How to define a pipe lot size?

[vesselguy]

Hi all,

Can someone show me how to define a pipe lot size for the purpose of NDE? I heard there could be many ways to do this but I don't know what they are as I don't do piping much. B31.3 specifically tells you that the amount of RT, or any NDE, is to be applied to a "lot" of pipe. So for RT, tracers is applied to a "lot", whatever that lot is as defined by the Owner. I would like to know the correct way and typical way people have define the "lot".

Thank you.

 

[stanweld]

You should define the lot during your bid if the Owner/Engineer has not predefined it. For a normal 5% examination, we like to define it as one shot for every 20 butt welds made with each WPS and will include at least 5% of a welder's butt welds. We define the lot in our Quality System and in our bid because most of our Customers do not and their Inspector may choose to interpret the lot differently during construction.

Per 344.1.3 Note 2, "The quantity or extent of of a designated lot should be established by agreement between the contracting parties before the start of the work."

 

[SJones]

Look in the product specification to see whether a lot is defined there (it is in A333, for example). If it isn't, and it has not been agreed, there are too many permutations and combinations to help you on here.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdoweb/

 

[vesselguy]

Stanweld,
Thank you for your suggestion; it is one choice for lot definition I could consider with my inspector to define before we start the job.

The other choice I have been advised (by piping fab shop) to use for field piping is to define the lot as the amount of welds done in a day. I know where they are coming from: it is to the fabricator's advantage. For the Owner's advantage point of view, I would think it is not a good idea as we have to pay for all those RT.

 

[vesselguy]

Sjones,
Thanks for your reply.

 

[stanweld]

We also define a "lot" as piping systems requiring 5% examination will contain 20 sequential welds, made by the same welder on the same or similar material. That way if progressive examination is required, the maximum number of butt welds examined will be 20 (100%) from that lot of 20 made by that welder.