Welding Preparation and Quality Control

Chapter Introduction

This chapter covers all the skills required to prepare, execute, and verify a welded assembly that meets the requirements of the Canadian Electrical Code, Chapter V and applicable CSA standards. For the Red Seal exam, you must master not only welding technique but also qualification procedures, defect acceptance criteria, and non-destructive testing (NDT) methods. This chapter is structured to follow the logic of the welding process: preparation, execution, inspection, and documentation.

Weld Joint Preparation

Joint Geometry and Welding Symbols

Joint preparation begins with selecting the appropriate joint type and bevel. The standard joint types according to CSA W59 (Welded Steel Construction) are:

Joint Type	Basic Symbol	Typical Application
Butt joint	I	Thin sheets (< 3 mm)
Tee joint	T	Reinforcements, gussets
Corner joint	L	Frames, chassis
Lap joint	—	Thin sheets, repairs
Edge joint	—	Boxes, enclosures

Standard welding symbols (per CSA W59 and AWS A2.4) include:

The reference line (horizontal)

The arrow (indicates the joint)

The basic symbol (weld shape)

Dimensions (throat size, length, spacing)

Finish symbols (grinding, peening)

Reading example: A symbol with a triangle above the reference line and the notation "6" indicates a fillet weld with a 6 mm throat. A "50-100" below the line indicates a 50 mm length spaced at 100 mm (center-to-center).

Bevel Angles and Root Openings

Standard bevel angles for carbon steel according to CSA W59:

Thickness (mm)	Bevel Type	Included Angle	Root Opening (mm)	Root Face (mm)
3 – 6	Single V	60°	1.5 – 2	1 – 1.5
6 – 12	Single V	60°	2 – 3	1.5 – 2
12 – 20	Double V	60° (total)	2 – 3	2
20 – 40	Asymmetric Double V	60° (total)	3 – 4	2 – 3
> 40	U or J	45° – 50°	3 – 4	2 – 3

Rule of thumb: The total included angle of 60° is the most common for SMAW (stick) and GMAW (MIG) welding. Too small an angle prevents electrode access to the root; too large an angle increases the volume of deposited metal and distortion.

Surface Cleaning and Preparation

Before welding, surfaces must be free of:

Mill scale (iron oxide) — remove by grinding or wire brushing

Oil, grease, paint — degrease with appropriate solvent

Moisture — preheat if necessary

Heavy rust — grind down to bright metal

CSA W59 requires cleaning over a minimum width of 25 mm on each side of the joint. For high-strength steels (e.g., ASTM A514), cleaning must be more extensive (50 mm) to prevent hydrogen-induced cracking.

Preheating and Interpass Temperature

Preheating slows the cooling rate, allowing hydrogen to diffuse out of the molten metal and reducing the risk of cold cracking. Minimum preheat temperatures according to CSA W59:

Steel Group	Thickness (mm)	Minimum Temperature (°C)
Mild steel (G40.20 260W)	≤ 20	5
Mild steel (G40.20 260W)	20 – 38	50
Mild steel (G40.20 260W)	> 38	95
HSLA steel (350W)	≤ 20	10
HSLA steel (350W)	20 – 38	65
HSLA steel (350W)	> 38	110
Quenched/tempered steel (A514)	Any	50 – 150 depending on thickness

Interpass temperature: The maximum temperature between passes is often limited to 250 °C for high-strength steels to avoid degradation of mechanical properties. For mild steel, the limit is less critical, but excessive temperature (> 300 °C) can cause a coarse microstructure.

Measurement methods: Temperature crayons, infrared thermometer, thermocouple. Preheat must be verified over a distance of 75 mm on each side of the joint.

Welding Procedures and Qualification

WPS and PQR

A Welding Procedure Specification (WPS) is a formal document describing all parameters necessary to perform compliant welding. Mandatory elements of a WPS according to CSA W47.1 (Certification of Welding Companies):

Base metal (type, thickness, diameter)

Filler metal (classification, diameter)

Welding position (1G, 2G, 3G, 4G, 5G, 6G)

Electrical parameters (current, voltage, polarity)

Travel speed

Preheat and interpass temperatures

Post-weld heat treatment (if required)

Shielding gas (flow rate, composition)

Welding technique (arc length, oscillation, number of passes)

The PQR (Procedure Qualification Record) is the report of the qualification test that validates the WPS. It includes the results of mechanical tests (tensile, bend, Charpy impact) and NDT results.

