From above options correct answer is (b) . Joint efficiency of head in both case will remain 1.
Its answer lies in UW-12(d) It's applicability is as described below:
The shells and heads of vessels which are considered seamless. The Efficiencies used to calculate these vessel parts are not found on Table UW-12 but are instead listed in paragraph UW-12(d).
It's states that
"Seamless vessel sections or heads shall be considered equivalent to welded parts of the same geometry in which all Category A welds are Type No. 1 (Why Type No.1 ? for ease in radiography).
For calculations involving circumferential stress in seamless vessel sections or for thickness of seamless heads, E=1.0 when the spot radiography requirements of UW- 11(a)(5)(b) are met. E= 0.85 when the spot radiography requirements of UW-11(a)(5)(b) are not met, or
when the Category A or B welds connecting seamless vessel sections or heads are Type No. 3, 4, 5, or 6 of Table UW-12 (Why for these types? Because these are not easily radiographable. Type 3 to 6 cannot be radiographed by Code rules)."
In above question, for both mentioned cases fabricator has satisfied minimum spot radiography requirements of UW- 11(a)(5)(b). So joint efficiency will be 1 in both case while calculating seamless head thickness. (This will be RT-2 Marking)
If in case they would have mentioned that head to shell junction is not satisfying minimum spot radiography requirements of UW- 11(a)(5)(b). then seamless head will be required to design with joint efficiency equals to 0.85 even though it is procured seamless. (This will be RT-3 Marking).
I would like to give one interesting example on above discussions :
Code Shop A buys a rolled and welded shell from Code Shop B.
Shop B fully radiographs the Type 1 weld and the shell part will be delivered to Shop A with a joint E of 1.0. which is essentially equal to a seamless shell.
Now Code Shop A welds on two seamless formed heads. Unless Shop A performs at least Spot RT on the Category B welds (or Category A weld in case of Hemi head) connecting the heads to the shell, Joint efficiency E will be 0.85 for calculating shell and head thickness. Even though Shop B has performed Full RT on rolled shell and made it equivalent to seamless. And Shop A has procured seamless heads.
Remember that there only two (2) joint efficiencies possible for Seamless Shell and Seamless Heads they are; 1.0 or 0.85
1.0 when the rules of UW-11(a)(5)(b) have been applied (UW- 52 Spot RT applied).
0.85 when the rules have not been applied. (UW-52 Spot RT not applied).
DO NOT GO TO TABLE UW-12 FOR THE 'E' TO USE IN SEAMLESS HEADS OR SEAMLESS SHELLS.
FYI : in above question hemispherical head is considered seamless. Actually as per code only eliptical and torispherical is considered as seamless. Not hemispherical. We can assume it seamless if Full RT is carried out on weld joints of hemispherical head. Still above rules apply while calculating hemispherical dish end thickness.
This is what I understood from UW-12 (d).
Members can share their views on it.
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On Wednesday, March 4, 2020 at 2:00:31 PM UTC+5:30, ibratech wrote:
Gents,Please help me to find the answer on the below question.1. Two head to shell joints, one joining a seamless hemispherical head to shell was radiographed for the full length and the other joint joining a seamless standard torispherical head to shell was spot radiographed. The weld joint efficiency for each of these joints will be: UW-12 (D)
a. 1, 0.85
b. 1, 1
c. 0.85, 1
d. 0.85, 0.85
Which will be the answer ?Thanks & Regards
Muhammed Ibrahim PK
https://materials-welding.blogspot.com/
https://www.linkedin.com/groups/122787
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