Last Updated on May 2022
Pipe welding or pipe fabrication is a method of joining two pipes together.
Different welding techniques can help achieve this like Arc Welding, MIG Welding, TIG welding, and several other welding techniques.
Pipe welding involves joining pieces of curved metal, making it much more challenging and complicated compared to flat metal sheets welding. It uses a gas-shielded arc welding process to bring together cylindrical metal tubes.
TIG welding is the number one go-to option for pipe welding applications.
Fundamentals of Pipe Welding
Pipe welding often uses thick, heavy-duty materials, and the open root nature of the welds means that care must be taken to ensure that you achieve full penetration.
Poorly penetrated welds on tough, industrial pipe welding jobs can be disastrous. However, it is unlikely that you will be able to weld from both the internal and external sides of the pipe; therefore, it is advisable to use a groove weld to prevent this potential problem.
Early preparation is essential for any welding job. Ensure that all safety and protective gear are ready; this includes an auto-dark helmet, apron, flame resistant clothing, safety goggles, work boots, and earmuffs. Prepare and sanitize your materials before you begin the actual welding.
In the world of welding, welders have always had a good and bad side, depending on whether the welder is left- or right-handed. The opposite side of your functioning hand is usually the challenge meaning the left-hand side of the pipe challenges right-handed welders while the right-hand side of the pipe challenges left-handed welders.
It is essential to continually keep in mind that gravity will affect the weld pool, so no matter what side is good or bad for you, it will always be more challenging to handle the bottom part of the pipe compared to the top.
Open root welding is the most common process used while pipe welding, where a welding joint does not use a tacked backing plate. You will essentially be welding across a gap, which is quite difficult; therefore, you must apply the correct technique to avoid messing up the whole project.
It is advisable that to securely hold your material together, begin by tack welding them. This action will give you enough time to weld carefully, accurately, and comprehensively. To reduce the number of imperfections in the finished product, cut out and feather your tacks.
Never begin and break your pipe weld in the gap – always do that on the sidewall. The arc should be the start point, and then allow the formation of the weld pool, gradually and carefully transverse from corner to corner onto the other side. Finally, slowly crisscross the surface along the open root of the first section of the pipe and continue until there is a need to switch your position.
Lastly, divide your pipe into various segments. Begin from the top, work clockwise, stopping at 45-degree angles to make sure you are comfortable and ready for subsequent steps. While at it, ensure you intertwine all your tacks appropriately. Repeat this until you have fully rotated the entire weld.
Positions Utilized in Pipe Welding
There are four leading pipe-welding positions, numbered one, two, five, and six (1, 2, 5, 6) highlighted below:
1G Rolled Position
The 1G position is the most basic welding position and is not frequently used. It is similar to flat welding because the pipe will be lying on its side – the horizontal position that you can rotate as you weld. Your weld position should be in the center of the puddle as your pipe rolls away from you. The welder’s position remains stationary, and welding is performed on the top of the pipe.
For a successful weld in the 1G position, your arc should begin at the center of your tack. Your gun and pipe should be perpendicular to each other with a 5 to 10-degree drag angle. Your stick out should be 5/8 inch or less.
The 2G Position
In the 2G welding position, the pipe is in the vertical position and can be rotated along the vertical (Y) axis. The welder’s position remains stationary, and welding is performed on the side of the pipe in a horizontal direction.
2G is also a fixed position. This position means you cannot rotate the pipe and weld at the same time. When in a fixed position, you place the pipe on its bottom part, making it more stable for welding.
5G Fixed Position
In the 5G welding position, the pipe lies in the horizontal position. Unlike the 1G position, the pipe is in a fixed position meaning the welder cannot rotate the pipe; therefore moves around the pipe in the vertical direction to perform the welding.
With 5G, welding begins at the center of a tack weld with a 5 to 10-degree drag angle with a matching stick out the length. Upon completion of the root pass, you will also need to grind out your starts and stops before making fill passes.
6G Pipe Welding Position
The 6G welding position is quite taxing as it involves fixing the pipe at a 45º angle. This means welding is done using all locations incorporating both the strong and weaker sides of the welder.
The pipe slopes at approximately 45° from the horizontal (X) axis or 45° from the vertical (Y) axis. The pipe is in a fixed position, meaning the welder must move around the pipe to perform the welding. This is an advanced welding position that requires a great deal of experience and technical expertise.
How to Test Your Pipe Welding
Testing allows you to examine the strength (or weak areas) of your pipe welding and the overall quality of work done.
