What Is Pipe?
Pipes are essential components in many industries, transporting various liquids and gases over long distances through complex networks.
They come in different sizes, shapes, and materials like metal, plastic, ceramic, or composite. Pipes can fail, and engineers must replace parts while still in use, making pipe welding a crucial aspect of maintenance and repair.
Pipe welding is a crucial process that ensures the longevity and safety of piping systems. It is crucial to understand the significance of proper pipe welding to ensure the safety and longevity of your piping. In this post, we will explore the basics of pipe welding.
What Does A Pipe Welder Do?
A pipe welder joins sections of pipes to create a continuous pipeline. They are responsible for welding various types of pipes, including steel, copper, and plastic, using different welding techniques, such as arc welding, gas tungsten arc welding (GTAW), and gas metal arc welding (GMAW).
Pipe welders work in various industries, including construction, manufacturing, and oil and gas. They may be responsible for fabricating and installing pipes for heating and cooling systems, gas and oil pipelines, and water supply systems.
Essential duties include installing metal pipes fittings, securing pipes to structures, and working with metal cutting, forming, and joining. Other essential responsibilities include interpreting blueprints and schematics, troubleshooting and diagnosing pipe problems.
As a pipe welder, it is crucial to focus on two key aspects to maintain the safety of pipe systems. Firstly, ensuring the quality of fittings, and secondly, ensuring their proper positioning. These factors are essential when dealing with substances like oil, gas, steam, chemicals, and water.
There are various welding procedures and types, each with advantages and disadvantages.
Which Type Of Welding Is Used For Pipes?
While there are many different methods of welding nowadays, Pipe welders usually use one of the following arc welding processes:
Shielded metal arc welding (SMAW)
Pipe welding often uses the Shielded Metal Arc Welding (SMAW) technique, commonly called stick welding.
This method uses a stick-shaped electrode to generate an electric arc that melts the metal during welding. The welder uses a flux-coated electrode to protect the weld metal and prevent atmospheric contamination.
When welding pipes, individuals often utilise SMAW to join hard-to-reach areas and thicker materials. SMAW is a versatile process that a pipe welder can apply to various metals, including carbon steel, stainless steel, and cast iron.
To begin the process, thoroughly clean the pipe area to be welded to remove rust, oil, or other contaminants. Then, position the electrode and establish an arc between the workpiece and the electrode. As the electrode melts, the flux coating vaporises, producing a shielding gas to protect the weld pool from atmospheric contamination.
By adjusting the angle of the electrode and moving it along the joint at a certain speed, the welder controls the size and shape of the weld.
Gas Metal Arc Welding (GMAW)
Gas metal arc welding (GMAW) is a process that uses a continuous wire electrode to weld metal. The arc between the electrode and the workpiece heats the metal, causing it to melt and join.
GMAW is a versatile process that can weld various metals, including carbon steel, stainless steel, aluminium, and magnesium. It is popular for welding pipes because it is easy to use and produces a high-quality weld.
To weld pipe with GMAW, you will need a welding machine, a welding gun, a wire electrode, and shielding gas.
The process of GMAW is relatively simple:
- To begin welding, connect the welding machine to the power source to provide the necessary electrical power to the arc.
- Connect the welding gun to the machine. This tool holds the electrode and delivers the necessary shielding gas to the weld area.
- Select the proper wire electrode and shielding gas for the type of metal you are welding. The wire electrode is responsible for melting and creating the weld. The shielding gas is tasked with protecting the molten weld pool by preventing exposure to the surrounding atmosphere.
- Position the welding gun at the joint and strike an arc between the electrode and the workpiece.
- Feed the wire electrode into the weld pool and move the welding gun in a circular motion once you establish the arc. As you do this, the wire electrode will melt and join the metal, forming a weld.
GMAW is a safe and effective welding process when used correctly. However, following all safety precautions when using GMAW equipment is essential. These precautions include wearing safety glasses, gloves, and a welding helmet while ensuring you ventilate the area where you will be welding.
Flux-Cored Arc Welding (FCAW)
Flux-Cored Arc Welding (FCAW) is an exceptional welding technique that employs a tubular electrode filled with flux instead of a solid wire. The flux safeguards the weld area against atmospheric contamination while also imparting additional elements to the weld to enhance its quality.
