Welding seams: types of seams and joints

In the process of performing welding operations, various connections are obtained. Welding seams are able to connect not only metals, but also other heterogeneous materials. Docked elements in an integral node are a connection that can be delineated into several sections.

Welding connection zones

The joint obtained in the welding process is divided into the following zones:

• The place of fusion is the boundary between the base metal and the metal of the seam obtained. In this zone there are grains, which differ in their structure from the state of the base metal. This is due to partial melting during the welding process.
• The area of thermal influence is the zone of the base metal, which has not undergone reflow, although during the heating of the metal its structure has been changed.
• Welding seam - the area that formed during crystallization during the cooling of the metal.

Types of welding joints

Depending on the location of the products to be joined with respect to each other, the joints are divided into the following types:

1. Buttock. Adhesion of structural elements is carried out in one plane by the ends facing each other. Depending on the thickness of the parts to be joined, the ends can be displaced vertically with respect to each other.
2. Gusset. In this case, the ends are aligned at an angle. Welding process is carried out on adjacent edges of parts.
3. The overlap. The welding parts are located in parallel with the partial overlap.
4. End connection. The welded elements are aligned parallel to each other and docked at the ends.
5. T-joint. In this case, the end of one piece adjoins the lateral part of the other at an angle.

Welding joints also characterize the types of welding seams, which can be classified according to some criteria.

Weld indexes

There are several parameters on which it is possible to characterize all the welding seams obtained:

• Width is the size between the seam boundaries, which are drawn by the visible lines of fusion;
• Root of the seam - the reverse side of it, which is located at the maximum distance from the front;
• Convexity - is determined in the most convex part of the seam and is indicated by the distance from the plane of the base metal to the boundary of the largest projection;
• Concavity - this indicator is relevant if it takes place in the weld, because, in fact, it is a defect; This parameter is determined in the place where the seam has the greatest deflection - from it to the plane of the base metal, the size of the concavity is measured;
• Suture - it takes place only in the corner and T-joint; This is measured by the smallest distance from the side surface of one welded part to the boundary line of the seam on the surface of the second.

Types of seams by the method of execution

• One-sided welding seams. They are performed with full penetration of the metal along the entire length.
• Two-sided execution. On technology, after performing one-sided welding, the root of the seam is removed, and only then welding is performed from the other side.
• Single-layer seams. Performed single-pass welding with a single fused roller.
• Multilayered seams. Their use is advisable at a large thickness of metal, that is, when welding in one pass is not possible by technology. The seam layer will consist of several rollers (passes). This will limit the spread of the area of thermal impact and get a strong and high quality weld.

Types of welding seams by their spatial position and extent

There are such positions of welding:

• Bottom when the welded seam is in the lower horizontal plane, i.e. at an angle of 0 ° with respect to the ground;
• Horizontal, the direction of welding is horizontal, and the part can be at an angle from 0º to 60º;
• Vertical, in this position the welded surface is in the plane from 60º to 120º, and welding is carried out in a vertical direction;
• Ceiling, when the work is carried out at an angle of 120-180º, that is, welding seams are located above the master;
• "In the boat," this applies only to angular or T-joints, the part is set at an angle, and welding is carried out "into a corner."

Breakdown by length:

• Continuous, so almost all seams are performed, but there are exceptions;
• Intermittent seams, they occur only in the corner joints; Double-sided seams of this type can be performed in both staggered and chain-like order.

Edge cutting

This design feature is used when the thickness of the metal used for welding is larger than 7 mm. Cutting edges - is the removal of metal from the edges in a certain form. This process is performed when single-pass butt welds are welded. This is necessary in order to get the correct weld seam. As for the thick material, the cutting is necessary in order to melt the original root pass and then weld the next rolls, evenly filling the cavity, to weld the metal over the entire thickness.

