A welded H-beam has long longitudinal welds, but their starts and ends often need particular attention. When the welding head starts moving, wire feed, current, travel speed and flux coverage must settle into a stable condition; when the arc stops, the weld pool still has to solidify. If these transitions remain directly at the finished ends, weld shape and integrity there may differ from the steady-state middle section. Run-on and run-off tabs installed to an approved procedure provide a way to place arc starting and stopping outside the finished component.
These tabs are not arbitrary pieces of scrap, nor do they replace acceptable fit-up, welding procedures or inspection. Longitudinal fillet welds between an H-beam's web and flanges, butt welds joining plate strips, and special joints requiring full penetration each need a separate decision on whether to use tabs, how to attach them, and how to remove and reinspect them. This article organizes station handovers around those four questions; it gives no universal dimensions or parameters detached from drawings and the welding procedure specification.
1. Mark the start, finish and finished-component boundaries first
A run-on tab allows the arc to start before the specified weld begins. A run-off tab, also called an end or crater tab, allows welding to continue beyond the specified weld end before stopping. To decide what is required, check the effective weld length, finished end face, joint type and welding direction on the drawing. Do not set travel distance from beam length alone.
For longitudinal H-beam fillet welds, the extension must continue the welding path formed by the web and flange so that the head, wire and flux supply can pass in their confirmed orientation. For butt welds joining plate strips, also check continuity between the extension and production joint in groove geometry, gap, backing or root-forming arrangement. These two joint types differ in restraint/loading and weld formation; a flat-plate butt-welding trial cannot simply be copied to every beam end.
The station drawing should identify at least the beam, all four longitudinal welds, welding direction, finished end face, run-on/run-off positions, removal lines and positions temporarily retained for inspection. For tapered beams or ends with cut-outs, end plates or connection holes, check whether the extensions interfere with later cutting or assembly. If drawings show only weld symbols without these arrangements, welding engineering should add the station requirements before production.
2. Check material, joint continuity and attachment before installation
Tab steel, thickness, shape, projection and attachment method must come from the approved welding procedure specification (WPS), station drawing or project technical requirements. Unidentified offcuts with obvious rust or oil should not be used merely because they will be removed after welding. They still participate in melting, heat transfer and joint restraint; an unstable attachment can also affect the production weld end.
Check fit-up continuously along the welding path: is the wire landing point centered; are there abrupt height changes, misalignment or abnormal gaps between the joint and extension; do tack welds obstruct the head; can flux coverage meet the procedure; and is there enough end clearance for the recovery inlet, guide wheels, tracking system and cables? A dry run can check travel and interference, but cannot replace actual welded specimens for verifying weld formation and fusion.
The attachment itself must follow the documents. Tack position, quality and attachment strength must maintain the intended geometry without introducing unqualified changes in restraint. Attachment conditions particularly affect end deformation at the run-off end of plate-strip butt welds. KOBELCO research on single-sided, multi-electrode submerged arc butt welding shows that run-off tab width, attachment, welding speed and electrode spacing jointly affect end cracking. This calls for validation of the complete arrangement; increasing or reducing one factor does not guarantee acceptable results for every H-beam joint.
3. Make arc starting and stopping an executable procedure
TWI guidance on submerged arc welding explains that current, voltage and travel speed affect bead shape and penetration, while flux coverage prevents the operator from directly observing the weld pool as in open-arc welding. Before welding, confirm the wire/flux combination, electrode extension, head position, flux supply and approved parameters. Do not rely on post-weld appearance to guess whether the process was stable.
The station procedure must state where the arc starts, what conditions establish stable welding at the production joint, how welding continues beyond the finished-component boundary, and how arc stopping, wire-feed stopping, travel stopping and flux supply are coordinated. If starting, stopping or parameter-transition functions are used, confirm what the actual control system supports and validate it on representative specimens. Do not describe them as standard on all equipment without confirming the configuration.
