Welds
are particularly susceptible to fatigue cracking not because
they are highly loaded but because
| 1. |
Slag and other defects they contain act as stress raisers. |
| 2. |
The
presence of residual tensile stress in a weld also increases
the total value of tensile stress when load is applied. |
Following
can cause these stress raisers:
1. Internal material defects such as slag, gas porosity, and
existing cracks, but they may also be
2. Due to sharp changes in section caused by poor design or
surface damage.
3. Surface damage during overhaul causes stress raiser effects
whilst
4. Over tightening of bolts induces a higher static stress
In some
situations such as piston crown it may be very difficult to
detect cracks due to scale and other deposits. Likewise during
the ballast tank inspections the areas usually that have cracks
can be short-listed based on the above criteria. The stress
risers must be identified and a closer inspection in such
areas should be carried out.
DO
WHATEVER YOU CAN TO TRY AND AVOID SUCH FAILURES!!
-
Article contributed by Technical Superintendent K Srinivas
Patnaik.
|
