Pipe Welding Technique Explained

Welding is a crucial joining procedure used to weld a wide variety of metals, shapes, and weldments. Pipe welding is one such procedure, which is essential in various industries such as petroleum, oil and gas, plumbing, nuclear, and more.

Welding pipes requires a unique set of skills that include understanding the materials and application, proper fit-up and alignment, and multi-pass operation. Since pipes transfer oil, gas, or toxic chemicals, welds must be of the highest quality and pass critical tests.

In this article, we'll thoroughly explain the pipe welding technique, including the processes, passes, and pipe welding positions.

Stick Welding Pipelines
Photo by @jarod814 (TikTok)

What Is Pipe Welding?

Pipe welding is a metal joining procedure that welders use to connect pipes in the construction industry, oil and gas fields, water industries, fabrication shops, and nuclear power stations, among others. Welders use one of many traditional welding methods, such as MIG welding, Stick welding, or TIG welding, to connect the pipes that carry water, oil, gas, petroleum, or various chemicals and transport them across great distances.

The connections between the pipes require critical welds that must adhere to strict welding standards and codes. Some examples are ASME B31.4, B31.8, ASME BPVC codes, AWS D10.12, and AWS D10.18 standards. These codes and standards dictate the weld properties, and the maximum allowed defects, if any, are permitted. Some welders refer to pipe welding as girth welding, as you weld around the circumference of two pipes.

Photo by @braddockgtaw7 (IG)

Pipe Welding or Pipeline Welding?

Pipe welding and pipeline welding are two similar terms in pipe joining. While in its core, welders use both to join pipes, there are some differences.

Pipe welding is a procedure welders use to join metal pipes inside plants or oil refineries. Welding these massive pipe structures inside the plants makes the working conditions more manageable.

Pipeline welding is a pipe joining procedure welders use to weld outdoor piping networks. These pipe country networks transport gas, water, oil, and other liquids over many miles. However, this means welders often work in harsh outdoor conditions, especially on the oil and gas piping in the north.

Source: https://www.youtube.com/shorts/lQwl8Tc05Ic

Types Of Piping

Pipes can transfer various chemicals or liquids, but there are several types of piping systems.

• Low-pressure (light structural) piping: These systems transfer non-critical chemicals that are not corrosive, combustible, or hazardous. The weld requirements are the lowest, but the welds still must ensure structural integrity.
• Medium-pressure piping: This piping transfers the low-pressure steam heat, corrosive or flammable chemicals, waste disposal, ship plumbing, and medium-service to heavy-service structural items. Some of the typical applications include welding highway signs, railings or light posts, trailer axles, and equipment frames or stands.
• High-pressure piping: These are the piping systems used in critical applications to transfer high-pressure steam, radioactive materials, or refinery reactor lines. We often see high-pressure piping in the Alaskan pipeline, and the welds must be of the highest quality to withstand harsh conditions and transfer high-pressure liquids across the states.

High-pressure Piping in the Alaskan Pipeline
Source: https://www.underwater.org/mermaid/passage/pipeline/index.html

Pipe Welding Techniques

Welders use one out of many manual, semi-automated, or fully automated arc welding methods to join pipes. Some commonly used pipe welding techniques are:

• Shielded Metal Arc Welding (SMAW)
• Gas Metal Arc Welding (GMAW)
• Gas Tungsten Arc Welding (GTAW)
• Flux Core Arc Welding (FCAW)
• Submerged Arc Welding (SAW)

Each pipe welding technique produces better or worse results in different applications. Understanding how each performs is crucial in making an informed choice, so we'll discuss each technique in more detail.

TIG Welding Pipe Welds
Photo by @jarod814 (TikTok)

Stick Welding In Pipe Welding

Stick welding, Shielded Metal Arc Welding (SMAW), or Manual Metal Arc welding (MMA) is one of the most popular pipe welding methods. Stick/Arc welding is a quick and cheap technique that uses self-shielded electrodes. That means you can successfully weld outdoors without using a shielding gas.

The welding equipment for Stick welding is portable and cheap, allowing welders to finish the job and move to another location. However, Stick welding is slower than some semi-automated methods, such as MIG or FCAW, and it produces more spatter, resulting in less visually appealing welds.