TWI guidance on solidification cracking says the crater should be adequately filled when terminating a bead to avoid an unfavorable concave shape. A run-off tab provides room to manage this transition, but relocating the crater onto the tab does not automatically establish that the production weld end is free of cracks, lack of fusion or other unacceptable imperfections. Record the stop position, process abnormalities and final inspection findings together.
4. Removal is followed by end reinspection
After welding, complete the specified cooling, slag removal and end inspection, then remove the run-on and run-off tabs and any other required attachments in the approved sequence. The removal line and method must protect the finished base material and specified weld extent. Do not knock tabs off and presume the end is acceptable. Whether thermal cutting is allowed, what grinding is required and whether specimens must be retained should be stated in the procedure or inspection documents.
After removal, check more than whether the tab is gone. Look for cutting damage, depressions or unacceptable notches in the removal area; check that the finished end face suits subsequent assembly and verify the production weld end's dimensions, continuity and surface condition. Mark and segregate suspected cracks, interrupted weld formation and other unresolved findings. Apply the approved repair method and reinspect; grinding or painting does not replace an acceptance decision.
Non-destructive testing methods, extent, timing and acceptance levels must follow project documents and applicable standards. SteelConstruction.info discusses visual inspection separately from surface and internal NDT, and notes that projects can require production testing of run-off tab specimens from specified joints. A satisfactory tab specimen cannot replace evidence that all production welds are acceptable. When specimens must be retained, link each specimen to its beam and weld identifiers before removal.
5. Use a handover sheet to keep end issues out of the next operation
| Handover stage | What to check | Suggested records |
|---|---|---|
| Fit-up to main welding | Finished boundaries, joint continuity, extension material, attachment and interference | Beam/weld IDs, WPS revision, station drawing, installation photos, inspector |
| Main welding to end finishing | Start/stop positions, parameter sequence, flux coverage and recovery, abnormal stops | Welding direction, program revision, abnormality location, welding batch, operator |
| End finishing to inspection | Removal line, removal and dressing methods, specimen retention | Before/after photos, specimen IDs, end-face and removal-area condition |
| Inspection to straightening or shot blasting | Production weld-end inspection, required testing complete, unresolved items closed | Inspection report number, accepted/repair status, reinspection results, release signature |
Record abnormal stops separately. If the arc stops within the finished component, do not simply move the head back a little and continue. Restart position, tie-in treatment, necessary cleaning and inspection must follow the procedure documents. Distinguish normal starts/stops from resumption after an intermediate stop so that repair location, quality review and subsequent procedure validation have reliable evidence.
For line planning, run-on/run-off arrangements also consume travel, flux supply/recovery, removal and inspection time and space. The machine working range must accommodate the component and necessary extensions; cycle-time calculations must include installation, removal and reinspection. For overall line assessment, see H-beam production line capacity and bottleneck analysis; for fit-up inputs, see H-beam assembly and tack welding.
Frequently asked questions
Must every H-beam weld use the same run-on and run-off tabs?
There is no universal rule. Conditions of use, material and dimensions depend on the joint, welding process, drawing, WPS and project standards. Check longitudinal fillets, plate-strip butt welds and special full-penetration joints separately. Similar beam shapes do not justify sharing an unverified station arrangement.
Can a weld be released if the crater is on the run-off tab and the production end looks sound?
The specified end inspection and testing must still be completed. Keeping the crater outside the finished component is a process arrangement; deciding whether the production end contains unacceptable imperfections is an acceptance assessment. Both need supporting evidence.
Can speed simply be reduced to prevent end cracking?
Welding engineering must validate any change first. Speed simultaneously affects heat input, the weld pool and weld formation. In specific single-sided, multi-electrode butt-welding trials, KOBELCO found that lower speed also required coordination with conditions such as electrode spacing. That trial is not a parameter table for H-beam fillet welds.
What end details are needed when discussing a production line?
Provide representative workpiece drawings, material and plate thickness, joint type, weld size or penetration requirements, approved start/stop and removal methods, extension geometry, inspection requirements and current abnormality records. Contact TitanWeld to discuss head travel range, flux supply/recovery interfaces and station handovers using this information. The project's approved documents still govern the actual procedure and acceptance requirements.