Reweld of Lifting Lug on Pressure Vessel

By Metalsaurus Date 02-23-2008 18:10

Can lifting lugs be rewelded for a pressure vessel using the same base metal on the PV (same footprint)?
How many times can the same base metal be rewelded (after all original weld metal has been removed) without affecting the integrity of the structural weld of the lifting lug?

All residual weld metal have been removed. New (virgin steel) lifting lugs will be used for the secondary weld. The lifting lugs will only be used once or twice in their entire life span.

Does the heat affected zone from the original weld in the parent metal of the PV shell alter the properties and integrity of secondary welds in the base metal of the PV shell?

An option is to move the lifting lug to another position and weld onto virgin metal in another location, or make the lifting lug larger (different shape) and encompassing the original footprint and welding onto new virgin metal adjacent to the original weld, or insert a re-pad encompassing and extending past the boundaries of the original weld, but is all this necessary?

The main question is: for structural welding of lifting lugs, does prior welding HAZ affect the integrity of the subsequent welding applications? How many times can this re-welding be performed?

By 803056

Date 02-23-2008 20:34 Edited 02-23-2008 20:39

A quick response is that "less welding is better", but that doesn't tell you what you need to know.

By the same token, there are a lot of factors that need to be known to answer you question fully and completely.

I will start with a few assumptions that may or may not be correct, thus my answer may not be applicable to your situation.

Assumptions:
Base metal - plain carbon steel
Preheat - none required
PWHT - none
Thickness - 1/2 inch or less
Welding process - SMAW, FCAW, or GMAW
Size of previous weld - 3/8 inch fillet, multiple pass

Given the above conditions, the HAZ is most likely 1/16 to 1/8 inch and no grain coarsening has occurred.

Those being the conditions, you can remove the existing lug and replace it with a like lug without any difficulty.

If the actual conditions are different, you need to provide additional information to get a response that is more appropriate for your specific situation.

Best regards - Al

By Metalsaurus Date 02-23-2008 23:48

Thank you for your quick response. Your assumptions are valid.
I could not find any sections in any codes that delt with this matter in depth.
As this will only be done once or twice, I was of the opinion there would not be a huge detriment to the base metal,
Thank you for your thoughts, they are similar to mine.

By bozaktwo1 (***)

Date 02-25-2008 17:59

It has a lot to do with pressure and temperature, as well. Hot water is far more corrosive than cold water. Each time you strike an arc on the base metal of any pressure vessel, you run the (theoretical) risk of initiating cracks. Often the only way to find these is to perform a thorough UT in the entire area. You might also be concerned a little bit with the size of the lugs and the effective area of the welds used to attach them. On smaller structures it's not a big deal, but as you increase size and weight, you run the risk of tearing that lug, along with the base metal it's welded to, right off the vessel.

By js55

Date 02-26-2008 15:35

What you will realize with carbon steel in repeated welding regimes is predominantly grain growth and carbide precipitation. Neither one of which 'generally' results to any damaging extent from welding regimes(especially if your using one of the cleaner pressure vessel steels). Grain growth will decrease toughness to some extent, but if your pressure vessel is of a higher temperature application this is less of a concern.
Carbide precipitation, taking carbon out of interstitial solid solutioning will weaken the matrix somewhat but it really takes a long time at temp for the result to be significant.
Think about your concerns with the HAZ of the base metal and compare it to a HAZ in a multipass weld where any given location in the weld may experience multiple heat cycles.

By Bill M

Date 02-27-2008 15:35

Would this pressure vessel repair require an "R" stamp?

By Mikeqc1 (****)

Date 02-27-2008 18:03

These Lifting lugs, are they welded to a shell, or a pressure retaining part, and what about stress relieving?
In the ASME code where would I find the fabrication rules and repair of lifting lugs, I have an idea of where to look and the rules are but I would like confirmation on this.
ThX

By Bill M

Date 02-28-2008 19:37

The local Jurisdiction (State or Province) governs the repairs. Typically specified is that repairs to boiler and pressure vessels will be done in accordance to the National Board of Boiler and Pressure Vessel Inspectors, NBIC Code.

The ASME Boiler and Pressure Vessel Codes are typically rules for construction, not for in-service repairs. The new construction of pressure vessel lifting lugs are covered there, but not for the repair, replacement, or alteration of the lifting lugs.

Go the the National Board website and get a copy of the NBIC for more info.