Stick Welding Pipe Process
Photo by @welded_visions (TikTok)

MIG Welding In Pipe Welding

Gas Metal Arc Welding, or Metal Inert Gas welding (MIG), is one of the most straightforward methods. Many beginners and new welders prefer it for home welding. The method uses the heat of an arc and automatically fed solid wire to melt and fuse the pieces.

In pipeline welding, MIG welding offers better weld speed and higher deposition than Stick welding. It is often semi- or fully automated to provide the highest-quality, repetitive welds.

However, MIG wire is prone to contamination and requires an external shielding gas. Wind and draft in outdoor jobs can blow away the shielding and create defects. So welders typically use MIG to join indoor pipes.

Indoor MIG Welding Pipe 
Photo by @pipeweld (TikTok)

TIG Welding in Pipe Welding

Gas Tungsten Arc Welding (GTAW) or Tungsten Inert Gas (TIG) welding is a manual method with the highest skill requirements of all arc welding methods. However, TIG produces some of the highest-quality and visually appealing welds, and welders use it to weld thinner pipes made of exotic metals.

TIG welding is, without a doubt, the slowest pipe welding technique. It also requires an external shielding gas to protect the weld, which is often necessary for critical pipe welding techniques such as nuclear plant pipes.

TIG Welding Stainless Pipe 
Photo by @arcshow (TikTok)

Flux core Welding In Pipe Welding

Flux-cored Arc Welding (FCAW) is a variant of MIG welding that uses an automatically fed wire and the heat of an arc to melt and fuse pieces. It also provides high welding speeds and depositions in pipe welding, but there is another advantage.

FCAW uses a self-shielded wire, known as flux-core wire, that doesn't need external shielding. Welders use it to weld outdoor pipes, but it is somewhat slower than MIG. Dual-shielded flux core welding provides the highest speeds among pipeline wire methods, but it can be expensive.

Dual-Shield Flux-Cored Welding on Pipelines
Source: https://www.youtube.com/shorts/0jAIfTMMaHg

Submerged Arc Welding In Pipe Welding

Submerged Arc Welding (SAW) is a semi-automated welding process used by welders in pipe welding. As the name states, the arc is submerged under a blanket of flux, producing defect-free welds.

SAW is also one of the fastest and cleanest pipe welding methods, but it is not without drawbacks. Since the arc is submerged under the flux, the arc is not visible, which can make tracing difficult.

Submerged Arc Welding
Source: https://www.youtube.com/watch?v=Zc3Fu1AVCjc

Pipe Welding Phases

Like traditional welding, pipe welding is also a procedure that includes several steps. Welding pipes requires a:

• Pipe edge preparation
• Part fit-up and alignment
• Pipe positions
• Pipe Welding
• Post-weld cleaning
• Weld inspection

The challenges of welding pipes, including the required preparation and complexity, are highly dependent on various factors. Therefore, before welding, you should first consider the pipe material, pipe diameter, and wall thickness, as well as welding location and conditions, pipe applications, and ergonomics.

However, some general rules apply to most pipe welding applications. We'll discuss them more to create a general image of what pipe welding looks like.

Stick Welding Pipelines
Photo by @conde_welding (IG)

Pipe Edge Preparation

Each welding type requires clean and well-prepared edges, and the same rules apply to pipe welding. Therefore, you must remove all oil, rust, dust, or surface contamination. However, welding pipes is more than just cleaning the edges.

Most pipe welding applications require grinding and beveling the edges before proceeding to the multi-pass operation. The standard pipe bevel angle for welding is 37.5 degrees, but the shape can differ depending on the thickness and diameter of the pipe.

Commonly used shapes for pipes are I-bevel, V-bevel, or U-bevel, either single or double-sided. I-bevel creates somewhat of a square butt joint for thinner pipes. V-bevels provide better reinforcement on thicker pipes, while U-bevels can fit the most filler metal, and welders use it on edges that are subjected to stress.

Common Pipeline Beveled Ends
Source: https://www.linkedin.com/pulse/pipeline-beveled-ends-kayla-wang

Pipe Fit-up And Alignment

After preparing the edges, you will have to fit up and align the pipes. Aligning the pipes and providing an even gap throughout the circumference of the pipe is crucial in achieving even pipe welding results.

