QW-402.4 The deletion of the backing in single welded groove welds. Double‐welded groove welds are considered welding with backing.
Note: From 1980 to 2019, this variable underwent many revisions, to fully understand backing, we need to review the definition of backing in definitions section.
Backing: a “material” placed at the root of a weld joint for the purpose of supporting molten weld metal so as to facilitate complete joint penetration. The material may or may not fuse (retainer) into the joint.
Backing gas: a gas, such as argon, helium, nitrogen, or reactive gas, which is employed to exclude oxygen from the root side (opposite from the welding side) of weld joints.
These two definitions address two different things. However, they are treated nearly the same, Do not confuse “Backing” vs “Backing gas”. The Backing gas essential defined in QW-408.5
Specially, on Double bevel welded groove (welded from both side, back-gouging and weld), the Backing is considered as filler metal from other side.
For practical purposes, backing is usually thought of as either a “Backing strip”, “Ceramic backing”, “double-welded joint”, or “as filler metal”. Be careful on how to address it on WPS so that the users understand it.
Review Table QW-253 in general welding processes, on the Nonessential Variables. The nonessential variables are items that must be considered and addressed on WPS, however, they need not be considered nor addressed on the PQR. Note that a PQR can be in compliance with ASME IX even if nonessential variables are not addressed or are incorrectly addressed on PQR.
Come back the definition of Nonessential: ASME IX has already given the Minimum Variables that must be considered. Nonessential variables normally will not affect the mechanical properties of a weldment.
There’s no guarantee, however, the nonessential variables will not affect the mechanical properties of a weld. Because ASME IX assumes that manufacturers have access to welding engineers as well as a metallurgist. ASME IX is not a “How to Weld” book, but be intended to be used by who know well on welding and are familiar with welding metallurgy.