The cap pass is the final layer of weld metal on a pipe joint, the bead an inspector actually sees after the hot pass. On a 6G test, the pipe sits fixed at 45 degrees, so that last bead runs through overhead, vertical, and near-flat orientations in a single uninterrupted circuit.
The cap must provide enough reinforcement to satisfy strength requirements without so much crown that the profile fails visual. Undercut deeper than the code allows ends the test before the coupon ever reaches a bend fixture.
AWS D1.1 sets profile and undercut acceptance limits; ASME Section IX and AWS B2.1 govern procedure qualification instead, so the numbers do not transfer.
What Is a Cap Weld in the 6G Pipe Test?
Every pipe weld faces the same tradeoff: build enough reinforcement to satisfy strength requirements without piling on so much crown that the weld fails visual inspection. The cap pass settles that balance: it is the last layer deposited and the one an inspector actually sees before Destructive Weld Testing.
In a standard groove weld sequence, the root pass ties the two pipe faces together and establishes penetration. The hot pass follows immediately, burning out slag and fusing the root into the joint. Fill passes then build up the groove in layers, restoring wall thickness. The cap pass finishes the job, capping the groove with a slightly convex, evenly rippled bead that provides the code-required reinforcement height and final surface profile. Because it is the visible layer, its width, height, and tie-ins are what acceptance criteria actually measure.
Cap Pass Versus Cover Pass
Welders often use "cap pass" and "cover pass" as synonyms, and in pipe welding that usage is correct. Some fillet-weld contexts reserve "cover pass" strictly for a cosmetic finishing bead over a structurally complete joint, but on groove welds in pipe, the two terms describe the same final layer.
Why 6G Makes the Cap Harder
In 6G Pipe Welding, the pipe is fixed at a 45 degree angle and never rolled, so the cap pass travels through flat, vertical, and overhead orientations in a single continuous weld. That forces constant adjustment of travel angle, arc length, and heat input to keep bead profile consistent across every position segment.
The 6G Pipe Test Sequence: Root, Hot, Fill, and Cap
The 6G pipe groove weld is built in four controlled passes. Each pass cleans and prepares the joint for the next, and the cap pass should not be rushed.
Capping Welding Techniques for All Positions
The 6G Stick Welding test fixes the pipe at a 45 degree angle, which means a single cap bead has to travel through overhead, vertical, and flat orientations without stopping to reset technique. Every restart is a potential defect, so the goal is smooth, deliberate motion that adapts as the clock position changes.
Reading the Pipe Like a Clock
Think of the bevel pipe joint as a clock face tilted 45 degrees. The 6 o'clock area sits overhead, 3 and 9 are vertical, and 12 approaches flat. Your body position, wrist angle, and travel speed all have to shift as you rotate around the fixed pipe, ideally in one continuous cap pass split into uphill halves that tie in cleanly at 12 and 6.
Travel Angle by Segment
- Overhead (5 to 7 o'clock): Use a slight push angle (5 to 10 degrees) to help the puddle release and keep slag from rolling into the bead. Keep the arc tight.
- Vertical (3 and 9 o'clock): Move to a neutral or slight drag angle as gravity stops fighting you. Consistent rhythm matters more than angle here.
- Flat approach (near 12 o'clock): Drag angle of 5 to 10 degrees. The puddle fluidizes, so pick up travel speed to prevent a crowned, ropey bead.
Heat and Arc Control
Drop amperage 5 to 10 amps for the overhead segment to keep the puddle manageable, then nudge it back up as you climb into vertical and flat. Hold a short arc throughout, roughly the diameter of the electrode core, and pause briefly at each toe to fuse the edge without carving undercut into the base metal.
Stringers vs. Weave
For Welder Certifications, most codes cap weave width at 2.5 to 3 times the electrode diameter. When in doubt, run overlapping stringers instead. They give you tighter heat control, cleaner tie-ins, and a more uniform cap profile that inspectors can measure without argument.
