Apply Weld Quality Control and Inspection Procedures

Applying Quality Control and Inspection Procedures for Welds

Introduction: The Welder's Role in Quality Control

As a certified welder, you are not just a performer: you are the first link in the quality control chain. The Canadian Construction Code and CSA standards (Canadian Standards Association) require that the welder possess practical knowledge of inspection procedures, not to replace the inspector, but to prevent defects before they become costly rejections. This chapter covers the full body of knowledge required for the Red Seal exam regarding non-destructive testing (NDT) methods, acceptance criteria, reference documents, and traceability procedures.

1. Reference Documents and Applicable Standards

1.1 Essential Canadian Standards

The Canadian regulatory landscape for welding is dominated by CSA group standards. For the exam, you must know the following documents:

Standard	Title	Primary Application
CSA W59	Welded Steel Construction (Metal Arc Welding)	Requirements for welded joints in structural steel
CSA W47.1	Certification of Companies for Fusion Welding of Steel	Qualification of procedures and welders
CSA W186	Welding of Reinforcing Bars in Reinforced Concrete Construction	Welded reinforcing bars
CSA B149.1	Canadian Electrical Code, Part I — Chapter V — Welding	Does not apply directly to welding, but to gases — watch out for confusion
CSA Z662	Oil and Gas Pipeline Systems	Welding of pressure pipelines

Crucial point for the exam: Standard CSA W59 is the primary reference for acceptance criteria for structural steel welds. Standard CSA W47.1 governs company certification (welding procedure qualification requirements — WPS, and welder qualifications).

1.2 Welding Procedure Specification (WPS) and Procedure Qualification Record (PQR)

WPS (Welding Procedure Specification): Document that describes the exact welding parameters (filler metal, amperage, voltage, travel speed, preheat, position, etc.). It must be qualified before use.

PQR (Procedure Qualification Record): Report of mechanical tests (tensile, bend, impact) that proves the WPS produces sound welds.

Golden rule: The welder must work exactly according to the WPS. Any deviation (change in amperage, speed, position) invalidates the weld's conformity, even if the result appears visually acceptable.

2. Non-Destructive Testing (NDT) Methods

2.1 Classification and General Principles

NDT methods are examination techniques that do not destroy the part being inspected. The choice of method depends on the type of defect being sought, material thickness, cost, and code requirements.

Method	Defects Detected	Typical Thickness	Advantages	Limitations
Visual Inspection (VT)	Surface defects: cracks, porosity, lack of fusion, profile	All	Fast, economical, first check	Surface only
Liquid Penetrant Testing (PT)	Surface cracks, open porosity	All	Simple, portable	Surface only, requires clean surface
Magnetic Particle Testing (MT)	Surface and subsurface cracks (up to ~6 mm)	All (ferromagnetic materials)	Fast, detects fine cracks	Ferromagnetic materials only
Ultrasonic Testing (UT)	Internal defects: lack of fusion, inclusions, cracks	6 mm to 300 mm	Volumetric detection, portable	Complex interpretation, requires qualified operator
Radiographic Testing (RT)	Internal defects: porosity, inclusions, cracks	3 mm to 75 mm (depending on source)	Permanent image, volumetric detection	Costly, radiation hazards, bilateral access required

2.2 Visual Inspection (VT) — The First Line of Defense

Visual inspection is mandatory in 100% of cases, before, during, and after welding. It is governed by standard CSA W59 for acceptance criteria.

Before welding:

Verification of edge cleanliness (absence of rust, oil, paint, moisture).

Verification of alignment and fit-up (gap) of parts.

Verification of preheat if required by the WPS.

During welding:

Monitoring of interpass temperature (do not exceed maximum interpass temperature).

Control of each pass profile (no excessive grooving).

After welding:

Weld dimensions (width, reinforcement height).

Presence of surface defects.

2.3 Liquid Penetrant Testing (PT) — Principle and Procedure

Liquid penetrant testing uses a penetrating liquid that seeps into surface-breaking cracks. The procedure involves 6 steps:

34.Cleaning: Complete degreasing of the surface (solvent).

