Welding Inspection: What Does a QC Engineer Actually Check?

Many people think welding inspection means looking at the finished weld and saying OK or not OK. In practice, it starts much earlier and goes on till the job is released.

A weld can look fine on the surface and still have a problem inside, or it may have been made with the wrong consumable or by a welder who was not qualified. That is why a QC Engineer or Welding Inspector checks the whole process, not just the final weld.

Here is what that actually looks like, stage by stage.

Before welding

Most problems can be stopped at this stage. Before any welding starts, the inspector checks:

• Approved drawing (latest revision)
• Approved WPS
• Welder qualification
• Material identification
• Consumables
• Fit-up
• Preheat, where required

Fit-up needs special attention. Root gap, root face, groove angle, alignment and mismatch (hi-low) should all be checked against the drawing and WPS. Tack welds should also be in good condition. Welding should go ahead only after the fit-up inspection is done and released. This is a QC hold point.

During welding

Once welding starts, the inspector keeps an eye on:

• Welding parameters, whether they are within the WPS range
• Preheat and interpass temperature
• Welding sequence
• Consumable control (correct electrode or filler wire, storage, baking/rebaking, issue and return records)
• Interpass cleaning
• Visual monitoring of the weld as it progresses

Welder identification should also be maintained so that every weld can be traced back to the welder.

After welding

After welding, the checks are:

• Visual inspection
• Dimensional inspection
• NDT as required by the ITP/specification (VT, DPT, MT, UT, RT)
• Weld repair, if needed
• Final acceptance

If any repair is done, it must follow the approved repair procedure, and the weld must be re-examined afterwards.

Documentation

Inspection is not complete without records. A QC Engineer should make sure the following are available and in order:

• WPS/PQR
• Welder qualification records
• Inspection reports
• NDT reports
• Traceability records

Common problems found during inspection

Some problems are small and can be corrected on the spot. Others need repair, re-welding or even engineering review. These are the ones that come up most often.

• Improper fit-up. Wrong root gap or root face, misalignment, excessive mismatch, wrong joint angle or poor tack welding. This directly affects penetration, fusion and final weld quality. The inspector should check the drawing/WPS and verify the joint before welding is allowed.
• Undercut. A groove along the weld toe or edge of the base metal. Usually caused by high current, high travel speed, wrong electrode angle or poor technique. Controlling parameters and technique helps prevent it.
• Porosity. Gas trapped inside the weld metal. Possible causes are moisture, contaminated surface, improper shielding gas, long arc length and poor consumable storage. Check the acceptance criteria and find out what went wrong in the welding conditions before repair.
• Lack of fusion. The weld metal does not fuse properly with the base metal or the previous layer. Causes include low heat input, wrong electrode angle, high travel speed and poor cleaning. This is a serious concern because the unfused area reduces the effective strength of the joint.
• Lack of penetration. The weld does not go through the joint root properly. It can come from wrong root gap or root face, low current, wrong electrode manipulation or poor joint preparation. Depending on the joint and code, it can be found by VT, RT or UT.
• Cracks. Among the most serious discontinuities. They can be longitudinal, transverse, crater, toe or root cracks. A suspected crack should not just be ground out and rewelded. The approved repair procedure and acceptance requirements must be followed.
• Excessive reinforcement and excessive weld size. Compare the actual condition with the drawing, WPS and acceptance criteria. An oversized fillet weld means more welding time, more consumable use, more distortion and unnecessary heat input. Use a proper weld gauge to check the size.
• Arc strikes and spatter. Arc strikes outside the weld area can cause localized heating, and may become a quality issue depending on the material and specification. Excess spatter points to poor parameters or technique, and it adds cleaning work before painting.
• Distortion. Welding heat can cause angular, longitudinal or transverse distortion and buckling. A proper welding sequence, controlled heat input, balanced welding and good fit-up all help. Dimensional checks should be done at the required stages, not only after the whole structure is complete.
• Wrong welding consumable. This can become a serious nonconformance. QC should verify the classification, batch/heat identification, storage condition, baking/re-baking and issue/return records.

A simple QC flow

Drawing Review → Material Identification → Fit-Up Inspection → Welding Parameter Check → In-Process Inspection → Visual Inspection → NDT → Dimensional Inspection → Repair if Required → Final Inspection

For fabrication jobs that also include painting, the flow continues with surface preparation, painting and DFT inspection before final inspection and release. Before painting, ambient temperature, steel temperature, relative humidity and dew point should be recorded. During painting, the paint system, mixing ratio, pot life, WFT, recoat interval and DFT should be checked.

Don't make the checklist a tick-mark exercise

A checklist is useful, but only if it is filled properly. For every inspection, record the requirement, the actual measured value, the status, and who inspected it and when.

Writing only "OK" does not tell anyone much later. The actual value does.

Final thought

Many welding problems can be prevented before welding even starts. Good fit-up, correct material identification, qualified welders, an approved WPS and proper consumable control reduce rework a lot.

A good QC inspection is not only about finding defects. It is about making sure defects do not move on to the next stage.