Pipe and pipeline welding is typically performed using one of several arc welding processes, including:
1. Shielded Metal Arc Welding (SMAW)
Shielded Metal Arc Welding (SMAW) also known as Manual Metal Arc Welding (MMA or MMAW), Flux Shielded Arc Welding or Stick Welding.
Also known as stovepipe welding, using SMAW for pipe welding means that no flux or shielding gas are needed during welding, making the welding equipment simple and portable. The metal is welded by melting the electrodes through the heat generated by an electric arc. Although SMAW has some advantages, the slow travel speed means that it is not as productive as other techniques.
2. Gas Metal Arc Welding (GMAW)
Gas Metal Arc Welding (GMAW) including Metal Inert Gas (MIG) Welding and Metal Active Gas (MAG) Welding.
Offering greater productivity than with SMAW, these techniques do require better control of the welding variables to deliver high quality, efficient work. Usually performed with semi or fully automatic equipment, GMAW offers high deposition rates with low fume generation.
3. Flux-Cored Arc Welding (FCAW)
Flux-Cored Arc Welding (FCAW) – including self-shielded and gas-shielded FCAW.
Gas-shielded FCAW uses semi-automatic machines to provide a high productivity welding solution for pipes, although windy conditions can disturb the shielding gas and lead to porosity defects. Self-shielded FCAW avoids this by not requiring a shielding gas, but has lower deposition rates.
4. Submerged Arc Welding
Submerged arc welding is a semi-automatic process where the arc is not visible, which can make tracing difficult. However, it offers the highest deposition rates of all the different pipeline welding methods as well as delivering defect-free surfaces.
5. Tungsten Inert Gas (TIG) Welding
Tungsten Inert Gas (TIG) Welding also known as Gas Tungsten Arc Welding (GTAW).
TIG welding has low deposition rates and higher equipment costs than the other methods for pipe welding. However, it produces very high quality welds (according to welder skill), making it perfect for critical and high-precision welding jobs.
As with all welding work, there are a number of steps that should be followed, starting with process selection, which involves the consideration of factors such as:
- Pipe material
- Pipe diameter and wall thickness
- Welding location
- Weldment properties
- Welding direction (Uphill or downhill)
- Required welding quality
- Economic considerations
- Health and safety
Once these factors have been addressed, you can determine which equipment is best suited for the work by assessing:
- Output power
- Duty cycle
With the process and equipment selection complete, it is time to begin the actual welding, typically with the following steps:
- Joint Preparation: Joint preparation should follow the appropriate guidelines as set out by the relevant standard
- Pipe End Cleaning: Remove an undesirable moisture or coatings including, oil, paint, rust or varnish. This will prevent defects and costly repair or re-welding.
- Welding: Having selected the correct materials (including electrodes) and parameters (preheat requirements, etc), according to the required specifications, the welding can begin with the root passes. Hot passes follow this before the welding fill and final cap passes.
- Repairs: Ideally, you will be able to skip this step, but it is worth checking the weld and making any defect repairs.
Pipe welds require several different weld passes:
- Root Passes: These first passes should fill the gap between the two sections of piping.
- 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 required to improve the weld beading and remove contamination before a final, finishing cap pass.
There are four types of pipe welding position; 1G, 2G, 5G and 6G. Each position details whether the pipe is stationary or rotating and whether the pipe is placed horizontally, vertically, or inclined at an angle.
- 1G Welding: This position places the pipe horizontally. The pipe can be rotated along the horizontal (X) axis, with the welder remaining stationary. The weld is completed on the top of the pipe and is the most basic of the pipe welding positions.
- 2G Welding: This position places the pipe upright in a vertical position. The pipe can be rotated along the vertical (Y) axis, with the welder remaining stationary. The welding is performed horizontally on the side of the pipe.
- 5G Welding: The 5G position places the pipe horizontally but, unlike with the 1G position, the pipe cannot be rotated. Instead, the welder must move around the stationary pipe in a vertical direction to create the weld.
- 6G Welding: This position inclines the pipe at a 45° angle to create a sloping surface. The pipe is fixed, as with 5G, and the welder must move around the pipe. This is the most advanced of the four positions and requires a greater level of expertise from the pipe welder.
Welders will learn each type of position in turn, with 1G being the easiest to master and 6G the most difficult. A welder will need to gain certification in each position in turn, so someone qualified in 1G positions cannot weld 2G, 5G or 6G, but if you are qualified in 6G you can weld in any of the other positions. These standardspreserve the safety of the work environment when performing pipe welds.
Welding pipes has a number of advantages over other joining techniques, such as screwed fittings. These advantages include:
1. Fewer Fittings
Welding eliminates the need for fittings to join straight sections of pipe. A screwed pipe requires a fitting between every joint while welding can quickly join pipes following end preparation of the parts to be joined.
2. Lower Costs
Welded pipe can use thinner wall pipe than with screwed connections, leading to significant cost savings for long runs and larger jobs. Screwing pipes together can also require higher labour costs along with the higher costs of the threaded fittings themselves.
3. Improved Flow
Screwed fittings create turbulence and fluid resistance in the flow through the pipe. Welded solutions can create smooth and streamlined surfaces to allow for improved flow.
4. Ease of Repair
Welded systems are generally easier to repair than screwed systems. Where a welded pipe can often be repaired in place, a screwed system requires disassembly and reassembly for repair. This obviously increases labour costs and downtimes for the pipe system.