35.Application of penetrant: Penetration time of 5 to 30 minutes depending on the manufacturer.

36.Removal of excess: Careful wiping (do not rinse if using a non-water-washable penetrant).

37.Application of developer: Thin white layer that draws the penetrant out of defects.

38.Examination: Under white light (red penetrant) or UV light (fluorescent penetrant).

39.Final cleaning: Removal of developer after inspection.

Critical limitations:

Penetrant testing only detects defects open to the surface.

Part temperature must be between 4 °C and 52 °C (except special products).

A rough surface can produce false indications (penetrant accumulation in surface irregularities).

2.4 Magnetic Particle Testing (MT) — Principle and Application

Magnetic particle testing is used on ferromagnetic materials (carbon steel, certain martensitic stainless steels). The principle: a magnetic field is applied to the part; cracks create a leakage flux that attracts magnetic particles.

Two types of equipment:

Yoke (portable electromagnet): Produces a longitudinal field. Lightweight and practical.

Coil or central conductor: Produces a circular field. Used in shop settings.

Orientation requirements: The magnetic field must be perpendicular to the expected defect to detect it. Therefore, two examinations must be performed at 90 ° to each other.

Exam trap: Magnetic particle testing does not work on aluminum, copper, austenitic stainless steels (unless cold-worked). For these materials, use liquid penetrant testing.

2.5 Ultrasonic Testing (UT) — Basic Principles

The ultrasonic method uses high-frequency sound waves (0.5 to 10 MHz) that propagate through the material. Reflections from interfaces (defects) are detected and displayed on a screen.

Essential terminology:

Transducer (probe): Transducer that emits and receives the waves.

Couplant: Gel or oil that ensures sound transmission between the transducer and the part.

Initial pulse (entry echo): Initial signal at the surface.

Back-wall echo: Reflection from the back face of the part.

Dead zone: Distance near the surface where echoes cannot be distinguished.

Distance calculation: The distance of a defect is calculated using the formula:

d = (v × t) / 2

Where:

d = distance (mm)

v = sound velocity in the material (steel: 5,920 m/s)

t = round-trip travel time (seconds)

Example: If the travel time is 10 microseconds (10 × 10⁻⁶ s) in steel:

d = (5,920 × 10 × 10⁻⁶) / 2 = 0.0296 m = 29.6 mm

2.6 Radiographic Testing (RT) — Principles and Safety

Radiographic testing uses X-rays or gamma rays to produce an image on film. Defects appear as darker areas (less absorbing material).

Sources:

X-rays: Electrical generator. Adjustable intensity.

Gamma rays: Radioactive isotopes (Iridium 192, Cobalt 60). Portable, but always emitting.

Safety rules (CNSC — Canadian Nuclear Safety Commission):

Minimum distance from source: calculated according to dose rate.

Controlled zones: delineated with tape and signs.

Personal dosimeters mandatory for operators.

The ALARA principle (As Low As Reasonably Achievable): minimize exposure time, maximize distance, use shielding.

Radiograph interpretation:

Porosity: Round dark spots, isolated or grouped.

Slag inclusion: Elongated, irregular dark areas, often at the root.

Crack: Fine dark line, often branched.

Lack of fusion: Straight dark line, parallel to the weld edge.

3. Acceptance Criteria According to CSA W59

3.1 Dimensional Tolerances

Standard CSA W59 defines precise criteria for fillet welds and full penetration welds.

Fillet welds:

Throat (throat size): The theoretical throat is calculated as 0.707 × the nominal size for a 90 ° angle.

Maximum reinforcement: 1.5 mm beyond the nominal size for fillet welds.

Convex or concave profile: Tolerance of 1.5 mm from the theoretical profile.

Full penetration welds:

Reinforcement: Maximum 3 mm beyond the part surface.

Excess penetration (root): Maximum 3 mm.

