Perform Testing, Inspection, and Quality Control

Performing Tests, Inspections, and Quality Control

Introduction to Quality Control in Boilermaking

Quality control (QC) is an integral function of the boilermaker's (or welder-boilermaker's) work. It is not an optional step, but a contractual, regulatory, and safety requirement. In the context of the Red Seal exam, you must understand that the boilermaker is not just an assembler of metal; they are the first inspector of their own work. Quality control encompasses verifying dimensions, conformity to drawings, weld integrity, and material traceability.

This chapter covers non-destructive testing (NDT) methods, destructive testing, dimensional inspections, applicable Canadian standards, and qualification procedures. The Red Seal exam will test your ability to choose the right testing method for a given situation, interpret results, and apply prescribed tolerances.

Canadian Reference Standards

In Canada, the boilermaker's work is governed by several national standards. It is imperative to know their acronyms and their areas of application. Exam questions often refer to these standards without citing them in full; you must therefore know which standard applies to which type of equipment.

CSA W47.1 – Certification of Welding Companies

This Canadian Standards Association (CSA) standard governs the certification of companies that perform welding on steel structures. It defines the requirements for welding procedures (WPS – Welding Procedure Specification) and the qualification of welders. A boilermaker working on a certified site must hold a valid qualification card according to this standard. Red Seal exams test your knowledge of welding symbols and required qualifications.

CSA B51 – Boilers and Pressure Vessels

This standard applies to the design, fabrication, and inspection of boilers, pressure vessels, and pressure piping. It is a cornerstone of the boilermaker's trade. It requires hydrostatic testing, non-destructive testing, and the presence of an authorized inspector (often an inspector from a province or territory). You should know that the Canadian Electrical Code, Part I applies to electrical installations, but for pressure equipment, CSA B51 takes precedence.

CSA W59 – Welded Steel Construction

This standard is the reference for welding steel structures in Canada. It covers design details, permitted welding processes, weld acceptance criteria, and testing methods. Dimensional tolerances for fillet welds, minimum weld sizes, and allowable defects are defined in this standard.

Other Relevant Standards

ASME Section VIII (Boiler and Pressure Vessel Code): used for the design and fabrication of pressure equipment, often cited in conjunction with CSA B51.

CSA Z662: oil and gas pipelines (less common for the boilermaker trade, but relevant in certain sectors).

ASTM E-10, E-18: hardness testing (Brinell, Rockwell).

Non-Destructive Testing (NDT)

Non-destructive testing methods are inspection techniques that do not destroy the part being inspected. They are used to detect surface or internal discontinuities. The boilermaker must know when each method is used, its advantages, and its limitations.

Visual Testing (VT)

This is the first and most fundamental of inspections. It is mandatory before, during, and after welding.

Before welding: checking edge cleanliness, absence of rust, oil, or moisture. Checking part alignment (gap, angle).

During welding: controlling interpass temperature, appearance of the weld pool, cleanliness of successive passes (slag removal).

After welding: looking for visible cracks, porosity, lack of fusion, excessive reinforcement, or undercut.

Visual inspection tools: weld gauges (fillet weld gauge, angle gauge), calipers, squares, rulers, and lamps. Visual inspection is often the only method used for non-critical welds, but it must always precede other NDT methods.

Penetrant Testing (PT)

This method detects surface-breaking cracks in non-porous materials (metals, ceramics). It is ideal for stainless steels, aluminum, and nickel alloys.

Principle: a penetrant liquid is applied to the surface. After a dwell time, the excess is removed and a developer is applied. The penetrant rises to the surface in the cracks, forming a visible indication (often red or fluorescent).

Typical procedure:

29.Surface cleaning (degreasing).

30.Application of penetrant (by spray, immersion, or brush).

31.Penetration time (generally 10 to 30 minutes depending on the manufacturer).

32.Removal of excess penetrant (with a clean cloth or solvent).

33.Application of developer (fine white powder).

34.Inspection after a development time (10 to 30 minutes).

Limitations: does not detect subsurface defects. The surface must be smooth and free of contaminants. The part temperature must be between 4 °C and 50 °C for most products.

Magnetic Particle Testing (MT)

This method detects surface and near-surface discontinuities in ferromagnetic materials (carbon steel, low-alloy steels). It does not work on aluminum, copper, or austenitic stainless steel.