FCAW is versatile enough to weld various materials, including carbon steel, low alloy, and stainless steel. To perform the task, you only require a steady voltage power supply and a wire feeder to move the electrode to the welding point. Once the electrode and the base metal form an arc, the electrode melts, creating a weld pool. The flux layer around it safeguards the weld from impurities, shapes it, and enhances its quality.
FCAW is a highly efficient and productive welding process that can generate high-quality welds rapidly and efficiently. It benefits welding pipes with thicker walls or those requiring higher deposition rates. One of the significant advantages of FCAW is its ability to provide a stable and consistent weld, thereby ensuring a robust and reliable final product.
Submerged Arc Welding
Submerged arc welding (SAW) is commonly used for welding low and high-alloy steel and carbon steel pipes. It involves creating a welding arc submerged beneath a flux layer, protecting the weld pool from atmospheric contamination.
SAW is an efficient and productive welding process that can produce high-quality welds with minimal operator intervention. Pipe welding applications commonly use it because it creates a robust and high-quality weld at a relatively fast speed.
The SAW process requires a constant voltage power source and a wire feeder that delivers the welding wire to the weld joint. The weld is created when the arc is struck between the wire and the base metal, melting the wire and creating a weld pool. The flux layer surrounding the weld pool protects the weld from atmospheric contamination and helps control the weld’s shape and quality.
Submerged arc welding effectively welds pipes of different diameters, thicknesses, and lengths. The pipe welding industry frequently requires long and straight seams, which make this technique particularly suitable for the job.
Tungsten Inert Gas (TIG)
Tungsten Inert Gas (TIG) welding, also known as Gas Tungsten Arc Welding (GTAW), is commonly used in pipe welding to weld stainless steel, aluminium, and other non-ferrous materials.
TIG utilises a non-consumable tungsten electrode which creates an arc with the workpiece, melting the electrode and the base metal to create a weld pool. A filler metal is added to the weld pool to create a durable weld.
TIG welding requires a constant current power source and an inert gas, such as argon or helium, to shield the weld area from atmospheric contamination. TIG welding is an exact and controlled welding process that can produce high-quality welds with excellent mechanical properties.
One of the main advantages of TIG welding is its ability to produce a clean, precise weld with minimal heat distortion. It can also weld fragile materials, making it well-suited for thin-walled pipes.
Pipe Welding Steps
As with all welding work, a project manager has several questions to answer for the project to be successful, 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 everything is agreed upon, it’s over to the engineer to begin the fabrication and welding of the pipework.
They have their own set of steps, such as –
Pipe End Cleaning
To ensure a good quality weld, the surfaces to be joined must first be cleaned.
Before welding can start, the pipe must be free from moisture, coating, rust, oxides, and other contaminants to prevent defects and costly repairs in the future. You can clean using any suitable means, such as a file, wire brush, grinding, buffing wheel, etc.
After cleaning the surfaces, you can prepare them for welding.
Aligning The Joint
Aligning the joint is critical for a successful welding application. A line-up clamp is ideal for this process as it securely holds both ends of the pipes in place to maintain correct alignment.
If a line-up clamp is unavailable, another option would be to develop a jig; with an angle suitable for smaller diameters or a channel or I-beam for larger pieces.
It is also essential to ensure the necessary root spacings. Root spacing should equal the filler rod used for arc and oxy-acetylene welding.
Root spacing should exceed the filler rods when using a backing ring at the root.
While this method allows for full penetration joints, it may not always be permissible because of other design limitations.
Backing Rings
The backing ring is a device that helps prevent the weld from penetrating too deeply into the pipe wall. It prevents any metal from entering the ID of the pipe through a burn-through or spatter sprayed around during the welding. This allows the weld to penetrate only the outer surface of the pipe, leaving the inner surface unwelded.
Positioning backing rings between two pipe pieces before connecting them helps align the pipes and ensures that their centrelines are in sync. However, the use of a backing ring is sometimes restricted by design factors such as when the design requires a smooth, undisturbed fluid flow inside the pipe.
To prepare for welding, fit one pipe with a backing ring and place the other pipe over it. Secure the backing ring and tack weld the pipes at four to six points around their circumference.
