Page 36 - igem-g-4 edition 2

IGEM/G/4 Edition 2
pipeline isolation valve (PIV)
Either a transmission pipeline valve or a distribution main valve (DMV) or a service isolation
valve (SIV).

pipework
System or part system of components designed to contain gas, for example pipe, valve, fitting
(including appliances) meter, regulator, etc.

piston
Moving part of a waterless or dry gasholder which allows the amount of stored gas to vary
while maintaining a constant pressure.

piston seal
Method of ensuring that gas cannot leak between a piston and the containing walls of a
waterless or dry gasholder.

planning horizon
Period of time considered to be appropriate for planning purposes and for evaluation of capital
investment decisions on major plant and equipment.

plumbing, relating to a watersealed gasholder
Measurement of columns to assess any changes in their position or alignment.

popping
Removal of all creases from the fabric seal of a dry gasholder by deliberate over-pressurizing,
normally prior to use.

post-purge
Purge which follows safety shut-down.

premises (HSWA 1974)
“Premises” includes any place, and in particular, includes:
(a) any vehicle, vessel, aircraft or hovercraft,
(b) any installation on land (including the foreshore and other land intermittently covered by
water), any offshore installation, and any other installation (whether floating, or resting on
the seabed or the subsoil thereof, or resting on other land covered with water or the
subsoil thereof, and
(c) any tent or movable structure.

premises pipework
Pipework provided by the occupier of premises which is not adopted by the upstream GT but
which is not “installation pipework”.

pre-purge
Purge which precedes an ignition attempt.

pressed joint
Joint in which tightness is achieved by making use of an appropriate tool for mechanically
deforming either a fitting including a sealing element onto a metallic pipe in order to form an
removable connection.

pressure
Exertion of a continuous force upon an area (including fluids, gases etc.), expressed in units of
force per unit of area.

pressure boundary (break)
An interface between two areas of an installation with different design pressures.

pressure deviation
Difference between measured pressure and set pressure.

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