickness used vs. the minimum thickness required. Thicker steel may have been used for other mechanical reasons, like supporting a platform, or simply because they had it in stock or could get it from their supplier sooner. Take a look at the minimums required for the unit.

 

[FixedEquipment]

I have resolved the issue. The vessels are actually 9/16" and 5/8" thick. On the data reports the numbers are written exactly like this: 1-9/16" and 1-5/8" thick.

I don't know what they were trying to indicate, but it caused me quite a bit of confusion until I figured it out. Thanks to everyone for your responses to my question.

 

[weldtek]

chaulklate makes a point which, to me, could lead to some comfusion.
Per ASME Sec VIII UW 40, the governing thickness for determining the need for PWHT, is the thickness at the welded joint. My point being, that regardless of minimum thicknesses required for design, the need for PWHT is driven by the thickness at the weld. If I have a welded shell plate 1-9/16" thick, but, only require 1.25" for design, PWHT is required.

 

[metengr]

Please no more confusion - the thickness for PWHT is based on nominal thickness as uniquely defined in Section VIII, Div 1 Part UCS-56 (a) and UW-40 (f).

 

[SnTMan]

1 ea. @ 9/16", 1 ea. @ 5/8"