Ace Your Bend Tests: Avoid These 7 Welding Mistakes

When certification day hits, you don’t want surprises in the bend jig or under radiography (RT). The fastest way to pass the first time isn’t luck—it’s eliminating preventable mistakes in fit-up, heat control, and WPS discipline. This practical guide walks you through proven routines, process and filler selection tips (GMAW, FCAW, GTAW, SMAW), common acceptance pitfalls, and how to keep essential variables tight when the pressure is on.

What Inspectors Actually See in Bend and RT

Bend tests and radiography both tell the same story: consistency. If your prep and variables are controlled, your coupons survive the bend and your film reads clean. If not, defects that were invisible on the surface become painfully obvious.

Common acceptance criteria pitfalls

Excessive reinforcement or underfill: Too high a cap can mask lack of fusion, while underfill/concavity triggers rejections.
Lack of fusion (sidewall or root) and incomplete penetration: Often revealed as linear indications in RT or opens on face/root bends.
Slag inclusions and worm tracking (FCAW/SMAW): Frequently caused by low heat, long arc, wide weaves, or poor cleaning between passes.
Porosity: Gas leaks, contaminated wire/flux, or moisture lead to scattered or clustered pores on film.
Tungsten inclusions (GTAW) and silicon islands (GMAW): Small but disqualifying indicators that show up clearly in RT.
Undercut and overlap: Edge defects that may pass the eye test but fail acceptance limits.
Bend coupons with nicked edges or wrong die diameter: Sharp edges act as stress risers and cause false failures.

Mistake 1: Sloppy Fit-Up and Prep

Good welds start before the arc. Uneven root openings, hi-lo, and dirty bevels are the seed of most bend and RT failures.

Prep the joint: Grind bevels to bright metal. Remove mill scale, paint, and oil at least 1 in (25 mm) from the joint. Deburr.
Control root opening and land: Keep uniform gaps with wedges or spacers. Match the land to your process (e.g., slightly smaller for GTAW roots, slightly heavier for FCAW fill passes).
Align the pipe/plate: Use a hi-lo gauge; correct mismatch with chain clamps and dogs. Excessive mismatch sets up internal concavity and sidewall LOF.
Tack with intent: Use short, clean tacks; feather the ends. Stagger and grind any tack inclusions; tie into tacks smoothly to avoid cold starts on RT.
Back purging (when required): Seal dams, tape gaps, and verify purge quality before striking an arc on stainless/nickel alloys. Target low oxygen levels for shiny internal roots.

Pro tip: Document your actual dimensions (root gap, land, bevel angle). If you need to defend a good procedure later, your notes help.

Mistake 2: Ignoring the WPS and Essential Variables

The WPS is not a suggestion. It’s your playbook—and it’s what you’ll be judged against.

Lock in the essentials

Process and polarity: Verify GTAW/GMAW/FCAW/SMAW settings and DCEP/DCEN as specified.
Filler classification and size: Use the exact wire/rod (e.g., ER70S-6, E7018, E71T-1). Don’t switch sizes mid-test without approval.
Shielding gas and flow: Confirm composition (e.g., 90Ar/10CO2 for GMAW spray, 100% Ar for GTAW), purity, and flow rate. Check for leaks.
Preheat/interpass temperature: Use temp crayons or IR thermometer; record values. Reheat if interpass drops below minimum.
Position, joint design, and backing: Don’t deviate on position or use backing/purge unless allowed.
Amps/volts/WFS/travel speed: Stay within ranges; make small, deliberate adjustments.

Under pressure, shrink your variables. Mark your machine, measure CTWD/arc length, and keep a travel-speed reference (e.g., time over a marked 4 in segment) to maintain heat input steadiness.

Mistake 3: Poor Heat Control and Interpass Management

Too hot and you risk undercut, burn-through, and distortion. Too cold and you invite LOF and slag inclusions. Control wins RT and bend tests.

Preheat and interpass: Follow the WPS minimums; don’t exceed maximum interpass. Preheat reduces hydrogen cracking and improves fusion. Recheck before each pass.
Heat input discipline: Keep a consistent arc length and CTWD. Small changes swing amperage and penetration dramatically, especially in FCAW/GMAW.
Stringers beat wide weaves: For RT-quality structural or pipe work, narrow stringers usually reduce slag trapping and porosity versus wide weaves.
Sidewall dwell: Pause slightly on the toes to fuse and wet in; avoid digging a groove that becomes undercut.
Interpass cleaning: Chip, wire-brush, and grind if needed. Remove silicon islands and slag completely before the next pass.

Heat input quick check

Track volts, amps, and travel speed. Even without doing the full math, consistent readings bead-to-bead correlate to consistent results on film and in the bend jig.

Mistake 4: Wrong Process or Filler for the Test

Your choice of process and filler can set you up for success—or for indications you can’t grind out later.

GTAW (TIG)

Best for RT-clean roots on carbon and stainless. Use proper purge for stainless/nickel; keep tungsten sharp and clean to prevent inclusions.
Filler tips: ER70S-2 (for dirtier steel) or ER70S-6 (for clean carbon steel), ER308L/309L for stainless where applicable.
Gas lens and larger cups improve shielding; keep gas at steady flow, not blasting.