Welder Qualification

According to CSA W47.1, each welder must be qualified for:

Each process (SMAW, GMAW, FCAW, GTAW)

Each position (flat, horizontal, vertical, overhead)

Each joint type (butt, tee, fillet)

Each metal group (mild steel, HSLA, stainless)

Validity period: Qualification remains valid as long as the welder works regularly (at least once every 6 months) in the qualified process and position. An interruption of more than 6 months requires requalification.

Typical practical tests:

Butt plate in 3G position (vertical) — root and face bend tests

Pipe in 6G position (45° inclined) — bend test and radiographic examination

Fillet weld in 4F position (overhead) — macro-etch test and throat measurement

Essential and Non-Essential Variables

Essential variables are those that, if changed, require requalification of the procedure:

Change of welding process

Change of base metal group

Change of filler metal type

Change of position (from flat to vertical, etc.)

Change of thickness beyond limits (generally ± 25%)

Change of pipe diameter beyond limits

Non-essential variables (e.g., electrode brand, current type) may be changed without requalification but must be documented in the WPS.

Weld Defects: Identification and Prevention

Defect Classification According to CSA W59

Defect Type	Description	Primary Cause	Prevention
Porosity	Trapped gas bubbles	Moisture, excessive current, insufficient shielding gas	Dry electrodes, reduce current, check gas flow
Wormhole	Aligned porosity at the root	Root contamination, hydrogen	Thorough cleaning, preheat
Slag inclusion	Slag trapped between passes	Insufficient cleaning between passes, incorrect electrode angle	Brush/grind between passes, correct angle
Lack of fusion	Absence of bond between deposited metal and base metal	Current too low, travel speed too fast, incorrect electrode angle	Increase current, slow down, correct angle
Lack of penetration	Unfused root	Insufficient root opening, current too low	Increase root opening, higher current
Longitudinal crack	Crack along the weld length	High restraint, hydrogen, rapid cooling	Preheat, low-hydrogen electrodes
Transverse crack	Crack perpendicular to the weld	Hydrogen, tensile stresses	Preheat, post-weld heat treatment
Undercut	Depression along the weld edge	Current too high, travel speed too slow	Reduce current, increase speed
Overlap	Metal deposited beyond the edge without fusion	Incorrect electrode angle, travel speed too slow	Correct angle, increase speed
Spatter	Metal droplets on the surface	Current too high, arc too long	Reduce current, shorten arc

Acceptance Criteria According to CSA W59

For "normal" quality welds (non-radiographed):

Porosity: Maximum diameter of 1.5 mm, no more than 4 pores per 25 mm of weld length

Slag inclusions: Maximum length of 6 mm, no more than 2 per 50 mm

Lack of fusion: Not permitted

Undercut: Maximum depth of 0.5 mm for a fillet weld, 0.8 mm for a butt weld

Cracks: No cracks permitted, regardless of size

For radiographed welds ("radiographic" quality), criteria are stricter:

Porosity: Maximum porosity index according to the standard's table

No elongated inclusion longer than 6 mm

No cracks, no lack of fusion

Calculating Throat Size

For a fillet weld, the theoretical throat is calculated as:

Throat = 0.707 × leg for a 90° angle

Throat = 0.5 × leg for a 60° angle

Example: A fillet weld with a 10 mm leg has a throat of 0.707 × 10 = 7.07 mm. Weld strength is proportional to the throat, not the leg.

Minimum requirement: The minimum throat is often specified as equal to the thickness of the thinner part (for sheets ≤ 6 mm) or 0.7 × the thickness of the thinner part (for thicker plates).

