PWHT 3

[fatcobra]

I am in the process of using localized Preheat on a non pressure attachment weld. I am using a manual log to record temp every 15 minutes, until weld is complete. The material is SA 335 P91 9 chrome. This is a pipe support weld, from dummy leg to base plate. I am pretty sure this is a non code weld. However I am wondering if the weld needs to be stress relieved.

 

[metengr]

fatcobra;
What exactly is Grade 91, the pipe base material or the non-pressure part attachment? This is NOT a routine weld job because the Grade 91 material is considered an enhanced creep strength material. If and I mean if your pipe base material is Grade 91 you ABSOLUTELY need to PWHT this weld and follow exactly the requirements in ASME B31.1. The Grade 91 can be altered by the use of an improper filler metal and PWHT. Do you have a qualified welding procedure for this Grade of material????

 

[fatcobra]

Yes I have a proper procedure, Actually the Pipe dummy leg is SA 335 P91, the Base plate is carbon steel. I belive PWHT would be benefical and is probably necessary for longevity of the weld. The line in question is a reheat header falling under Section 1. The debate here is, is this weld classified as a code weld, as the weld it self is not in contact with the actual Pipe. I have changed our procedure for these welds today, currently we are using ceramic pads to preheat, and charting the preheat with recorder, and I plan to stress relieve them when finished. I was catching some flak, and just want to be sure I'm interpeting this correctly. I can find no allowance for P91 not being stress relieved in Section 1.

 

[metengr]

What is your weld filler metal for this application? If you are not welding directly to the pressure boundary of the reheat header, the weld would not fall under ASME Section I.

The requirements for PWHT would be dictated by the pressure boundary base material. Since Grade 91 is a non pressure part attachment and you are welding to a carbon steel base plate (non-pressure part), I would butter the Grade 91 first, with an E9018 B3, PWHT the Grade 91 pressure part per Section I, and then weld the buttered part to the carbon steel header directly using E9018 B3.

However, why would you use Grade 91 in this application? It is not necessary.

 

[0707]

If it is a non pressure resistant weld I suppose you can avoid the PWHT by welding the dummy pipe P91 grade material to your carbon steel base plate (filet weld?) with a pre heat and a Inconel filler weld followed of slow cooling.

 

[fatcobra]

The filler metal we are using E9018B9, it is what the procedure calls out. The reason we are using P91 material is, that is what the engineering company specified. Thanks for the information, I was Pretty sure this weld was not a code weld. Stress Relief is under way already, so I'm sure that we are covered either way now.

 

[stanweld]

PWHT of the weld as you described is highly recommended. I have had to repair a number of such welds made without PWHT by some of our suppliers; base plates fractured from the dummy legs in transit. Weld metal and HAZ hardness in excess of 450 BHN.

 

[fatcobra]

Stanweld,

That is what I was afraid would happen. I will pass this information on during my next quality meeting.
Thanks.

 

[0707]

Fatcobra

If you are using E9018B9 as the filler metal, which is what the procedure calls out, in that case you have to PWHT to avoid cracking in heat affected zone. If heat treatment is impracticable and your welding is in a non-pressure part, and fillet weld is not wider than 6mm, in that case you can use high nickel electrodes such as inconel 182 as filler metal without the need of posterior PWHT.

Hope it helps

Luis