Derating factor-Y 2

[pdp123]

Hello all!
Per 31.3/31.1, there is a relation between Temperature and De-rating factor (value of coefficient) in the Table provided.
Is there any relation with Pipe thickness and practical aspect in piping.

Thanks for your valuable comments....

 

[LittleInch]

Not that I am aware of. (I assume you mean whether thickness affects the de-rating factor?)

What practical aspect are you thinking of - this is a vague question....

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[pdp123]

By Practical aspect I mean to say what is the benefit of using this coefficient in the formula provided.

Thanks

 

[XL83NL]

From what I recall of my B31.3 course given by ASME committee members/instructors, the Y-value is to compensate for creep.
For lower temperatures, the result is a smaller required thickness as for larger temperatures, the Y-value increases.
Be aware of the limitations of the Y-factor for thicker components ( T>=D/6)

 

[weldstan]

Deposited weld metal and the affects of welding heat on the HAZ of the base metal adversely effect the long term creep strength of the material. There is empirical evidence for this and as a result B31.3 imposed a further safety factor. Premature failures have occurred in welded P91 alloy laterals in less than 5 years when those laterals were not subject to normalizing and tempering after welding. They only received a B31.1 PWHT.