Backing Gas
When you are welding, you are heating up two pieces of metal to join them together. However, as the metal heats up, it can react with the air around it, causing oxidation and other chemical reactions that can weaken the weld. This is where backing gas comes in.
Backing gas is a type of gas that is used to protect the back side of the weld from atmospheric gases during the welding process. It is commonly used in welding processes such as gas tungsten arc welding (GTAW) and gas metal arc welding (GMAW).
The purpose of backing gas is to prevent oxidation and other atmospheric contaminants from entering the weld area, which can negatively impact the quality and strength of the weld.
In GTAW, welders often use argon gas as a backing gas. The argon gas flows around the back side of the weld and creates a shield that prevents oxygen and other atmospheric gases from entering the weld area. This helps to ensure that the weld is strong and free from defects.
The type and composition of backing gas used depend on the welding type and the welded materials.
Backing gas is an important consideration in welding, as it can greatly impact the quality and strength of the final weld.
Tack Welding
Tack welding is a form of spot welding where two metal pieces are joined using small, temporary beads of molten metal.
Just like a tailor uses pins to hold two pieces of fabric in place before sewing, people use it to keep the parts ready for the final weld.
Tack welds offer the advantage of easy removal and reapplication if necessary, allowing for precise alignment due to their size and fragility.
The number of tacks required depends on the pipe diameter, with larger pipes potentially requiring up to eight tack welds.
This technique holds the pipes securely without affecting their alignment due to shrinkage caused by root passes.
Welding
Pipe welding is a specialised practice that requires careful preparation and consideration of materials, electrodes and welding parameters.
When welding starts, you must perform the initial passes, known as the “root pass,” followed by a “hot pass,” before proceeding to the filling and final cap passes.
Let us dive into passes in more detail.
Pipe Welding Passes
Pipe welding involves several sequential passes to create a perfect, strong weld.
The welding passes refer to the order of execution required when carrying out the pipe welding process.
The four passes typically used in pipe welding include the root pass, hot pass, fill-up pass and capping.
Root Passes
A root pass is the first step in any welding process and involves joining two pieces to form one structure.
In this step, we heat the filler metal to an exceptionally high temperature and pass it through the gap between the pipes.
Utilising the root pass requires more expertise than the following passes, so it is essential to exercise caution.
To ensure complete fusion, the welder should use quality control measures like backing gas.
In order to complete the weld pass, you must keep the root face smooth and uniform. If there are any imperfections on the weld face, you can correct them by grinding it out, so it does not have to be smooth or uniform initially.
Hot Passes
When completing a butt weld, the hot pass is the second phase which involves using higher amperage to produce a hotter weld. This helps to eliminate any impurities left behind by the root pass, resulting in a flatter and more uniform weld.
The hot pass is also known as the “welding pass” and is used to connect the root weld to both faces of a pipe.
By heating and joining the area around the root weld with the pipe’s face, this process can quickly remove any trapped slag that traditional chipping and wire brush methods cannot.
Additionally, welders can use a high current setting and faster-than-normal speeds during this process to reshape or modify the root weld.
Fill Passes
The filler passes are the intermediary steps in welding pipe joints.
This involves making a series of weld passes and filling the groove with molten metal.
The welder can make the filler passes using a series of stringer beads or a weave bead, depending on experiance.
Stringer beads require less metal to be molten at one time and are, therefore, simpler for beginner welders to perform.
After completing the filler passes, the welder has properly welded the joint.
Cap Passes
The cap pass is the final stage of welding a pipe joint.
It requires a thin weld with minimal build-up beyond the surface. To achieve optimal strength, the engineer must perform good beading and remove any contamination before completing the cap pass. You should also clean up the weld edges and use a file to remove any spatter.
Electrodes Used
For pipe welding, you can use either E6010 or E6013 electrodes for the full weld or to perform the root pass. Use E7018 electrodes to finish the joint.
Welding Positions For Pipe
Welding positions for pipe describes the technique used to join metal object in their existing positions or with specific components.
All welding processes have different capabilities and can fall into one or more of the following weld positions: horizontal, flat, vertical, overhead, or even on the floor.
