Back weld and backing weld Symbol

Back weld and backing weld Symbol Back weld and backing weld (backing run) Symbol are same and they are basic weld symbols. In the AWS system, it’s possible to indicate whether a symbol represents a back …

Back weld and backing weld Symbol

Back weld and backing weld Symbol

Back weld and backing weld (backing run) Symbol are same and they are basic weld symbols. In the AWS system, it’s possible to indicate whether a symbol represents a back weld, a backing weld, or a run by writing “BACK WELD” or “BACKING WELD” in the tail of the reference line, as illustrated in the figure below.

The example in the figure below depicts a single-V groove/butt weld and an alternative AWS system that uses two reference lines to show the order of operations. In both cases, the first operation is represented by the reference line closer to the arrow.

Here, left hand side symbol shows a Back weld where groove is first welded followed by back run welding.

right hand side welding symbol represents a backing weld joint, where first a backing weld is deposited on the root side followed by welding the complete groove.

What is Back weld and backing weld?

A back weld refers to a weld made on the side of a joint opposite to the side that is visible or accessible during welding. This type of weld is typically used to reinforce or provide additional strength to the joint.

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Difference between Back weld and backing weld?

A back weld is created on the opposite side of a groove or butt weld after the main weld has been completed. On the other hand, a backing weld is done before the main weld is made.

ISO Back Run Weld and Backing Run weld Symbol

The “ISO Backing Run Weld” symbol is used to indicate a weld made on the back side of a groove weld to provide support and prevent the weld metal from falling through the joint. It is represented by a straight line with a half circle placed on the reference line as shown in below figure.

Note: A Back Run or Back weld is made after the Groove weld is welded from face side while a Backing weld is made before welding the face side of the groove weld.

Example of Backing Welding Symbol

In below example, a back weld is made after welding the face side groove. Here, first groove is completely filled and then back weld is deposited on the other side of the weld.

Backing weld vs Melt through welding symbol

The “Backing Weld” symbol is used to indicate a weld made on the back side of a groove or butt joint to provide support and prevent the weld metal from falling through the joint.

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The “Melt-Through Welding” symbol is used to indicate a weld in which the weld metal penetrates through the joint and melts through to the other side. 

The key difference between these two symbols is that the “Backing Weld” symbol indicates that the weld is made on the back side of a joint for support, while the “Melt-Through Welding” symbol indicates that the weld penetrates through the joint and melts through to the other side.

A Backing weld symbol is similar to melt-thought although it is not dark in color like melt-through symbol. Below is an example of a Melt-through welding symbol for a V-Groove Weld.


Sandeep Kumar is a highly experienced welding professional and author known for his expertise in welding symbols. With certifications including IWE, AWS-CWI, and ASNT NDT Level III.

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