Electrode Travel Angles and Bead Placement by Position Segment
The travel angles below apply to the 6G cap pass, commonly welded with SMAW. Keep the electrode angle pointed to the pipe center and use a slight push angle from bottom to top. Stringer beads are the default, with a slight weave only where needed on the vertical-upward portion.
| Position Segment | Travel Angle | Bead Type (Stringer/Weave) | Overlap % | Heat Control Notes |
|---|---|---|---|---|
| All position segments | Point electrode toward pipe center at all times. Use a slight push angle from bottom to top and keep the same angle for all passes. | Stringer beads, with a slight weave motion on the vertical-upward portion only | 25% to 50% overlap between adjacent stringer beads | Maintain a short arc length of about 1/8 in. Check interpass temperature, with a maximum interpass temperature for carbon steel typically 500 deg F per the WPS. |
| Overhead segment | Same as all positions: point toward pipe center, slight push from bottom to top. | Stringer beads, no weave | 25% to 50% overlap between adjacent stringer beads | No segment-specific heat adjustment specified. Use short arc and check interpass temperature. |
| Vertical-upward segment | Same as all positions: point toward pipe center, slight push from bottom to top. | Stringer beads with slight weave motion on the sides to prevent sagging and a lump in the middle | 25% to 50% overlap between adjacent stringer beads | Use a slight weave on the vertical-upward portion to control sagging and central lumping. No numerical heat setting specified. |
| Flat segment | Same as all positions: point toward pipe center, slight push from bottom to top. | Stringer beads, no weave | 25% to 50% overlap between adjacent stringer beads | No segment-specific heat adjustment specified. Use short arc and check interpass temperature. |
SMAW Cap Pass Settings: E7018 Amperage, Polarity, and Travel Speed
The table below lists common SMAW cap-pass settings for E7018 electrodes on 6G pipe. All listed polarities are direct current electrode positive (DCEP). For vertical-up and 6G uphill segments, a travel speed of 3 to 7 in/min is typical, and reducing amperage by 10 to 20 amps helps control slag.
| Electrode Diameter | Amperage Range | Polarity | Travel Speed | Notes |
|---|---|---|---|---|
| 3/32 in | 70 to 110 A | DCEP | N/A | N/A |
| 1/8 in | 100 to 150 A | DCEP | 4 to 6 in/min at 115 A; 7 to 9 in/min at 140 A | Stringer-bead travel-speed figures. Use the lower range where the 6G segment is vertical or overhead and maintain a short arc. |
| 5/32 in | 130 to 200 A | DCEP | N/A | N/A |
GTAW, GMAW, and FCAW Cap-Pass Parameters
This table summarizes typical cap-pass parameters reported for GTAW, GMAW, and FCAW in 6G pipe welding. Some values are drawn from limited published excerpts, so treat ranges as starting points rather than universal settings. Where a source reported an unusual filler classification, such as E71T-1 under GMAW, the table reflects the data as provided.
| Process | Filler/Electrode | Diameter | Amperage/Voltage | Polarity | Travel Speed |
|---|---|---|---|---|---|
| GTAW | ER70S-2 or ER70S-6 | 3/32 in | 85-250 A (ER70S-2) | Not specified | Not specified |
| GMAW | E71T-1 (reported) | 1.2 mm | 90-160 A (ER70S-6) | Not specified | 40 mm/min |
| FCAW | E71T-1 | .035 in | 125-200-250 A, 27-31 V | DC reverse polarity, electrode positive | 8-14 IPM |
AWS B2.1 Visual Acceptance Criteria for 6G Pipe Cap Welds
AWS B2.1 sets visual acceptance limits for qualified 6G pipe welds, including the cap pass. The following criteria apply to the completed weld profile and surface condition. Measurements are taken at the weld face and toe transitions unless otherwise specified.