3.2 Surface Defects — Acceptance Criteria

Defect	Acceptance Criterion (CSA W59)
Cracks	No cracks are acceptable (all cracks are rejections).
Surface porosity	Maximum diameter: 1.5 mm. The sum of diameters over 25 mm of length must not exceed 3 mm.
Lack of fusion	Not acceptable (rejection).
Undercut	Maximum depth: 0.5 mm for welds subject to fatigue; 1 mm for others. Limited cumulative length.
Overlap	Not acceptable.
Spatter	Must be removed if it interferes with inspection or service.

3.3 Internal Defects — Acceptance Criteria

For full penetration welds subject to radiographic or ultrasonic testing:

Slag inclusions: Maximum length of 3 mm for 6 mm thickness; for greater thicknesses, the maximum length is 1/3 of the thickness, up to 12 mm maximum.

Internal porosity: Maximum diameter of 2 mm or 1/4 of the thickness (whichever is smaller). The sum of diameters over 25 mm must not exceed 6 mm.

Internal cracks: No cracks are acceptable.

4. Dimensional Control and Measurements

4.1 Measuring Instruments

Weld gauge (fillet weld gauge): Measures the throat of fillet welds, reinforcement, and undercut.

Ruler and caliper: General dimensions.

Square: Verification of part angles.

Alignment gauge: Verification of pipe misalignment (permissibility according to code).

4.2 Calculating the Throat of a Fillet Weld

For a 90 ° fillet weld with equal legs (nominal size z), the theoretical throat a is:

a = z × cos(45 °) = z × 0.707

Example: A fillet weld with a nominal size of 10 mm has a theoretical throat of:

a = 10 × 0.707 = 7.07 mm

Exam trap: Do not confuse leg size and throat. The throat is always smaller than the leg for a 90 ° angle.

5. Traceability and Documentation

5.1 Welder Identification Marking

Each welder must apply their identification mark (stamp or tag) near the weld they have completed. This requirement is specified in CSA W47.1 and CSA W59.

The marking must be legible and permanent.

It must be placed at a maximum distance of 150 mm from the weld.

If marking is impossible (painted surface, corrosive environment), a traceability register must be maintained.

5.2 Inspection Records and Reports

The following documents must be retained for each project:

122.Qualified WPS and corresponding PQR.

123.Welder certificates (validity of qualifications).

124.Visual inspection reports (dated, signed).

125.NDT reports (RT, UT, MT, PT) with films or recordings.

126.Heat treatment register (preheat, post-weld heat treatment).

Retention requirement: Documents must be kept for the duration specified by the contract or code (often 3 to 7 years after completion of work).

6. Welding Defects — Classification and Causes

6.1 Classification According to ISO 6520 (CSA Reference)

Category	Type of Defect	Typical Causes
Cracks	Hot crack, cold crack, crater crack	High stresses, hydrogen, rapid cooling, poor width/depth ratio
Cavities	Porosity, blowholes, wormholes	Dissolved gases, moisture, insufficient shielding gas flow, drafts
Inclusions	Slag, oxides, tungsten	Poor cleaning between passes, amperage too low, unsuitable electrode
Lack of fusion	Lack of sidewall fusion, lack of penetration	Incorrect electrode angle, amperage too low, travel speed too fast
Shape defects	Undercut, overlap, excessive reinforcement, grooving	Unsuitable parameters, incorrect technique

6.2 Cracks — The Most Serious Defect

Cracks are always unacceptable in welds according to CSA W59. You must distinguish:

Hot crack: Occurs during solidification. Characterized by an intergranular appearance, often at the crater or weld center. Promoted by sulfur and phosphorus.

Cold crack: Occurs after cooling, often in the heat-affected zone (HAZ). Related to hydrogen, stresses, and high hardness. Prevention: preheat, hydrogen control, post-weld heat treatment.

Preheat calculation: Standard CSA W59 provides methods for calculating the minimum preheat temperature based on thickness, carbon equivalent (CE), and electrode type.

