Welding and Assembling Components
Module Introduction
Welding and assembly are the heart of the boilermaker trade. This chapter covers welding processes used on job sites, mechanical assembly techniques, applicable Canadian standards, as well as the calculations and inspections required to ensure joint integrity. You must master these concepts to pass the Red Seal exam and to work safely in the industry.
Welding Processes: Principles and Applications
Shielded Metal Arc Welding (SMAW)
SMAW (Shielded Metal Arc Welding), also called stick welding, is the most widely used process by boilermakers. It uses an electric arc established between a consumable coated electrode and the base metal. The coating melts to form a protective slag that prevents oxidation of the weld pool.
Essential parameters:
Current: Direct current (DC+) or alternating current (AC), depending on the electrode
Polarity: Reverse polarity (DC+) provides deeper penetration
Amperage: 90 to 130 A for a 3.2 mm (1/8 in) electrode
Travel speed: Must be constant to avoid slag inclusions
Common electrodes:
| AWS Classification | Coating Type | Position | Typical Use |
|---|
| E6010 | Sodium cellulose | All positions | Roots, pipe welding, deep penetration |
| E6011 | Potassium cellulose | All positions | Work on alternating current |
| E7018 | Basic low hydrogen | All positions | Structural steel, critical joints |
| E7024 | Iron powder rutile | Flat | Fast fill, heavy plate |
Golden rule: E7018 electrodes must be stored in an electrode oven at a minimum of 120 °C. Any damp electrode must be re-dried at 260 °C for 1 hour; otherwise, it will produce hydrogen-induced cracking.
Gas Metal Arc Welding (GMAW/MIG)
GMAW uses a continuous wire electrode and a shielding gas (CO₂ or Ar/CO₂ mix). For boilermakers, this process is used in the shop and on some job sites for thick plate.
Parameters:
Voltage: 18 to 28 V depending on thickness
Wire feed speed: Determines the current
Gas: Pure CO₂ for penetration, Ar/CO₂ (75/25) for less spatter
Transfer mode: Short-circuit (thin plate), globular (medium), spray (thick plate, flat position)
Flux-Cored Arc Welding (FCAW)
FCAW is similar to GMAW but uses a tubular wire containing flux. It offers a high deposition rate and good penetration. Two variants:
FCAW-G: With external shielding gas (CO₂)
FCAW-S: Self-shielded, no external gas — ideal for windy outdoor job sites
Submerged Arc Welding (SAW)
SAW is used for long, straight welds on thick plate (tanks, boilers). The arc is submerged under a granular flux. This process is automatic or semi-automatic and is only suitable for the flat position.
Advantages: Very high deposition rate, no spatter, excellent metallurgical quality.
Joint Preparation and Welding Symbols
Joint Types
| Joint Type | Symbol | Typical Thickness | Use |
|---|
| Lap | — | All | Thin plate, reinforcements |
| Tee | — | All | Stiffeners, supports |
| Butt | — | All | Pipe, thick plate |
| Corner | — | All | Corners, frames |
Edge Preparation
Edges must be prepared according to metal thickness:
Less than 6 mm: Square edge, no bevel
6 to 12 mm: Single V bevel at 60° (included angle)
12 to 25 mm: Double V or single V with a root face of 2 to 3 mm
Over 25 mm: U bevel or double V to reduce the volume of deposited metal
Root gap: 2 to 3 mm to allow complete penetration. A gap that is too small causes lack of fusion; a gap that is too large causes excessive weld beads on the back side.
Welding Symbols (AWS A2.4 Standard)
The basic symbol is an arrow pointing to the joint, with a reference line. The weld is indicated:
Above the line: Weld on the opposite side of the arrow
Below the line: Weld on the arrow side
Triangle: Fillet weld
V: V bevel
Throat size: Indicated to the left of the symbol (e.g., 8 mm)
Welding Techniques Specific to the Boilermaker
Vertical Position Welding (3G)
The triangle or zigzag technique is used to build up the bead. The electrode is tilted 10–15° upward. Travel speed must be controlled to prevent molten metal from running.
Overhead Position Welding (4G)
This is the most difficult position. Use a lower current (10–15% less) and a short arc. Move the electrode in small circular motions to keep the weld pool small.