Sometimes, you cannot achieve all welds successfully in a horizontal/flat position, and you may need to use other positional welding techniques. This is necessary to design and manufacture assemblies and adapters in the desired orientation, regardless of the shape and size of the workpiece.
Pipe Welding Positions
When welding pipes, it is important to consider the position of the pipe. The position can be determined based on whether the pipe needs to be stationary or rotating. It is also based on whether it is placed horizontally, vertically, or at an angle. These factors combine to determine the welding position of the pipe.
There are four pipe welding positions; PA Position, PC Position, PF and H-L045 (uphill)/J-L045 (downhill).
Welders will learn each type of position, with PA being the easiest to master and H-L045/J-L045 the most difficult.
To ensure safety while performing pipe welds, welders must be certified in each position before taking on different poses. Consequently, someone with a qualification in PA cannot weld PC, PF or H-L045/J-L045. Only those with H-L045/J-L045 certification are eligible to attempt any other pose.
These standards preserve the safety of the work environment when performing pipe welds.
Let’s take a look at each welding position.
PA Welding (1G)
PA Welding is a position where the workpiece remains stationary, and the welder rotates around it to create a weld. In this position, the welder performs a 360-degree rotation around the workpiece, evenly distributing the welding material and forming a strong and secure weld.
Welders often use this position to weld pipes, ensuring a complete and even weld by welding all around the circumference of the pipe. The PA welding position requires good technique and dexterity to control the electrode and maintain proper weld penetration and fusion.
PC Welding (2G)
When performing PC Welding, also known as 2G welding, the welder holds the components stationary while placing the pipe in an upright vertical position and allowing it to rotate along its Y-axis. The welder performs the welding horizontally on the side of the pipe, using heat and pressure to join two pieces of metal.
Welders commonly use this technique to join pipes by vertically placing the pipe and rotating around it while welding. In PC welding, the welder must maintain a consistent electrode angle and control the welding process to ensure proper heat input and penetration. Good agility, control and physical endurance are required from the welder to work in an overhead position for extended periods, are necessary for this welding position.
PF Welding (5G)
PF Welding is where the pipe is placed horizontally, and the welder moves around it vertically to create the weld. This method eliminates the need to rotate the pipe, which can be difficult or impossible in specific welding scenarios, and allows for more accurate welds with less effort.
Welding in the PF position requires good control and dexterity from the welder to maintain proper electrode angle and weld bead shape, as well as to prevent weld spatter and ensure proper weld penetration. The vertical movement of the welder in the PF position also requires physical endurance, as the welder must be able to work in a confined space for extended periods.
H-L045 Welding (6G)
H-L045 is a method used to weld pipes at a 45° angle. This welding position requires more expertise from the welder than 5G welding, as the welder must move around the pipe while maintaining a fixed position. Highly experienced welders usually perform the H-L045 welding position, which is considered the most complex of the four welding positions. The H-L045 position is uphill, whereas J-L045 is downhill.
Welding in the H-L045 position requires good control and dexterity from the welder and a high level of welding skill to maintain proper electrode angle and weld bead shape, prevent weld spatter, and ensure proper weld penetration. Additionally, due to the angle of the weld, the welder must prevent gravity from affecting the weld pool and maintain proper welding techniques to ensure a strong and secure weld.
Categories Of Piping
Low-pressure or light structural piping
Low-pressure piping is an economical option for the reliable distribution of non-critical materials in industrial settings. People typically use it for transporting water, non-combustible chemicals, and other non-hazardous materials. Because its contents are not hazardous or flammable, low-pressure pipes provide a safe and cost-effective solution for many applications.
Example – PVC or Thin-walled stainless
Medium-pressure piping
Many industrial and commercial applications utilise medium-pressure piping as an important component. Low-pressure steam heating systems transport corrosive or flammable chemicals and waste. Additionally, medium-pressure piping constructs highway signs, railings, light posts, trailer axles, equipment frames, and stands.
Example – Schedules 10 to 40 or EN10255(BS 1387) medium/heavy pipe
High-pressure piping
Various industries use high-pressure pipes to transport steam, radioactive materials, and other fluids in pipelines, fired or unfired boilers, and refinery reactor lines. Engineers design these systems to withstand extreme pressure and temperature levels to meet safety protocols.
