ASME VIII Div. 1 UCL-34 1

[VeryPicky]

Could any of my esteemed colleagues guide me to Code interpretations for ASME VIII Div. 1 UCL-34? Just the number, please I will find it than.

I would also like to know your interpretation.
1. Does the paragraph deal with PWHT to relieve the stress after corrosion resistant weld overlay application?
2. What is the governing thickness in the case of overlaying the flange?

My interpretation is following:
Cr/Mo vessel with SS cladding. Shell roll-cladded, flanges overlayed.
The PWHT time should be calculated on the thickest weld. If the flange is ovelayed the thickness of the flange shall NOT govern the time of entire vessel PWHT.
E.g thickest weld 2" and flange thickness 8" -> 2" is the governing thickness. Flange thickness to be taken to account for heating/cooling rate calculations.

Putting Human Factor Back in Engineering

 

[metengr]

VeryPicky;
The following are my interpretations of UCL-34 to answer your questions. UCL-34 was written to assure that base metals used in the construction of pressure vessels with corrosion resistant integral cladding, weld metal overlay cladding, or applied linings receive PWHT as required by other general requirements of Section VIII, Div 1. In other words, the application of cladding does NOT drive the PWHT for the vessel, it is the vessel weld joint thickness.

1. Yes to your first question. Clarification, PWHT is done once to take credit for both the stress relief of the welded joints in the vessel as required by other general requirements AND the application of the corrosion resistant weld metal overlay cladding or applied corrosion resistant lining. There is a key statement in UCL-34 that requires the PWHT to be performed AFTER cladding unless it is exempted from other general requirements. Meaning the vessel can be PWHT and subsequently clad, if permitted.

2. The nominal thickness that governs PWHT for the vessel would be the thickest base metal weld joint of the vessel, not the thickest component of the vessel that is clad.

 

[bmoorthy]

This is an interesting situation. Let us say there is a Low alloy Tube sheet which needs to be overlayed with 316L. What would be the guiding thickness for the purpose of PWHT?

I think this matter is not properly addressed in ASME.

Good Luck
B.Moorthy
moorthykar@yahoo.com

 

[VeryPicky]

Regarding the tubesheet. There is not much difference between the tubesheet situation and the flange face and bore WOL from philosophical point of view. Additional issue with overlayed tubesheet is dimensional stability that might not be so much pronounced in the case of flange.

To my knowledge the governing thickness should be the thickness of thickest WELD on the vessel/exchanger. It seems we have a consensus, metengr. Do you know of any code interpretation to support our point of view?

Putting Human Factor Back in Engineering

 

[metengr]

VeryPicky;
I will scan thru the interpretations to see if one exists for this item. Most people have to realize that the rules in the ASME Boiler and Pressure Vessel Code are intended to provide the minimum technical requirements for designing a pressure vessel that will be safe to operate. The designer has the option to add other technical requirements, like sub-critical stress relief of components, above and beyond the Code minimum requirements, to assure added margin for both reliable and safe operation.


bmoorthy;
The definition of nominal thickness for an overlay would be the weld deposit thickness of the overlay NOT the thickness of the tubesheet. In most cases, the weld deposit thickness for cladding would be under 1/4", which would exempt you from PWHT for most alloys per the requirements in UCS-56.

 

[VeryPicky]

metengr

I appreciate your help.

I have no problem with understanding the spirit of the code, specifically when it comes to PWHT but I have a code interpretation dispute on my hands and I am in the process of preventing the manufacturer from overcooking my vessel. Meeting the minimum code requirements is a legal requirement and we want to make sure that we are satisfying AI, the code and that the all engineers are comfortable making final decision on PWHT holding time at temperature.

That's why I am looking for some formal response from the Committee in the form of interpretation.

Putting Human Factor Back in Engineering

 

[metengr]

Here are some interpretations regarding UCL-34;

Volume 14, VIII-1-83-192 File # BC82-655
VIII-1-83-189 File # BC81-531

 

[VeryPicky]

Thanks metengr.

The closest to my case seems to be Reply(3) of VIII-1-83-192.

bmoorthy

do yourself a favour and check those interpretations, too. They will give you some indication.

Putting Human Factor Back in Engineering