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PIPING VENTS AND DRAINS AN OVERVIEW

Posted by Antony Thomas at Wednesday, November 23, 2011

VENTS AND DRAINS


• Vents are needed to let gas (usually air) in and out of systems.
• When a line or vessel cools, the pressure drops and creates a partial
vacuum which can cause siphoning or prevent draining.
• When pressure rises in storage tanks due to an increase in
temperature, it is necessary to release excess pressure.
• Air must also be released from tanks to allow filling and admitted to
permit draining or pumping out liquids.
• Unless air is removed from fuel lines to burners, flame fading can
result.
• In steam lines, air reduces heating efficiency.

HYDROSTATIC TESTING


• After piping is erected, it is often necessary to subject the system to a
hydrostatic test to see if there is any leakage.
• In compliance with the applicable code, this consists of filling the lines
with water or other liquid, closing the line, applying test pressure and
observing how well pressure is maintained for a specified time, while
searching for leaks.
• As the test pressure is greater than the operating pressure of the
system, it is necessary to protect equipment and instruments by
closing all relevant valves.
• Vessels and equipment usually are supplied with a certificate of code
compliance.
• After testing, the valved drains are opened and the vent plugs
temporarily removed to allow air into the piping for complete draining.

VENTS AND DRAIN ARRANGEMENTS

SOCKET WELDED/SCREWED VENTS AND DRAINS

• Positions of the required vent and drain points are established on the
piping drawings.
• PIDS shows only process vents such as vacuum breakers and process
drains.

VENTING GASES


• Quick opening vents of ample size are needed for gases.
• Safety and safety-relief valves are the usual means.
• Gases which offer no serious hazard after some dilution with air ma be
vented to atmosphere by means ensuring that no direct inhalation can
occur.
• If a combustible gas is toxic or has a bad odor, it may be piped to an
incinerator or flarestack, and destroyed by burning.
DRAINING COMPRESSED AIR LINES
• Air has a moisture content which partially carried thru the compressing
and cooling stages.
• It is this moisture that tends to separate, together with any oil, which
may have been picked up by the air in passing thru the compressor.
• If air for distribution has not been dried, distribution lines should be
sloped toward points of use and drains : Lines carrying dried air need
not be sloped.
• If the compressed air supply is not dried, provide:-
1. Traps at all drains from equipment forming or collecting liquid –
such as intercooler, aftercooler, separator, receiver.
2. Driplegs with traps on distribution headers (at low points before
rises) and traps or manual drains at the ends of distribution
headers.)

LIQUID REMOVAL FROM AIR LINES

SEE ALSO

Hydrostatic Test Vents and Drains –Guidelines

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