Quality/Joint Factors B31.3

[reichertc]

Hi folks.

Does anyone out there have any background on how the weld joint quality factors (Ej) in Table 302.3.4 of ASME B31.3 were derived?

I am trying to put together an argument that 100% radiography of welded pipe is not required because any flaws in the weld are more than compensated for by the additional thickness required due to the reduced joint factor, but it would be nice to have some background information.

Any help appreciated. This has been cross posted in the Piping & Fluid Mechanics Engineering forum.

 

[prex]

I don't think you can quantify exactly the derivation of those factors: they are the summary of decades of experience (and of accidents) coupled with some insight about the quality attainable with the different processes (that BTW may evolve in time, and the code is usually not fast in following such evolutions).
Moreover I'm not sure to understand your goal: if you have an electric fusion weld you will get a factor of 1.0 with 100% RX, and hence an overthickness if the pipe thickness is already defined; on the other side, if the actual thickness allows for a lower factor, then there are two possibilities:
-you are forced to do 100% RX by some rule or client specification, and this represents a required added quality that IMO you can't exchange with an overthickness
-or you are not required to do 100% RX, then you can avoid it.

prex

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[reichertc]

My company can be ridiculously over conservative at times. I am specifically looking at a line class that is using A403 seamless fittings, or A403 welded fittings with 100% RT. This corresponds to a pressure rating for straight pipe with a manufacturing tolerance of -12.5% and an Ej of 1.0.

The pipe has been specified as A358 Class 1 (100% RT). This gives a manufacturing tolerance of -0.01" and an Ej of 1.0.

To take advantage of the tighter manufacturers tolerance on the pipe, I want to drop the 100% RT requirement on the pipe and use A358 Class 5 (Spot RT) with an Ej of 0.9. The fitting calculation would still govern, and I wouldn't be paying $14/ft for RT of the pipe...

Nobody seems to have a problem with me doing this when I am talking about a Class 150 or Class 300 system, but when I start doing this on a Class 1500 or Class 2500 system everybody gets all queasy. Assuming that there are not issues with hardness or corrosion of the HAZ, and the only issue here is internal pressure, I do not see why we automatically need to specify 100% RT. The answer that I get is that "we have always done it that way", and that does not necessarily cut it in my books.

 

[prex]

I now understand and agree with you: there's no reason to go beyond a code requirement just because the rating is high: otherwise the code should impose 100% RT in that conditions and it doesn't.
Other factors I would consider to face the we have always... argument are:
-the single pipes are hydrotested (?)
-the whole system is hydrotested
-if we don't start changing something to lower production costs, we will soon be out of the market...

prex

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