Do plug welds require a separate PQR under AWS D1.1?

Not if you use prequalified geometry per AWS D1.1 Clause 5. Prequalified plug and slot welds can be written as a prequalified WPS without a supporting PQR, provided all hole geometry and fill-depth limits in the standard are met. If geometry is outside prequalified limits, a PQR is required.

What position can plug welds be made in under prequalified requirements?

AWS D1.1 limits prequalified plug welds to the flat (1F) position only. Overhead or vertical plug welds are not prequalified — you would need a PQR to qualify those positions.

How deep must a plug weld be filled?

For plates 5/8 in (16 mm) thick or less, the plug weld is filled flush to the surface. For plates thicker than 5/8 in, the depth of fill must be at least one-half the plate thickness, with a minimum of 5/8 in (16 mm). Your WPS must record this limit.

Can a groove weld PQR qualify plug welds?

A PQR for groove welds qualifies the welding process variables but does not automatically qualify plug weld geometry — you still need to meet the hole dimensions and fill-depth requirements of the standard. If you are working outside prequalified geometry, the test assembly for the PQR must represent the plug or slot weld configuration.

Plug and Slot Weld WPS Requirements: AWS D1.1

Plug and slot welds have specific prequalified geometry and WPS documentation requirements under AWS D1.1. Here is what your procedure must show.

Plug and slot welds appear on structural drawings more often than most CWIs expect — attaching deck plates, connecting cover plates to flanges, and securing built-up sections where access from only one side is possible. Despite their frequency, the WPS documentation requirements for plug and slot welds are frequently incomplete. The holes are often correct; the paperwork is not.

What plug and slot welds are

A plug weld fills a circular hole drilled through one member to fuse it to the underlying plate or shape. A slot weld fills an elongated (rectangular or oval) opening for the same purpose. Both transfer shear between members in situations where a conventional lap fillet weld cannot provide adequate strength or access.

You will see them most often on:

Steel deck-to-beam connections in composite floor systems
Cover plate attachments to wide-flange flanges
Double-plate shear tab connections in tight erection clearances
Repair of oversized or damaged holes where plug welding restores net section

Prequalified requirements under AWS D1.1

AWS D1.1 Clause 5 allows plug and slot welds to be written as prequalified WPSs — no PQR test assembly required — provided the joint geometry stays within defined limits. The four parameters that must be within limits are hole diameter, hole spacing, depth of fill, and welding position.

Minimum hole diameter. The minimum diameter for a plug weld hole in the through-member must be at least equal to the thickness of the through-member plus 5/16 in (8 mm). So for a 1/2 in (13 mm) plate, the minimum hole diameter is 13/16 in (21 mm). Undersized holes restrict access for the welding electrode and prevent proper fusion at the root.

Maximum hole diameter. The standard sets an upper limit as well. For through-members 7/8 in (22 mm) thick or less, the maximum diameter is 2-1/4 times the plate thickness. Oversized holes reduce net-section shear area and the design engineer's calculations are based on the nominal diameter — verify with the EOR if field modifications have enlarged a hole.

Hole spacing. Center-to-center spacing of plug welds in the direction of loading must be at least four times the hole diameter. Transverse spacing must be at least three times the hole diameter. These limits control stress concentration and ensure each weld can develop its design shear capacity.

Depth of fill. For through-members 5/8 in (16 mm) or less in thickness, fill the hole flush to the surface of the through-member. For thicker members, fill at least one-half the thickness of the through-member with a minimum fill of 5/8 in (16 mm). Never leave a crater or depression — a concave surface creates a stress riser and fails visual acceptance criteria.

Position. Prequalified plug and slot welds are limited to the flat (1F) position. If the detail requires vertical or overhead plug welds, you are outside prequalified territory. A PQR test assembly in those positions is required before you can issue that WPS.

