MAINTENANCE & REPAIR
BY BART COLLINS
PSV Inspection: Test Only, or Full Inspection and Overhaul?
In today’s ever-changing, fast-paced
world, uptime is at a premium, while
remaining in compliance with governmental and plant regulations is a requirement. With increasing demands placed
on plants to produce, it is necessary to
look at different ways to perform inspections on pressure relief devices and minimize plant downtime. Many plants in the
United States have opted to modify their
plant PSM (process safety management)
programs to allow a “test only” on each
pressure relief device in lieu of a complete disassembly and “VR” overhaul.
The intent of this article is to explain the
pro’s and con’s of both methods, while
balancing additional demands of productivity, cost, safety and environmental
issues.
ter for verification of relief pressure and
seat leakage testing.
Test Only
A “test only” can be performed by two
different methods: ( 1) “In-situ” online
testing while the valve is still in service;
or ( 2) bench testing—removing the valve
and sending it to a local repair/test cen-
In-situ testing
PRO’S: In-situ testing gives the end
user an economical advantage over
other methods as it allows the plant to
keep the process unit running while testing is being performed. While this type
of testing is typically more expensive on
a per-valve basis than bench testing, it
is much more economical for the end
user in the total overall cost of perform-ing the test.
CON’S: In-situ testing produces very
little results regarding the total functionality of the valve. While it does provide a
start-to-discharge point (the pressure in
which the valve actually starts to lift), it
does not put the valve into lift, does not
provide any type of external joint leakage
testing (back pressure test), does not
allow for a visual inspection of the inlet
and outlet, and typically cannot accurately inspect for seat leakage. In addition, in-situ testing can become very
time-consuming depending on the location of the valve and the process it is in.
In some cases, the valves will be located
in a “fresh air” application or in an area
that requires the equipment to be intrinsically safe.
Bench testing
PRO’S: Bench-testing allows a full
functional test to be applied to each valve
by putting the valve into lift (lift may
vary based on volume of test equipment).
It also allows the valve to blow down and
reseat and allows for a seat leakage test.
In addition, the valve is back-pressure
tested to inspect for any external leakage
from bolted or threaded joints. While this
is usually the most economical of all PSV
inspections on a per-valve basis, the end
user typically experiences internal costs
such as loss of production, use of plant
manpower to remove and install the
valves, additional materials required for
the installation, and any other peripheral
safety concerns dictated by the location
of the valve.
CON’S: Bench testing is typically
known as the “norm” for test-only
inspections; but it also has its own pitfalls. While it does provide both a full
functional and seat leakage test, it does
not provide the end user with a dimensional and visual examination of the
PSV’s internal working components. All
manufacturers of ASME-certified PSV’s
provide dimensional tolerances, clearances and visual inspection points that
are required to maintain the valve’s
integrity and ensure that it is in “like
new” condition. Additionally, a “test
only” does not provide an internal visual
inspection for corrosion and/or erosion of
the body and bonnet cavities, internal
parts, bearing points and spring—all of
which can affect the valve’s performance
and its total life in service.
