Page 121 - Quick Guide to Welding and Weld Inspection by S.E. Hughes, Clifford Matthews

Fracture Modes and Welding Defects

Figure 7.16 Undercut

fatigue fracture can propagate. Undercut is normally
assessed by length, depth and profile (sharp or smooth)
with acceptance specified by the design code. Causes of
undercut include:
. excessive amps/volts;
. excessive travel speed;
. incorrect electrode angle;
. incorrect welding technique;
. electrode too large.
Crater pipe
A crater pipe results from shrinkage of the weld pool on
solidification. It is usually caused by switching off a high
welding current or breaking the arc resulting in the rapid
solidification of a large weld pool. It can be effectively
prevented when using the TIG process by progressively
reducing the welding current (using a slope-down control) to

105

Woodhead Publishing Ltd – A Quick Guide to Welding and Weld Inspection
Data Standards Ltd, Frome, Somerset – 17/9/200907QG Welding chap7.3d Page 105 of 107