Anything that we see around us is a miracle of technological advancement. In the Oil and gas industry, welding plays a crucial role in every aspect. Welding, as it sounds, is much more complex than our imaginations due to the extension of different branches. Welding cannot be considered a single entity as it attributes to many interdependent functionalities. For successful welding, many factors need to be considered, such as weld quality, weld strength, material, etc. But, here, we will talk about an essential requirement of the welding process that would determine the quality of the weld. That is the Welding sequence or welding pass.
What are welding passes?
Welding passes are nothing but the flow of the welding process or the sequence in which welding should be carried out.
The welding sequences are known as welding passes. A typical welding process comprises four passes.
They are Root Pass, Hot Pass, Fill up Pass and Capping.
Types of Welding Passes
Root pass refers to the first pass in any welding process, which combines two pieces or members into one structure. Subsequent passes increase the weld depth to the desired thickness, yielding the necessary strength. The first pass usually provides the base for subsequent filler passes.
Let’s consider a root pass on a set of pipes. The root pass is welded with a technique called drag method. The tip of the electrode is held in contact with both pipes and dragged around the circumference of the pipe, advancing vertically downward.
After completing the root pass welding, the welding slag over the weld bead is adequately removed by chipping, grinding and wire brushing.
Next in the sequence that needs immediate action is the “hot pass”.
When your root (first) pass doesn’t go just as desired, a hot pass may be in order. The Hot pass is a process that helps smoothen or resurface the already done root pass and make it usable without grinding and cleaning up the weld. You should know that the hot pass should not be too hot; rather, it should have few amps above the root pass. These little extra amps will help melt out the top of the root pass and restructure the convex weld into a concave form.
Fill Up Pass
To fill the bevel portion, the pass that is made is known as a “fill up pass”.
It is also referred to as a fill pass as it is the amount of weld bead necessary to fill the weld joint. This pass comes after the root pass or hot pass and before the cap pass or capping.
When the bevel is filled correctly, subsequent passes are made, known as reinforcement passes, also known as “capping”. Capping is the end process in a weld sequence. Capping may be completed either in a stringer bead or by a back-and-forth weaving motion.
How to determine the number of welding Passes required?
The basic procedure to determine the number of welding passes required is by the following the Welding Procedure Specification. But, in case there is no mention of the necessary number of passes, you are free to use the number of passes depending upon your skills and the following factors.
Travel Speed – Travel speed is directly proportional to the number of welding passes. Higher the travel speed, lower the weld volume and more the number of passes.
Width of the weave (oscillation) – It works in a way like the travel speed.
Joint configuration – A bevel groove needs more passes than a V-groove, keeping other conditions constant.
Electrode diameter – Larger electrode diameter increases the volume per pass and decreases the number of passes.
If the processes used in Oil and gas engineering sound exciting and you are looking for job-oriented courses after graduation, check the oil and gas Piping engineering course in detail.
by Debashree P
Debashree is an Aeronautical engineer by education and a curious researcher by passion. She is passionate about engineering and technology. She is an avid technology writer who has a knack for developing content for websites, newsletters, blogs, articles, advertising and marketing materials based on the requirements. Technologies of her interest include Aviation, Oil & Gas and AI.