Carbon Equivalent (CE) — IIW formula (International Institute of Welding):

CE = C + (Mn / 6) + (Cr + Mo + V) / 5 + (Ni + Cu) / 15

Example: Steel with C = 0.20%, Mn = 1.2%, Cr = 0.1%, Ni = 0.1%:

CE = 0.20 + (1.2 / 6) + (0.1 + 0 + 0) / 5 + (0.1 + 0) / 15

CE = 0.20 + 0.20 + 0.02 + 0.007 = 0.427

A CE greater than 0.40 indicates reduced weldability and requires higher preheat.

7. Heat Treatments

7.1 Preheat

Preheat is the heating of the part before welding. Its objectives:

Reduce the cooling rate.

Allow hydrogen diffusion.

Reduce thermal stresses.

Typical temperatures: 50 °C to 150 °C depending on material and thickness. The temperature must be verified with a contact thermometer or temperature indicating crayons at a distance of 75 mm from the weld.

7.2 Post-Weld Heat Treatment (PWHT)

PWHT is used to:

Reduce residual stresses.

Improve toughness.

Restore ductility of the HAZ.

Typical parameters: Temperature of 600 °C to 650 °C, holding for 1 hour per 25 mm of thickness (minimum 1 hour), controlled slow cooling.

8. Practical Exam — Tips for Red Seal Exam Questions

8.1 Types of Frequent Questions

160.Identification of defects on photographs or diagrams.

161.Selection of the appropriate NDT method based on material and defect sought.

162.Calculations of throat, carbon equivalent, UT distance.

163.Acceptance criteria: knowing whether a defect is acceptable or not according to CSA W59.

164.Safety: radiation protection rules, gas handling.

8.2 Response Strategy

Read the question carefully: Red Seal exams often use traps (for example, "which of these methods detects internal defects?" — the answer is RT or UT, not MT).

For calculation questions, check the units (mm, m/s, µs).

For acceptance criteria questions, remember: any crack is a rejection.

Pitfalls to Avoid

171.Confusing liquid penetrant and magnetic particle testing: Penetrant testing works on all materials; magnetic particle testing only on ferromagnetic materials.

172.Forgetting that magnetic particle testing does not detect deep internal defects: It only detects surface and subsurface defects (up to ~6 mm).

173.Confusing the leg and throat of a fillet weld: Throat = 0.707 × leg for a 90 ° angle.

174.Accepting a crater crack: Any crack, regardless of size, is a rejection according to CSA W59.

175.Ignoring the maximum interpass temperature: The WPS specifies a maximum temperature; exceeding it can degrade mechanical properties.

176.Using radiography on an unsuitable material: RT is effective for volumetric defects, but less so for planar cracks (orientation dependent).

177.Forgetting interpass cleaning: Slag left between passes causes inclusions, a major defect.

178.Not verifying the validity of the welder's certification: A welder must be qualified for the specific position, process, and thickness.

179.Confusing CSA W59 and CSA W47.1: W59 provides acceptance criteria; W47.1 governs certification of companies and welders.

180.Neglecting radiographic safety: Minimum distances and dosimeters are mandatory; safety questions are frequent on the exam.

Summary

Quality control in welding is based on a systematic approach that begins before welding and continues after. The essential points to remember:

184.CSA W59 and W47.1 standards are the primary Canadian references for structural steel welding.

185.Visual inspection is mandatory and must be performed at every stage of the process.

186.NDT methods complement each other: VT and PT for surface, MT for surface and subsurface (ferromagnetic materials), UT and RT for internal.

187.Acceptance criteria are strict: no cracks are tolerated, porosity and inclusions are limited in size and density.

188.Traceability is mandatory: welder marking, registers, inspection reports.

189.Calculations of throat (0.707 × leg), carbon equivalent, and ultrasonic distance are skills assessed on the exam.

190.Safety (particularly radiological) is a recurring theme: respect distances, dosimeters, and the ALARA principle.

The competent welder does not just produce beautiful welds: they know how to verify that they are conformant, document their work, and identify deviations before they become defects. This skill is at the heart of the trade and the Red Seal exam.