Root Pass Welding in Pipe
The root is the first pass that ensures complete penetration. Techniques:
E6010 electrode: "Whipping" technique (slight arc withdrawal) to control the pool
E7018 electrode: "Push" technique with a slight drag angle
Backing ring: Used for pressure pipes, but prohibited under certain codes (see Section 4)
Repair Welding
Before any repair:
61.Identify the type of base metal (chemical analysis if necessary)
62.Determine the cause of failure (crack, corrosion, fatigue)
63.Grind out the crack to sound metal (dye penetrant testing)
64.Preheat according to specifications
65.Weld using the qualified procedure (WPS)
66.Inspect after welding (NDT)
Canadian Standards and Applicable Codes
CSA W47.1 — Certification of Welding Companies
This standard requires that companies that fabricate or repair welded steel structures be certified by an accredited organization. It covers:
Qualification of welding procedures (WPS)
Qualification of welders (WPQ)
Company responsibilities (quality control, inspections)
CSA W59 — Welded Steel Construction
CSA W59 is the reference standard for the design, fabrication, and inspection of welded steel structures. Key points:
Clause 4.2: Requirements for welding procedures
Clause 5.1: Dimensional tolerances for welds
Clause 6.1: Non-destructive testing (NDT) methods
Table 5.1: Minimum fillet weld sizes based on base metal thickness
CSA B51 — Boilers and Pressure Vessels
This standard applies to boilers, pressure vessels, and pressure piping. It requires:
The use of qualified procedures per ASME Section IX
Inspection by an authorized inspector
Marking of equipment in accordance with the code
Canadian Electrical Code, Part I (CE Code)
Although this code concerns electricity, it applies to boilermakers for electric welding:
Rule 8-200: Requirements for arc welding circuits
Rule 8-202: Protection of welding conductors
Rule 8-204: Grounding of welding machines
CSA B149.1 — Natural Gas and Propane Code
Applies to welding work on gas pipelines. Requirements:
Clause 6.4: Qualification of welders for pipelines
Clause 6.6: Pressure testing after welding
Clause 7.2: Repair of pipelines in service
Calculations and Measurements for Welding
Calculating Fillet Weld Size
The throat is the minimum distance between the root and the face of the weld. For a 45° fillet weld:
Theoretical throat = 0.707 × leg size
Example: 10 mm leg → throat = 7.07 mm
Minimum leg size per CSA W59:
| Base Metal Thickness (mm) | Minimum Leg (mm) |
|---|
| ≤ 6 | 3 |
| 6 to 12 | 5 |
| 12 to 20 | 6 |
| 20 to 38 | 8 |
| > 38 | 10 |
Calculating Volume of Deposited Metal
For a single V weld at 60° on 12 mm plate:
Cross-sectional area = (width × depth) / 2 = (12 × tan 30° × 12) / 2 ≈ 41.6 mm²
Volume = area × weld length
Mass = volume × density of steel (7.85 g/cm³)
Preheat Calculation
The preheat temperature depends on:
Thickness of the metal (thicker = more preheat)
Chemical composition (carbon equivalent)
Ambient temperature (minimum 5 °C for carbon steel)
Carbon equivalent (CE) formula:
CE = C + (Mn/6) + (Cr + Mo + V)/5 + (Ni + Cu)/15
If CE > 0.40%, preheat is generally required.
Mechanical Assembly
Bolting
Bolted assemblies are used for demountable structures and critical connections. Types of bolts:
Ordinary bolts (ASTM A307): General purpose, low strength
High-strength bolts (ASTM A325, A490): Structures, structural frames
Anchor bolts: Foundations, heavy equipment
Tightening torque: Must be applied according to manufacturer specifications. Use a calibrated torque wrench. Tightening can be:
Torque method: Precise but depends on lubrication
Turn-of-nut method: Initial tightening + additional rotation (preferred method for large bolts)
Direct tension method: Verification by ultrasound or extensometer
Riveting
Although less common, riveting is still used for certain historical repairs and specific structures. Types:
Round head rivets: General purpose
Countersunk head rivets: Flat surfaces
Pan head rivets: Pressure vessels
Rivet diameter: Generally equal to 3 times the thickness of the thinnest plate. The hole must be drilled 1.5 mm larger than the nominal diameter of the hot rivet.
