Page 104 - Quick Guide to Welding and Weld Inspection by S.E. Hughes, Clifford Matthews

Chapter 7

Fracture Modes and Welding Defects

Imperfection categories
Imperfections can be broadly classified as those formed
during fabrication and those formed during service.
Fabrication imperfections include:
. Cracks
. Porosity and cavities
. Lack of fusion
. Solid inclusions
. Profile imperfections
. Wrong sizes
Service failure modes include:
. Brittle fractures (cracks)
. Fatigue fractures (cracks)
. Stress corrosion cracking (SCC)
. Re-heat cracking
. Creep failure
Cracks
Cracks can be classified by shape (longitudinal, transverse or
branched) and position (HAZ, base metal, centreline, crater).
An inspector will rarely classify a crack as a particular type
(i.e. fatigue, HICC or SCC) because in most cases it will not
be possible to determine the precise cause of a crack until an
examination is carried out. The shape and position are facts,
anything else is supposition.
Hydrogen-induced cold cracking (HICC)
HICC may occur in the HAZ of all hardenable steels (i.e. C,
C/Mn) or in the weld metal of high strength low alloy
(HSLA) steels that are microalloyed with small amounts of
titanium, vanadium or niobium (typically <0.05%). The

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Data Standards Ltd, Frome, Somerset – 17/9/200907QG Welding chap7.3d Page 88 of 107