Align Different Pipe Fittings in Different Methods
Source: https://www.youtube.com/watch?v=gH5B2MSl45U

To provide an even gap, welders create a root opening between two pipes. Depending on the welding specification, pipe diameter, and personal preference, welders typically create a 1/16 or 3/32 in root opening.

The best way to align the pipes and ensure an even gap is to use an electrode of the same diameter as the desired root opening. Use the electrode as a spacer between the pipes, and then tack the pipe to help it stay in place.

Failing to align the pipes before the welding can create misalignment, also known as highs-lows. If you proceed to weld, misalignment causes a noticeable ridge that can collect bacteria and lead to corrosion and weld failure.

What is Highs-Lows in Pipe Welding
Source: https://www.youtube.com/watch?v=y4sQY3i3hPA

Pipe Welding Positions

Depending on the specific conditions, pipes can stay stationary or rotate. They can also be horizontal, vertical, or inclined, and their position dictates the complexity or challenges of the job.

Common Pipe Welding Positions
Source: https://www.weldingandndt.com/welding-positions/

Common pipe welding positions include:

• 1G (Horizontal rolled position): This is the most basic welding position, where the pipe is horizontal and rotates along the x-axis. You deposit the welds on top of the pipe while remaining stationary, making 1G one of the basic and most straightforward pipe welding positions.
• 2G (Vertical position): In 2G, the pipe is vertical while you weld horizontally across the joint. The pipe can rotate around the y-axis so the welder remains stationary. Welding in 2G can be challenging even though it is ergonomically pleasant. The issue is gravity, which pulls the molten puddle to the lower part of the joint.
• 5G (Horizontal fixed position): In 5G, the pipe is also horizontal, like in 1G, but it remains fixed. Instead of welding on top, you have to weld vertically, from the bottom to the top of the pipe, making it highly challenging. Longer periods of welding in 5G can cause fatigue and repetitive strain injuries.
• 6G (Inclined position): In 6G, the pipe is inclined at 45 degrees and fixed, like with 5G. These conditions make 6G one of the most challenging positions, requiring a lot of skill and operator expertise. Welding around inclined pipes is physically demanding, and achieving desirable results is also challenging.

6G Stick Welding Open Root Pipe Welding
Source: https://www.youtube.com/watch?v=7Q3MDgSZWyc

Pipe Welding Procedure

Once everything is well aligned and prepared, you can proceed to weld the pipes. Beveling the edges creates a large opening in the weld joint, which must be welded in a multi-process operation. Simply laying one weld won't produce the desired strength.

Pipe welding requires several different passes:

Pipe Welding Multi-Pases
Photo by metalartspress.com & https://www.reddit.com/r/Welding/

• Root pass: A root pass is the first pass in the multi-pass pipe welding procedure. Welders use it to fill the root opening and create a strong foundation for the following passes. Welders commonly weld a root pass with stick welding and E6010 or E61011 electrodes or TIG weld when the highest quality is needed.
• Hot pass: The hot pass comes right after the root pass, and welders use it to join the root weld to both groove faces. This pass is not necessary, but you can use it if there are some issues with a root pass.
• Fill pass: Fill passes are used to fill the groove. Depending on the size of the bevel, you can make several passes to ensure the appropriate weld strength. You can fill the groove with Stick welding and E7018 electrodes.
• Cap pass: A cap pass is the final pass, laid on top of the groove. Welders weld it with as little build-up beyond the surface of the pipe as possible. The welders can weld a cap pass with TIG to ensure better weld aesthetics or continue it with Stick welding in non-critical, non-aesthetic applications.

With a cap pass, you put a crown onto your weld, creating a solid and everlasting bond between two pipes. After a long process of reparation and alignment, your welding is complete, and it is time for the post-weld treatment.

Finishing the Weld with a Cap Pass
Photo by @westernweldingacademy (TikTok)

Post-weld Cleanup

Post-weld cleanup in pipeline welding includes removing spatter and slag from the welds. The key is to have a uniform weld across the pipe's weld joint, which means there is no excessive reinforcement or undercutting.

