Definition and Purpose
Backing is the material or device (non-consumable) placed on the back side of the joint to be welded.
But it may also be placed on both sides (in the case of electroslag and electrogas processes).
It's purpose is to support the molten metal during the execution of the welding.
By holding the weld pool, backing prevents the leakage or loss of molten weld metal and facilitates full penetration.
- Allows full penetration of the joint.
- When full penetration is required and the parts to be welded are large, there is no need to turn or reposition the part for gouging. This can be a big improvement in productivity.
- It takes time to install it. For small parts it may be more advantageous to weld on both sides.
- The backing must be kept dry in order to avoid moisture and hence the addition of hydrogen or weld defects.
Backing can be partially fused as it does not necessarily need to fuse during soldering. The material can be metallic or non-metallic.
- Weld bead.
- Metallic (usually the base metal).
- Iron powder.
Please note that:
- Backing can be permanent or temporary. In some cases it may not be permissible or desirable to leave backing where they were used. Welded equipment or structures subject to significant cyclic stresses must not have the backing left in position.
- It should be noted that welding using a ceramic backing requires more training than in the case of a steel backing.
We generally consider the weld on both sides of a butt joint as a backing weld.
This is because the first weld we made is the backing of the second weld, thus supporting its molten material. The same as:
- When we weld by one side, using a different welding process in the root. For example: A typical TIG and SMAW welding.
TIG welds the root and is considered a joint without backing. SMAW is considered to be a backing weld due to the presence of the root made with TIG.
In welding procedure qualifications, some welding standards classify the use of backing as an essential variable (eg DNV-OS-F101) while others consider it a non-essential variable (eg ASME section IX).
In the case of DNV-OS-F101, it is noteworthy that even the change in the type of the backing is considered an essential variable.
Considering welder's qualification, most standards consider the presence or absence of backing as an essential variable.
The fact that a welder produces quality welds on a joint with backing does not demonstrate that he is capable of doing the same in a joint without one.
The absence of a backing increases the difficulty in performing a weld. The fact that a welder performs a weld without backing demonstrates that he is also capable of producing quality welds with a backing.
When you need to include a fact or piece of information in an assignment or essay you should also include where and how you found that piece of information (Backing).
That gives credibility to your paper and it is sometimes required in higher education.
To make your life (and citation) easier just copy and paste the information below into your assignment or essay:
Luz, Gelson. What is Backing (Definition, Purpose, Benefits). Materials Blog. Gelsonluz.com. dd mmmm. yyyy. URL.
Now replace dd, mmmm and yyyy with the day, month, and year you browsed this page. Also replace URL for the actual url of this page. This citation format is based on MLA.