Root Opening (Definition, Why and more) 👨‍🏭 2022

Also known as:
  • Gap
  • Joint opening
  • Root gap


A separation at the joint root between the workpieces.

Note: The root opening is the smallest distance separating the members to be joined.

Examples: Butt and Angle Joint

Depending on the end use or service condition of the welded joint, the welding engineer or designer can choose between an open or narrow root. 

Closed roots occur when adjacent metal touch, with no gap or space between the two. 

On the other hand, an open root has a predefined opening or space.

Why do we need root opening?

We usually set a distance for easy access with the electrode or torch and thus ensure complete penetration. 

This opening can also allow welding on one side only, being necessary for some specifications and standards of welded equipment.

When is root opening not required?

When there is no need for full penetration, also known as partial penetration, this is usually the case for a “no liability” weld. 

When there is a requirement for full penetration, great care must be taken as a subsequent gouging or grinding operation is required. 

The absence of root opening is generally not recommended in manual welding processes for quality reasons (to ensure penetration) and for productivity as well.

Which is the ideal root opening?

There are a number of factors that can also guide the decision to use an open or closed root assembly when welding. 

Perhaps most important is the thickness of the base metal we are trying to put together. Small thickness materials do not tolerate a large root opening for most welding processes. 

Thicker materials, on the other hand, should use more open root joints to improve weld penetration. The welding position also affects how much opening we use. 

If we are welding in the flat position, the liquid in the weld pool may fall out completely if we use a large root opening. 

The type (or quality) of the material to be welded can also influence whether or not we use a more open or closed root. 

In any case, knowledge of the metallurgy of materials and the experience of the welder are of great value in choosing and defining the root opening.

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Materials: Root Opening (Definition, Why and more) 👨‍🏭 2022
Root Opening (Definition, Why and more) 👨‍🏭 2022
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