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CSA W186-M1990: Welding of Reinforcing Bars in Reinforced Concrete Construction – A Comprehensive Technical Overview
Scope, Requirements, and Implementation Guidelines for Welding Deformed Steel Reinforcing Bars in Concrete Structures
CSA W186-M1990, titled Welding of Reinforcing Bars in Reinforced Concrete Construction, is a Canadian standard that establishes comprehensive requirements for welding deformed steel reinforcing bars used in structural concrete. Published by the Canadian Standards Association (CSA), this metric standard (indicated by the “M”) applies to both shop and field welding and covers material selection, welding process parameters, joint design, qualification of procedures and personnel, inspection, and acceptance criteria. While later editions exist, W186-M1990 remains a foundational reference for ensuring the structural integrity of welded bar connections in reinforced concrete.
Scope
The standard applies to the welding of deformed reinforcing bars that meet the requirements of CSA G30.12 (now superseded by CSA G30.18) or equivalent specifications such as ASTM A615 or A706. It is limited to bars with diameters ranging from 10M to 55M (approximately 11.3 mm to 55.7 mm). The following welding processes are covered:
- Shielded Metal Arc Welding (SMAW)
- Gas Metal Arc Welding (GMAW) – solid wire only
- Flux Cored Arc Welding (FCAW) – self‑shielded and gas‑shielded
Joining configurations addressed include full‑welded splices (for end‑to‑end bar continuity), partial‑welded connections (e.g., for tying bars to plates), and shear or moment connections where bars are welded to structural steel or other reinforcing bars. The standard covers all types of reinforced concrete construction, including bridges, buildings, pavements, and liquid‑containing structures.
Important: CSA W186-M1990 does not cover tack welding for position retention only, nor does it apply to wire fabric or plain (undeformed) bars except when specifically allowed by the engineer.
Technical Requirements
Material Control and Carbon Equivalent
The weldability of reinforcing bars is primarily governed by their chemical composition. The standard imposes a maximum carbon equivalent (CE) value to reduce the risk of hydrogen‑induced cold cracking. For bars with a nominal yield strength up to 400 MPa, the CE (calculated as C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15 or as specified in the material standard) must not exceed 0.55%. Higher CE values require special welding procedure qualification.
Welding Consumables
Only low‑hydrogen electrodes are permitted for SMAW (meeting AWS A5.1/A5.5 or CSA Z66.1‑C1) in the as‑purchased condition. Electrodes must be stored and handled in accordance with the manufacturer’s recommendations and baked or redried if moisture exceeds limits. For GMAW and FCAW, filler metals must produce weld metal with a minimum yield strength of 480 MPa and impact properties as specified.
Preheat Requirements
Preheat and interpass temperature control is mandatory to avoid cracking. The required minimum preheat for a bar depends on its carbon equivalent, diameter, and ambient conditions. The table below is representative of the values specified in the standard:
| Bar Diameter | Carbon Equivalent (CE) ≤ 0.40% | CE 0.41% – 0.50% | CE > 0.50% (up to 0.55%) |
|---|---|---|---|
| 10M – 25M | 10°C (50°F) minimum | 40°C (100°F) minimum | 95°C (200°F) minimum |
| 30M – 35M | 10°C (50°F) minimum | 60°C (140°F) minimum | 120°C (250°F) minimum |
| 40M – 55M | 40°C (100°F) minimum | 95°C (200°F) minimum | 150°C (300°F) minimum |
Interpass temperature must be maintained throughout welding and should not exceed 315°C (600°F) for most low‑alloy bars. When bars are exposed to wind, moisture, or temperatures below 0°C, preheat must be increased by an additional 30°C.
Tip: Use resistance or induction heaters for uniform preheat. Never heat bars with an oxyfuel torch directly on the weld area; use a soaking heat within 75 mm of the joint for several minutes before welding.
Joint Design and Weld Dimensions
For full‑welded splices, the standard requires that the weld develop at least 125% of the specified yield strength of the bar (or a specific percentage based on bar grade). Typical groove weld sizes for butt splices are detailed in tables within the standard, based on bar diameter and the type of backing (ceramic, metal, or no backing). Single‑bevel and V‑groove configurations are specified with minimum weld leg lengths of 8 mm for smaller bars and up to 20 mm for larger bars. The length of a partial welded lap splice must be at least 200 mm for all bar sizes and must meet minimum fillet‑weld leg dimensions.
Mechanical Testing
All procedure qualification weldments must pass a tension test and, for certain bar sizes, a guided bend test. The finished weld must exhibit a tensile strength at least equal to the minimum specified tensile strength of the bar (commonly 125% of yield). No single test coupon may fail below 95% of that value. Macroetch examinations are required to verify full fusion and absence of harmful cracks or porosity in the weld throat.
Implementation Highlights
Successful application of CSA W186-M1990 in the field or shop relies on a structured quality control program. Key implementation steps include:
- Procedure Qualification: For each combination of bar size, process, filler metal, and preheat, a Welding Procedure Specification (WPS) must be qualified by testing. The standard specifies the number of test specimens required, typically four tensile samples and two macroetch samples per bar size grouping.