Non-Destructive Testing (NDT)

NDT Methods and Applications

Method	Principle	Detects	Applicable Thickness	Advantages	Limitations
Visual (VT)	Inspection by eye or with instruments	Surface defects, dimensions, distortion	Any	Simple, economical	Surface only
Magnetic Particle (MT)	Magnetic particles attracted to flux leakage	Surface and near-surface cracks (≤ 6 mm)	Any (ferromagnetic materials)	Fast, sensitive to fine cracks	Ferromagnetic materials only
Liquid Penetrant (PT)	Penetrating liquid revealed by a developer	Open surface cracks	Any (non-porous materials)	Simple, portable	Surface only, requires clean surface
Ultrasonic (UT)	Sound waves reflected by defects	Internal defects, thickness measurements	6 mm to 300 mm	Detects planar defects, portable	Requires qualified operator, clean surface
Radiographic (RT)	X-rays or gamma rays absorbed differently	Volumetric defects (porosity, inclusions)	3 mm to 75 mm (X-ray), up to 150 mm (gamma)	Permanent record, detects internal defects	Costly, radiation hazards, does not detect fine cracks
Eddy Current (ET)	Induced currents disrupted by defects	Surface and near-surface cracks	Up to 5 mm	Fast, automatable	Conductive materials only, smooth surface required

Choosing the Method Based on the Defect Sought

Surface fatigue cracks: Magnetic particle (MT) or liquid penetrant (PT)

Internal porosity: Radiography (RT)

Lack of fusion: Ultrasonic (UT) — best detection of planar defects

Thickness measurement after corrosion: Ultrasonic (UT)

Slag inclusions: Radiography (RT) or ultrasonic (UT)

NDT Operator Qualification

According to CSA W178.2 (Certification of Welding Inspection Organizations), NDT operators must be certified to CAN/CGSB-48.9712 (or equivalent) for each method. Certification levels:

Level 1: Performs tests under supervision, cannot interpret

Level 2: Performs, interprets, and evaluates against criteria

Level 3: Establishes procedures, supervises, approves techniques

Visual Inspection Procedure

Visual inspection is the first and most important NDT method. It must be performed:

104.Before welding (checking preparation)

105.During welding (between passes)

106.After welding (final inspection)

Visual inspection tools:

Fillet weld gauge (to measure fillet weld throat)

Undercut gauge (to measure undercut depth)

Caliper (for dimensions)

Magnifying glass (5× to 10× magnification)

Ruler and square (for alignment)

Porosity gauge (to compare pore sizes)

Post-Weld Heat Treatment (PWHT)

Objectives of PWHT

Post-weld heat treatment (also called stress relieving) aims to:

Reduce residual stresses

Improve toughness (by refining the microstructure)

Allow hydrogen diffusion

Restore mechanical properties in the heat-affected zone (HAZ)

PWHT Parameters

According to CSA W59 and piping codes (e.g., CSA B51 for pressure vessels):

Material	PWHT Temperature (°C)	Holding Time (min/mm of thickness)	Minimum Time
Mild steel (≤ 350 MPa)	600 – 650	2.4	60
HSLA steel (350 – 450 MPa)	550 – 620	2.4	60
Chrome-molybdenum steel	650 – 700	2.4	60
Austenitic stainless steel	None (unless required)	—	—

Rule of thumb: The heating rate must not exceed 200 °C/h for thicknesses ≤ 25 mm, and 100 °C/h for thicknesses > 25 mm. The cooling rate must be controlled (generally ≤ 250 °C/h down to 400 °C).

Heating Methods

Resistance heating (electric elements) — most common

Induction heating — fast, precise

Gas heating — for large parts

Furnace — for small parts

Temperature must be measured by thermocouples attached to the part, at a maximum distance of 150 mm from the weld.