Studs and Fasteners
Welded studs (stud welding) are used to attach insulation elements, supports, or anchors. The process uses a stud gun with a ceramic ferrule. Parameters:
Current: 400 to 800 A depending on diameter
Time: 0.1 to 0.5 seconds
Lift: 1.5 to 3 mm before arc initiation
Quality Control and Inspection
Non-Destructive Testing (NDT)
| Method | Principle | Detects | Advantages | Limitations |
|---|
| Visual (VT) | Eye inspection | Surface defects, dimensions | Fast, economical | Surface only |
| Liquid Penetrant (PT) | Capillary action | Surface cracks | Simple, portable | Surface only |
| Magnetic Particle (MT) | Magnetic fields | Surface and near-surface cracks | Fast, sensitive | Ferromagnetic materials only |
| Ultrasonic (UT) | Wave propagation | Internal defects, thicknesses | Depth of detection | Requires qualified operator |
| Radiographic (RT) | X-rays or gamma rays | Internal defects | Permanent image | Radiation hazard, costly |
Acceptance Criteria (CSA W59)
Surface defects:
Cracks: Unacceptable in all cases
Porosity: Maximum diameter of 1.5 mm, no more than 4 per 25 mm of length
Blowholes: Unacceptable if they break the surface
Lack of fusion: Unacceptable
Reinforcement: Maximum of 1.5 mm beyond the nominal dimension
Internal defects (depending on method):
Porosity: Surface percentage ≤ 3% in radiography
Slag inclusions: Maximum length of 6 mm, spaced at least 50 mm apart
Internal cracks: Unacceptable
Required Documentation
WPS (Welding Procedure Specification): Official document describing parameters
PQR (Procedure Qualification Record): Proof that the WPS has been tested
WPQ (Welder Performance Qualification): Proof of welder competency
Inspection reports: NDT results, inspector signatures
Welding Safety
Personal Protective Equipment (PPE)
Welding helmet: DIN shade 10 to 13 depending on process and amperage
Welding gloves: Leather, long cuffs
Clothing: Flame-resistant cotton, no synthetic fibres
Respiratory protection: Depending on fumes (P100 filters for welding fumes)
Hearing protection: In noisy environments
Specific Hazards
Welding fumes: Stainless steel fumes contain hexavalent chromium (carcinogenic). Use local exhaust ventilation.
UV radiation: Can cause eye burns (flash) and skin burns. Protect people nearby with screens.
Electrical hazard: Open-circuit voltage of 80 V (SMAW) can be lethal. Never touch the electrode or holder with bare hands.
Fire: Keep a fire extinguisher within 10 metres. Check for combustible materials within a 15-metre radius.
Hot Work Permit
Mandatory on most job sites. It must include:
The exact location of the work
Protection measures (screens, fire extinguishers)
Validity period (generally 24 hours)
Gas testing (if confined space)
Pitfalls to Avoid
179.Confusing electrodes: E6010 is cellulosic (deep penetration, root), E7018 is basic (low hydrogen, critical joints). Never substitute one for the other without approval.
180.Forgetting preheat: On thick steel (> 25 mm) or high-strength steel, insufficient preheat causes cold cracking. Always check the temperature with a contact thermometer or temperature-indicating crayon.
181.Neglecting electrode drying: Damp electrodes produce porosity and hydrogen-induced cracking. E7018 electrodes must be removed from the oven just before use and never re-stored damp.
182.Ignoring welding symbols: A triangle on the reference line indicates a fillet weld; a V indicates a bevel. Misreading a symbol can result in an unacceptable weld.
183.Welding without an approved WPS: On sites governed by CSA W47.1, welding without a qualified procedure is a serious violation. Always verify that the WPS is posted or available.
184.Confusing standards: CSA W59 for structures, CSA B51 for boilers, CSA B149.1 for gas. Each code has its own qualification and inspection requirements.
185.Poor edge preparation: A bevel that is too narrow or an insufficient root gap causes lack of fusion. Always measure the angle and gap before welding.
186.Forgetting post-weld controls: Hydrogen bake-out for hardened steels, post-weld heat treatment (PWHT) for thick plate. These steps are sometimes mandatory per the code.
187.Using excessive current: Causes excessive spatter, metal overheating, and distortion. Follow the WPS parameters.
188.Neglecting ventilation: Welding fumes are dangerous. In confined spaces, use a fume extractor and appropriate respiratory protection.
Summary
SMAW is the boilermaker's primary process; master the E6010 (root) and E7018 (fill and cap) electrodes.
Welding parameters (current, voltage, speed) must comply with the approved WPS.
Joint preparation (bevel, root gap, angle) determines the quality of penetration.
Canadian standards CSA W47.1, CSA W59, CSA B51, and CSA B149.1 govern the qualification, inspection, and acceptance of welds.
Calculations for throat, volume, and preheat are essential for compliance.
Non-destructive testing (VT, PT, MT, UT, RT) is used according to code requirements and joint criticality.
Safety is paramount: PPE, ventilation, hot work permits, and adherence to procedures.
Self-Assessment Questions (Exam-Type)
200.Which electrode do you use for a pipe root pass with complete penetration?
201.What is the theoretical throat of a fillet weld with an 8 mm leg?
202.At what minimum temperature must E7018 electrodes be stored?
203.Which code applies to boilers and pressure vessels in Canada?
204.Which NDT method detects internal defects in a 30 mm thick weld?
205.What is the maximum carbon equivalent before preheat is required?
206.What is the minimum leg size for a fillet weld on 15 mm plate per CSA W59?
207.What is the safety radius for combustible materials during hot work?
This chapter covers the essential knowledge for the Red Seal exam in welding and assembly. Review the cited standards, practice the calculations, and familiarize yourself with welding symbols before moving on to the exam.
