Pipe welding is prevalent in the gas and petroleum industries. The most effective way to join two pipe pieces is by welding. As pipes have different shapes, welding them is more challenging than welding two plain metal pieces. A fair amount of mastery goes into pipe welding. There’s a lot to know about how to pipe weld.
As mentioned earlier, pipe welding is not like typical welding, where you weld two metal pieces together. Before commencing the procedure, factors like welding types, pipe material, required tools, preparing the two pieces, their position, etc. come into play.
The factors I just mentioned above are the elementary knowledge of pipe welding. Before you go to hands-on training, these are the things you have to learn and keep in mind.
Welding has a completely practical aspect. Even then, I will discuss each one of these in detail to understand the mechanics and procedure of pipe welding.
Welding Types for pipe weld
There are four major welding types; gas metal arc welding (GMAW), also known as MIG or metal inert gas welding, gas tungsten arc welding (GTAW) or tungsten inert gas (TIG) welding, stick welding or shielded metal arc welding (SMAW) and flux-cored arc welding (FCAW).
All the welding types are suitable for pipe welding. SMAW was widely used for welding pipes. But as technologies have advanced, TIG welding has become the weld of choice. It is versatile; you can weld a wide range of metals with TIG welding.
It also produces small puddles, which gives the welder more control and results in a cleaner weld.
Pipes in various industries are subjected to frequent pressure, lateral loading, and compression. TIG welding is less prone to contaminants and yields stronger joints. In orbital TIG welding, the welding machine rotates 360 degrees around the workpiece using a rotary tool.
Scientists developed this machine, particularly for welding tubes and pipes using TIG welding.
With all these technologies combined, no other welding method comes close to the finish and quality of TIG welding when welding pipes. However, manual TIG welding and other welding methods are still frequently used for pipe welding.
Necessary Equipment for pipe weld
You’ll need various types of equipment for pipe welding. The variety and number depend on factors like your workplace, pipe size, what type of machine the pipe is in, etc. All the equipment can be divided into three groups:
- Handling Equipment
Handling tools are for carrying pipes from one place to another on the welding site. Pipes are heavy and impossible to carry by hand. Such equipment is pipe carts, pipe stands, etc.
- Alignment Tools
Alignment tools are used for aligning the two workpieces. These tools are different types and sizes of clamps. Some clamp types are hydraulic external pipe clamps, chain clamps, internal pipe alignment clamps, etc.
- Pipe Purging System
Pipe purging means cleaning the welding site of various contaminants such as dust, oxygen, etc. Any contaminants will result in weak weld joints. A purging system comes in a box or suitcase containing various purging materials.
Needless to say, you will also need basic welding equipment besides the specific pipe welding tools. The basic tools include a welding machine, helmet, gloves, welding jacket, ear protection, marking tool, angle grinder, pliers, chipping hammer, etc.
Joint Preparation
Joint preparation is the precursor to successful welding. There are two elements to joint preparation: shaping the joint and cleaning it subsequently. There are several joint types in arc welding, and each type comprises various shapes.
Pipe welding takes place in the same plane, so it is a butt joint. Let’s take a look at the butt joint subtypes preferred for pipe welding:
- Joint Shaping
Butt joints subtypes are square groove or I-type, single bevel, single V groove, double V groove, single J, double J, single U, double U, etc. The type of butt joint depends on the thickness of the pipe and the welding type.
Preparing any bevel for pipes with less than 3mm thickness is unnecessary. Standard arc welding techniques can penetrate the entire depth in a single pass. This butt type is called square groove or single groove.
For pipe thickness between 3 to 20mm, a V bevel is used. This is necessary so that the welder can make a root pass at the bottom of the joint. The angle of the V is between 60 to 75 degrees. Also, J joints are frequently seen in pipe welding of this thickness range.
If the pipe thickness exceeds 20mm, welding time and cost become a more significant issue. More thickness means more weld material and excessive time consumption. So, to mitigate both effects, modified bevels are used.
For example, double angle V grooves require 20% less weld material for 20mm thick pipes. The savings is about 35% for 30mm thick pipe welding. Similarly, single and double-angle J grooves are used for thicker pipes.