Documentation and Traceability

Documents Required on a Job Site

WPS (Welding Procedure Specification) — approved and dated

PQR (Procedure Qualification Record) — referenced in the WPS

Welder qualification certificates — valid and up to date

Welding records — welder number, date, actual parameters

NDT reports — method, results, interpretation

Material certificates — mill sheets for base metal and electrodes

Weld Marking

Each welder must apply their stamp number near their welds, as required by the contract or code. The marking must be:

Legible and permanent

At a distance of 25 to 50 mm from the weld

Made with a letter stamp or indelible marker (depending on the code)

Material Traceability

CSA W47.1 requires that materials be identified and traceable from receipt to final assembly. Minimum information:

Steel grade (e.g., G40.20 350W)

Heat number

Supplier certificate of conformance

Mechanical test results (if required)

Common Pitfalls to Avoid

154.Confusing throat and leg: The throat is the perpendicular distance from the root to the weld face; the leg is the distance from the toe to the end. For a 90° angle, throat = 0.707 × leg. Never use the leg to calculate strength.

155.Forgetting the maximum interpass temperature: For high-strength steels, excessive interpass temperature reduces strength and toughness. Always check the WPS.

156.Neglecting cleaning between passes: Slag left between passes causes inclusions. Each pass must be brushed or ground before the next.

157.Using a moist electrode: Low-hydrogen electrodes (E7018) must be stored in an oven at 120 – 150 °C. A moist electrode causes porosity and hydrogen-induced cracking.

158.Ignoring welder qualification limits: A welder qualified in the 1G position (flat) cannot weld in the 3G position (vertical) without additional qualification.

159.Confusing acceptance criteria: Criteria for radiographed welds are stricter than for visually inspected welds. Always verify the quality level required by the contract.

160.Forgetting preheat for high-strength steels: Even in warm weather, preheating is mandatory for HSLA steel thicknesses > 20 mm.

161.Using the wrong shielding gas: For GMAW, pure CO₂ gives deeper penetration but more spatter; an Ar/CO₂ mix (75/25) gives a more stable arc. Check the WPS.

162.Not checking part alignment: Poor alignment (misalignment > 10% of thickness) causes stress concentrations and may be rejected at inspection.

163.Forgetting marking requirements: An unmarked weld is considered untraceable and may be rejected, even if technically compliant.

Summary

Joint preparation includes choosing the bevel type, angle, root opening, and surface cleaning. The 60° included angle is the most common.

Preheating is mandatory for significant thicknesses and high-strength steels. Maximum interpass temperature is often limited to 250 °C.

A WPS is a mandatory document describing all welding parameters. It must be validated by a PQR.

Welders must be qualified for each process, position, and joint type. Qualification expires after 6 months of inactivity.

Common defects are porosity, slag inclusions, lack of fusion, lack of penetration, cracks, and undercut. Each has specific causes and prevention methods.

NDT methods include visual inspection, magnetic particle, liquid penetrant, ultrasonic, and radiographic testing. Method selection depends on the type of defect sought.

PWHT reduces residual stresses and improves toughness. Typical temperatures are 600 – 650 °C for mild steel.

Complete documentation (WPS, PQR, qualifications, records, NDT reports) is essential for compliance and traceability.

CSA W59 acceptance criteria define the size and frequency limits for defects. No cracks are permitted.

Self-Assessment Questions

177.What is the theoretical throat of a fillet weld with a 12 mm leg?

Answer: 0.707 × 12 = 8.48 mm

179.What is the minimum preheat temperature for G40.20 260W steel 25 mm thick?

Answer: 50 °C (according to the CSA W59 table)

181.Which defect is best detected by radiography?

Answer: Porosity (volumetric defects)

183.What is the maximum period of inactivity before a welder must be requalified?

Answer: 6 months

185.What is the main purpose of post-weld heat treatment?

Answer: To reduce residual stresses and improve toughness

187.Which NDT method is most suitable for detecting a surface fatigue crack on carbon steel?

Answer: Magnetic particle testing (MT)

189.What is the minimum cleaning width on each side of the joint according to CSA W59?

Answer: 25 mm

191.What is the basic symbol for a butt joint?

Answer: The letter "I" (or a simple vertical line)

193.What is the storage temperature for low-hydrogen electrodes?

Answer: 120 – 150 °C

195.Which document validates a welding procedure?

Answer: The PQR (Procedure Qualification Record)

Welding Preparation and Quality Control