The safe isolation of plant and equipment (HSG253) - Health and ...

Table B Summary of isolation techniques
Technique Brief
description
Primary devices
Valves The simplest
form of
isolation device
Health and Safety
Executive
Appendix 5: Isolation methods
1 Physical isolation of pressurised systems is primarily achieved using various
combinations of valves, spades and blank flanges.
2 Pipelines often have long sections of pipe between valves. You may need
to use techniques such as pipe plugs or pipe freezing to enable the isolation of
intermediate sections of pipe for maintenance purposes, when it is not reasonably
practicable to use primary devices (see Table B below). Such techniques are not
appropriate for standard use on process plant and should be subject to taskspecific
risk assessment and senior-level authorisation.
3 A summary of isolation techniques is given in Table B. This indicates the key
features and applications of each device.
Typical use (process
plant or pipelines)
and pressure
■
■
Standard use for
process plant and
pipelines
Suitable for
all fluids at all
pressure ranges
Features – pros Features – cons Comments,
refs to
industry
codes
■
■
■
■
■
■
Does not require
intervention into the
pipe – no significant
hazard to the person
performing isolation
Facility already
installed, locations
identified from P&IDs
Isolation is fast and
removal to reinstate
plant is easy
No specialist training
or materials required
Continual attendance
or monitoring not
usually required
Low cost
May not give tight
shut-off due to seal
damage
Positive indication of
complete isolation is
not always available,
additional monitoring
may be required
Requires locking off
to prevent inadvertent
operation
May not be in
optimum position,
resulting in large
inventories beyond
the isolation
Additional cost
of valve and
maintenance
throughout the lifetime
of the plant
Not all valve types are
suitable for isolation
use (Appendix 4)
The safe isolation of plant and equipment Page 52 of 81
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■
■
■
■
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Valves to be
suitable for
service fluid
and rated to
the maximum
differential
pressure
See:
ISO 14313 22
for pipeline
valves
API 6D