What are some of the Weld Joint Design Considerations

Question: What are some of the Weld Joint Design Considerations

Author: Erin Leier, P.Eng. RFS Engineering Services Ltd.

Answer: 

When considering your weld joint design, you first and foremost need to understand any applicable codes and/or standards for the project.  This may focus your joint design options, which are meant to suit the end use or service conditions of the project.

When codes or standards apply, they are based on a level of standard to allow the welds we produce the best opportunity to meet and exceed the safety and quality expected for the end use based on research and trials that have been compiled over the years.

It is essential to know if there are any specific requirements for a joint, such as strength, loads and moments, impact resistance, service temperatures, service environments (such as corrosive), etc.  Even something like geographical location must be considered in many instances.  For example, a new stadium built in Rosetown, Saskatchewan, Canada may have different joint designs than the same stadium being built in Vancouver, British Columbia, Canada based on seismic requirements alone.  All of these can play a factor in how a joint is selected and designed.

Corrosive environments may call for continuous welds instead of intermittent welds.  Specific loads or moments may require complete joint penetration (CJP) welds as opposed to fillet welds.  Fillet welds may be satisfactory, given the specific project or code requirements.  More is not always better.  The design must reflect the conditions required for the project.

As an example, industry standard tends to call up a ¼” (6mm) fillet weld as the minimum weld size, unless noted otherwise.  This works well as often, a ¼” (6mm) fillet weld will suffice in regular fabrication.  Utilizing an E49XX type electrode, a 6” long weld (152.4mm) will produce 142kN of shear resistance for a connection.  This compares to 113kN for a single ¾” diameter A325 bolt with the threads excluded in a single shear connection (i.e. bolted through one clip or plate as opposed to two clips for double shear).

Equally important is the consideration of the accessibility of the joint and how all the pieces fit together for the entire assembly.   If the joint is not accessible for the welder, then we are not doing anyone any favours to ensure the design will meet the overall safety and quality requirements of the project.  It’s one thing to put pen to paper to create the weld joint design, but it’s another to make sure it’s feasible and realistic.  This is where it is important for communication and information to be shared on all levels of a project team.  In the end, the point of any project is to work together to make sure everyone can successfully and safely complete a quality project.

Erin R Leier, P. ENG (SK, AB)