Width of PWHT Band Around a Vessel

[Sharik]

What is now the new minimum requirement for the width of a PWHT band circumferentially around a vessel if a new nozzle is installed? In the older AMSE Codes the band had to extend past the nozzle attachment weld by t or 2", which ever is less on both sides of the band.

The 2004 ASME Section VIII, Div. 1, Paragraph UW-40(5) no longer has this specific minimum width requirement. It only requires the nozzle or attachment to be included in the circumferential band.

 

[metengr]

Is this new construction or an in-service vessel?

 

[Sharik]

This is an alteration, new 6" nozzle addition, to an in-service vessel fabricated in 2005. Shell is SA-516 70N, 1.75" thick.

 

[metengr]

Sharik
Ok. You should be using the NBIC for guidance. Regarding PWHT, there has been an addition to the 2004 Edition of the NBIC where we introduced local PWHT using something similar to a bulls eye method. All of the information is in RD 1100.

 

[Sharik]

This creates a problem, the Contractor's QC Program requires repairs and alterations to be completed to the Code of Fabrication. In this case, ASME Section VIII, Div. 1, which requires a circumferential band to be PWHT'd which includes the nozzle.

NBIC, RD1100 allows for a 'bulls eye' heating band.

ASME Section VIII, Div. 1 only allows for a 'bulls eye' for nozzles on spherical shells or curved heads.

This alteration nozzle is going into a cylindrical shell.

I know we have to have the AI involved, we are trying to get everything organized before presentation to the AI. In this local, the NBIC is only a reference, not a recognized, enforced standard by the AI.

 

[metengr]

Sharik;
That may be so. However, you can still make a case for local PWHT using the NBIC as a recognized standard to the AI. You may need to have the Quality Manual revised to accommodate alternative PWHT methods. However, I don't see this as any great obstacle. We had put this alternative PWHT option as a deliberate method to avoid heating an entire circumferential band around a pressure retaining item. In some cases, using a PWHT band may be detrimental to the object because of attached piping and supports. Code of construction is one thing, in-service repairs is another.

 

[Texastrav]

Sharik
This PWHT appears to be a code requirement based on thickness. You should insure that there are no "service" related requirements for PWHT before employing any type of local PWHT. Local PWHT for service is usually a bit more complex than a standard local PWHT for code compliance.