GMAW (MIG)

Know the mode: Many codes prohibit short-circuit on open roots for RT-quality. Choose spray or pulsed-spray for fills and caps.
CTWD control: About 1/2 in (12–15 mm) for spray. Too long reduces penetration and increases spatter/porosity.
Advanced waveforms (pulsed, RMD/STT): Great for controlled heat input and tie-ins, but ensure the WPS allows them.

FCAW

Choose the right classification: E71T-1/-1C/-9 for all-position structural; confirm impact requirements if applicable.
Watch worm tracks and slag lines: Keep heat adequate, arc tight, and clean between beads.
CTWD usually longer than GMAW (often ~3/4 in). Stable stickout equals stable penetration.

SMAW (Stick)

E7018 needs a rod oven: Moisture means hydrogen, porosity, and RT failures. Discard compromised rods.
Short arc and tight arc length: Long arcs increase spatter and porosity; keep 10–15° push/drag angle as appropriate.
Restart discipline: Grind back to sound metal; feather and tie in to avoid cold laps and crater cracks.

When in doubt, use GTAW for the root and fill/cap with SMAW or FCAW per WPS to balance fusion quality and productivity.

Mistake 5: Inconsistent Technique and Bead Placement

Technique is where most essential variables become visible. Keep it steady, especially on the root and hot pass.

Open-root keyhole control: For GTAW, keep a tight arc and feed evenly; for SMAW, keep a small, consistent keyhole with slight pauses at the sidewall. Don’t whip excessively.
Hot pass urgency: Seal the root and burn out slag/oxide immediately. This reduces trapped inclusions.
Bead sequence: Plan stringers to minimize trap points. Stagger starts/stops and grind tie-ins smooth.
Cap profile: Aim for slight convexity with clean toes. Excessive convexity suggests low fusion; concavity/underfill risks rejection.
Stop-start technique: Back-step, preheat the crater, and add filler to prevent crater cracks visible in RT and in bends.

Mistake 6: Dirty Gas, Moisture, and Contamination

More RT failures come from contamination than most admit. Treat your gas and consumables like critical components.

Leak check: Soap-test connections and inspect O-rings. Confirm flow at the torch with a flowmeter/peashooter.
Shielding quality: Avoid drafts; use screens. For stainless GTAW, keep post-flow long enough to protect the puddle and tungsten.
Consumable storage: Keep wires and rods clean and covered. Store 7018 in a rod oven. Replace rusty or oily wire.
Silicone and shop grime: Remove anti-spatter residues and oils. Silicon islands from GMAW caps can pop on film—lightly grind/brush before final pass if needed.
Purge verification: Use an oxygen analyzer for critical stainless/nickel roots; dull gray color often means poor purge.

Mistake 7: Bad Test-Day Routine and Documentation

Test day is about controlling the controllables. A simple routine reduces nerves and mistakes.

Step-by-step test-day checklist

Read the WPS like a contract: Highlight essential variables and limits. Confirm position, backing/purge rules, and acceptance notes.
Verify equipment: Calibrate voltage/amperage displays if possible. Confirm polarity, program/mode (spray, pulse), and wire diameter in the machine.
Kit to bring: Clean wire brush, grinder with fresh wheels, carbide burr, files, acetone and lint-free rags, temp crayons/IR gun, hi-lo and bridge-cam gauges, feeler gauges, spare tungsten/cups/contact tips, flowmeter, and a good ground clamp.
Fit-up and ID: Measure and record root gap/land/angle. Stamp coupon IDs per instructions and mark orientation for bend specimen extraction.
Dry run: Practice torch/rod access, cable routing, and ground placement to avoid arc blow and unstable angles.
First arc discipline: Strike on scrap to verify parameters and gas. Make a short test bead to confirm puddle behavior and fusion.
Interpass control: Log temps and parameters. Clean thoroughly between passes and inspect with a light and mirror.
Coupon extraction and prep: Cut bend specimens cleanly, remove sharp edges, and radius the corners to avoid notch-induced failures. Verify bend die size per thickness before bending.

New tools can help: Digital power sources with pulsed programs, data logging, and locked WPS presets reduce drift. Just be sure the test agency allows those features.

Key Takeaways

Master the basics: Uniform fit-up, clean prep, and disciplined interpass cleaning prevent most indications.
Live inside the WPS: Verify gas, filler, polarity, parameters, preheat/interpass, and position. Control CTWD/arc length and travel speed.
Pick the right process/mode: GTAW roots and spray/pulsed GMAW or controlled FCAW fills typically produce RT-friendly results.
Document and measure: Track variables, temps, and bead sequence. Prepare bend coupons carefully to avoid false failures.

Conclusion

Passing bend and radiography tests on the first try isn’t about tricks—it’s about repeatable control. Nail your fit-up, stay faithful to the WPS, manage heat like a pro, and choose process/filler combinations that set you up for clean fusion and sound profiles. Build your test-day routine, measure what matters, and the bend jig and film reader will reward you.