What your WPS must document

Even for a prequalified plug weld WPS, the written document must address every parameter a welder needs to make a conforming weld. Review your WPS against this list:

Welding process — SMAW, GMAW, FCAW-G, or FCAW-S. Avoid GTAW for plug welds in structural steel; the low deposition rate makes it impractical and it is rarely specified.
Base metal specification and group — pull from AWS D1.1 Table 6.9 (base metal groups) or confirm the steel is in the prequalified base metal list.
Filler metal classification — AWS A5 classification, strength level, hydrogen designator (especially for SMAW E7018 H4R or GMAW ER70S-6). Low-hydrogen electrodes are required for prequalified SMAW on most structural steels.
Minimum preheat and maximum interpass temperature — per Table 5.3 for prequalified procedures (based on base metal group and thickness). Plug welds in thick plates can concentrate heat — document the interpass limit and measure it.
Hole diameter range — record both the minimum and maximum diameter the WPS covers, staying within the prequalified limits described above.
Depth of fill — state the requirement explicitly (flush for t ≤ 5/8 in; 1/2t min for t > 5/8 in). Welders should not have to calculate this from the standard.
Current type, polarity, and amperage range — for SMAW, include the electrode size, amperage range, and polarity. For GMAW/FCAW, add wire diameter, voltage range, and wire feed speed range.
Welding position — specify flat (1F) only for prequalified procedures.
Welding progression — for flat position plug welds on deep holes, specify whether circular motions or stringer-bead lifts are used to build up fill without slag entrapment (especially for SMAW).

Slot weld specifics

Slot welds follow the same thickness-based minimum width rule as plug welds — minimum width equal to the through-member thickness plus 5/16 in — but the maximum width is not explicitly capped the same way as a circular hole. The length of the slot is limited to 10 times the through-member thickness. Ends of the slot must be semicircular or have corners rounded to a radius not less than the through-member thickness, except at the edge of a part. Sharp corners are stress risers that initiate fatigue cracks in cyclic loading applications.

The same fill-depth rules apply: flush for members 5/8 in and under, one-half depth for thicker members. For long slots, specify the weld progression — starting from one end and working toward the other prevents vapor pressure buildup that can cause porosity.

Inspection requirements

Visual inspection per AWS D1.1 applies to completed plug and slot welds:

Surface of the completed weld must be flush with the surface of the base metal or shall not exceed a specified convexity limit.
No undercut, overlap, or cracks.
Porosity is limited by AWS D1.1 visual acceptance criteria — consult Table 8.1 (statically loaded) or Table 8.2 (cyclically loaded) for allowable porosity sizes and density.

Because the root of a plug weld cannot be directly observed, the fill sequence and visual appearance of the completed surface are the primary quality control tools. If the EOR has specified additional NDE (MT or PT), coordinate that with your NDE contractor before the inspectors move to the next joint.

Common WPS deficiencies CWIs flag

Missing hole diameter range on the WPS. The WPS lists process parameters but does not state the hole diameter range it covers. When the inspector asks "does this WPS qualify a 1-1/8 in diameter plug weld?", there is no answer on the document.

No depth-of-fill statement. The welder fills until the hole looks full. On a 3/4 in plate, flush fill is correct; on a 1 in plate, the weld should be at least 1/2 in deep — but if the WPS is silent, the welder has no written instruction and the CWI has no criterion to enforce.

Position not specified. A generic WPS written for flat SMAW is pressed into service for a vertical plug weld during erection. Position is an essential variable for plug weld requalification — this is a nonconformance.

Incorrect preheat for base metal. The shop handles A36 day to day and uses the same WPS for an A572 Grade 50 plug weld on a 1 in plate. Table 5.3 requires higher preheat for Group II steels above 3/4 in thickness — the WPS used does not reflect this, and neither does the preheat actually applied.

Keeping the WPS library current

If your fab shop is writing WPSs for every job from scratch, plug weld procedures tend to be afterthoughts — generated in the field when the PM realizes the drawings call for plug welds and there is no WPS on record. A better approach is a pre-written library of prequalified plug weld WPSs covering the diameters and base metal groups you routinely encounter, ready to issue before work starts. See welding procedure library for audit-ready shops for how to organize that library so third-party auditors and AHJs can pull the right WPS in seconds.

For the WPS itself, use a structured format — the AWS D1.1 Annex M form covers all required fields for groove and fillet welds, and the same structure maps to plug welds with the addition of hole geometry fields. Read WPS template vs. Annex M form explained for guidance on adapting the format. If you want to generate and manage WPS documents without rebuilding templates for every project, WPS drafting software at /pricing can handle plug weld parameters alongside your standard groove and fillet procedures.

Rule library based on AWS D1.1:2025; verify against your governing edition. The AHJ or project contract may specify AWS D1.1:2020 or an earlier edition — confirm before issuing procedures.