- Joint Cleaning
The joint shape is achieved by cutting the ends with a cutting machine, an oxy-fuel torch, a plasma cutter, etc. Waterjet and laser beam cutters are also not uncommon. The cutting and grinding depend on the pipe material. Whatever the procedure is, this leaves residue on the edges, which is detrimental to weld quality.
So, you have to clean the joint area thoroughly with an appropriate solvent. Any type of grease, oils, paints, dyes, dirt, etc., must be completely removed to ensure contaminant-free welding. Furthermore, you must clean the cleaning solutions you used before welding.
A dirty weld surface will result in porosity, cracking, weak joints, discoloration, etc.
Different Pipe Welding Positions
Pipe welding is most common in the oil and gas industries. Pipe welding technicians’ biggest job sites are gas and oil fields. In such areas, pipes can be in any position. They can be either stationary, movable, big, small, etc. The technician has to work with whatever the position is.
Different positions bear different challenges for the welder. The common positions are designated using numbers and letters, which are 1G, 2G, 5G, and 6G.
Different technicians are trained for different weld positions, which is stated on their resumes for the convenience of both workers and employers. Let’s take a look at what these four positions mean:
1G Welding Position
In this position, the pipe sits horizontally. The welder can rotate the pipe along its horizontal or X-axis. The welding technician remains stationary and rotates the pipe according to his needs. The position of the welder is on the top of the pipe. The 1G welding position is one of the most basic weld positions.
2G Welding Position
The pipe stays upright in the 2G welding position. The welder doesn’t change places when welding in this position. The pipe can rotate along the Y-axis or the vertical axis. The welder performs the weld from the side.
5G Welding Position
This position is similar to the 1G position, but the difference is that the pipe stays fixed in its position; it can’t be rotated. The welder moves around the pipe to complete the weld.
6G Welding Position
This is the most difficult position. In the 6G position, the pipe position is at 45 degrees to the surface. Also, the pipe remains fixed in this position. The welder moves around the pipe during the welding. This position is the most challenging, and the welder has to be a master of this craft to weld in this position.
The significance of these positions is the ease of recruitment. The 6G position is the most difficult as we know it. So, when someone is a certified 6G welding technician, you can automatically assume that he’s proficient in other welding positions.
However, this only indicates his expertise in the welding position, not materials. Someone with a certification of 6G welding in carbon steel means his training is only in carbon steel pipes. He may not be an expert in stainless steel pipe welding or nickel-chromium pipe welding.
Pipe Welding Passes
Pipe welding requires multiple passes unless the pipe is too thin. Four passes are the most common. They are root pass, hot pass, filler pass, and cover pass. I will briefly discuss each below. Let’s go:
Root Pass
A root pass is the first pass in multipass welding. It joins the edges of the bevel of the two pipe pieces and provides the basis for subsequent passes. The technician has to be very skillful to perform the root pass. The root face of this pass has to be smooth.
Hot Pass
The hot pass follows the root pass and comes before the filler pass. Hot passes fill the bevels and join the root with the grooves. A hot pass helps to release gasses trapped between the first bead and the wall of the pipes. The hot pass resurfaces the surface of the root pass to reduce the amount of grinding or clean-up.
The temperature of the hot pass should be just a few degrees higher than the root pass. If the temperature is blazing hot, a heat-affected zone can occur, subsequently weakening the weld joint. There are various methods and motions to implement hot passes depending on the material and the condition.
Here are some hot pass rules to follow:
- Always maintain the center of the pipe.
- Use a stitching motion (also known as whipping) to let the weld pool freeze before moving forward.
- Use amperage that works for you. There is no restriction.
Filler Pass
The filler pass is for filling the grooves; even after the two passes, there is often an abundance of cavities and irregularities. So, the welder has to perform an additional pass known as the “filler pass” to overcome the issues. The bead motion depends on many factors.
Filler passes also have some basic rules to follow:
- Maintain the center of the pipe similar to the hot pass.
- Make sure the weld bead lays flat.
Cover Pass
The cover pass is for the final covering of the weld beads. The main goal here is to fill the groove up until the surface of the pipe. Any additional weld material is subsequently smoothened by grinding and polishing.
How To Test The Quality Of Pipe Welds?
