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A
few examples of Pressure Vessel Design / Analysis performed by Pressure Equipment
Engineering Services, Inc. are as follows in PDF format:
Here
are some more examples:
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Fitness for service
evaluations were performed for hundreds of vessels and heat exchangers
experiencing generalized corrosion. Based on the half life criteria of
the inspection codes, more frequent inspections must be performed for
these vessels and heat exchangers to avoid violating the code or
jeopardizing the safety of the equipment. In some cases, these vessels
and exchangers start approaching scenarios indicating life depletion
because of the loss of intended corrosion allowance. The code
calculations are performed (using Pressure Vessel & Heat exchanger
COMPRESS) for each component of the vessel / exchanger to
calculate the minimum retirement thickness for that component for the
intended design parameters. The combined set of minimum thickness for
all components acts as a guide for future inspection interval for the
vessel / exchanger. The calculated minimum thickness values are
compared to the actual field measured values to make sure that there
is sufficient future safe and useful life available for all the
components of the vessel / exchanger. If enough life is not available
for several components, then de-rating of vessel / exchanger may be
necessary. In case one or two components are limiting the MAWP, local
repairs may be specified to maintain the original MAWP of the vessel /
exchanger.
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Fitness for service
evaluation was performed for several pressure vessels experiencing
temperature lower than the MDMT. The fitness for service criteria was
used to evaluate the MSOT (Minimum Safe Operating Temperature) for the
vessel. Based on the evaluation, it was concluded for some cases that
the MSOT for the vessel was below the intended temperature of
operation and thus the vessel was re-rated to the lower requested
temperature. However, when the MSOT for the vessel is above the
intended temperature of operation, the vessel can not be re-rated to
the lower requested temperature.
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Fitness for service
evaluation for several tall vessels was performed before being
subjected to in-situ PWHT at temperature of 1150 °F. Sometimes the
vessel is heat treated for the circumferential zone containing the
repair areas and at other times, the vessel is heat treated using gas
firing such that the entire vessel is subjected to PWHT temperature.
The actual vessel stresses due to dead weight and wind loading are
calculated at the location of the circumferential PWHT zone and
compared to the allowable stress values. For cases where the actual
stresses are within the allowable stresses, the vessels can be post
weld heat treated without any external support. For the other cases,
it is found that the vessel stresses exceed the allowable stress
values. In these cases, it is recommended that the vessels must be
supported with the help of a crane before PWHT is performed for the
circumferential vessel zone.
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Fitness for service
evaluation was performed for the top bed of a stainless steel reactor
with the intent to calculate the maximum permissible pressure
differential allowed by the structural capacity of the bed. The packed
bed had 3 distinct stainless steel fabricated beams. The bed was
getting plugged during operation. This was causing significantly
higher pressure drop on the bed leading to very high stresses in the
beams. The intent was to shut down the reactor before the pressure
drop reaches a scenario causing the structural failure of the bed. The
structural calculations (per AISC code) were performed to check the
stresses in the beams, welds and the beam support grating. These
structural calculations were automated using MathCAD to
calculate the maximum allowable pressure drop through the bed for
design case, upset case and failure case. For each of these cases, the
limiting pressure drop for the three distinct structural beams and the
associated grating support was calculated. The design pressure drop
through the reactor bed was 100 psig. The maximum allowable pressure
drop for the upset case was specified to be 138 psig. At this pressure
drop, all the design criteria were satisfied and this pressure drop
was safely permissible. The maximum allowable pressure drop for the
failure case was specified to be 158 psig. At this pressure drop, the
code allowable stress criteria were not satisfied and the structural
components start to yield. Using the pressure drop guidelines
specified by these set of calculations, the plant increased the safe
operating time before the next shut down.
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Fitness for service
evaluation for a large spheroid vessel experiencing general corrosion. FEA using ANSYS was performed to complete the evaluation. The
life of the vessel got extended by a few years. Some
details of this analysis are enclosed
herewith in the PDF format.
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Fitness for service
evaluation for a horizontal reactor vessel for higher design loading.
FEA using ANSYS was performed to complete the evaluation. The
results of the analysis indicated that we did not need additional
stiffener rings as was being pointed out by conventional stress
analysis. Some
details of this analysis are
enclosed herewith in the PDF format.
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Fitness for service
evaluation for the bottom head of a reactor experiencing pitting
corrosion. FEA using ANSYS was performed to complete the
evaluation. The life of the vessel got extended by a few years. Some
details of this analysis are enclosed
herewith in the PDF format.
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