- Welder Performance Qualification: Each welder or welding operator must pass a performance test using the same process and bar size as intended for production. The test includes visual inspection, tensile testing, and optional bend testing for smaller bars. Renewal is required if the welder is not engaged in rebar welding for six consecutive months.
- Inspection and NDE: Visual inspection is required for 100% of welds. Additionally, for critical structures (e.g., bridges, seismic force‑resisting frames), 10% to 25% of splices must be examined using ultrasonic testing (UT) or magnetic particle testing (MT) to detect internal flaws. Acceptance criteria for discontinuities are based on linear indications, cracks, and porosity limits defined in the standard.
Best Practice: Integrate rebar welding inspections into a daily “hold point” clearance system. Before welding each batch of splices, verify that the WPS is on‑site, welders are certified, and that preheat temperatures are achieved using calibrated temperature‑indicating crayons or infrared thermometers.
Compliance Notes
Adherence to CSA W186-M1990 is typically required by provincial building codes in Canada or referenced in contract documents for infrastructure projects. Owners and contractors should consider the following:
- Documentation: Maintain copies of all qualified WPSs, supporting PQRs (Procedure Qualification Records), welder performance test records, and material certificates (including chemical analysis of the rebar). These must be available for review by the engineer or inspector.
- Marking and Traceability: Each welded splice should be identified by the welder’s stamp or approved marking system, along with the date and inspection status. Traceability is essential for chain of responsibility.
- Repair and Re‑weld: Welds that fail visual or NDE acceptance criteria must be repaired by grinding out the defect and re‑welding using the same qualified procedure. A maximum of two repairs per splice is permitted before the bar must be rejected.
- Deviation: Any deviation from the standard (e.g., altered weld geometry or reduced preheat) requires prior written approval from the engineer of record, usually supported by additional qualification testing.
Caution: Reinforcing bars are often used in zones subject to fatigue or seismic loading. Splices that fall below the specified strength or exhibit poorly fused root passes can lead to brittle fracture in service. Strict adherence to preheat, low‑hydrogen electrode handling, and proper inspection is non‑negotiable.
Although more recent editions of CSA W186 (such as W186-18) have updated some procedural details, M1990 remains a widely referenced benchmark for rebar welding in Canada. Many jurisdictions still recognize it for legacy designs and for maintenance of existing structures built under its provisions.
Frequently Asked Questions
Q: Which welding processes are explicitly covered by CSA W186-M1990?
A: The standard covers Shielded Metal Arc Welding (SMAW), Gas Metal Arc Welding (GMAW) with solid wire, and Flux Cored Arc Welding (FCAW) both self‑shielded and gas‑shielded. Submerged arc welding (SAW) and other processes require special approval by the governing engineer.
A: The standard covers Shielded Metal Arc Welding (SMAW), Gas Metal Arc Welding (GMAW) with solid wire, and Flux Cored Arc Welding (FCAW) both self‑shielded and gas‑shielded. Submerged arc welding (SAW) and other processes require special approval by the governing engineer.
Q: What is the purpose of the carbon equivalent (CE) limit in the standard?
A: The CE limit (typically 0.55% maximum for most bars) ensures the steel has good weldability by reducing the tendency for hydrogen‑induced cold cracking during cooling. A lower CE allows lower preheat temperatures and reduces the risk of brittle welds in high‑strength bars.
A: The CE limit (typically 0.55% maximum for most bars) ensures the steel has good weldability by reducing the tendency for hydrogen‑induced cold cracking during cooling. A lower CE allows lower preheat temperatures and reduces the risk of brittle welds in high‑strength bars.
Q: What minimum tensile strength must a welded splice achieve under CSA W186-M1990?
A: A full‑welded splice must develop at least 125% of the specified yield strength of the reinforcing bar. For example, for a 400 MPa yield bar, the splice must resist a minimum of 500 MPa in tension. In no case may the average of all tested samples drop below 100% of the bar’s specified tensile strength.
A: A full‑welded splice must develop at least 125% of the specified yield strength of the reinforcing bar. For example, for a 400 MPa yield bar, the splice must resist a minimum of 500 MPa in tension. In no case may the average of all tested samples drop below 100% of the bar’s specified tensile strength.
Q: Is preheat always required, or can it be omitted for small bars?
A: Preheat is always required, but the minimum temperature depends on bar size and carbon equivalent. For smaller bars (10M – 25M) with a very low CE (≤0.40%) and a minimum ambient temperature of 10°C, no additional preheat above ambient is needed. However, the standard still mandates a minimum of 10°C and monitoring of interpass temperature. For all other cases, table‑based preheat values (see above) must be applied.
A: Preheat is always required, but the minimum temperature depends on bar size and carbon equivalent. For smaller bars (10M – 25M) with a very low CE (≤0.40%) and a minimum ambient temperature of 10°C, no additional preheat above ambient is needed. However, the standard still mandates a minimum of 10°C and monitoring of interpass temperature. For all other cases, table‑based preheat values (see above) must be applied.
Published: 2026