I had a welding engineering student ask me why weld inspection to Canada's structural steel welding code seemed like a confusing task. To his credit, he was trying to follow code requirements in an assigned inspection task and chose not to take a shortcut to make accept/reject decisions on weld quality. In thinking about that question and looking at ways to simplify the task of weld quality inspection as per CSA W59, I quickly found that proper inspection per code requirements will remain a task requiring diligence in the interpretation of documented acceptance criteria. This article will attempt to clarify some aspects of the evaluation of weld quality made in accordance with CSA W59-2018: Welded Steel Construction.
In evaluating weld quality, inspectors should make accept/reject decisions based on comparison of the discontinuity with the applicable acceptance criteria as shown below.
This acceptance of the WQCP may require OSM personnel to witness the welder(s) welding test plates and the testing of those plates before accepting the WQCP. The same is true of the PQR. C) Remind the contractor to provide adequate notice prior to starting any welding work (request one week minimum advance notice).
This criteria is usually defined in the applicable code while in other cases may be defined by the customer. In an ideal world, this criteria would provide clear instructions or features to make rejection decisions of all potential discontinuities. The reality however, is that many considerations can influence the acceptance evaluation making decisions a challenging task. In at least some cases, this results in Inspectors taking shortcuts in making judgement calls especially for discontinuities including porosity, undercut or convex fillet welds. Due diligence to evaluate based on code requirements would require taking the time and using suitable gauges, perhaps a magnifying glass and yes, arithmetic.
In making accept/reject decisions, the following items may need to be considered:
- Is fabrication statically loaded (clause 11) or dynamically loaded (clause 12)
- All welds must be visually inspected per clause 184.108.40.206 or 220.127.116.11 but welds subjected to additional NDE inspection may have further criteria defined
- In clause 12, porosity criteria differs for groove and fillet welds
- In clause 12, undercut criteria differs when direction is transverse vs parallel to primary stresses
- Each discontinuity needs to be identified with the correct industry standard term as criteria differs based on the type of discontinuity
The Inspector should have the clear confirmation from the Engineer regarding the first four points above for proper weld quality evaluation.
The Easy Stuff
- A welding inspector must measure the size and length of every structural weld. Field welds on brace frames are critical. These welds are often welded out of position or can be undersized if there is a gap between the tube and gusset plate. The fillet weld size must be increased by the size of the gap.
- Ing acceptance criteria for heat tint on stainless steel welds, consideration should be given to post weld cleaning methods that will be carried out on the welds or whether it is deemed that a certain level of heat tinting present on the joints will provide acceptable corrosion resistance in the particular ap-plication or environment.2.
- INDEPENDENT LIFTING NDT INSPECTION VISUAL WELD INSPECTION SERVICES LIMITED DIVISION ACCEPTANCE CRITERIAGas-shielded metal-arc welding in which the shielding is provided by achemically active gas.Metal Inert-Gas Welding (MIG Welding)Gas-shielded metal-arc welding in which the shielding is provided by an inertgas, e.g. Argon or helium.Tungsten Inert-Gas Welding (TIG Welding)Gas-shielded arc welding using a non-consumable pure or activated tungstenelectrode where the shielding is provided by a.
- Table 341.3.2 Acceptance Criteria for Welds and Examination Methods for Evaluating Weld Imperfections (Cont’d) NOTES: (1) Criteria given are for required examination. More stringent criteria may be specified in the engineering design. 341.5 and 341.5.3. (2) Longitudinal groove weld includes straight and spiral seam.
Away from the complexity of the considerations listed above, some discontinuities are simple to evaluate. For both clause 11 and 12, any discontinuities interpreted as the following have a zero tolerance and must be rejected:
- No surface cracks
- No visible lack of fusion between welds and base metal
- No craters
Weld Profile Evaluation
All welds for both clause 11 and 12 must have shapes or profiles in accordance with clause 5.9 which in turn references Fig. 5.3 and is shown below. I'm not so sure the maximum convexity criteria from this always gets proper scrutiny with the steps required to properly evaluate. In some cases, judgement call shortcuts may be taken instead of using the steps described here.
The illustration below shows the steps to evaluate the maximum convexity of a 3/8 inch fillet weld in using this criteria and measuring the actual throat. While the profile requirements are the same for statically and dynamically loaded structures, this criterion is especially important for clause 12 inspections. As convexity increases so does that notch effect or stress concentration at the fillet toe as a location for crack initiation in fatigue loading applications.
Once the maximum throat dimension for a specific fillet size is known, it can then be measured as shown on the right. The bridge cam gauge shows a measured actual throat of 3/8 or 0.375' (9 mm). This should be rejected based on the convexity criteria resulting in a maximum throat dimension of 0.364. If the arithmetic required is too cumbersome during shop floor inspection, it is simple enough to make your own reference table using this method to list maximum throat dimensions permitted for common fillet sizes like these examples:
Fillet Leg Length = Max Actual Throat: 1/4 = 0.264, 3/8 = 0.364, 1/2 = 0.465
As a rounded discontinuity, porosity tends not to result in stress concentrations leading to crack initiation which is the rationale for structural codes permitting it in specified amounts.
Clause 11 Porosity Acceptance Criteria
- The sum of diameters of visible porosity does not exceed 3/8' in any 1' length of weld;
- The sum of diameters of visible porosity does not exceed 3/4' in any 12' length of weld;
- Any individual porosity pore shall not have a dimension exceeding 3/32'
Visual Weld Inspection Acceptance Criteria Asme
Clause 12 Porosity Acceptance Criteria
Visual Weld Inspection Acceptance Criteria Aws D1.1
- The frequency of visible porosity in fillet welds does not exceed one in any 4' length of weld and it's diameter does not exceed 3/32';
- For fillet welds connecting intermediate transverse stiffeners to the web, the sum of the diameters of visible porosity does not exceed 3/8' in any linear 1' of weld and the sum of diameters of visible porosity does not exceed 3/4' in any 12' length of weld;
- In groove welds, no porosity is permitted
Welding Inspection Acceptance Criteria Sample
Important differences exist in W59 with regards to the amount of undercut permitted in clause 11 vs clause 12. In the previous 2013 version of W59, the mandated Fig 11.4 was difficult to interpret particularly for thinner member thicknesses. Thankfully, that figure is no longer specified although it is still shown in the latest 2018 version.
Clause 11 Undercut Acceptance Criteria
- Material less than 1' thick: not exceeding 1/32' deep for any length or 1/16' deep for any accumulated length of 2' in any 12' length of weld
- Material 1' or thicker: not exceeding 1/16' deep for any length of weld
Clause 12 Undercut Acceptance Criteria
- Undercut is not more than 0.01' deep when its direction is transverse to the primary stress in the part or not more than 3/32' deep when its direction is parallel to the primary stress in the part
Nondestructive Evaluation Criteria
When NDE is specified after visual inspection, additional acceptance criteria may be specified based on which NDE method is used.
In PT testing, the same criteria used in visual inspection are used.
Radiographic and Magnetic Particle Testing
Although the visual inspection criteria permits no fusion type discontinuities, during RT or MT inspection specified amounts are permitted based on total length compared to weld throat size. Refer to clause 18.104.22.168 or 22.214.171.124 for details including stress loading and spacing of discontinuities.
Depending on the UT technique used, the NDE inspector would refer to the following tables in evaluating inspection results.
- Fixed attenuation (FA) technique = Table 11.3 (clause 11) or Table 12.5 (clause 12)
- Time corrected gain (TCG) technique = Table X.6 (clause 11) or Table X.7 (clause 12)