VESSEL HEAD thickness below the calculated as per ASME 2

[Saver2008]

Hi!

Currently where I´m working, I have already calculated the minimum thickness required as per ASME VIII DIV 1 and the minimum thickness is 38 mm and the plate thickness was for head forming was purchased in 1.625inches (41.275 mm). After forming, we checked thicknesses on the formed head and we detected that there are zones which we have less than 38 mm of thickness (33.9 mm was the highest). I was thinking to performed the analysis of the head with these thickness variations using FEA but I do not know if after doing the analysis, supposing FEA analysis shows that head with thickness variations can withstand design temperature & inlet pressure....ASME will recognize the results and can approve the calculation knowing that as per ASME, the current head thickness is below from ASME calculation.


What do you think?

thanks
RS

 

[david339933]

See UG-16 and 46-4.

 

[r6155]

What does the manufacturer say?

Regards

 

[david339933]

Did you give the manufacturer the min. required? Something doesn't add up.....an additional 1/8" for thinning?
Did you get a COC with the min. stated on it?
Sounds like you or the supplier did something wrong.

 

[r6155]

More info: type of head, material, dimensions, ..etc.

Regards

 

[Saver2008]

Hi

To r6155. There were problems with the machine during the forming of the head. And problably will add some welding to the head to solve it but it will be so much welding additional

To david339933, the requirement as per client is 38mm. Values like 35 to 37 mm were taken. The manufacturer bought 1.625in plate ....the problem came when forming....they PUSHED more than required and some parts are less than minimum. So your conclusion about the mistake of the supplier is correct...they did it wrong.

As per FEA, the head can withstand the design conditions (pressure and temperature) but it does not meet ASME criteria. So....the manufacturer is adding welding to the head right now. I thought with FEA analysis can solve this but it did not.

Regards

 

[r6155]

[pre]So....the manufacturer is adding welding to the head right now. I thought with FEA analysis can solve this but it did not.[/pre]
What !!!!

This head is SCRAP
Contact a lawyer.

Regards

 

[DriveMeNuts]

The head is scrap. As far as I can tell, your manufacturer is progressing down dodgyville lane.
Are you saying that the manufacturer is doing a weld overlay on the over thinned section? I have come across various clauses in my career stating that any assumed strength from weld overlay shall be disregarded.
I would perhaps consult your ASME AI before consulting your lawyer.

 

[r6155]

AI may also need a lawyer. LOL

Regards

 

[Christine74]

Interpretation VIII-1-86-112 is possibly relevant:

https://cstools.asme.org/Interpretation/InterpretationDetail.cfm?TrackingNumber=7859

Question (1): A formed head or segment of carbon or low alloy steel is to be supplied under the provisions of UG-11(b) or UG-77(c) without a Manufacturer's Partial Data Report and part stamping. Indications and/or underthickness are detected after forming which require welded repairs and/or welding to restore thickness. The material is located at the plant of the head manufacturer where the repairs are to be made. May the head or segment still be considered material?

Reply (1): Yes.

Question (2): Is agreement between the head manufacturer and purchaser all that is required to permit weld repair or weld build-up per SA-20?

Reply (2): Yes.

Question (3): Does compliance with Section VIII, Division 1 require agreement from the Inspector prior to effecting welded repair or weld build-up?

Reply (3): Yes.

Question (4): Is the head manufacturer required to complete a Partial Data Report on completion of weld repair or weld build up to restore thickness?

Reply (4): No.

Question (5): Is part stamping by the head manufacturer required upon completion of welded repairs or weld build-up?

Reply (5): No.


-Christine

 

[DriveMeNuts]

That interpretation is surprising. How do you handle fatigue design for such a repair? What Fatigue penalty factor do you apply?
The OP may need a really good lawyer, or perhaps they have a competently produced purchase spec.

I suppose some bottom support heads for severe cyclic service, have weld build up on the head, which the skirt is then welded to.

Lots of unnecessary weld creates chaos.

 

[r6155]

1) I waiting info from (OP), see my post 4 Jan 24
More info: type of head, material, dimensions, ..etc.

2)This is not a defect in the plate material (SA-20), it is an incorrect manufacturing procedure.
Interpretation VIII-1-86-112 does not work in this case.

Regards

 

[Trestala]

The standard practice with most Vendors and head forming shops is they buy plates that are 15%~20% thicker than the required calculated thickness to consider the reduction in thickness after forming. It seems that wasn't considered.

 

[GD2]

OP,
The specified thickness the plate 41.275 mm looks good to take the control of the fibre elongation. It was the fabricator who didn't have a good control on the thinning.
I would reject this head. Why should I be penalizing the Owner?
My acceptable minimum thickness would be: 37.7 mm (UG-16).

By doing a FEA, it will essentially kick of the 'Fitness-For-Service" even before the equipment is placed in service.

I wouldn't even agree to weld repair the entire knuckle periphery as this is the highest stress point of the head.

The head has run out of control during forming.

GDD
Canada