Principle: the part is magnetized. Magnetic flux lines are diverted by a discontinuity, creating a magnetic pole. Magnetic particles (dry or suspended in a liquid) are applied and accumulate at the point of flux leakage.

Types of currents:

Alternating current (AC): detects surface defects, but not subsurface defects.

Direct current (DC): detects surface and subsurface defects (up to approximately 6 mm deep).

Magnetic field orientation: the field must be perpendicular to the defect to detect it. It is therefore necessary to magnetize in two directions (longitudinal and transverse) or use a circular field.

Advantages: fast, inexpensive, highly sensitive to small cracks. Limitations: requires a clean surface and a ferromagnetic material. A thick coating (paint) can mask defects.

Ultrasonic Testing (UT)

This method uses high-frequency sound waves (0.5 to 20 MHz) to detect internal discontinuities (lack of fusion, porosity, internal cracks, slag inclusions). It is used for thick welds, plates, and forgings.

Principle: a transducer emits ultrasonic waves into the part. The waves reflect off interfaces (walls, defects). The return time and signal amplitude are analyzed on a screen (A-scan).

Advantages: detects deep defects, penetrates thick materials (up to several meters), requires no chemicals. Limitations: requires a highly qualified operator, a smooth surface (couplant gel or water), and interpretation is subjective. Defects oriented parallel to the beam can be missed.

Types of waves:

Longitudinal waves: for inspecting the interior of parts.

Shear waves (transverse): for weld inspection, as they propagate at an angle and can reach vertically oriented defects.

Radiographic Testing (RT)

This method uses X-rays or gamma rays to detect internal discontinuities (porosity, inclusions, cracks, lack of fusion). It produces a permanent image on film or a digital sensor.

Principle: the part is placed between the radiation source and the film. Denser areas (sound metal) absorb more radiation and appear lighter on the film. Less dense areas (defects) appear darker.

Advantages: provides a permanent record, detects volumetric internal defects (porosity, inclusions). Limitations: costly, requires radiological safety precautions, does not detect fine, flat cracks (lamellar) well if they are not aligned with the beam. Radiography is more effective for volumetric defects than for planar cracks.

UT vs RT Comparison:

Characteristic	Ultrasonic Testing (UT)	Radiographic Testing (RT)
Detection of planar cracks	Excellent	Poor (depending on orientation)
Detection of porosity	Fair	Excellent
Permanent record	No (except digital A-scan)	Yes (film)
Maximum thickness	Very large (several meters)	Limited (approximately 75 mm for steel)
Safety	No radiological hazard	Radiological hazard (controlled area)
Cost	Moderate	High

Eddy Current Testing (ET)

This method is primarily used to detect surface cracks and measure coating thickness on tubes and heat exchangers. It is based on electromagnetic induction.

Principle: a coil is energized with an alternating current, creating a magnetic field. This field induces eddy currents in the part. Defects alter the coil's impedance, which is detected.

Advantages: very fast, does not require direct contact (can be used on tubes in service). Limitations: limited to conductive materials, limited penetration depth (skin effect), requires precise calibration.

Destructive Testing

Destructive testing is used to qualify welding procedures and welders. It involves the destruction of the sample (coupon) to evaluate its mechanical and metallurgical properties.

Tensile Test

This test measures tensile strength, yield strength, and elongation of a material. A standardized specimen is subjected to an increasing tensile force until fracture.

Key formula: Stress (σ) = Force (F) / Cross-sectional area (A), expressed in MPa (megapascals) or psi.

Expected result: fracture should occur in the base metal, not in the weld or heat-affected zone (HAZ), if the weld is stronger than the base metal.

Bend Test

This test evaluates the ductility and weldability of the joint. A specimen taken across the weld is bent to a specified angle (generally 180°) around a mandrel of a given diameter.

Root bend: the weld root is in tension.

Face bend: the weld face is in tension.

Side bend: the side of the weld is in tension (used for thick sections).

Acceptance criteria: no crack or discontinuity greater than 3 mm (1/8 in) in the bend zone.

Hardness Test

This test measures the resistance to penetration of an indenter. It is used to verify that the HAZ hardness does not exceed specified limits (risk of cold cracking).

Brinell (HB): steel ball or tungsten carbide indenter.

Rockwell (HRC, HRB): diamond cone or ball indenter.

Vickers (HV): diamond pyramid indenter.

