Hydrocarbon Processing - May 2022 - 84

Valves, Pumps and Turbomachinery
er in June 2008 that killed one worker and injured six others at
the Goodyear Tire and Rubber Co. in Houston, Texas.1
One of
PRDs requiring onstream maintenance are,
in general, provided with isolation valves on
inlet and outlet (if applicable) pipelines. ASME
code requires administrative controls to be
in place for proper operation of the isolation
valves in the relief path so the equipment's
overpressure protection is not compromised.
the root causes of this accident was failure to properly follow
the procedure of opening the PRD inlet piping isolation valve
before placing the heat exchanger into service.
Option 3. This is the least preferred option, as it involves
operating the process equipment without overpressure protection
under administrative controls. One of the first things
that the plant operator is required to do in this option is to
identify all potential overpressure sources beforehand and attempt
to eliminate or minimize the likelihood of overpressure
from such sources for the duration of the PRD maintenance.
In this option, assuming that there are isolation valves in place,
the PRD must be first isolated by closing the inlet and outlet
isolation valves before the maintenance can begin. Closure of
the isolation valves would lead to blocking the relief path and
to operating the protected equipment with a risk of overpressure.
Plant operators are required to stay in compliance with
the ASME code for proper implementation of administrative
controls. ASME BPVC-XIII Appendix B-7(d) states:
" Procedures are in place to provide pressure relief
protection during the time when the system is isolated
from its pressure relief path. These procedures should
ensure that, when the system is isolated from its
pressure relief path, an authorized person should
continuously monitor the pressure conditions of the
vessel and should be capable of responding promptly
with documented, pre‐defined actions, either stopping
the source of overpressure or opening alternative
means of pressure relief. This authorized person should
be dedicated to this task and should have no other
duties when performing this task. "
Plant operators should consider several factors to safely rely
on administrative controls for monitoring unprotected equipment.
One such factor is the duration of maintenance. Can the
relief device be returned to service in a reasonable amount of
time? Another factor is training. What kind of training would
be required for authorized persons to respond promptly in an
event of pressure excursion in the process service? If possible,
process engineers and plant operators should steer away from
this option, as this involves several factors that cannot be fully
accounted for during the plant design.
Multiple overpressure scenarios. There can be more than
one overpressure scenario that is applicable for a PRD. Over84
MAY 2022 | HydrocarbonProcessing.com
LITERATURE CITED
1
U.S. Chemical Safety and Hazard Investigation Board, " Goodyear Heat
Exchanger Rupture, " January 2011 (report released), online: https://www.csb.
gov/goodyear-heat-exchanger-rupture/
2
ASME Boiler and Pressure Vessel Code, Section XIII-2021, " Rules for overpressure
protection. "
PRANAY K. NAMILAKONDA is a Process Engineer with Samsung Engineering
America, a global EPC firm based in Houston, Texas. He is a licensed professional
engineer and has more than 15 yr of experience in front-end engineering execution
of various hydrocarbon projects. He also leads the process engineering group,
with an emphasis on engineering automation. Mr. Namilakonda earned an MS
degree in chemical engineering from Oklahoma State University, and a BTech
degree in chemical engineering from Osmania University, India.
pressure due to an external pool fire is a well-known scenario
that is applicable for process equipment at grade level. Additional
overpressure scenarios include blocked outlets
and auto-control failures, among others (see API 521
for more information). The process engineer should
review all applicable overpressure scenarios when
determining the need for a spare PRD.
It is a generally accepted industry practice not to
provide spare PRDs in the following applications, as
the PRD maintenance interval typically aligns with
the protected system maintenance interval:
* PRDs installed exclusively for protecting
equipment from external fire (fire-only PRD)
* PRDs installed in cooling water service
exclusively for protecting the equipment from
thermal expansion (cooling water thermal).
Multiple PRDs. Multiple PRDs are often provided when a
single PRD is not adequate to handle the required relief flowrate.
The ASME code allows staggering the PRD set pressures
in this case. For multiple PRDs:
* A single spare PRD may be installed with the basis
that administrative controls are in place to perform
maintenance on one PRD at a time. When a single spare
PRD is installed, performing maintenance on multiple
PRDs would result in inadequate relief protection,
which is a possible code violation.
* The spare PRD should have an orifice flow area
identical to the operating PRD with the largest area.
* When the spare PRD is put into operation, at least
one PRD should have a set pressure at 100% of the
maximum allowable working pressure.
Takeaway. The ASME code does not mandate installing a
spare PRD. However, in the absence of an alternate and adequate
relief path, the ASME code mandates the implementation
of proper administrative controls for safe isolation and
subsequent monitoring of the protected system for the duration
of PRD maintenance. Administrative controls play a
critical role in the safe operation of any plant, and many plant
operators prefer to install a spare PRD to provide an adequate
and equivalent overpressure protection. Process engineers
and plant operators must be conversant with the applicable
regulatory requirements and must review all PRDs on a caseby-case
basis for determining whether an installed spare PRD
is, or is not, necessary.
https://www.csb.gov/goodyear-heat-exhanger-rupture/ https://www.csb.gov/goodyear-heat-exhanger-rupture/ http://www.HydrocarbonProcessing.com
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