Piping - Pad and Reinforcement

The various steel materials are divided into "P-groups" of similar composition, similar or identical welding procedures, and so on. There are other CR4 posters who are very knowledgeable about this and can describe it better. I bet we will from some shortly. Excellent question.

Hi Abusaleem,

Regarding the pad or reinforcement for the piping; using same material meaning you will use Pipe also but with the same specification as the pipe you will be reinforcing with.

Thanks for All

For more detail, for now we use A106, we are going to use A36 as pad and reinforcement, is it accepted?

for using pipe same material how we are going to cut it and to be suitable for pad or reinforcement?

Hello,

Material are said to be same when their P-Number are same.P-Numbers for diff.material you will find in Appendix -A in ASME B31.1.

Dear Lahane/Tornado

Thank you very much for your support,

Yes I found P-No. is same both of them are P-No. 1 (A106 & A36)

But I try to understand what is P-No., most of the code talk about preheating & PWHT regarding the P-NO., its just grade for material or what?

P-numbers are groups of materials that are by chemistry and physical properties similar. That is to say that for the purposes of fabrication and welding, the same practices will apply generally for all the materials in that group.

P nos and Gr (group) nos listed are depending upon its Chemical & Mechanical properties of the various base materials . They also depends up on its usability factors and it also helps to reduce the no. of WPS & PQR testing when metals fall under same/similar P nos and group nos.

One more aspect we have to consider during fabrication is the category of material (plate, pipe, forging, casting etc.) and whether is it a pressure part or a non-pressure part.

Hence when you are selecting SA 106 Gr. B Pipe, a Carbon Steel pipe falling under P1 Gr.1 for your pressure part welding and it has to be strengthened by inducing a reinforcement pad surrounding the pipe / nozzle , we can select a similar carbon steel, but not necessarily a high quality material but in a plate form and it could be A 36 or a equivalent CS plate. On the same basis for SS pipe it could be a SS plate etc.

But the pre heating, inter pass temperature, PWHT are purely depends upon the thickness of the base CS used (or) in Alloy Steel the types alloy elements (C,Mn, Cr, Mo, Ni, V etc.) and its percentage.

That is why we calculate the C E ( Carbon Equivalent) to arrive at a definite pre heating temperature range and the requirement is see that, the weld joint or its adjacent HAZ should not become hard / brittle (due to sudden rise in temperature and fast cooling rates) and crack up during the welding or at a later stage. This is applicable for both CS & AS materials as well as Cast iron due to its Carbon percentage Cu etc. For SS, the temperature during (heat input) welding should be controlled to avoid evaporation of alloy elements.

The PWHT is used to soften the materials after welding i.e., to remove the high stress concentration induced during welding operation. This will also help to reduce the distortion after machining if carried out and provides a longer life for the joint.

Trust above details help you to decide upon your pre heat and PWHT requirements.

All the technical information is mostly available in Welding/fabrication hand books.

Sridhar.

Didn't go through Sridhar's post . In case he missed it, the similarity of the metals of the same P nos are haveing one important use- to eliminate galvanic corrossion- predominant when different chemistries are welded together.

it must be same material or should be higher grade.So you can used your 2nd way of thinking about purchase plate............ Normally,what all the fabricators' practice is "use ans cut one more step bigger OD of pipe"ok! the pad size is decided by piping engineer .meaning cross sectional area of pad,thickness,........