Pipe welding refers to a method of joining two pipes together. Pipe welding can be performed by welding processes including arc welding processes such as MIG welding and TIG welding.
Some make a distinction between pipe welding and pipeline welding, where pipe welding refers to the welding of metal pipes at plants/producers/refineries and pipeline welding refers to the pipes used to transport gas, water, oil, and various liquids over long distances.
Pipe welders and pipeline welders will perform work in construction related industries, oil and gas fields, water industries, fabrication shops, nuclear power plants, and more. Pipe welding work generally is to connect any and all pipes to new or repair old ones, and will be performed to meet codes and standards.
Types Of Welding Used
Pipe welding and pipeline welding are generally done by using one of various arc welding processes, including:
1. Shielded Metal Arc Welding (SMAW)
Shielded Metal Arc Welding (SMAW) known as Manual Metal Arc Welding (MMA or MMAW), Flux Shielded Arc Welding or Stick Welding.
SMAW will sometimes be referred to as stovepipe welding, which specifies that no flux or shielding gas is necessary during welding, which provides a simple method of welding that is highly portable.
The metal is joined by melting the electrodes using the heat of an electric arc. SMAW has some advantages like simplicity and portability, but a slow travel speed does not have the productivity that some other processes have.
2. Gas Metal Arc Welding (GMAW)
GMAW (also referred to as Metal Inert Gas (MIG) welding, and Metal Active Gas (MAG) welding).
These welding processes can yield higher production levels than SMAW but they require better control of welding variables for high-quality work production and efficiency. While often using semi- or fully automatic machines, GMAW provides very high rates of deposition with less fume production.
3. Flux-Cored Arc Welding (FCAW)
FCAW (including self-shielded and gas-shielded FCAW). Gas welded FCAW provides a high-production option for pipe welding utilizing semi-automatic machines, but the effects of windy conditions can create issues by disbursing shielding gases leading to porosity defects. The self-shielding capability of FCAW avoids this issue, but with a reduced overall deposition rate.
4. Submerged Arc Welding
Submerged arc welding is a semi- automatic process and the arc is not visible which makes tracking challenging. However, it has the highest deposition rates of all the pipeline welding processes as well as leaving defect free surfaces.
5. Tungsten Inert Gas (TIG) Welding
TIG welding also known as gas tungsten arc welding (GTAW). In terms of pipe welding, TIG has the lowest deposition rates, equipment costs will be higher than the other methods, and the overall production will be less than other welding processes.
However, TIG produces very high-quality welds (dependant on the welder’s skill) and is more suitable for critical or high- precision welding work.
Steps to Pipe Welding
As with almost all welding, there are a number of steps to follow in pipe welding, second starting with the process selection which takes into consideration such factors as;
- Pipe Material
- Pipe Diameter And Wall Thickness
- Welding Location
- Weldment Characteristics
- Welding Direction (Uphill Or Downhill)
- Required Welding Quality
- Economic Factors
- Health And Safety
Once you have taken care of the listed factors, you can consider what equipment is most appropriate for the work, have considered:
- Output Power
- Duty Cycle
- Portability
- Safety
Now that you have taken care of the process and essentially evaluated the equipment, you are ready for the actual welding with the following steps:
- Joint Preparation: Joint preparation should be done with the appropriate standards.
- Pipe Ends Cleaning: Remove an undesirable moisture or coatings such as oil, paint, rust or varnish. This will at least prevent defects and costly repair or re-welding.
- Welding: With the appropriate materials (electrodes) and parameters (for instance, any preheat requirements), according to the required specifications, the actual welding can commence using root passes, followed by hot passes, fill passes then a final cap passes
- Repairs: Ideally, this step does not apply to you, it is still worth checking the weld and if there are defects repairing them
Pipe Welding Passes
Pipe welds are required to follow several different weld passes:
- Root Passes: These first passes should fill the gap between the two sections of pipe.
- Hot Passes: These join the root weld to both groove faces.
- Fill Passes: These passes fill out most of the groove before the final cap passes are made.