Example – Schedule 80 to 160
How To Test Your Welds
Testing pipe welds are essential to any welding project to ensure quality and strength.
Non-destructive testing (NDT) is the most commonly used method for weld evaluation. It evaluates weld integrity and size without damaging it.
Here is an overview of the NDT testing methods.
Visual Inspection of the Weld
Visual inspection is a non-destructive testing weld quality check process. The examiner visually checks the weld during the test to determine surface discontinuities.
An experienced welding inspector must conduct the process. Visual inspection of welded connections is the most common weld quality testing method.
This type of inspection is the most underrated and often misused method of welding inspection because of its simplicity.
X-Ray Testing
NDT professionals frequently use radiographic and ultrasonic inspection to inspect welds by passing X-rays generated by an X-ray tube or gamma rays from a radioactive isotope through the weld.
As the radiation penetrates the solid object, it creates an image of its interior structure on a destructive testing film.
The same basic principles apply in both medical radiography and X-ray weld inspection.
The Liquid Dye Penetration Test
The Liquid Dye Penetration Test is a non-destructive testing technique used to inspect finished products and components for surface-breaking defects such as cracks, porosity or lack of fusion.
This method uses capillary forces to draw a liquid penetrant into surface discontinuities, making the flaws visible to the naked eye.
This process can be used on welds and parent materials but not highly porous materials.
The dye penetrant method helps determine flaws in manufactured parts, which are vital to ensuring their quality and performance.
Ultrasonic Testing
Ultrasonic Testing (UT) is a non-destructive testing technique that uses high-frequency sound waves to detect internal defects, measure thickness, and evaluate the material properties of various objects.
The ultrasonic transducer produces high-frequency sound waves that travel through the object being tested during testing. Any changes in the material, such as defects or interfaces between different materials, reflect back to the transducer when the sound waves encounter them. The transducer then converts the reflected waves into an electrical signal, which analysts use to determine the characteristics of the material being tested.
Various industries use UT for quality control and inspection of materials such as metals, plastics, composites, and ceramics, including aerospace, automotive, construction, and manufacturing. Some typical applications of UT include detecting cracks or flaws in welds, measuring the thickness of pipes or plates, and evaluating the bonding between layers of materials.
Magnetic Particle Testing
Magnetic Particle Testing (MPT) detects surface and subsurface defects in ferromagnetic materials like iron, steel, and nickel using a non-destructive testing technique.
To test the material, we magnetize it by applying a magnetic field. Next, we apply a liquid suspension of magnetic particles to the surface, and these particles are attracted to any areas of magnetic flux leakage caused by defects in the material, forming a visible indication on the surface. We can examine the indications to determine the size, shape, and location of the defects.
MPT is commonly used in the aerospace, automotive, and construction industries for quality control and inspection. It is handy for detecting surface-breaking cracks in welds, castings, and forgings, as well as fatigue cracks in gears and other components subject to cyclic loading.
The below two are examples of destructive testing.
Macro Etch Testing
Macro Etch Testing is a destructive method of material testing used to evaluate welded joints.
This process requires a small sample from the weld joint, then polished and etched with a mild acid.
The acid etching of this sample reveals the depth of penetration and any lack of fusion, root penetration issues, internal porosity, or cracking shown at the base material fusion line.
Macro etch testing can also be used to identify welding problems such as crack initiation in failure analysis.
Sampling inspection using this method provides an overview of the overall quality of production welds.
Fillet Weld Break Test
The Fillet Weld Break Test is a type of welding test used to determine if there are any discontinuities within a sampled weld.
To perform this test, a sample fillet weld that has been welded on one side only is loaded with a press, and the force gradually increases until a break occurs.
After the sample fails, it undergoes an inspection to identify and measure any present welding defects like lack of fusion, internal porosities and slag inclusions.
The Fillet Weld Break Test provides a more comprehensive understanding of the entire length of the specimen, unlike the macro etch test, which only speculates at cross-sections. Combining the two tests can yield more detailed results.
Common Welding Issues
Welding issues can be frustrating and costly. Poor welding techniques can cause many problems, including inconsistent welds, weak joins, contamination, and dissolved base materials.
It is essential to ensure that the welding process is properly controlled to avoid these issues.
