CAWI cheat sheet

Inspection personnel certification under CSA W178.2 is by level: Level 1 performs visual inspection only; Level 2 may perform visual and non-destructive inspection; Level 3 may develop procedures and certify Level 1/2 inspectors.

A Welding Inspector's authority to accept or reject work derives from the applicable code or standard cited in the contract, not from personal certification alone.

The inspector's primary documents are the contract drawings, the welding procedure specification (WPS), procedure qualification records (PQR), and the applicable code; inspection without a current WPS is non-conforming.

Visual inspection is the most widely used method and must be performed before, during, and after welding; it is the only method required by most structural welding codes as a minimum.

Non-destructive examination (NDE) methods include visual (VT), liquid penetrant (PT), magnetic particle (MT), ultrasonic (UT), and radiographic (RT); method selection is governed by the code and joint configuration.

A nonconformance report (NCR) documents the deviation, the code clause violated, the disposition (repair, rework, use-as-is, or reject), and the sign-off authority.

Inspection records must be traceable to the specific weld, heat/lot number, welder ID, and date; retention periods are set by the contract or code.

Certification bodies require continuing education and periodic re-examination; lapse in certification removes the inspector's authority to sign off on code-required inspections.

A WPS is a written, qualified document that specifies variables (process, filler, current, voltage, travel speed, preheat, shielding gas); a change to an essential variable requires requalification.

A PQR records the actual variables and test results used to qualify a WPS; the WPS must be supported by a PQR that brackets its essential variables.

Essential variables differ by process and code: for SMAW, electrode classification and current type/polarity are essential; for GMAW, transfer mode and shielding gas composition are essential.

Welder performance qualification (WPQ) tests the individual's ability, not the procedure; a welder qualified on one joint type and position may be qualified for a range defined by the code.

Position qualifiers: 1G/1F flat, 2G/2F horizontal, 3G/3F vertical, 4G/4F overhead; a welder qualified in a higher position may be qualified for lower positions per code rules.

Preheat and interpass temperature are essential variables for many materials; exceeding the maximum interpass temperature can degrade toughness and requires procedure review.

Common processes: SMAW (stick), GMAW (MIG), FCAW (flux-cored), GTAW (TIG), SAW (submerged arc); each has distinct essential variables and typical applications.

Procedure qualification test coupons are subjected to destructive tests (tensile, bend, impact) and, where required, NDE; failure of any required test invalidates the PQR.

Carbon equivalent (CE) predicts hardenability and cold-cracking risk: CE = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15; CE above about 0.40 typically requires preheat and low-hydrogen practice.

Hydrogen-induced cold cracking requires three conditions: susceptible microstructure, diffusible hydrogen, and tensile stress; controlling preheat, hydrogen input, and cooling rate prevents it.

The heat-affected zone (HAZ) experiences peak temperatures below the melting point; grain growth and hard phase formation (martensite) in the HAZ are common causes of cracking.

Austenitic stainless steels are susceptible to sensitization (chromium carbide precipitation at grain boundaries) between roughly 425°C and 870°C, leading to intergranular corrosion; low-carbon or stabilized grades mitigate this.

Aluminum and its alloys form a tenacious oxide film with a melting point far above the base metal; GTAW with AC and argon shielding is commonly used to break up the oxide during welding.

Weldability is the capacity of a material to be welded under imposed conditions into a specific, suitably designed structure and to perform satisfactorily in service.

Cooling rate affects microstructure: fast cooling promotes hard, crack-susceptible phases; slow cooling promotes softer, tougher microstructures but may reduce strength.

Dissimilar metal joints require attention to thermal expansion mismatch, dilution, and galvanic corrosion; nickel-based fillers are often used between carbon steel and stainless steel.

Visual testing (VT) detects surface discontinuities such as undercut, overlap, spatter, incomplete fusion at the surface, and crater cracks; it requires adequate lighting and access.

Liquid penetrant testing (PT) detects surface-breaking discontinuities in non-porous materials; it is not suitable for rough or porous surfaces and requires cleaning before and after.

Magnetic particle testing (MT) detects surface and near-surface discontinuities in ferromagnetic materials only; it cannot be used on austenitic stainless steel or aluminum.

Ultrasonic testing (UT) detects internal planar discontinuities and requires a qualified operator, calibrated equipment, and reference standards; it is sensitive to orientation of the defect.

Radiographic testing (RT) detects internal volumetric discontinuities; image quality is governed by source size, film or detector resolution, and geometric unsharpness.

Acceptance criteria are code-specific: for example, undercut depth limits, porosity size and distribution limits, and reinforcement height limits are defined in the applicable code.

Destructive tests include tensile, guided bend, Charpy V-notch impact, and hardness tests; they verify mechanical properties of the procedure qualification.

Code compliance requires that all inspection, testing, and records be performed and documented in accordance with the contract-specified code edition; using a superseded edition is a nonconformance.