joint efficiency of the welds

[AmoorSaleh]

Dear All,
I need your help choosing the joint efficiency of the welds,
Assume
Given:-
• hemispherical head which assembled to the shell by "type No (2):- single
Welded butt joint with backing strip… see sketch UW-13.1 (i) ".
• the manufacturer decides to do Spot just for the longitudinal weld!!!
• the circumferential weld for the assembled head to shell is done without any Radiographic examination!!
• I have to draw your attention to: the hemispherical head was formed by one piece only(seamless)
The question is:
The joint efficiency for the head thickness according to the Book should be 0.65, 0.85 or 1 ?

Could you please explain to me how to use it?

 

[Duwe6]

Buttweld using a backing strip is not elegible for 85% or 100%. Making this a VERY poor engineering choice. You spent the money for a hemispherical head, and now the engineer wants to only use a little over half of the available thickness [via a low joint efficiency].

Based on the cost of hemi heads, in the USA we always use full-penn weld joints and "Full RT" to get 100% joint efficiency. Thus we can use 100% of the thickness of that expensive hemi head in our pressure calc's.

 

[weldstan]

Duwe6,
It is unfortunate that some Engineers have no idea of costs. Engineers in name only! A bit more radiography to provide thinner walls is most often miniscule compared to the greater material and welding costs.

 

[Duwe6]

Yep weldstan, you got that right.
No RT = 70% joint efficiency = can only use 70% of the as-built material thickness.
Spot RT = 85% E = a 21½% increase in usable material thickness.
On a small vessel where only one welder did all the long seams, that is about 1 to 4 RT's. Total cost $200 - $500 to add 21½% thickness to your $10K to $85K vessel. Talk about cost efficient project amnagement!

And there are still a bunch of "engineers" that cannot grasp this basic principle.

 

[AmoorSaleh]

Hello Duwe6's and weldstan,
Thank you a lot ..
I agree with you that it is a very poor design!!
But in this case the E joint efficiency should be 0.8, is it true?

According to UW-12