Sam,

My suggestion was based on the facts as I understand them namely...

You are working in a D/T ratio beyond 100.

You have a mitred elbow.

You have a paper in hand discussing a welding elbow above D/T 100 and wish to use its cited SIF and h for you relatively thin high D/T elbow.


My Suggested "Now comes the situation of 150-200% additional safety factor" is really a margin for ignorance. We don't know how the miter will behave exactly but we are absolutely positive that a mitered elbow behaves far differently then a wrought elbow. How great a difference can only be adressed by three dimensional analysis such as testing or FEA.

You are in unknown territory your choices are....
1)Perform FEA/ Testing to determine the correct SIF / h

2)Fudge the SIF from the code with a factor of ignorance

3)Ignore the whole problem, build it, and do a full sized fatigue test (either with or without informing the owner I guess)

Obviously number 1 is the best choice, followed by 2, before I would ever go to 3 I would probably walk away from the mess.

Having had this actually problem myself in the past I opted for either 1 or 2 at times, and one time washed my hands of the deal... I told the designers and my boss go ahead with your scheme but when it breaks its all yours. (The components did break a few years later (fatigue).

I hope this helps its a dicey problem!