Joint Efficiency Seamless Head to Seamless Shell 2

[saganami]

Hello,

I have a situation that i would like some help on calculating the joint efficiency of a seamless head to a seamless shell.

My shell is SA-106B Seamless carbon steel 8" sch 40.
My head is SA-234 WPB 2:1 ellipsoidal Seamless carbon steel 8" sch 40.
I have not performed any radiography the design.
The joint type is 1 for a head to shell weld.
It is category B because it is a pipe to Ellipsoidal head and not hemispherical.

The problem is that i am stuck between using an efficiency of 85% or 70%. My boss believes that the efficiency should be 85% and he sites UW-12(d). We also have one AI that agrees with my boss and another that disagrees. I am currently on the fence.

I can see where the one AI believes it should be 70% due to table UW-12, but i can also see in UW-12(d) where it says "E=0.85 when the spot radiography requirements of UW-11(a)(5)(b) are not met". I have also looked at the non mandatory appendix L and the flow chart would seems to indicate it should be 70%.

I know if i can bring sufficient evidence to my boss and AI that they would listen but i am just unsure about trying to correct an engineer and an AI with much more experience than myself.

Any help would be appreciated.

 

[weldstan]

85% is correct. Appendix L is not mandatory. Why not Spot RT the Cat B welds and get 100%?

 

[saganami]

So the 85% is due to the UW-12(d).

As for the radiography we calculate or MAWP for the vessels with the 85% as a standard and if a customer wants a higher pressure we will offer radiography or increased shell thickness as an option. Typically the pressures we need for the systems my company builds doesn't require the higher pressure granted by the 100% efficiency.

So its more of a cost/production time savings for our company rather than anything else.

Thanks for the help.

 

[SnTMan]

Agree w/ weldstan. UW-12(d) governs.

Though its not really Apx L anymore, it has in the past contained the occasional error. In the case of the flowcharts, seems more a matter of a bit of incompleteness rather than error.

Regards,

Mike

 

[Duwe6]

what weldstan said: for the price of the 2ea. Spot RT's, the usable shell thickness goes from 85% to 100%. That is a substantial increase in Corrosion Allowance for the cost of two Spots. Best bargain the customer will see this month.

 

[MrPDes]

What is the purpose of these two spots?

Could a defect in a circ seam weld potentialy cause an initiation point for a longitudinal crack even if the cylinder is seamless?

 

[saganami]

I don't think the purpose of the radiography is to find a crack in the seamless shell due to the welding because it is only spot and not full radiography. I think that it mainly has to do with the amount of examination that is performed on the weld. The more the examination to the welded joint the more efficiency you can use on the calculations.

I did have a really interesting situation with a seamless ellipsoidal head. Same situation as my original post with a seamless head and shell weld. Both parts were inspected and no defects were found by our quality department. The welder welded the head to the shell and didn't see any defects. When we sent the vessel off to be radiography they sent it back saying it wasn't required because as it had cooled after welding a 2" crack had formed in the head. I have attached a picture of the head crack this is after we cut it off of the shell. We ended up using the same shell with a different head and we did dye penetrate on the head and shell along with Full radiography on the new weld to make sure no defects were in the shell.

I thought it was kind of strange to have such a defined crack in a seamless head and after inspecting the MTR on the part it was a seamless part, so i guess it was just an internal defect.

 

[Duwe6]

Nice photo. Weird defect; it runs parallel to the forming stress when the head was made. The flat plate that the head mfr started with must have been seriously flawed. Can't blame this one on the welder.