- Cap Passes: These final passes should complete the weld with as little build up beyond the surface of the pipe as possible. You can grind this layer back if needed to enhance the weld beading and also to remove contamination prior to a final, finishing cap pass.
Pipe Welding Positions
There are four types of pipe welding position; 1G, 2G, 5G and 6G. Each position describes if the pipe is stationary or rotating and in which orientation whether horizontally, vertically, or inclined at an angle.
- 1G Welding: The 1G position puts the pipe in a horizontal position. The pipe can be rotated about the horizontal (X) axis while the welder remains stationary. The weld can be completed on the top of the pipe, and is the simplest of the pipe welding positions.
- 2G Welding: The 2G position puts the pipe in a vertical position or upright position. The pipe can be moved about the vertical (Y) axis while the welder remains in a stationary position. The welding will take place horizontally on the side of the pipe.
- 5G Welding: In the 5G position, the pipe is again in a horizontal position, however, unlike the 1G position, the pipe cannot be moved. In this position, the welder must move around the stationary pipe in a vertical way to create the weld.
- 6G Welding: The 6G position is where the pipe is positioned at a 45° angle to create a slope surface. The pipe is in a fixed position, as it is for 5G, and thus the welder will have to walk around the pipe. The 6G position is the most complex of the four positions, putting the greatest skill-set and thought requirement upon the pipe welder.
The welder will learn each of the types of position in order, from simplest 1G to most complex 6G, and will be required to achieve certification in the correct order.
A welder who is qualified for 1G position cannot weld in 2G, 5G or 6G positions, but a welder who is qualified in the 6G position can weld in any of the other positions. These standards are in place for safety to ensure the health of workers and people affected by the completed pipe welds.
Advantages Of Pipe Welding
There are a few advantages to welding pipes over other joining methods like used for screwed fittings and other joining methods that require fittings. These advantages are:
1. Fewer fittings
Welding takes out all the fittings needed to join straight sections of pipe. Each screw joins let the fittings slip one in between each piece of tubing it connects, welding can quickly attach two pipes after end preparation of the two parts to be joined.
2. Reduced Costs
Welded pipe can use wall thinner than using screwed connections, this can have significant cost savings for longer runs and large-scale jobs. Screwing pipe together often also permits higher labour cost in addition to all of the threaded fittings cost.
3. Better Flow
Screwed fittings create turbulence and resistance for the flow running through the pipe.Welded systems can provide seamless and flush surfaces to facilitate improved flow.
4. Simple Repair
In general, welded systems are simpler to repair than screwed systems. A welded pipe can usually be repaired in place, but a screwed system would need to be disassembled and reassembled to fix the issue. Obviously, this costs more in terms of costs due to reassembly time and greater downtime for the pipe system.
5. Fewer leak points
A welded pipe can generally accommodate vibration better than a screwed system, therefore potentially resulting in less leakage.
6. Easier to insulate
Welded pipes are easier to insulate without having to worry about getting over nasty bumps due to threaded connections.
7. Location
Welded pipes can be placed closer together than threaded pipes, which require more space for a wrench and tools to operate.
8. Labor
When comparing welded to screw pipe labor for small pipes, there may not be much difference, however, as the size increases, the labor or cost associated to install a welded pipe decreases, while the labor or cost to install a screwed pipe increases.
You also need different tooling for different screw pipe sizes while a skilled welder only needs to use one welding machine for a number pipe sizes.
Common Issues
The best way to avoid common errors in pipe welding is by understanding the associated process and working conditions of the pipe welding process.
First, it is essential that the pipes to be joined are correctly prepared, involving making sure the edges to join the pipe are straight and clean. If this is not completed properly there can be issues involving lack of fusion in the weld, slag trapments and inclusion’s of hydrogen.
Capacity of the welder is not the only issue to deal with, there are several issues to get through just based on the conditions of the welder’s work environment.
The process of welding creates a risk of injury unless the welder takes the proper precautions, the risks are based on the heat of the welder’s tools, the bright light created from the arc, and the release of particles or gasses.
