| Situation:
The equipment had progressive wear and high temperature
deterioration which were believed to be the cause of repeated
refractory failures and shell fatigue cracks during operation.
Several unscheduled shut downs were required to inspect and
repair the shell and refractory, interrupting plant production
and causing undesirable plant shut down/start up cycles. The
cause of the wear and high temperature deterioration on the
equipment was known. What was needed was confirmation that the
observed wear and high temperature deterioration resulted in the
refractory failures and shell fatigue cracks. Ultimately, a
remediation design was needed to prevent the unscheduled shut
downs from occurring in the future.
Solution:
A three-dimensional stress finite element model (FEM) was built
for the original equipment design. This FEM was used to
determine original shell deflections and stresses which were
known to be acceptable. The model was then modified to account
for the deteriorated condition to understand how deflections and
stresses changed over time and to confirm that theses changes
were the cause of the observed failures. External stiffening
rings were added to the FEM to achieve deflection and stress
values equal to or lower than the original design. A remediation
design fix was prepared for installation in the field.
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