Welding a pipe involves joining two pipes together in a process called welding. Welding techniques used for pipework include arc welding, as well as MIG or TIG welding, which are both arc welding processes. The term pipeline welding is sometimes used to refer to the pipelines that transport gas, water, oil, and other liquids over a wide distance. Some people make a distinction between pipe welding and pipeline welding, where pipe welding refers to pipes that transport metals and liquids within plants and refineries.
Pipe and pipeline welders perform various tasks that require welding skills, such as welding in the construction industry, the oil and gas industry, the water industry, fabrication shops, and nuclear power stations. A pipe welding job is generally conducted in order to turn old pipes into new ones by welding them together and then repairing them in accordance with relevant codes and standards.
Types Of Welding Used
There are several arc welding processes that can be used for welding pipe and pipelines, including the following:
1. Shielded Metal Arc Welding (SMAW)
The process of shielded metal arc welding (SMAW) can be referred to as Manual Metal Arc Welding (MMA or MMAW), Flux Shielded Arc Welding, or Stick Welding.
It is also called stovepipe welding, and is often used for welding pipes because flux or shielding gas is not required during the welding process, making the welding equipment simple to use and portable. The metal is welded by melting the electrodes using the heat that is generated by an electric arc, which melts the electrodes in the process. There are some advantages to the SMAW as it has a slow travel speed, but this does not mean that it is as productive as other methods due to its slow travel speed.
2. Gas Metal Arc Welding (GMAW)
A process called Gas Metal Arc Welding (GMAW) includes the use of both MIG and MAG gases to weld the metal together.
The process of welding with these techniques can offer greater productivity than with SMAW, but there is also need to better control the variables in the welding process in order to achieve high-quality, efficient results. As GMAW is usually performed with semi-automated or fully-automated equipment, it brings high deposition rates with little fume generation to the table.
3. Flux-Cored Arc Welding (FCAW)
Flux-Cored Arc Welding (FCAW) – A type of welding that includes both self-shielding and gas-shielding.
In the gas-shielded FCAW welding process, semi-automatic machines are used in order to provide high-productivity welding solutions for pipes, although windy conditions can disturb the shielding gas and result in porosity defects. A self-shielded FCAW avoids this problem by not using a shielding gas to shield the source of energy, but it has a low deposition rate as well.
4. Submerged Arc Welding
The submerged arc welding process is a semi-automatic process where the arc is not visible, which makes it difficult for the tracing process to be performed. Despite this, it offers the highest deposition rates of all pipeline welding methods on top of delivering a surface free of defects compared to many of the other pipeline welding methods.
5. Tungsten Inert Gas (TIG) Welding
Tungsten Inert Gas Welding (TIG) is a type of welding that is also referred to as Gas Tungsten Arc Welding (GTAW).
The TIG welding process has a low deposition rate and higher equipment costs than the other methods of jointing pipes. However, it produces extremely high quality welds (depending on how skilled the welder is), making it perfect for critical and precise welding jobs that require precision and continuity.
Pipe Welding Steps
As with any welding process, there are a number of steps that must be taken in order to achieve the best results. The first step is deciding on the welding process itself, which takes into account 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
Based on these factors, you can determine which equipment is most appropriate for the job by evaluating:
- Output power
- Duty cycle
As soon as the process and equipment selection are complete, it is time to start welding. Typically, the following steps are taken:
- Joint Preparation: The joint preparation should comply with the guidelines as stated in the relevant standards regarding the preparation of such a document.
- Pipe End Cleaning: Remove any unwanted moisture or coatings from the pipe end, such as oil, paint, rust, or varnish. By doing this, you will be able to prevent defects and costly repairs and rewelding from occurring.
- Welding: After selecting the correct materials (including electrodes) and parameters (preheat requirements, etc), in accordance with the required specifications, the welding process can begin with the root passes. There are then several hot passes that follow, before a welding fill is completed and a final cap pass is completed.
- Repairs: Ideally, you will not have to take this step, but if it is necessary, you should check the weld and make any repairs that are required.
Pipe Welding Passes
There are several different weld passes required for pipe welds:
- Root Passes: The root passes are the first passes that are required to fill in the gap between the two sections of piping.
- Hot Passes: These passes connect the root weld to the groove faces on both sides of the groove.
- Fill Passes: The main purpose of these passes is to fill out most of the grooves before making the final cap passes.
- Cap Passes: The final passes of the welding procedure should be done in order to provide a weld that is complete with as little buildup on the surface of the pipe as possible. Before running a final finishing cap pass and making a final weld beading pass, you can grind this layer back to improve the weld beading and remove any contamination that may have remained.
Pipe Welding Positions
The pipe welding positions can be categorized as 1G, 2G, 5G, and 6G, according to their welding positions. In each position, you can see whether the pipe is stationary or rotating, whether it is oriented horizontally, vertically, or at an angle, as well as whether it is angled upward or downward.
- 1G Welding: The pipe is placed in this position horizontally prior to welding. The pipe can be rotated along the horizontal (X) axis, while the welder remains stationary, while the pipe is rotated along the X axis. There are several welding positions where the weld can be complete and the top of the pipe is the most common position for completing a pipe weld.
- 2G Welding: The 2G welding position consists of the pipe being arranged upright in a vertical position. The pipe can be rotated along the vertical axis (Y) while the welder remains stationary while the pipe is rotating along the vertical axis. In order to weld the pipe, it is necessary to do so horizontally on the side.
