Joint types and welding positions

A weld is only as good as the preparation of the joint it is laid in. The joint type and joint preparation determine how the welding wire can penetrate and bind the material together, and the welding position determines how difficult the work is to perform.

The joint type describes how the parts are positioned relative to each other. The most common are the butt joint, where two plates or pipes meet edge to edge (butt weld, BW on the certificate), and the fillet weld (FW on the certificate), where the parts meet at an angle — for example a T-joint or a corner joint.

• 01Butt joint: the parts meet edge to edge
• 02T-joint: one component stands perpendicular to another
• 03Corner joint: the items meet in a corner
• 04Overlap joint: the parts lie partially on top of each other

With thicker material it is often necessary to prepare the edges so the weld can penetrate completely. This can be grinding or cutting a chamfer on the edge so a V or X groove is formed and adjusting a suitable root gap between the workpieces. The preparation ensures good fusion in the root of the weld.

The welding position describes the orientation of the workpiece and the weld seam in space. Welding horizontally downward is easiest because the molten metal pool lies nicely. Vertical and overhead are harder because gravity pulls on the molten metal. The positions have standardized designations used in both training and certification.

Typical postures

• 01Horizontal downward: the melt pool lies calmly, easiest to weld
• 02Horizontal on vertical surface: requires control of the pool
• 03Vertical: can be welded up or down with different techniques
• 04Over the head: the hardest requires good craftsmanship

The standard ISO 6947 (4th edition from 2019) gives each main position a code. The codes appear in welding procedures, in the AMU objectives and on your certificate.

• 01PA: Flat, welded from above (flat position)
• 02PB: Horizontal-vertical (fillet weld, welded from above)
• 03PC: Horizontal weld on a vertical wall
• 04PD: Horizontal overhead (fillet weld, welded from below)
• 05PE: Overhead
• 06PF: Vertical, welded upwards
• 07PG: Vertical, welded downwards
• 08PH: Pipe, welded upwards
• 09PJ: Pipe, welded downwards
• 10PK: Pipe, orbital welding (welded all the way round)

There are also test positions for pipes lying at an angle, e.g. H-L045: the pipe is inclined at 45°. Such positions have been included in the standard since the 2011 edition.

When you weld a test piece, the part may deviate no more than ±5° in slope and ±10° in rotation from the main position. If a test is welded in a position outside the main positions (a special test position, SP), the slope and rotation must be recorded, and in production it then covers ±15°.

Abbreviations on the certificate

• 01BW: butt weld
• 02FW: fillet weld
• 03P: plate
• 04T: pipe
• 05t: the material thickness
• 06D: outside diameter of the pipe

An example from the blacksmith training regulations: the AMU objective «Lys b svejs-stumps plade pos PA-PF» says «BW-P-PA, 2-n strenge». That means a butt weld in plate, welded in the flat position, with two or more runs.

Both weld type and welding position are included in what a welding certification is valid for. A test in one position and joint type does not necessarily cover all others. That's why training is done consciously in the positions and weld types that the work and test require.

Horizontal positions are learned quickly but vertical and overhead positions require more training. Mastering them makes the welder versatile and able to perform welds where the object cannot be turned to the easy position.