Quality control and inspection

A system, not a final check

Quality in steel building fabrication is built in at each stage rather than inspected in at the end. A fabricator's quality system defines who checks what, when and against which acceptance criteria, and records the result. The backbone is an inspection and test plan (ITP) that lists every control point of the fabrication process, the standard that applies, the frequency and whether the client or a third party wishes to witness or hold the point.

Control points along the line

Weld inspection methods

• Visual testing (VT) – applied to all welds; checks size, profile, undercut, porosity, cracks and spatter (ISO 17637). The single most valuable inspection.
• Magnetic particle testing (MT) – detects surface and near-surface cracks in fillet welds and at weld toes, especially at knees, base plates and end plates (ISO 17638, ASTM E709).
• Ultrasonic testing (UT) – volumetric examination of full- and partial-penetration butt welds, such as flange splices and end-plate CJP welds (ISO 17640, AWS D1.1 clause 8).
• Radiographic testing (RT) – used occasionally for butt welds; less common in PEB shops because of handling and radiation safety.

The extent of supplementary NDT depends on the governing standard and the level of the work: EN 1090-2 sets percentages by execution class and weld type, AS/NZS 5131 links inspection to construction category and AS/NZS 1554.1 weld category (GP or SP), and AWS D1.1 leaves extent to the contract documents. Acceptance levels follow ISO 5817 quality levels (C or B for EXC3), AS/NZS 1554.1 or AWS D1.1 tables. Inspectors are qualified to ISO 9712 or ASNT SNT-TC-1A, and welding inspectors to AWS CWI, ISO 14731 or equivalent schemes.

Dimensional control

For a bolted PEB, dimensional accuracy is what makes erection fast. The critical items are member length between end plates, depth at the end plate, hole pattern and gauge, end-plate flatness, base-plate hole positions and the location of purlin clips and flange brace holes. Members are checked with tapes, squares and templates; complex members may be checked against the 3D model. Typical permitted deviations are given in AISC 303 and the MBMA Metal Building Systems Manual, AS/NZS 5131 Section 14 and EN 1090-2 Annex B – see erection tolerances for site values.

Checking cladding, secondary members and bought-out items

Quality control of a PEB does not stop at the welded frames. Many site complaints relate to cladding colour, coating damage, wrong fasteners or missing accessories, so the inspection plan also covers these items.

Colour consistency is important for façades: sheets for one elevation should come from one coil-coating batch wherever possible, and the colour difference against the approved sample is checked instrumentally (ΔE) rather than by eye under workshop lighting.

Certification and the quality dossier

World Steel operates a certified welding quality system to ISO 3834-2, fabricates to EN 1090-2 EXC3 and AS/NZS 5131 CC3, holds IAS AC472 accreditation for metal building systems (first in Asia) and BC1 registration for Singapore. Each project receives a quality dossier with mill certificates, WPS/PQR and welder qualifications, NDT, dimensional and coating reports and non-conformance records. Third-party inspection by the client's agency is welcomed at agreed hold points. Requirements for CSA W47.1, AISC Certification or CE marking are confirmed per project – see market compliance and US PEB standards.

Agree the ITP, NDT extent and acceptance criteria in the contract. Changing them after fabrication has started costs time and money.