If there are special circumstances such as a pipe these can introduce other hazards of conditions involved with the environment that pipe is located in, as examples the welder will be in awkward positions and locations (e.g. underground or underwater welding).
Other conditions can be as extreme as where the location will be either a hot or cold installation, depending on the location of the pipe and what could potentially be in the pipe (including sewers or oil). However, by planning and equipment use many of these challenges can be solved.
Applications and Examples of Pipe welding
Since pipe welding is only connecting metal pipe, this is practically unlimited in applications for this skill. The amount of applications is only limited by the measure in which welding is one of the most economical means to connect numerous sections of pipe.
This means pipe welding is useful in many industries; as an example being, the transportation of natural resources (such as oil, gas, and other natural recourses) to an oil re-fineries; to possible domestic use by cross-country or international pipeline; to mineral processing plant).
Pipe welders also serve on jobs in chemical process plants, food and beverage plants, power generation plants, and utilities providing gas and water, and they also serve various work/job sectors, such as in construction and other ancillary work.
FAQ
Is pipe welding more difficult?
Yes, pipe welding is usually considered harder than most forms of welding and requires higher skills than most types of welding. There are environmental factors (e.g., a safety hazards, working heights, soil conditions), pipe position (which the difficulty increases from 1G to 6G), travel angle of the weld and diameter of the pipe.
Is pipe welding dangerous?
Yes, pipe welding can be serious dangerous job if the proper precautions are not taken. Welders are usually on a daily basis exposed to fumes, dust and airborne particles, really hot temperatures and very dangerous levels of light (that will injure via burning skin and/or other physical injury). Still, the nature of hazards can result from where and how the welding is being performed.
What type of welding is pipe welding?
Pipe welding is usually arc welding (with arc welding process examples including shielded metal arc welding (SMAW), gas metal arc welding (GMAW) – which includes both MIG and MAG welding, flux-cored arc welding (FCAW), submerged arc welding, and tungsten inert gas (TIG) welding).
How long does it take to weld a pipe?
Generally, it takes an average welder 140 inches of weld per hour to complete a weld on a pipe; therefore, if you could cross-reference this (hourly speed) with the diameter of the pipe, you would have a good idea of how long it would take to weld the pipe, but this number takes into account many factors of which: pipe size, working conditions and the welder’s skillset etc.
Also, different jobs will require different numbers of passes, and different welding methods have different deposition rates (MIG is generally faster than TIG).
What is Stove Pipe Welding?
Stove pipe welding (or sometimes called ‘stovepipe’ welding) refers to a variant of the manual/shielded metal arc welding (MMA/SMAW) method. Stove pipe is one of the most widely used methods for welding pipelines in service to the pipeline industries that transport oil, gas and water.
The stove pipe welding allows positional welding but with high production rates, for laying steel pipelines. You can find stove pipe welding information in our FAQ here.
What is 5g Pipe Welding?
5G pipe welding refers to the position in which the pipe is welded. In 5G pipe welding, the pipes are fixed horizontal and the welder rotates around the pipe welding them vertically.
What is 6g Pipe Welding?
6G pipe welding refers to the position in which the pipe is welded. In this position, the pipe is fixed, and the pipe is rotated approximately 45° from the horizontal (X) and the vertical (Y). The welder rotates around the fixed pipe and welds it in this position this is the most complex pipe position to weld.
What is Downhill Pipe Welding?
Downhill pipe welding is where you weld downwards as opposed to uphill pipe welding, which is where upwards welding is performed. It is believed that welding uphill is stronger and better for thicker materials; however, downhill pipe welding is quicker to do and can be more prone to burn through than uphill welding.
In addition, downhill welding on thinner pipe walls allows the welder to run ‘hot and fast’ helping with production where heat penetration is not a concern.
What is a Pipe Welder Called?
Pipe welders (as opposed to pipeline welders) can also be called pipefitters, steamfitters, or just ‘fitters.’ Pipe welders are responsible for assembling, installing, maintaining and repairing piping systems and fixtures.