Plug Welds

Main Member Type: Welded plate girder or rolled beam
Attached Member/ Detail Type: Bolted attachment location
Error Type: Plug welded hole
Description of Error: PLUG WELDS SHOULD NOT BE USED. However, sometimes they are made.

For example, say a person drilled hole(s) in wrong location, then attempted to conceal error

by filling hole(s) with weld. Person may or may not be qualified welder.

Plug welding is prohibited on a load carrying member.

Weld location may be exposed or concealed by other elements

(diaphragms, splice plates, etc.).

Solution Recommended: If position permits, drill out entire plug weld and install high strength bolt with 2 hardened washers.

Drill must be slightly larger than and centered on original hole to remove most of HAZ and potential microcracks present.

Before installing bolt, MT and PT inspection by contractual ASNT Level II at fabricator's expense.

If position (or stress) precludes the above bolted repair, drill out and inspect the plug weld as above, then fill the hole either cosmetically or structurally.

If the drilled hole is partially or completely covered but stresses and proximity of other connections don't require solid metal (for example a bolted diaphragm angle),

fill hole with steel pin secured by brazing, epoxy, etc. and ground flush.

(if pin is welded in, grind flush and MT area.)

If stress, bolts within 1 bolt diameter, welds within 1"/25mm, or other considerations dictate restoring solid metal, insert pin half way into back of hole,

prep transition into/out of hole by grinding or gouging, and weld with stringer passes.

Go to back side and gouge /grind out fill pin to sound metal and weld with stringer passes.

Grind both sides flush and have UT and/or RT inspection by outside Level II at fabricator's expense.

Required Final Checks / Verification: QA to oversee and review NDE results.
Was Repair Successful ?: Has been to date. Extent of documentation and NDE expense /delays tends to discourage repetition.
Other Possible solutions: Thermal stress relief, but confidence is low; remove portion of member and replace (not good idea for rolled beam); drill out and cover with bolted plates; or leave in and cover with full moment connection.
Remarks: Most fabricators will not sanction plug welds, but workers don't realize their potential detriment. A number of in-service fatigues have been caused by the stress concentrations and inherent defects of poorly made plug welds. Some owners still require these in "non-tensile areas" such as attaching web thickening plates at pins, but these represent long-term risks.

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