Quality Control for Steel Structures: Fabrication & Erection

Steel structures form the backbone of modern buildings, bridges and industrial facilities. Ensuring quality during fabrication and erection is critical to achieve structural integrity, safety and durability.

Who this helps

This article is for quality control engineers, fabrication supervisors, welding inspectors and site engineers who oversee steel fabrication shops and erection works on site. It explains practical steps to maintain quality from mill to project handover.

Foundations

Steel structures are made up of columns, beams, trusses, bracing members and connection plates. Quality control starts with understanding the specifications, drawings and codes such as IS 800 in India or AISC/BS 5950 in GCC. Material grades (e.g. Fe410, Fe500, ASTM A572) must meet project requirements and be traceable to mill certificates.

Step-by-Step Quality Control

1. **Material procurement & traceability**: Verify mill test certificates (MTCs), chemical composition and mechanical properties. Mark each plate and section with heat number and store under cover.

2. **Cutting and machining**: Check that cutting lines are marked accurately. Inspect cut edges for burrs and maintain tolerances for length, squareness and hole positions. Holes should be drilled (not gas cut) to avoid defects.

3. **Welding & fabrication**: Ensure welders are qualified and welding procedure specifications (WPS) approved. Inspect fit-up, root gap and bevel angles. Conduct pre-heating if required. After welding, conduct visual inspection followed by NDT such as ultrasonic testing or radiography as per project specification.

4. **Surface preparation**: Clean surfaces by blast cleaning to the specified standard (e.g. SA 2.5). Check surface profile and cleanliness. Apply primer coats within the specified time window and inspect dry film thickness.

5. **Trial assembly**: Pre-assemble components in the shop to verify fit-up, bolt hole alignment and overall geometry. Make adjustments before dispatch to site.

6. **Transportation & storage**: Protect fabricated pieces with wooden spacers and tarps. Mark lifting points and ensure no damage occurs during loading, transport and unloading.

7. **Erection**: Use proper lifting equipment. Check foundation levels and anchor bolt positions. Align columns and beams using theodolites and spirit levels. Tighten bolts progressively to specified torque values and inspect welds.

8. **Final inspection & documentation**: Record all inspections, tests and corrective actions. Prepare as-built drawings and quality dossiers for handover.

Example QC Parameters

| Parameter | Acceptance Criteria |

| --- | --- |

| Dimensional tolerance (beam length) | ± 3 mm |

| Hole diameter deviation | +1.0 / -0 mm |

| Weld throat thickness | ≥ leg size × 0.707 |

| Paint dry film thickness | 80–100 µm per coat |

| Bolt torque for M20 grade 8.8 | 270–300 N·m |

Formulas

- **Weld throat thickness** = leg size × 0.707

- **Bolt tension** = 0.785 × (shank diameter)^2 × allowable stress

- **Paint consumption** (L) = (area m^2 × dry film thickness × specific gravity) / (solids content × 1000)

India vs GCC

In India, fabrication often follows IS codes and uses Fe410 or Fe500 steel, with site welding more common due to labour availability. Monsoon conditions require protection against rust and humidity. In GCC, standards such as BS 5950 or AISC are widely adopted. Higher grades (ASTM A572 Gr50) and prefabrication under controlled conditions are common. Desert climates demand care against sand contamination, and bolted connections are preferred to reduce hot work on site.

Mistakes & Fixes

- **Misaligned holes**: Re-drill holes using templates and ensure jigs are aligned.

- **Incomplete penetration welds**: Re-weld after back gouging and use qualified procedures.

- **Rough gas-cut edges**: Grind smooth and maintain edge preparation angles.

- **Inadequate surface preparation**: Repeat blast cleaning and reapply primer.

- **Incorrect bolt tightening sequence**: Follow star pattern and re-check torque.

Mini QA/QC Checklist

- Mill test certificates verified and materials tagged

- Cutting layouts approved and tolerances checked

- Welders qualified; WPS & PQR approved

- Fit-up inspections carried out before welding

- NDT testing conducted as per plan (UT, RT or MPI)

- Surface cleanliness and profile inspected before painting

- Paint dry film thickness measured with gauge

- Bolt torque inspected and bolts marked after tightening

- Erection alignment (verticality and plumb) within tolerance

- Final inspection records compiled and approved

FAQs

**Q: What is the difference between WPS and PQR?**

A WPS (Welding Procedure Specification) outlines how to perform a weld (parameters, filler material, positions). A PQR (Procedure Qualification Record) is the test record proving that a WPS produces acceptable welds.

**Q: How often should visual inspection be done?**

Visual inspection should be continuous: before welding (fit-up), during welding (bead run) and after welding. Any defects must be marked and repaired before proceeding.

**Q: What tolerance is allowed for column plumb?**

Typical tolerance for verticality of steel columns is H/1000 (e.g. 4 mm per 4 m height). Always check project specifications.

Call to Action

Level up with **BHADANIS – Construction Project Planning & Management Level 5**, **Tendering & Construction Contracts Management Level 3 & 4** and **Quantity Surveying & Estimation Level 1** to master steel fabrication and quality control along with cost management. These courses cover planning, contract clauses and quantity take-off for steel works. By following the steps above and gaining deeper knowledge from these courses, you can deliver safe and compliant steel structures.