Typical steps to help minimise weld defects include:
- Using the right tools.
- Pre-weld preparation.
- Maintaining consistency when welding and proper post-weld treatment.
Here are some of the most common problems with welding and how to fix them.
Porosity
Porosity is a weld defect which occurs when nitrogen, oxygen and hydrogen are absorbed into the molten weld pool. The weld solidifies and releases this gas, which creates tiny cavities within the weld metal.
Various factors can cause porosity, such as:
- Moisture or debris on the plate edges,
- Insufficient shielding gases or
- Welding on small gaps with air pockets.
To prevent porosity in a weld joint, the welder should:
- Use fresh welding consumables,
- Check for gas nozzle leaks in the welding torch
- Ensure that the plate edges are clean and dry
Furthermore, it is important to double-check the shielding gas types and flow rates and keep an appropriate torch angle to the plate.
Lack Of Fusion
Lack of fusion in welding can result from either incomplete root penetration or incomplete root fusion.
Incomplete root penetration occurs when the weld metal fails to reach both sides of the joint, while incomplete root fusion happens when the weld doesn’t join on one side.
To fix these issues, employ a wider root gap and larger electrodes relative to the size of the gap width of the material being welded.
In addition, use a slower travel speed and weaving technique between two plates, which should assist in getting the outcome you want.
Misalignment
HiLo, also known as misalignment, is the difference between two piping systems’ inner and/or outer heights.
This mismatch can significantly negatively impact the integrity of a welded joint – it weakens it and makes it less able to withstand fatigue over time.
Poor fit-up is usually the cause of HiLo; when the fittings being welded onto the pipe have different dimensional tolerances, HiLo occurs.
Such an issue will create a flawed pipeline system that can cause corrosion and contamination due to bacterial colonies and blocked drainage. Misalignment usually happens more with larger pipes (6 inches or more in diameter) which can become warped during storage or transport, making them harder to fit correctly.
Improving pipe fit-up is essential to reduce HiLo before welding.
Common Pipe Issues
Several common issues can affect pipes, which can cause disruptions in the flow of liquids or gases through them. Some of the most common pipe issues are:
Cracks
Cracks are a common issue with pipe welding. There are many reasons for cracks, including improper weld preparation, poor quality materials, and improper welding techniques. You should fix any cracks in your pipes as soon as possible to prevent them from worsening and causing leaks.
Leaks
Leaks occur when water escapes from the pipe due to damage or corrosion. Cracks, holes, or pinholes can cause leaks in the pipe. When repairing leaks, make sure to use high-quality materials and proper techniques.
Corrosion
Corrosion occurs when metals react with oxygen and moisture in the air. This causes rust to appear on metal surfaces. You can remove rust using a wire brush, sandpaper, or steel wool. It is advisable to apply a layer of paint to safeguard the surface after removing the rust.
Fretting
Fretting is a condition where the ends of two pieces of metal rub together, causing them to wear down. It can be prevented by keeping the pipes clean and dry.
Stress Fractures
Stress fractures are small breaks in the pipe wall that occur when the pipe is under extreme pressure. Either overloading or incorrect installation can cause cracks to occur in the pipe. Keep the pipe at a constant temperature to prevent stress fractures and avoid bending or twisting.
Pitting
Pitting is a type of corrosion that occurs when the inside of the pipe becomes pitted. It can occur due to excessive exposure to sunlight or chemicals in water. To prevent pitting, keep the pipe out of direct sunlight and ensure the water does not contain chlorine or other chemicals.
Dents
Dents are small indentations that occur on the outside of the pipe. Heavy objects or vehicles can cause dents through impact or collision. To prevent dents, drive slowly and avoid hitting the pipe.
Pipe Welding At Varlowe
Our highly experienced pipework fabricators have years of expertise in fabricating and prefabricating. They possess the necessary skills and credentials to provide top-quality services that meet the demands of today’s market.
As a result of our excellent service, our customer base has grown, and we have established a stellar reputation over our 17 years of trading. Our accurate, reliable, efficient, and high-quality pipe services have made us the preferred choice for many in the industry.
We offer a wide range of pipe-related services, including welding and installation.
Call us on 01902 861042 or email info@varlowe.co.uk.
