Attachment welds for lethal service vessel

[jtseng123]

Dear all,
Can fillet weld without full penetration for internal and external attachments (such as tray support rings, platform support clips) be used for lethal service vessel ?

 

[racookpe1978]

An odd question.
Why do you think an appropriately designed fillet weld using an appropriate filler material and PWHT as required could not be used?

Existing tank and new weld for new attachment?
Existing tank, new weld to repair a failed attachment?
New design tank with new fillet weld?

 

[Duwe6]

What racookpe said. The requirement for 100% full-penn welds is for pressure-boundary, pressure retaining items. Your brackets have nothing to do with pressure retention. But install everything you can think of, and maybe a couple of spares prior to PWHT. Adding something 'later' to a Lethal Service vessel is brutally expensive.

 

[jtseng123]

There are certain services and/or material that full penetration weld for attachment is not just preferred, but mandatory by many companies that put into their own specs, such as hydrogen service, wet sour service, cyclic service, or low alloy material in high temperature service.

I am seeking the opinion if lethal service shall be doing the same to avoid traping the lethal content in crevice that may be inhaled during maintenance or repair in the future. I do see a thread saying using integrally reinforced nozzle for lethal service, and for sure nozzle has to be full penetration weld. By the same token, shall at least all internal attachment welds be full penetration ?

Whoever who has experience in design and purchase lethal service in the past, please advise.

 

[paulshark]

I'm new in this forum so first of all, hello to everybody

With lethal service all welds that connect internal plates to the clad/w.o. shall be full penetration. This is mandatory.
Personally, I would suggest to perform always full penetration welds on all attachments (internal or externals) to the pressure vessel body.

 

[jtseng123]

Paulshark,

This is not neccessary to be a cladded vessel for lethal service. Is your point still valid for using full penetration weld for CS parts to CS vessel ? Where can I find a document saying full penetration shall be used ? Thanks.

 

[Duwe6]

jtseng, the reason you are having a hard time finding that prohibition is that it does not exist. Nothing 'magical' about Lethal Service, just get all vessel details approved by your AI *prior* to starting construction, including your proposed NDE methods and locations.

 

[paulshark]

My experience was on hydrogen and sour service only.
For a carbon steel vessel on lethal service have firstly a look a the code, and then check the client specifications.
If no restriction are present go further with the weld you desire.
As I remember ASME doesn't have rules for welds on structural attachments.

greetings