Pipe Butt Joint

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FAQ

Welding thick parts (plates and tubes) together requires welding over the total thickness of the parts to ensure mechanical continuity of the assembly. To achieve this, bevels are created on the end faces of the components to be assembled before they are welded together.
The special feature of pipe butt welding is that the welder usually does not have access to the inner surface of the joint. Therefore, all welding operations must be carried out from the outside. The edges must therefore be prepared accordingly.
The different welding standards (ASME, AWS, ISO, EN, etc.) usually give instructions to be followed in terms of bevel geometry. This article describes the most common preparations in the industry, depending on the wall thickness of the pipes to be welded together.

Types of Welding Joints
Butt Welding Joint
A Butt Weld is a circumferential butt welded joint, and the most common type of joint employed in the fabrication of welded pipe systems. A butt joint is the most universally used method of joining pipe to itself, fittings, flanges, Valves, and other equipment. This welding technique is widely applied in situations where a quality weld desired, and the weld by X-ray technically should be investigated.
When the material to be welded exceedss 3/16" in thickness, the ends of pipes, fittings and flanges must be chamfered at approximately 37.5°, flared on a small upright side (Root face); in practice we talk about the Welding Bevel.

Lap Welding Joint
Lap welding joints are used most often to joint two pieces with differing thicknesses together. Also considered a fillet type, the weld can be made on one or both sides. A Lap Joint is formed when 2 pieces are placed in an over lapping pattern on top of each other.

Fillet Welding Joint
Fillet welded joints such as tee, lap and corner joints are the most common connection in welded fabrication. In total they probably account for around 70 to 80% of all joints made by arc welding. No edge preparation is needed and assemblies in piping systems are simpler. Therefore, fillet welds are usually cheaper than butt welds.

Edge Welding Joint
Edge welding Joints are often applied to sheet metal parts that have flanging edges or are placed at a location where a weld must be made to attach to adjacent pieces. Being a groove type weld, Edge Joints, the pieces are set side by side and welded on the same edge. For heavier applications filler metal is added to melt or fuse the edge completely and to reinforce the plate.

Tee Welding Joint
Tee welding joints are formed when two members intersect at a 90 deg angle which makes the edges come together in the centre of a plate or component. Tee Joints are considered a type of fillet weld, and can also be made when a pipe or tube is welded onto a base plate. Extra care is required to ensure effective penetration into the roof of the weld.

Pipe end bevels
chamfering
Bevelling is the operation of creating a flat angled surface at the end of a pipe. The opening created by the bevelling operation gives the welder access to the total thickness of the pipe wall and allows him to make an even weld, thus ensuring the mechanical continuity of the component. A root weld channel is formed at the bottom of the bevel, which forms the basis for filling the bevel angle formed by two bevels in successive welding passes.
Face
Facing is the term used for the operation of creating a platform, which consists of creating a flat surface at the end of the pipe. Correct facing makes it easier to align the pipes with each other prior to welding and also helps to have constant root openings between the parts. These are essential parameters for maintaining the correct weld pool and ensuring that the root weld passes completely through the joint.
Internal counterbores
Tube production tolerances may result in variations in thickness around the circumference of the tube. This may in turn lead to variations in the thickness of the root face when making bevels. This is why a reaming operation is often recommended in welding procedures.
This operation involves light machining of the inner surface of the pipe to ensure that the edge band or root face has a constant width around the entire circumference of the pipe. Having a constant width of the edge band will make the root alignment easier. This parameter is essential when using an automatic welding process, as the machine is unable to assess and compensate for any possible irregularities in the ground, which is clearly not the case with manual welding.

Pipe wall thickness
T ≤ 3MM (.118")
When butt welds are required for tube wall thicknesses of less than 3 mm (.118"), bevelling of the tube ends is usually not required. The arc welding technique (111, 13x, 141) is able to weld through the entire depth of the pipe in one pass.
When automatic welding techniques are used (orbital welding or processes using high density energy), the pipe ends must be treated to ensure that the weld edges are perfectly vertical. Depending on the application or the process used, the opening between the parts will be between g=1/2t and g=0 (especially for processes using high density energy).
3 ≤ T ≤ 20MM (.787")
When the welder has access to only one side of the joint to be welded, the preparation of parts with open square edges usually does not allow complete penetration of the weld metal if the wall thickness exceeds 3 mm (0.787"). Therefore, a bevel must be made so that the welder can make a root weld channel at the bottom of the joint, which can then be filled by one or more additional weld channels.
The root channel is usually made using the 141 process to provide the best possible depth of fusion (the root channel is used as the basis for subsequent weld channels). For economic reasons, the following channels are called "filler" or "filler" channels and are made using the 13x or 111 process, which has a higher productivity (amount of metal deposited, feed rate, etc.) than the 141 process.
20MM (.787") ≤ T
As the wall thickness of the part to be welded increases, the amount of weld metal to be deposited in the weld seam increases in a similar proportion. From the point of view of labour and consumables, in order to avoid long and costly welding operations, the preparation of welded joints thicker than 20 mm (.787") is carried out using a bevel, which reduces the total volume of the bevel