Weld seam preparation for TIG welding : for high quality welds

When it comes to orbital TIG welding, the seam preparation is essential in order to obtain optimum quality weld.

Here you can find information exploring, the standardized codification as well as types and modes of assembling.


Welding thin tube

A weld seam preparation is not needed for tubes with a small wall thickness of less than 3 mm (less than 0.118”). For thicker tubes weld seam preparation is a must to ensure good welding execution.

During the squaring operation, a tool machines the end of the tube. Every time a highly precise surface finish quality is required, tube squaring is the best solution. 


What about thicker tube ?

When welding a joint with a bevel, several welding passes will be necessary during the orbital welding process.  Different end preparations will be used to weld J or V bevels.

Read more about the importance of pipe end preparation bevel before welding.

We do not recommend a V bevel in orbital TIG welding, as the final result will not be acceptable. The weld seam will have a hollow root and a negative penetration. In order to avoid this, you would choose a J bevel with a land of about 2 mm / .080” (according to the thickness of the tube). Then you will need to fill the groove.


So, two kinds of preparations are compatible:

  1. Tulip (J Bevel) without counterboring : pipe between 3 and 10 MM / .118" - .390" wall ( for reference only)
  2. Tulip bevel with counterboring: pipe thickness > 10 MM/ >.390" wall

Counterboring consists in a slight machining of the internal diameter of the pipe in order to guarantee an equal thickness of the land at any point.

In fact, differences of the thickness of the land can also lead to irregular thicknesses at the edge of the tube.

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Orbital welding : standardized codification,
types and modes of assembling codification

Technical welding specifications generally contain letters which indicates the position of the welding assembly for the test position. The standard NF EN 288-3 describes the various codes (for information: the standard NF 3N 15614-1:2005 replaced the NF EN 288-3 from June 1992 and its amendment of the 1st of August 1992. The types and modes of assembling are not concerned by this modification).

In the United States, the ASME Bioprocessing Equipment (BPE) standard is a certification which provides requirements on how to design and build equipment and systems used in the production of bioprocessing and pharmaceutical industries.



  • P: Sheet / Plate
  • T: Tube / Pipe
  • B: Butt welding
  • FW: Angle assembly
  • P-BW: Sheet / Plate butt welding
  • T-BW: Tube / Plate butt welding
  • P-FW: Sheet / Plate filled weld
  • T-FW: Tube / Plate filled weld

  • SS: welding at one side
  • BS: welding at both sides
  • NG: no back gouging
  • GG: with back gouging
  • NB: welding without backing gas
  • MB: welding with backing gas
  • SS.NB: welding at one side without backing gas
  • SS.MB: welding at one side with gouging or backing gas

Note: some welders use the term “NG” for Narrow Gap welding!

The preparation of a good bevel before welding is essential. In this way you will obtain a clean and high quality weld.

Discover all our beveling machines in our catalogues.

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Écrit par
Alicia Wendland

Marketing Manager