Backing strip symbol
Also called Backing bar, Backing
A backing strip is a bar or strip under the root of a groove weld that supports the weld metal. It either stays in place or is removed after welding.
What the backing strip symbol means
A backing strip is a bar or strip under the root of a groove weld that supports the weld metal. It either stays in place or is removed after welding.
AWS A2.4 and ISO symbols
Permanent backing strip (M). M in a rectangle for a permanent backing strip, MR for a removable one.
ISO SVGWhere you see it
Groove welds made from one side, such as box sections and joints that cannot be reached from the back.
How it is inspected
Inspection of a backing strip usually covers fit-up and root gap before welding and, for removable backing, the root once the backing is off. Each inspection is recorded against the weld, so the joint can be signed off with its evidence. See the ITR guide.
Related symbols
Frequently asked questions
What does the backing strip symbol look like?
On AWS A2.4 drawings: A rectangle on the side opposite the groove symbol. An R inside means the backing is removed after welding. In ISO 2553: M in a rectangle for a permanent backing strip, MR for a removable one.
Is the backing strip symbol the same in ISO and AWS?
No. M in a rectangle for a permanent backing strip, MR for a removable one.
Where is a backing strip used?
Groove welds made from one side, such as box sections and joints that cannot be reached from the back.
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