Hydrocarbon Processing - April 2022 - 27

Special Focus Maintenance and Reliability
S. RUPESH, Consultant, Kerala, India
Mechanical impact of rerating process equipment
Process equipment operating in a
brownfield environment is often rerated
pertaining to the changes in process parameters
during debottlenecking. Rerating,
with regard to process equipment,
means redesigning the equipment to adhere
to new rerated conditions.
Often, the design pressure and design
temperatures are increased, and the equipment
must be reevaluated for more severe
design conditions-this is known as uprating.
It is very important to reverify the
mechanical design of the existing equipment
to meet the new rerated conditions.
Most of the existing equipment would be
nearing the end of its life, and the impact
of corrosion over the years would, most
likely, be substantial. Therefore, it is necessary
to reevaluate whether the equipment
has sufficient corrosion allowance
until the next inspection or whether the
equipment should be retired from service.
Rerating existing equipment can be cost
effective vs. purchasing new equipment.
The author has been involved in many
rerating studies to check the mechanical
design adequacy for existing equipment.
The following are important considerations
when reverifying the mechanical
design for process equipment.
Existing equipment drawings. Before
starting any design verification, it is important
to have existing drawings of the
equipment. It is often noticed that there
will be a lack of existing documentation.
At times, only general arrangement drawings
will be available and detailed drawings
may be missing, or vice versa. Make
sure you have legible copies of drawings.
A good place to start is looking at the final
data book for the equipment submitted
by the original manufacturer, if available.
However, for older equipment, data
books may not be available. Any subsequent
revisions, modification drawings
by the same or different manufacturer, or
marked-up drawings must be traced out,
as they can provide vital information.
Once the relevant drawings are obtained,
review them meticulously to
understand the modifications that have
been made on the equipment chronologically,
along with the present status of
the equipment. Try to obtain any other
available documents, such as the original
manufacturer's design calculations, inspection
documents, material certificates,
the manufacturer's data reports and/or
previous equipment inspection reports.
All of these documents will eventually
contribute significantly to understanding
and finalizing the rerating study.
Site visit/interaction with operations
personnel. Once you are familiar
with the drawings, conduct a site visit
with the operations personnel in charge of
the area. Physically see where in the plant
the equipment is located to verify that the
equipment matches the drawings. Operations
team members should know much
more about the equipment than other
personnel, and they will be helpful in clarifying
the missing links that may not appear
on drawings. Record all information
provided by the operations personnel.
Since this is an important step at the
beginning of the process, it is suggested to
go to the site with a fresh copy of existing
drawings, and to mark up any visible ambiguities
on the drawings. For example,
if an additional nozzle is shown on the
equipment, mark it on your drawing copy.
Every intricate detail visible on the equipment
should be marked up on your copy
and clarified with the operations personnel.
This exercise will help to understand
chronological changes in the equipment.
Engaging the inspection team or
third-party
inspectors. Conduct a
meeting with the onsite inspection team
or have a third-party inspection compaEquipment
modeling and design
calculations. Equipment should be
Hydrocarbon Processing | APRIL 2022 27
ny carry out the equipment inspection.
Share all the information available, along
with marked-up copies. Highlight all the
ambiguities found during the site visit,
record them, and make a meeting log, as
this will help to obtain more accurate results
during the actual inspection of the
equipment. Accurate thickness checks
should be done using available advanced
technology (e.g., infrared checks) to determine
shell thinning, and to inspect
heads, nozzles and other pressure-retaining
parts. This is equally important for
supports and external attachments. Photographs
of internal areas and external
parts should be included in the inspection
report for additional clarity. The inspection
report should be prepared comprehensively
and should clearly mention the
areas of concerns found by the inspector.
Inspection report and rerating process
conditions. After
receiving the
inspection report, review it carefully and
check for any points that can potentially
derail the design reverification process.
Anything abnormal on the inspection report
should be discussed with the owner
and sorted out prior to commencing the
design reverification activity. Ensure that
the rerating process conditions are available
for each piece of equipment.
Sometimes, there will be fluctuating
process parameters, such as temperature
and pressure. In such cases, check to see if
the owner can provide the complete table
with the corresponding values relevant
to that equipment. Since the allowable
stresses change with temperature,
it
is
important to have this table to determine
the required thickness, as sometimes an
odd combination of pressure and temperature
can have detrimental effects on
the equipment design.

Hydrocarbon Processing - April 2022

Table of Contents for the Digital Edition of Hydrocarbon Processing - April 2022

Contents
Hydrocarbon Processing - April 2022 - Cover1
Hydrocarbon Processing - April 2022 - Cover2
Hydrocarbon Processing - April 2022 - Contents
Hydrocarbon Processing - April 2022 - 4
Hydrocarbon Processing - April 2022 - 5
Hydrocarbon Processing - April 2022 - 6
Hydrocarbon Processing - April 2022 - 7
Hydrocarbon Processing - April 2022 - 8
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Hydrocarbon Processing - April 2022 - 11
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Hydrocarbon Processing - April 2022 - 88A
Hydrocarbon Processing - April 2022 - 88B
Hydrocarbon Processing - April 2022 - 89
Hydrocarbon Processing - April 2022 - 90
Hydrocarbon Processing - April 2022 - Cover3
Hydrocarbon Processing - April 2022 - Cover4
Hydrocarbon Processing - April 2022 - GP-1
Hydrocarbon Processing - April 2022 - GP-2
Hydrocarbon Processing - April 2022 - GP-3
Hydrocarbon Processing - April 2022 - GP-4
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Hydrocarbon Processing - April 2022 - GP-10
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Hydrocarbon Processing - April 2022 - GP-19
Hydrocarbon Processing - April 2022 - GP-20
Hydrocarbon Processing - April 2022 - GP-21
Hydrocarbon Processing - April 2022 - GP-22
Hydrocarbon Processing - April 2022 - GP-23
Hydrocarbon Processing - April 2022 - GP-24
Hydrocarbon Processing - April 2022 - GP-25
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Hydrocarbon Processing - April 2022 - GP-27
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