After welding pipes, checking the quality of the weld is a must. Any fault in the weld can be disastrous in the future. Here are some methods to test the weld quality in pipe welding:
- Visual Examination
As you can realize, visual examination involves checking the weld surface with the naked eye. By visual examination, you can detect any noticeable irregularities, deformities, etc. Internal defects are undetectable in this method, so other advanced techniques are preferable.
- Radiographic Method
X-ray, gamma-ray, etc., can handily detect minute internal defects. This method is extensively used in big industries to test sensitive welding. Radiographic tests are highly accurate but also expensive.
- Liquid Dye Test
In this method, a special dye is sprayed on the surface of the weld and then cooled off. After a certain time, defects on the surface of the weld become visible. The drawback of this method is that it can only detect surface defects.
- Magnetic Particle Test
The weld is placed in a magnetic field perpendicularly and then, small magnetic particles are applied to show any defects on the surface. Similar to the dye test, this method can only detect surface anomalies.
- Ultrasonic Test
In this technique, the weld is subjected to vibration. The reflected waves are then measured with a specialized electronic detector to detect any irregularities. The ultrasonic method is quite competent at detecting structural defects all through.
Some Common Mistakes In Pipe Welding
Pipe welding is unlike any other welding technique. Even the veterans of this sector mess things up sometimes. There are some common issues that you might come across as a beginner, and it’s important to know them. Let’s go:
- Misaligning the Pipes
Properly aligning the pipes beforehand is very important for optimal weld results. Many welders are unaware of it and rush into it. This result is a steep angle bevel. The filler material can adjust minor misalignments, but when the difference is large, it can cause a horrible weld.
- Faulty Joint Preparation
Tacking is very important for pipe welding, and many welders often disregard it. Tacking is welding in small lengths around the full diameter of the two pipes so that they remain stable during the procedure.
The number and positions of the tacks depend on the pipe size, but the standard is tacking in 10, 12, and 2 o’clock positions for half of the diameter.
The landing area has to be heavy for stick welding, with the gap as narrow as possible. For TIG welding, the landing area is like a knife-edge. TIG welding also has a wider gap than stick welding. The root opening for TIG welding is 1/8 inch and 3/32 inch for stick welding.
- Wrong Use of Shielding Gas
More shielding gas doesn’t mean better protection of the weld. In fact, it can harm the weld quality. Too much shielding gas can cause an influx of oxygen into the weld, which can cause porosity. Also, buying premixed gas is better than mixing the gas yourself using a flow regulator or something.
- Faulty Tacking
Tacking is very important for pipe welding and many welders often disregard it. Tacking is welding in small lengths around the full diameter of the two pipes so that they remain stable during the procedure.
The number and positions of the tacks depend on the pipe size, but the standard is tacking in 10, 12, and 2 o’clock positions for half of the diameter.
Tacking material and filler metal has to be the same. Tack becomes a part of the weld. So, it is equally as important as the weld material itself. Improper tacking can weaken the weld or even misalign the pipes.
- Porosity
Porosity is the most common anomaly in welding. It can occur for various reasons, such as the presence of unwanted gas in the weld, the wrong proportion of shielding gas, the presence of dust or debris, a faulty welding machine, etc.
You have to maintain complete protocol and thoroughly know the welding type to avoid porosity.
Advantages Of Pipe Welding
As pipe welding is quite complex, you might wonder why industries prefer welding to joint pipe pieces. There are tons of advantages of pipe welding over other methods. First of all, no other method can provide a stronger joint than welding.
Using screws to join pipe pieces together is lengthy and less effective than welding. It’s also less economically viable. The chance of leakage is impossible to reduce without welding.
If the pipe requires insulation, that will be difficult to achieve due to the presence of screws and plates on the pipe surface. In such cases, welding is the only method to solve the problem.
Welding is less prone to damage and is also easier to repair. Welding pipe is an all-arounder in terms of labor time, cost, and efficacy.
Conclusion
For something as intricate as pipe welding, understanding the fundamentals is rudimentary before going to a practical work line. Welding positions, joint preparation, welding types, and how each type affects the overall approach are the key steps of becoming a proficient pipe welder.
I believe I could answer all your queries about how to pipe weld. Best of luck on the field!