- 5G Welding: The 5G welding position uses a horizontal screw to fix the pipe in place, rather than rotating it as you would in the 1G welding position. The welder will have to move towards the stationary pipe in a vertical direction in order to complete the welding process.
- 6G Welding: This is the position in which the pipe is inclined at a 45° angle to form a sloping surface when welded. A pipe is fixed, as with 5G, and the welder is required to move around the pipe in order to weld it. The pipe welder’s role in this position is the most advanced of the four and requires a higher level of ability and expertise.
A welder will learn each type of position in turn, with 1G being the easiest to master and 6G being the most difficult to master. The welder will need to gain certification in each position, in turn, so if someone has a qualification for 1G, but does not have a qualification for 2G, 5G, or 6G, but has a qualification for 6G, they can weld in any of the other positions. It is crucial that these standards are followed when performing pipe welding because they preserve the safety of the working environment.
The welding method differs from other joining methods, such as screwing fittings to the pipes, in that it gives a number of advantages. A few of these advantages are as follows:
1. Fewer Fittings
There is no need for fittings to be used when joining straight sections of pipe together due to welding. While a screwed pipe requires a fitting between each joint, a welding process can quickly join pipes after the end preparation of the pieces to be joined is complete.
2. Lower Costs
Welded pipes allows to use thinner walled pipes than screwed connections which can result in significant cost savings for long distances and larger projects that require large amounts of pipe. There is also a possibility that screwing pipes together can have an increased labour cost along with the higher price of the threaded fittings available on the market.
3. Improved Flow
A screwed fitting creates turbulence and prevents the flow of fluid through the pipe and thus creates fluid resistance. There are numerous benefits to welding solutions, such as smoother, streamlined surfaces that allow improved flow through a system.
4. Ease of Repair
A welded system can generally be repaired more easily than a screwed system because of the way they are attached. While a welded pipe can usually be repaired in place, if a screwed system needs to be disassembled and repaired, then it must be dismantled. Obviously, this leads to a higher cost of labour as well as more downtime for the pipe system.
5. Fewer Leaks
There is generally a better resistance to vibrations when a pipe is welded than when it is screwed, which makes it more efficient in terms of leak prevention.
6. Easier Insulation
The process of insulate welded pipes is much easier than insulate threaded pipes, as there are no threads to create bumps that have to be covered in order to insulate.
A welded pipe can be placed close to another, but a threaded pipe requires extra space so that you can put wrenches and other tools on it.
When the pipe size is increased, so does the labor cost and the time required to install the welded pipe by the screwed pipe. During the process of installing the weld pipe, although the labour cost and time required to install the screwed pipe is about the same, as the pipe size increases. Screwed pipes also require specialized tooling for different pipe size variations, whereas a welder who is skilled can use the same welding machine for a whole range of pipe sizes, which is not true with screwed pipes.
The best way to avoid common mistakes when welding pipes is to thoroughly understand what the process entails as well as the conditions that accompany the process.
First of all, the pipes that are going to be joined need to be prepared correctly, making sure that the edges of the pipes are clean and straight before connecting them together. It is important to know that if this process is not done properly there can be problems such as resistance to fusion in the weld, slag inclusion in the weld, and hydrogen inclusion in the weld.
Aside from the preparation for welding, there are a number of challenges that welders have to deal with when it comes to working conditions. The process itself can pose a risk of injury if the correct precautions are not taken to prevent injury during the process. As mentioned above, some of the risks related to welding include the high temperatures created by the tools, the bright light produced by the arc, and the release of gases or particles into the air.
The working conditions associated with pipes can make pipe welding a more hazardous process due to the conditions in which it is carried out. This includes having to work in uncomfortable or even dangerous positions and locations, including underground or underwater, which may be uncomfortable or even dangerous for the worker. Other factors may include working in a very hot or cold environment, depending on the location of the pipe, as well as hazards associated with the content of the pipe, whether it be sewage or oil, and the degree of exposure to those substances during the process itself.
While many of these challenges are indeed difficult to resolve, but with the right preparation, training, and equipment, many of them can be overcome.
Applications and Examples
Pipe welding refers to the process of joining metal pipes together, so it is a skill with a wide range of applications since it involves welding the metal to the metal. It is likely that the number of applications will only increase in the near future, since welding is one of the most cost-effective methods for attaching several sections of pipe together.
Therefore, pipe welding has become an important technology in a wide variety of industries, such as the transporting of natural resources and the building of pipelines for transporting them across country and international borders, as well as to mining facilities.
There are also pipe welders who work in chemical and food processing plants, food and beverage manufacturing facilities, and in the power generation industry, and they are also employed to create the infrastructure for water and gas utilities, the construction industry, and other industries that require infrastructure.
the water industry, fabrication shops, and nuclear power stations.
They are able to perform various tasks that require welding skills, for example, they can weld in construction, in the oil and gas industry, in the water industry, in fabrication shops, and in nuclear power plants, all of which require welding skills.
A welding process involves joining two pipes together.
In the construction industry, the oil and gas industry, the water industry, fabrication shops, and nuclear power stations, pipe and pipeline welders perform various tasks that require welding skills.
A pipe can be welded with a stick or TIG welding process, but it can also be welded with FCAW (Flux-cored), GMAW (MIG), or submerged arc welding. TIG welding is primarily, however, employed when a high level of integrity is required for the welded joints when welding pipes.
Welding pipes is often more challenging without welding education and requires more skilled welders due to many factors, such as the pipe’s position, the weld’s travel angle, and the pipe’s size.