| Criterion | Acceptance Limit | Measurement/Notes |
|---|---|---|
| Cracks and incomplete fusion | Not permitted. | N/A |
| Incomplete joint penetration | Not permitted in groove welds, except where partial-joint-penetration groove welds are specified. | N/A |
| Undercut | Shall not exceed the lesser of 10% of the base-metal thickness or 1/32 in [1 mm]. | Measure the depth of the undercut at the base-metal/weld interface; compare the measured depth with both 10% of base-metal thickness and 1/32 in [1 mm], accepting only if it does not exceed the lesser value. |
| Face and root reinforcement | Shall not exceed 1/8 in [3 mm]. | Measure the maximum height of weld metal projecting beyond the adjacent base-metal surface, normal to that surface. |
| Porosity | No single pore shall exceed 3/32 in [2 mm] diameter. | Measure the maximum visible diameter of each individual pore; the largest single pore must be no greater than 3/32 in [2 mm]. |
| Porosity frequency | Frequency shall not exceed one pore in each 4 in [100 mm] of weld length, and maximum diameter shall not exceed 3/32 in [2.4 mm]. | Count visible pores over successive 4 in [100 mm] lengths of weld; no more than one pore is permitted in each such length, and measure the largest pore diameter. |
| Overlap | Welds shall be free from overlap. | N/A |
| Arc strikes outside the weld zone | Rejectable regardless of size. | N/A |
| Cap-weld profile | The weld face shall be flush with the base-metal surface and shall merge smoothly with the base metal. | Visually assess whether the weld face is flush and whether the transitions at both toes merge smoothly with the base metal; no numeric toe-transition dimension was provided in the retrieved source. |
| Weld craters | All craters shall be filled to the full cross section of the weld. | Visually inspect crater areas for a filled weld cross section; the retrieved source provides no separate numeric crater-dimension limit. |
How Much Reinforcement Can a 6G Cap Pass Have and Still Pass Visual Inspection?
AWS B2.1 sets strict visual limits for the completed cap pass on a 6G pipe test. Reinforcement, or weld height above the pipe surface, is one of the first things an inspector checks. Exceeding the maximum reinforcement fails the test before destructive testing begins.
Related Articles
ASME Section IX vs AWS D1.1: Cap Pass Acceptance Differences
Acceptance criteria for cap welds are not interchangeable across AWS D1.1, ASME BPVC Section IX, and AWS B2.1. AWS D1.1 provides explicit visual workmanship rules for production welds, while ASME Section IX and AWS B2.1 primarily qualify procedures and personnel rather than judge finished cap geometry; use each code's table of contents and index to locate clauses on cap profile, weave width, reinforcement, undercut, and porosity. For authoritative interpretation, consult official AWS and ASME websites for code books, errata, and interpretive rulings, use AWS and ASME technical committees and welding technology programs for code navigation training, reference BLS.gov for career context, and verify the applicable code edition plus any local jurisdiction amendments with a certified welding inspector (CWI) or an AWS/ASME technical representative.
| Criterion | AWS D1.1 | ASME Section IX | AWS B2.1 |
|---|---|---|---|
| Cap-pass geometry | Code profile limits | No production visual profile acceptance limit | No production visual profile acceptance limit |
| Reinforcement height | Controlled by profile acceptance limits | Not specified for production welds | Not specified for production welds |
| Undercut | Max 1/32 in for material under 1 in thick; max 1/16 in for material 1 in and over | Not addressed as production visual acceptance | Not addressed as production visual acceptance |
| Porosity | Table 6.1 visual acceptance limits | No comparable production visual porosity table | No comparable production visual porosity table |
| Cap alteration to mask defects | Not permitted | Not applicable | Not applicable |
| Primary use for pipe welding qualification | Structural service acceptance | Procedure and performance qualification | Procedure and performance qualification |
Common Cap Weld Defects: Causes, Prevention, and Fixes
Cap pass defects are often the visible result of problems that started in earlier passes or in parameter selection. The table below summarizes five common weld imperfections, their typical appearance, root causes linked to previous work, and practical prevention or repair actions for 6G pipe welding.
