Page 40 - Quick Guide to Welding and Weld Inspection by S.E. Hughes, Clifford Matthews

Analysis of a Fusion Weld

moisture and other possible weld contaminants. Internal
contaminants such as sulphur or oxides can be present
within the material and may also have to be removed or
neutralised during welding. In effect, the process must be
able to ‘clean’ the material and weld pool during welding
to afford the correct protection. Protection from con-
taminants can be achieved by:
○ mechanical cleaning of the component (grinding, wire
brushing, abrasion, etc.);
○ chemical cleaning of the component and filler wire/rods
(acid, acetone, etc.);
○ use of a flux (containing deoxidisers);
○ use of correct polarity (d.c. +ve or a.c. when welding
Al or Mg alloys to remove the surface oxide layer,
called cathodic cleaning).
. Adequate mechanical properties. The finished welded joint
must have adequate properties such as strength, tough-
ness, hardness and ductility in the base material (including
the HAZ) and weld metal. These properties are achieved
(depending on the welding process) by:
○ using the correct base materials;
○ using the correct consumables (filler wire, electrodes,
shielding gas, flux);
○ using correctly prepared consumables (correctly heat-
treated electrodes, etc.);
○ using the correct pre-heat and/or post-weld heat
treatments;
○ using the correct heat inputs (voltage, current and
travel speeds).
All of the above factors can be achieved by adhering strictly
to the requirements of an approved welding procedure
specification, which contains the essential, supplementary
essential (ASME IX only) and non-essential variables
necessary to produce a sound weld.
In practice, when welders get lazy, take shortcuts and do
not fully comply with a correctly tested and qualified welding

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Woodhead Publishing Ltd – A Quick Guide to Welding and Weld Inspection
Data Standards Ltd, Frome, Somerset – 17/9/200903QG Welding chap3.3d Page 25 of 35