Typical values: for carbon steel, the maximum HAZ hardness is often limited to 350 HV (approximately 350 HB) to prevent cold cracking.

Charpy Impact Test

This test measures the energy absorbed during the fracture of a notched specimen under impact. It evaluates the toughness of the material, particularly at low temperatures.

Result: expressed in joules (J) or foot-pounds (ft-lb). Minimum requirements are specified in the standard (e.g., 27 J at -20 °C for certain applications).

Macro-Examination and Micro-Examination

Macro-examination: a cross-section of the weld is polished and chemically etched to reveal the structure. Penetration, fusion, and the absence of porosity and inclusions are checked.

Micro-examination: microscopic examination to evaluate the HAZ microstructure, the presence of brittle phases (martensite), and precipitates.

Dimensional Inspection and Tolerances

The boilermaker must verify that the dimensions of the work correspond to the drawings and specified tolerances. Dimensional errors are a frequent cause of rejection.

Measuring Tools

Tape measure: for large dimensions (accuracy ± 1 mm).

Caliper: for external, internal, and depth dimensions (accuracy ± 0.05 mm).

Micrometer: for precision measurements (accuracy ± 0.01 mm).

Spirit level: to check horizontality and verticality.

Plumb bobs: for verticality.

Theodolite or laser level: for large structures (tanks, towers).

Weld Tolerances

Fillet weld tolerances are defined in CSA W59. Here are the key values:

Parameter	Tolerance (CSA W59)
Fillet weld size	± 1.5 mm (1/16 in) for sizes ≤ 12 mm; ± 3 mm (1/8 in) for sizes > 12 mm
Weld reinforcement	Maximum 1.5 mm (1/16 in) above the base metal surface
Undercut	Maximum 0.8 mm (1/32 in) deep, unless otherwise specified
Surface porosity	Maximum diameter 1.5 mm (1/16 in), no more than 5 per 25 mm of weld length
Edge misalignment	Maximum 1.5 mm (1/16 in) for plates of equal thickness

Tank Geometry Control

For storage tanks (e.g., per API 650 or CSA Z662), the following tolerances are common:

Circularity: the maximum deviation between the measured radius and the nominal radius must not exceed 1% of the diameter.

Verticality: the maximum inclination is 1/500 of the tank height.

Bottom flatness: tolerance of 3 mm over 3 meters.

Pressure Testing

Pressure tests are destructive or non-destructive depending on the context. They are mandatory for pressure equipment and piping.

Hydrostatic Test

This is the most common test. The part is filled with water (or another liquid) and pressurized to a value above the service pressure.

Test pressure: according to CSA B51 and ASME Section VIII, the test pressure is generally 1.5 times the design pressure (or maximum allowable working pressure), multiplied by a temperature correction factor if necessary.

Formula: P_test = 1.5 × P_design × (S_test / S_design), where S is the allowable stress at test temperature and design temperature.

Procedure:

109.Completely fill the part with water, purging all air.

110.Increase the pressure gradually (in increments of 10% of the test pressure).

111.Maintain the pressure for a minimum duration (often 30 minutes for boilers).

112.Visually inspect all welds and joints for leaks.

113.Release the pressure slowly.

Safety: the hydrostatic test is dangerous. The stored energy is enormous. A safety zone must be maintained, and you must never stand in front of a plug or flange during pressurization.

Pneumatic Test

The pneumatic test (with air or an inert gas) is more dangerous than the hydrostatic test because the compressed energy is much greater. It is only used when the hydrostatic test is impossible (e.g., for parts that cannot be filled with water).

Test pressure: generally 1.1 to 1.25 times the design pressure. The pressure is increased in very cautious increments, with hold times to check for leaks with a soapy solution.

Risk: a rupture during a pneumatic test can propel deadly fragments. Extreme precautions are necessary.

Quality Control During Fabrication

Quality control is not limited to final inspection. It is a continuous process.

Material Control

Verification of material certificates (mill certificates): they must correspond to the drawing specifications (steel grade, thickness, heat treatment).

Traceability: each part must be identifiable by a heat number or marking.

Identity check: verify that the material received is indeed what was ordered (spark test, portable spectroscopic analysis).

Edge Preparation Control

Bevel angles: check with an angle gauge.

Root gap: check with a feeler gauge.

Cleanliness: edges must be free of rust, oil, paint, and moisture over a width of at least 25 mm on each side of the joint.