Below we shall highlight non-destructive testing (NDT) methods of testing pipe welds. NDT means that the welds must remain intact without dismantling your pipe weld to test the strength and quality of each one.
- X-ray testing
It is the most practical method of spotting internal faults of the weld and is primarily used in jobs where the weld quality is essential for safety reasons. It works similarly to x-rays done on the human body, making it sensitive hence carried out only by trained professionals. While it remains the most effective, it is also the most expensive method.
- Fillet break test
This test seeks to examine root penetration, including the potential failure points of the weld, which are usually the beginning and end of a weld. If the weld bends without falling to pieces, it has passed the test. However, the exceptions to cracks or fractures are that they must never go beyond 10 mm.
- The liquid dye penetration test
In this test, you spray a dye on the metal surface. The liquid is given time to seep into any surface flaws, and excess liquid is removed. Once the surface dries up, the dye highlights all imperfections that initially, were invisible to the naked eye. It is a more effective method than a visual inspection and is relatively low cost.
- Macro etch testing
The process involves cutting a sample from the welded joint, polish it, and then apply an acid solution. This will allow you to examine your macro-structural integrity as they will show cracks, center voices, unsoundness, pinholes, inclusions, porosity, grain size, hydrogen flakes, mold slag, and other defects.
- Bend test
The primary purpose of conducting bend tests is to determine the rigidity to breakage of that material. The specimen usually is bent 180 degrees.
The bend test determines the quality of a weld at the façade (face) and foundation (root) of a welded joint by imposing tension in these areas.
- Visual Inspection of the Weld
This is the oldest and by far the cheapest, quickest and easiest. It should be done by qualified inspectors and is common where poor quality welds are not a danger. It is subjective and involves looking at the weld to determine its quality, identifies discontinuities and flaws that could prevent the piping system and weld failure. However, this method is utterly unreliable for detecting internal weld defects.
Common Mistakes in Pipe Welding
Whether you are a beginner or an expert, mistakes in pipe welding can happen, and understanding these help to prevent their occurrences. Pipe welding processes need to be top-notch because defects can cause significant harm to both machines and human lives. Read more of such real-life incidents and their impacts in these examples: faulty weld and The Kursk Submarine Disaster.
Let us examine some of the common mistakes in pipe welding that can be avoided:
- Lack of enough preparation
Preparation is a critical step in pipe welding. Proper cleaning, joint preparation, and part fit-up help ensure access to the joint and the necessary penetration and weld strength. Ensure the edges to be joined are smooth by grinding the surface before actual welding.
Pipe welding applications require quality and consistency. You can only achieve long-term productivity in terms of time and costs by taking the time to follow specified procedures and ensure proper weld preparation beforehand.
A spatter refers to the scattering of material that has melted on or near your welding arc. You can reduce this by using shorter arc lengths, applying the correct polarity, and decreasing currents while increasing the working angle. Also, ensure that you are moving in the right angle for that particular weld.
- Misalignment of parts
Parts fit-up is a standard procedure in pipe welding, but sometimes welders rush through their projects and skip this vital step. Misaligned parts frequently result in situations like a bevel with too steep of an angle.
When a welder does not grind and clean the surface before welding it, nitrogen, oxygen, and hydrogen get absorbed into your weld pool, causing porosity. Temporary disruption of the flow of gas can also create porosity in the welds.
Various issues cause this: very high voltages, long arcs, wrong angles, the incorrect electrode for the depth of the plate, and an unsteady welding pace. Once you correct this, you have prevented undercutting from occurring.
Cracks are difficult to amend because they require that you begin a new weld altogether. Therefore, prevention is the key here by Prevent cracks by using the precise temperature, proper grinding of the surface and before welding, and cleansing the plate edges to create a natural fit.
- Slag inclusion
Flux coating is the primary cause of slags. To minimize the formation of slags, a welder must use the appropriate speed and angle, clean the inside of weld passes, and ensure that the amount of voltage for the welding wire is accurate.
Pipe welding is a field that demands a perfect and robust weld. Preparation is a critical component, and if you do not spare some prepping time, then welding will be an uphill task.
The top-performing welders are those that go beyond the basic act of welding and take the initiative to fully understand all the tips and tricks needed to create a perfect weld joint.
Because pipe welding is a challenging field, those who master it get an added advantage in their careers because the opportunities are endless. They go further in their careers as they get to learn new techniques every day.
Therefore, to remain competitive in a sustainable way, keep active by obtaining the necessary certifications from a reputable school, and keep practicing to keep up with the dynamic demands of the market.
Excellent pipe welding is a continuous improvement effort.