However, keep in mind that in a multi-pass operation, you need to clean the slag after each pass. Trapped remains of solidified flux can create slag inclusion that can interfere with the structural integrity of the weld and create weak spots.

Clean the slag after each pass in multi-pass operation.
Source: https://blog.red-d-arc.com/welding/multipass-welding-techniques-benefits

Weld Inspection In Pipeline Welding

The final step in pipe welding is the weld inspection. The process of inspecting the structural integrity and strength of the welds is crucial, especially in critical applications and pipes that transfer hazardous substances.

Therefore, inspecting the quality of the welds ensures the welds can withstand the applied pressure or stress, promote safety by avoiding accidents, and ensure there are no leaks. Welding inspectors use a series of destructive testing and non-destructive tests to check the newly formed welds. Some examples are:

Visual testing: The most straightforward method in which you visually observe the newly formed welds. In pipeline welding applications, you can detect most defects, such as uneven welds, porosity, overwelding, or undercutting, by eye. However, most of these are surface contaminants, while pipe welding defects often lie deeper within the weld.

Pipe Welding Visual Inspection
Source: https://resources.arcmachines.com/how-to-do-a-pipe-welding-visual-inspection-ami/

Destructive testing: In destructive testing, the inspectors simulate the pressure, tests, bends, and real conditions pipeline welds would face in reality. They detect the point of failure, analyze the weld quality, and study the impact of load and stress on the joint. The final results help them understand the properties of the joint and come up with solutions that would work well in real-life pipe applications.

Non-destructive testing: Non-destructive testing methods involve checking the integrity of the welds without damaging the pipes or the welds. Methods like ultrasonic testing and radiographic testing use advanced waves that travel through welds and check for discontinuities, cracks, or holes inside the welds. They can give welders a better image of what the inside of the welds looks like, and they are crucial in avoiding weld failure.

Some pipeline inspection methods, such as liquid penetrant testing, combine visual and non-destructive testing. In this test, the dye can detect cracks or pinholes, making it crucial in many pipe welding applications.

Liquid Penetrant Testing
Source: https://www.onestopndt.com/ndt-articles/liquid-penetrant-testing-basics-usage-and-benefits

Common Issues In Pipe Welding

Now that you understand the basics of pipe welding, it is time to talk about the common issues. As you can notice, the entire process can be long, and the defect can occur in any phase or even between two passes, which makes pipe welding highly challenging.

The most common defects in pipe welding are:

• Lack of fusion: This defect occurs if you fail to penetrate both edges of the pipe properly. The welds sit on top of the joint, often caused by a lack of heat or improper technique.
• Porosity: Tiny holes in the weld surface, or porosity, occur once contaminants or atmospheric gases get trapped in the weld. They form small holes that appear on the surface or inside the weld, affecting its overall strength.
• Cracks: Cracks are one of the most common and concerning defects in welding, including pipe welding. They can occur during solidification (hot cracks), during cooling (cold cracks), or due to a lack of strength (stress cracks).

Cracks in Pipe Welding 
Photo by Piping/NDT/Welding.com.ph on Facebook

• Undercutting: This defect forms a groove-like depression along the toe. Poor welding parameters or operator technique cause this groove to weaken the joint and reduce its load-carrying capacity.
• Excessive reinforcement: Overwelding, or excessive reinforcement, occurs once the welds exceed the required size or profile. Applying too much weld metal can cause dimensional inaccuracies, stress concentration, and potential failure.
• Incomplete penetration: This defect occurs once welds fail to properly penetrate the pieces, commonly due to a lack of heat and operator expertise.

Photo by @bhamzkievlog5624 (YouTube Shorts)

Final Thoughts

Pipe welding is a metal joining procedure used to join two pipes. While it sounds straightforward, it is a long process that involves cleaning, preparing, and aligning the pipes.

The welding itself can be challenging and depends heavily on the thickness and diameter of the pipe, the welding position, or the given conditions. Pipe welding often involves working in uncomfortable or even dangerous positions and locations, including underground or underwater.

Inspection methods are valuable in assessing the quality of the weld. This is essential in critical applications where pipes transfer hazardous substances under high pressure and over long distances.