Page 56 - Quick Guide to Welding and Weld Inspection by S.E. Hughes, Clifford Matthews

Materials and Their Weldability

gas absorption (due to poor shielding) or by dissolving
contaminants such as dust (iron particles) on the surface.
On the positive side, solidification cracking and hydrogen
cracking are not normally found in titanium or its alloys.
A thin layer of surface oxide generates an interference
colour at the weld that can indicate whether the shielding was
adequate or not. Typical colours are as follows:
. Silver or light straw is acceptable.
. Dark blue may be acceptable for certain service condi-
tions.
. Light blue, grey, white or yellow powders are not
acceptable.
Defect avoidance
Titanium is very expensive and many defects can be avoided
if the following precautions are taken:
. Avoid steel fabrication operations near titanium compo-
nents.
. Have dedicated tools used only for titanium.
. Scratch-brush the joint area immediately before welding.
. Do not handle the cleaned component with dirty gloves.
. Cover components to avoid airborne dust and iron
particles settling on the surface.
. Maintain adequate shielding gas, trailing gas and purging
gas levels.
. In short – keep it clean.
Duplex stainless steel
Duplex stainless steels have a two-phase structure consisting
of almost equal parts of austenite and ferrite. They have
become very popular because they are approximately twice as
strong as common austenitic stainless steels but less
expensive, owing to the lower levels of nickel they contain.
The characteristic benefits of duplex stainless steels (strength,
toughness, corrosion resistance and resistance to stress

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Woodhead Publishing Ltd – A Quick Guide to Welding and Weld Inspection
Data Standards Ltd, Frome, Somerset – 17/9/200904QG Welding chap4.3d Page 41 of 48