A valuable academic lesson is to ask a group of students to write instructions for making a peanut butter and jelly sandwich. They will leave steps out, assuming that whoever follows the instructions will be able to fill in the gaps. Inevitably, when the most literal possible interpretation of the instructions is followed, the result is not a peanut butter and jelly sandwich. The lesson is used to demonstrate the need to account for every detail and avoid assumptions.
In metalworking, welding procedure specifications (WPS) are the equivalent of sandwich-making instructions. They require a similar level of detail and an awareness of how the instructions will be understood by the welder following them. A WPS must account for the material, the welding process, and the industry standards that govern a project to ensure a satisfactory weld. Welding procedure specification training must teach welders to account for all of the variables involved, so that a WPS is easy to follow and effective across the whole project.
The Relationship Between Welding Procedures and Qualifications
A WPS isn’t just something that a welding engineer writes and signs off on. It must be tested and its performance verified. A weld must be made to the variables set out in a WPS, and then tested to ensure it has the strength and other qualities required. This is what is called a Welding Procedure Qualification (WPQ). A Welding Procedure Qualification Record (WPQR) documents the variables and the results of testing.
Weld procedure qualification testing is usually destructive. Material welded under a WPS is placed under force until the weld or surrounding material gives way. Alternatively, the weld is cut in half for a visual inspection or an inspection using specialized instruments that can verify that the resulting weld has the needed qualities. If the WPS meets these requirements, it is considered to be qualified. Subsequent welds will be performed to the variables laid out in the WPS and will undergo non-destructive testing to check for weld defects and abnormalities. If none are found, the weld is considered to have been made to specification. The requirements the weld must meet during WPQ are laid out in welding codes that govern different industries and different project types.
Understanding Welding Codes and Welding Procedure Specifications
Where welding procedure specification training becomes complicated is in the codes that govern welding. There are several national and international codes that lay out welding requirements, and there are several industry codes that can supersede these. In the U.S., for example, welding codes that govern a wide range of welding processes and project types are put out by the American Welding Society (AWS) and the American Society of Mechanical Engineers (ASME). However, big bore pipe welding for the oil industry, for example, is more likely to be governed by the industry standards put out by the American Petroleum Institute (API). Supplementary codes from organizations like the National Association of Corrosion Engineers (NACE) may also apply. A WPS will set out welding variables that satisfy these codes.
At the most basic level, a WPS will set out the following variables:
Material Procurement and Preparation
- Base Metal Type: The WPS will specify the group of metal to be used in the workpiece, such as steel, stainless steel, aluminum, copper, or a more exotic metal like Monel®. It should also specify acceptable grades of metals within those groups.
- Base Metal Thickness: The exact plate thickness or wall thickness, in the case of pipe or tube, should be clearly specified in the WPS.
- Fill Metal Type: If a fill metal is to be used, the thickness of the fill metal, as well as acceptable grades of fill material, should be specified.
- Dimensions: The dimensions of the workpiece or diameter of pipe or tube to be welded should be part of the WPS. The dimensions of the joint to be welded should also be clear in the WPS.
- Joint Type and Angle: The type of joint to be welded should be specified. The angle of the pieces to be joined relative to each other should also be specified, as well as their distance from other relevant parts of the project, like walls, brackets, or other structural materials.
- Joint Preparation: Any machining that may be required, such as bevels or grooves, should be specified in the WPS, as well as what constitutes acceptable and unacceptable joint prep work.
Welding Typification
- Weld Type: Whether the weld is a butt, joint, lap joint, fillet weld, or another type of weld will be made explicitly clear in the WPS.
- Welding Process: Whether the process is a gas, arc, or laser welding process should be clear from the WPS. If it is an arc welding process, the WPS should make explicitly clear which type or types of arc welding are acceptable or unacceptable.
- Current Type and Polarity: The WPS should specify whether the current used for arc welding should be alternating or direct, and whether it should be straight or reverse polarity.
- Amperage: The WPS should clearly state the acceptable range of amperage settings for the welding power supply type to be used.
Temperature Considerations
- Preheat: Certain metal group types like iron, stainless steel, and Inconel® are vulnerable to distortion or cracking when heated too quickly. Preheating the materials evenly prior to welding may prevent this, and should be specified if necessary.
- Interpass: If the temperature needs to be kept at a certain level between welding passes or if the weld needs to be allowed to cool down to a certain point between passes, this should be specified.
- Postheat: Any required post-welding heating that is needed to lower the heat evenly and prevent cracking or other damage should be mentioned along with the methods to be used and the temperature ranges to be met.
Welding procedure specification training involves learning which elements apply, which elements could be applied, and how variable specifications could be misinterpreted. The most critical aspect of developing a WPS is not welding procedure specification training. Instead, it’s in developing the hands-on experience needed to determine what the most applicable information is when developing a WPS.
The Value of Welding Procedure Specification Training
The true value of welding procedure specification training is similar to what students gained from the old academic lesson of writing instructions for making a peanut butter sandwich. It gives a welder insight into what is most critical in creating acceptable welds and communicating those critical elements. Welding procedure specification training isn’t the end of wisdom, it is the beginning. Effectively, WPS training allows a welder to enter the world of high-specification tube welding or high-purity pipe welding.
This is especially true in high-specification welding processes like orbital welding. In industries like semiconductor manufacturing, a welder cannot even consider working on a manufacturing plant until they receive training on orbital welding machines, training in working to WPS, and a basic understanding of how to develop welding procedure specifications. Welding procedure specification training is in many ways an entry pass into high-level industry. Due to its narrowly high-specification use profile, this training is most often available from the manufacturers of orbital welding equipment.
Arc Machines, Inc. leads the industry in orbital welding weld heads, power supplies, and orbital welding procedure specification training. Contact AMI to learn more about training, or contact sales@arcmachines.com to learn more about AMI welding machines.
