Re: [MW:31446] B31.3 PWHT & Preheat Exemption

Hello Mr. Nazeer,

Yes, your understanding and interpretation is absolutely correct.

Control thickness is not to identify the PWHT requirement. It's to evaluate the holding time, holding temperature range and cooling range.

Whereas nominal thickness is the governing thickness for PWHT requirement , which in your case is lesser than 25mm , so PWHT is exempted.

Hope you are not dealing with Hydrogen , Amine , Oxygen or any Nace service while dealing with this case. 

Thanks and Regards

Atul Khatri

On Mon, Sep 14, 2020 at 1:32 PM Nazeer <naz.mhd@gmail.com> wrote:

Dear All,

Request Clarification on which thickness (Control thickness / Nominal thickness) to be applied in the B31.3 2014 -Table 331.1.3  for PWHT & Preheat exemption. Details furnished below.

Weld Joint Details:

Joint : Header Pipe to Weldolet

Weld Type: Integrally Reinforced Branch Connection (B31.3, Fig 3285.4)

Material: P.No 1

Header Pipe Size: NPS 16 , 12.7mm thick

Weldolet Size: NPS 16 x NPS 3 , sch 40

joint groove Thickness (At crotch of Header pipe & weldolet): 22mm

Nominal Thickness (Tm) As per B31.3, Fig 3285.4 : 22mm

Calculated Control Thickness (Tm+Tc):  28mm (22 + 6mm)

Based on above scenario, we had applied weldolet nominal material thickness Tm of 22mm (thicker member of the joint) on B31.3 Table 331.1.3  and not performed PWHT & preheat of 95 Deg C.

Whereas for PWHT exemption, Client is applying the control thickness  of 28mm on B31.3 Table 331.1.3 and insisting us to perform PWHT on the joint due to 95 Deg C preheat not applied.

In my opinion, nominal Thickness to be applied for PWHT exemption and control thickness to applied for calculating Minimum PWHT holding time.

Please advice and enlighten further, whether PWHT is mandatory for the above specified weld joint.

Thanks & Regards

Nazeer

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