Cutting edges can be performed if the metal thickness is not less than 3 mm. Because its lower value will lead to burns. Cutting is characterized by such design parameters: gap - R; Angle of cutting edges - α; Blunting - with. The location of these parameters shows the drawing of the welding seam.

Cutting edges increases the number of consumables. Therefore, this amount is tried in every possible way to minimize. It is divided into several types of constructive execution:

• V-shaped;
• X-shaped;
• Y-shaped;
• U-shaped;
• Crevice.

Features of cutting edges

For small thicknesses of welded material from 3 to 25 mm, one-side V-shaped cutting is usually used. Bevel can be performed on both ends or on one of them. Metal thickness of 12-60 mm is advisable to weld with two-sided X-shaped cutting. The angle α for cutting in the X, V form is 60 °, if the bevel is performed only on one edge, then the value of α will be equal to 50 °. For a thickness of 20-60 mm, the most economical is the consumption of the weld metal at U-shaped cutting. The bevel can also be made one at a time or at both ends. Blunting will be 1-2 mm, and the gap value will be 2 mm. For a large thickness of metal (over 60 mm), the most effective way is to slit the edge cutting. For a welded joint this procedure is very important, it affects several factors of the seam:

• Serviceability of the connection;
• Strength and quality of the weld;
• Economy.

Standards and GOSTs

1. Manual arc welding. Weld seams and joints in accordance with GOST 5264-80 include types, design dimensions for welding, covered with electrodes in all spatial positions. This does not include only steel pipelines.
2. Welding of steel pipelines. GOST 16037-80 - defines the basic types, edge cutting, structural dimensions with a mechanized welding method.
3. Welding of pipelines from copper and copper-nickel alloys. GOST 16038-80.
4. Arc welding of aluminum. Welded seams. GOST 14806-80 - shape, dimensions, preparation of edges for manual and mechanized welding of aluminum and its alloys, the process is carried out in a protective environment.
5. Under the flux. GOST 8713-79 - welding seams and joints are performed by automatic or mechanized welding by weight, on a flux cushion. It extends to a metal thickness of 1.5 to 160 mm.
6. Welding of aluminum in inert gases. GOST 27580-88 - standard for manual, semi-automatic and automatic welding. It is performed by a non-consumable electrode in inert gases with a filler material and extends to an aluminum thickness of 0.8 to 60 mm.

Designation of the weld

According to regulatory documents, the presence of welding seams is shown on assembly drawings or in general form. Welds are shown in solid lines, if they are visible. And if on the contrary - then dashed lines. Leaders with one-sided arrows are assigned from these lines. The designation of welding seams is carried out on the shelf from the leader. The inscription is made above the shelf, if the seam is on the front side. In the opposite version, the designation will be under the shelf. This includes information about the seam in the following sequence:

• Auxiliary signs. At the intersection of the leader with the shelf can be an icon:

○ - closed seam;

┐ - welding of the seam is done during installation.

• Designation of welding seams, their structural elements and GOST connection.
• The name of the seam according to the standard.
• Welding method according to regulatory standards.
• The catheth is indicated, this item only applies to corner joints.
• Intermittence of the seam, if any. Here you specify the step and location of the welding segments.
• Additional auxiliary value icons. Consider them a separate item.

Auxiliary Symbols

These signs are also applied on top of the shelf, if the welding seam in the drawing is visible, and under it, when invisible:

• Removal of reinforcement;
• Surface treatment, which will ensure a smooth transition to the base metal, eliminating rips and unevenness;
• The seam is performed on an open line; This mark applies only to the weld seams visible in the drawing;
• Cleanliness of surface treatment of the welded joint.

For simplicity, if all the seams of the structure are made according to one GOST, they have the same edges and dimensions, the designation and the welding standard are specified in the technical requirements. In the design may not be all, but a large number of identical seams. Then they are divided into groups and assign them serial numbers in each group separately. On one seam indicate the full designation. On the others, only serial numbers are placed. The number of groups and the number of seams in each of them must be indicated in the regulatory documentation.