Pre-qualified Weld Joints and W59
CSA W59 is the code that governs welded steel construction in Canada. In Alberta, this code means that the majority of equipment built that isn’t piping related is covered by this code.
W59 has a convenient section of “pre-qualified” welds that make the job of specifying weld procedures much easier since most the work is actually complete. Pre-qualified welds are common welds that have a long history of low failure rate (when done properly), and therefore get special rules regarding what documentation and testing is required.
W59 sets out to define these pre-qualified welds and the parameters they are governed by. This includes all of the basic joints that are common to the welding trade. There are many joints that are above and beyond these pre-qualified joints and require the involvement of the Canadian Welding Bureau (CWB) and possibly a welding engineer to specify.
How to Spec a Weld Using W59
1. Select a process
When specifying a weld, the first step is to determine which process will be used. Selecting an appropriate welding process is usually based more on what is available than what would be ideal. If you have the opportunity to select a variety of processes, or are purchasing equipment specifically for the weld, then you will want to be familiar with the pros and cons of each process.
2. Determine minimum pre-qualification
Once you have determined which process will be used, the next step is to read the basic pre-qualification clauses associated with the selected process. These requirements will be fairly broad and will outline some of the maximum parameters for each process. This section may also help you determine which process is more appropriate. An index for this section can be found under 10.1.3.1.
3. Select a joint
The next step is to specify the type of joint. There are 5 basic joint types and a few ways to prepare each type. You can watch this video for an example of each weld joint type. Geometry of components is the biggest factor when selecting a joint type. Other factors to consider are:
– minimizing required deposition
– joints that cause lamellar tearing
4. Determine if its static or cyclical loading
W59 has two separate sections for joints under cyclical loading and those that are considered static. This code makes the distinction between cyclical and static based on joints that have more or less than 10,000 cycles. There are a few differences between recommendations of the two scenarios but the largest two are the allowance of partial penetration welds and how to calculate the factored resistance of the weld.
5. Look up weld for details.
The tables at the end of section 10 have detailed joint preparation and weld specifications as well as the proper weld symbol to use. This section is organized by welding process.
6. Determine size
Calculating the required size of the weld is a little out of the scope of this article. The tables to guide you through the process are in W59-11.2 for static and 12.2 for cyclical loading.
7. Determine electrode
To choose an appropriate electrode for your project, use table 11.1 for static welds and table 12.1 for cyclical loads as a guide. These tables will get you in the correct family of electrode but won’t specify other important features such as the hydrogen content, position or composition.
An Example of How to Effectively Specify a Weld:
Let’s say we are building a stand that holds an expensive piece of equipment and we want to properly spec the weld using W59. We are in a shop that uses gas metal arc welding (GMAW) and we know from a structural analysis that the plate needs to be ½” 44W material and that it is a static system. We determine that we want the joint to look like this (welded in the flat position):
For the example above, follow these steps:
1. Select a process – Based on the description of where this is getting welded we know this will be a GMAW process.
2. Determine minimum pre-qualification – Flipping to section 10.5.2 we learn that only GMAW with pulsed transfer or spray transfer is allowed by W59. We also learn that a 0.035” wire diameter is recommended for this weld.
3. Select a joint – the joint in this example was already selected
4. Determine if its static or cyclical loading – Based on the description, this will be a static loading scenario (section 11).
5. Look up weld for details – Looking up the appropriate joint from the tables in section 10 we find the following:
This outlines proper joint preparation as well as the weld symbol. This is a generic table so it does not specify size of weld.
6. Determine size – Determining the size of the weld is something that an engineer who is familiar with the structural analysis should be doing. See an engineer for help calculating the factored resistance to welds.
7. Determine electrode – The description said this was 44W which is a CSA G40.21 material designation (American standard) which we can look up on table 11.1 needs to come from a B-G 49AX XXX family of electrode.
In our experience, this is how you should spec a weld using W59. Leave a comment to let us know if this was helpful.