5. Fewer Leaks
A welded pipe is generally able to handle vibration better than a screwed system, making it less prone to leaks.
6. Easier Insulation
It is easier to insulate welded pipes, as there are no threaded connections to create difficult bumps that need covering.
Welded pipes can be placed close together but threaded pipes need extra space so that wrenches and other tools can be used.
While the labour required to weld or screw smaller pipes is about the same, as the pipe size is increased, so the labour costs and time required to install the welded pipe decreases as the screwed pipe increases. A screwed pipe also requires different tooling for different pipe sizes, while a skilled welder can use the same welding machine for a range of pipe sizes.
The best way to avoid common mistakes in pipe welding is to understand the process and working conditions associated with the process.
Firstly, the pipes to be joined need to be prepared correctly, making sure the edges to be joined a clean and straight. If this is not done correctly there can be problems including a lack of fusion in the weld, slag trapments and hydrogen inclusion.
Aside from the preparation, there are a number of challenges associated with welder working conditions. The process itself can produce a risk of injury unless the correct precautions are taken. The risks include the heat created by the welding tools, the bright light created by the arc, and the release of particles or gases.
Pipe welding can add additional hazards due to the working conditions associated with pipes. This includes having to work in uncomfortable or even dangerous positions and locations, including underground or underwater. Other factors may include working in very hot or cold conditions, depending on the location of the pipe as well as hazards associated with the contents of the pipe, whether sewage or oil.
However, with the correct preparation, training and equipment many of these challenges can be solved.
Since pipe welding refers to the connecting of metal pipes, there are a wide range of applications for this skill. The number of applications is increased further as welding is one of the most cost-effective methods for connecting several sections of pipe.
Consequently, pipe welding is used across a range of industries including transporting natural resources to oil refineries, through cross-country or international pipelines, and to mineral processing plants.
Pipe welders also work in plants for chemical processing, food and beverage manufacture and power generation, as well as to provide infrastructure for water and gas providers, the construction industry and more.
Is Pipe Welding Difficult?
Pipe welding is often more challenging than other types of welding and requires a higher level of welder skill. This can be due to the working conditions as well as factors such as the travel angle of the weld, the pipe position and the diameter of the pipe. The difficulty increases as the position changes from 1G to 6G (see ‘Pipe Welding Positions’ above).
Is Pipe Welding Dangerous?
Pipe welding can be dangerous if the correct precautions are not taken. Welding can expose welders to fumes, dust and other airborne particles, as well as heat and dangerous levels of light that can be harmful without the correct safety equipment. The hazards are increased due to the conditions that pipe welders may be required to operate in, making pipe welding potentially dangerous.
What Type of Welding is Pipe Welding?
Pipe welding uses arc welding techniques, including shielded metal arc welding (SMAW), gas metal arc welding (GMAW) – including 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?
The amount of time taken to weld a pipe depends on factors such as the size of the pipe, the working conditions and the welder’s level of skill. In addition, the amount of passes required can change for different jobs and the different welding techniques have different rates of deposition (MIG is generally faster than TIG, for example). However, as a rule of thumb, the average welder can complete 140 inches of weld per hour. By checking this hourly speed against the diameter of the pipe, you can get an idea of how long a pipe will take to weld.
What is Stove Pipe Welding?
Stove pipe welding (sometimes called ‘stovepipe’) is a variant of the manual/shielded metal arc welding (MMA/SMAW) technique. It is one of the most commonly used methods for welding pipelines in industries transporting oil, gas and water and allows for positional welding and high production rates for steel pipeline laying. You can find out more about stove pipe welding in our FAQ here.
What is 5g Pipe Welding?
5G pipe welding relates to the position in which the pipe is welded. In 5G welding, the pipes are placed horizontally in a fixed position and the welder moves around the pipes, welding in a vertical direction.
What is 6g Pipe Welding?
6G pipe welding relates to the position in which the pipe is welded. In this position, the pipe is placed at an angle so that it slopes at around 45° from the horizontal (X) axis or vertical (Y) axis. The pipe is fixed and the welder moves around the pipe to perform the weld. This is the most advanced pipe welding position.
What is Downhill Pipe Welding?
Downhill pipe welding is when the welding is carried out with a downward progression, as opposed to uphill pipe welding, where the welding is carried out with an upward progression. Although uphill welding is considered stronger and is better for thicker materials, it takes longer to perform and has a greater potential for burn through than with downhill welding. On thinner pipe walls, downhill welding lets the welder run ‘hot and fast,’ improving productivity where heat penetration is not such an issue.
What is a Pipe Welder Called?
Pipe welders, as opposed to pipeline welders, are also sometimes called pipefitters, steamfitters or simply just ‘fitters.’ They are responsible for the assembly, installation, maintenance and repair of piping systems and fixtures.
Pipe welding uses arc welding to join metal pipes together. While a distinction is sometimes made between pipe welding and pipeline welding, there are many similarities between the two.
Pipe welders, sometimes called pipefitters, work in the construction industry, at oil and gas fields, in the water industries, at fabrication shops and in power generation, among other industries.
Pipe welding can be a difficult skill and can also involve working in uncomfortable or potentially hazardous places, however with the correct expertise, safety measures and standards, welding is often preferable to other pipe joining methods.
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