| Defect | Typical Appearance | Root Cause (Earlier Passes) | Prevention/Repair |
|---|---|---|---|
| Undercut | A groove melted into the base metal adjacent to the weld toe or weld root and left unfilled by weld metal. | Faulty electrode manipulation, excessive welding current, excessive arc length, and slow travel speed. | Use the prescribed welding current for the electrode size; adjust electrode angle to fill the undercut area; correct travel speed and arc length; gouge and weld with a low-hydrogen electrode when repair is required. |
| Overlap | The face of the weld extends beyond the toe of the weld. | Contamination, slow travel speed, incorrect welding technique, and excessive welding current. | Use a higher travel speed or welding current, reduce the electrode diameter, or change the electrode angle so arc force does not push molten weld metal over unfused base-metal sections. |
| Porosity | Gas-related voids or cavities in the weld caused by gas becoming trapped in solidifying weld metal. | Dirt, rust, or moisture on the base metal or welding consumables; insufficient shielding-gas coverage; or excessive gas flow that creates turbulence and exposes molten weld metal to oxygen. | Clean the base metal fully; check shielding-gas flow and torch angle; protect the weld area from wind; remove defective material and reweld where required. |
| Slag inclusions | Nonmetallic slag trapped in the weld deposit or between weld metal and base metal; it may appear as elongated internal slag lines or isolated inclusions. | Incomplete removal of slag from a previous bead, poor joint access, or inefficient partitioning of inclusions. | Chip and brush or otherwise clean each pass completely; maintain proper current and heat input; remove the defect by chipping or grinding back and reweld. |
| Excessive reinforcement | Weld metal built up above the quantity required to fill the groove weld joint, producing excessive cap height. | Excessive weld metal added because of poor manual technique, poor parameter selection, too much filler for the travel speed, or poor selection of individual bead sizes in a multi-run weld that overfills the joint. | Increase travel speed or voltage where appropriate, control filler-metal addition, and select bead sizes that avoid overfilling; grind or otherwise remove excess reinforcement to the specified profile. |
Interpass Temperature, Preheat, and Cooling Management
What preheat and interpass temperature should you run for a 6G carbon steel pipe test? There's no single number that covers every joint. The right figure depends on wall thickness, alloy chemistry, and the welding procedure you're qualified under, but the underlying logic is consistent: too much heat softens the puddle and flattens or undercuts the cap, while too little heat, especially with low-hydrogen electrodes like E7018, raises the risk of lack of fusion and hydrogen cracking in the root pass and fill layers beneath your cap.
Preheat Ranges by Wall Thickness
Thicker pipe walls hold more mass and pull heat away from the puddle faster, so they generally need more preheat than thin-wall pipe of the same material. Typical starting points from the AWS D1.1 Preheat Table and common carbon-steel WPS documents include:
- Thin wall (up to ~20 mm, think Schedule 40 on smaller diameters): roughly 10 degrees C minimum.
- Medium wall (~20 to 38 mm): roughly 10 to 65 degrees C.
- Heavy wall (over 38 to 65 mm, closer to Schedule 80 or XXS): 65 to 110 degrees C is common field practice.1
Maximum interpass temperature is just as important. Many WPS documents cap it somewhere between 230 and 300 degrees C2 for plain carbon steel, though some material specs, like A709 HPS 70W, limit it to 200 degrees C. Your qualified WPS is the only document that governs, not a generic chart.
Measuring and Maintaining Temperature
Check temperature with temperature-indicating (Tempilstik-type) crayons or a calibrated infrared thermometer, reading the joint area and adjacent base metal, not just the weld bead, before starting each pass. If the pipe drops below minimum preheat between passes, reheat it. If it climbs toward the maximum, stop and let it cool in still air before capping.
Why You Shouldn't Force Cool
Never quench a hot joint with water or blast it with forced air unless your procedure specifically qualifies that practice. Rapid cooling can trap hydrogen and shock the microstructure, producing cracks that no amount of cap-pass cosmetics will hide during destructive testing.
From Cap Pass to Destructive Testing: Next Steps
Visual Inspection Comes First
Before any coupon reaches a bend fixture or tensile machine, it must pass visual inspection. If the cap fails on undercut, incomplete fusion, excess reinforcement, or profile irregularities, the test ends there. A weld that cannot clear the naked-eye acceptance limits will not be sent forward, so treat your cap pass as the gatekeeper for everything that follows.
How Cap Quality Drives Bend Results
Guided bend tests punish anything that concentrates stress. Excessive reinforcement, sharp toe transitions, or undercut along the cap edge act as stress risers, and the coupon tends to crack or open at exactly those points during the bend. A flat, evenly tied-in cap with smooth toes distributes strain across the weld and helps the specimen survive the required bend radius without opening discontinuities beyond the allowed limits.
Typical 6G Destructive Tests
For 6G qualification, coupons are usually cut into specimens for:
- Guided bend tests: face and root bends check ductility and fusion through the full cross section.
- Tensile tests: verify the joint meets the required strength of the base metal.
- Fracture or macro tests: reveal internal fusion, porosity, and root soundness.
Strong, consistent hot pass, fill, and cap fusion is what carries you through all three.
Each destructive test is covered in detail in the next step.