Fit-Up Control

Alignment: parts must be aligned within specified tolerances.

Tack welds: tack welds must be of good quality and not crack.

Preheat: if specified, the temperature must be checked with a contact thermometer or temperature-indicating crayon.

Welding Parameter Control

The welder must follow the qualified welding procedure (WPS) . Key parameters are:

Amperage (A): must be within the specified range.

Voltage (V): must be within the specified range.

Travel speed: must produce the correct heat input.

Interpass temperature: must not exceed the specified maximum value (often 250 °C for carbon steels).

Heat input: Q = (V × I × 60) / (S × 1000), where Q is in kJ/mm, V in volts, I in amps, S in mm/min. Excessive heat input can degrade HAZ toughness.

Weld Defects: Classification and Causes

It is essential to know weld defects, their causes, and their remedies. Exam questions often focus on identifying defects from a description or an image.

Surface Defects

Defect	Description	Main Causes	Remedy
Undercut	Groove along the weld edge	Excessive amperage, travel speed too fast, incorrect electrode angle	Reduce amperage, slow down, correct angle
Surface porosity	Small visible holes	Dissolved gases, moisture, drafts	Clean, dry, protect from wind
Spatter	Adhered metal droplets	Excessive amperage, arc too long	Reduce amperage, shorten arc
Crater cracks	Cracks at the end of the weld	Abrupt stop, unfilled crater	Fill the crater, use arc-down feature

Internal Defects

Defect	Description	Main Causes	Remedy
Internal porosity	Internal gas cavities	Moisture, contamination, insufficient shielding gas	Clean, dry, check gas flow rate
Slag inclusion	Trapped slag in the weld	Insufficient cleaning between passes, poor technique	Brush and grind between passes
Lack of fusion	Absence of bond between weld and base metal	Insufficient heat input, incorrect angle	Increase amperage, correct technique
Lack of penetration	Root not fused	Insufficient root gap, amperage too low	Increase gap, increase amperage
Internal cracks	Cracks in weld metal or HAZ	High stresses, hydrogen, rapid cooling	Preheat, use low-hydrogen electrodes, control interpass temperature

Cold Cracking (Delayed Cracking)

This is the most dangerous defect. It occurs several hours or days after welding. The three necessary conditions are:

148.Hydrogen: present in moisture, oil, paint.

149.Stress: high in thick or rigid joints.

150.Sensitive microstructure: hard martensite in the HAZ.

Prevention: preheating, interpass temperature control, use of low-hydrogen electrodes (classification E7018, E7016), slow cooling.

Qualification Procedures

Welder Qualification (CSA W47.1)

A welder must be qualified for each process, position, and joint type. Qualification is done through a practical test (coupon) which is then subjected to destructive testing (bend, tensile) or non-destructive testing (radiography, ultrasonics).

Welding positions:

Position	Description	Code
Flat	Welding on a horizontal surface	1G (groove), 1F (fillet)
Horizontal	Weld axis horizontal, face vertical	2G, 2F
Vertical	Weld axis vertical	3G, 3F
Overhead	Welding from underneath	4G, 4F

Key rule: a qualification in a more difficult position (e.g., vertical) qualifies the welder for easier positions (flat, horizontal), but not the reverse.

Procedure Qualification (WPS/PQR)

A qualified welding procedure specification (WPS) must be validated by a procedure qualification record (PQR) . The PQR documents the tests performed and the results obtained. Essential variables (process, base metal, filler metal, thickness, position, heat treatment) cannot be changed without requalification.

Welding Symbols

Reading welding symbols is a basic boilermaker skill. Symbols are defined in CSA W59 (and AWS A2.4).

Structure of a welding symbol:

Reference line: horizontal line on which the symbol is placed.

Arrow: points to the joint to be welded.

Tail: contains additional information (process, specification).

Basic rules:

Symbol below the reference line: weld on the arrow side.

Symbol above the reference line: weld on the opposite side of the arrow.

Symbol on both sides of the line: weld on both sides.

Weld size: indicated to the left of the symbol (e.g., 6 mm). Length is indicated to the right (e.g., 100 mm). Pitch is indicated after the length (e.g., 100/150).

Example: a fillet weld symbol with "6" on the left and "100/150" on the right means: 6 mm fillet weld, 100 mm segments, spaced 150 mm apart (center to center).

Leak Testing

In addition to pressure tests, there are leak tests for tanks and piping.

Air Test (Soap Test)

A low air pressure (0.1 to 0.5 bar) is applied, and a soapy solution is applied to the joints. Bubbles indicate a leak. This test is simple but only detects significant leaks.

Ammonia Test

A strip of indicator paper (phenolphthalein) is placed on the external surface. Ammonia is injected inside. A color change (pink) indicates a leak. This test is highly sensitive and used for critical joints.

Helium Leak Test

Helium is injected, and a mass spectrometer detects leaks. This is the most sensitive test, used for high-vacuum systems or hazardous gases.

Documentary Quality Control

The boilermaker must know which documents are required and how to complete them.

Typical Documents

Inspection report: date, part number, test method, results, inspector's name.

Certificate of conformity: attests that the work conforms to drawings and standards.

Welding log: list of welders, procedures, weld numbers.

Heat treatment register: temperature curves for post-weld heat treatment (PWHT).

Post-Weld Heat Treatment (PWHT)

PWHT is often required for thick steels or pressure parts. It aims to:

Reduce residual stresses.

Improve HAZ toughness.

Eliminate hydrogen.

Typical temperatures: 600 °C to 650 °C for carbon steels (A36, A516 steel). The duration depends on thickness (generally 1 hour per 25 mm of thickness).

Pitfalls to Avoid

Here are the most frequent errors on the Red Seal exam for this chapter:

195.Confusing NDT methods: penetrant testing (PT) only detects surface defects; magnetic particle testing (MT) detects surface and subsurface defects but only on ferromagnetic materials; ultrasonic testing (UT) and radiographic testing (RT) detect internal defects. Never choose magnetic particle testing for aluminum.

196.Forgetting the safety factor in the hydrostatic test: the test pressure is 1.5 times the design pressure, not 1.1 or 1.25 (the latter is for the pneumatic test).

197.Reversing the sides of the welding symbol: symbol below the line = arrow side; symbol above = opposite side. This is a classic trick question.

198.Ignoring the position qualification rule: a vertical position (3G) qualification qualifies for flat (1G) and horizontal (2G), but a flat qualification does NOT qualify for vertical.

199.Confusing weld tolerances: maximum reinforcement is 1.5 mm, maximum undercut is 0.8 mm. Do not reverse them.

200.Not considering interpass temperature: for carbon steels, the maximum interpass temperature is often 250 °C. Excessive temperature degrades toughness.

201.Choosing radiography to detect planar cracks: radiography is excellent for porosity and inclusions, but ultrasonics are better for planar cracks (lack of fusion, fatigue cracks).

202.Forgetting that the tensile test measures strength, not ductility: ductility is measured by the bend test and elongation.

203.Neglecting safety during pneumatic tests: the pneumatic test is more dangerous than the hydrostatic test due to compressed energy. The test pressure is lower (1.1 to 1.25 times).

204.Confusing the standards: CSA W47.1 = certification of companies and welders; CSA W59 = welding of steel structures; CSA B51 = boilers and pressure equipment. Do not mix them up.

Summary

Quality control is a continuous responsibility of the boilermaker, from material receipt to final inspection.

Non-destructive testing (NDT) includes visual testing (VT), penetrant testing (PT), magnetic particle testing (MT), ultrasonic testing (UT), radiographic testing (RT), and eddy current testing (ET). Each method has its strengths and limitations.

Destructive testing (tensile, bend, hardness, Charpy, macro/micro-examination) is used to qualify procedures and welders.

Dimensional tolerances are strict and defined in CSA W59 (structures) and CSA B51 (pressure equipment).

The hydrostatic test is performed at 1.5 times the design pressure; the pneumatic test at 1.1 to 1.25 times, with increased safety precautions.

Welding symbols must be read accurately: symbol position (arrow or opposite), size, length, and pitch.

Cold cracking is prevented by preheating, hydrogen control, and interpass temperature management.

The key Canadian standards are CSA W47.1, CSA W59, and CSA B51. The Canadian Electrical Code, Part I, applies to electrical installations, not pressure equipment.

Final exam tip: read each question twice. Red Seal questions are often written to test your practical judgment, not just your memory. If a question describes a situation (e.g., "a crack is suspected in a weld on a carbon steel tank"), ask yourself: which method is the most appropriate, the fastest, the most economical, and the safest? The correct answer is often the one that combines these criteria optimally.