IM 25.000AA UA (B/6-00)
CHLORINE HANDLING MANUAL
PAGE 12
4.7 PRESSURE RELIEF DEVICES
There are two types of pressure relief devices in use in chlo-
rine piping systems. The first, as shown in Figure 13, is
usually employed in liquid chlorine piping to protect the
piping from rupture due to high pressure from thermal ex-
pansion of the liquid chlorine. It consists of a rupture disc
that ruptures before the pipe line itself can rupture, an expan-
sion chamber that allows for relief of the over-pressure con-
dition without releasing chlorine to the atmosphere, and a
pressure switch to warn of the disc rupture.
The second type, as shown in Figure 17, is usually used in gas
piping at the evaporator discharge. This system consists of
a rupture disc that keeps chlorine out of the valve during
normal operation, a pressure relief valve, and a pressure
switch to warn of disc rupture.
Figure 17 – Evaporator Pressure Relief System
GAS PRESSURE RELIEF VALVE 500 PSIG
1/2” FEMALE NPT FOR 115V
ELECTRICAL CONNECTION
PRESSURE SWITCH
DIAPHRAGM SEAL UNIT
1” FEMALE NPT INLET
RUPTURE DISC 400 PSI
UNION HEAD
1-1/2” FEMALE NPT RELIEF CONNECTION
WARNING: THE RELIEF LINE MUST TERMINATE
IN AN AREA WHERE GAS FUMES CANNOT CAUSE
DAMAGE OR INJURY TO PERSONNEL. DO NOT
TERMINATE THE RELIEF LINE AT A LOCATION
ROUTINELY USED BY PERSONNEL, SUCH AS
WORK AREAS OR PATHWAYS, NOR NEAR WIN-
DOWS OR VENTILATION SYSTEM INTAKES. IF AN
AREA MEETING THESE REQUIREMENTS IS NOT
AVAILABLE, REFER TO THE CHLORINE
INSTITUTE’S CHLORINE MANUAL AND PAM-
PHLET NO. 9 FOR AN ALTERNATE METHOD OF
RELIEF DISPOSAL.
4.8 PREPARATION FOR USE
Normal plumbing practices will result in the entry of cutting
oils, greases, and other foreign materials into the piping.
In addition, the line will have been open to the atmosphere
during construction, allowing moisture to enter. It is there-
fore essential that all piping be thoroughly cleaned and dried
prior to exposure to chlorine.
WARNING: INCOMPLETE CLEANING CAN RE-
SULT IN VIOLENT REACTIONS BETWEEN CHLO-
RINE AND THESE MATERIALS.
Steam cleaning is an acceptable method for removal of the
above materials. Provision must be made for removal of
condensate and foreign materials. For alternate methods if
steam is not available, refer to Chlorine Institute Pamphlet
6, Piping Systems for Dry Chlorine.
After proper cleaning, all chlorine piping should be hydro-
statically tested to one and one half times the expected maxi-
mum operating pressure. Prior to testing, all gauges, switches,
rupture discs, etc., that could be damaged during testing
must be removed and connections plugged. Any moisture
absorbing packing or gaskets left in the system during hydro-
static testing must be removed and replaced with new pack-
ing or gaskets. After hydrostatic testing, it is essential that all
piping be thoroughly dried with inert gas (e.g., nitrogen) or
dry air having a dew point of -40° F or below. The dew point
of the air or gas leaving the piping must be checked and
drying continued until the dew point is at or below -40° F,
which may require quite some time.
WARNING: MOISTURE MUST BE REMOVED FROM
ANY PART OF THE EQUIPMENT THAT IS NOR-
MALLY EXPOSED TO DRY CHLORINE ONLY.
WHILE DRY CHLORINE IS NON-CORROSIVE,
MOIST CHLORINE IS EXTREMELY CORROSIVE
TO COMMON METALS, SUCH AS BRASS OR STEEL,
POSSIBLY RESULTING IN A LEAK AND SEVERE
PERSONAL INJURY. ALSO, IF WATER IS TRAPPED
IN A SECTION OF PIPING OR EQUIPMENT, SUBSE-
QUENT HEATING OR FREEZING OF THE WATER
MAY RESULT IN HIGH ENOUGH PRESSURE TO
RUPTURE THE PIPING OR EQUIPMENT, POSSIBLY
CAUSING SEVERE PERSONAL INJURY.
A very acceptable alternate to hydrostatic testing, if proper
facilities do not exist for drying, is to test with nitrogen or dry
air having a dew point of -40° F or below. The same provision
of removing equipment that could be damaged by test pres-
sure applies.
WARNING: TO AVOID SEVERE PERSONAL IN-
JURY, BEFORE PLACING THE PIPING SYSTEM
INTO SERVICE, PRESSURE TEST WITH CHLORINE
GAS, NOT LIQUID. EACH VOLUME OF CHLORINE
LIQUID THAT LEAKS AND THEN EVAPORATES
RESULTS IN APPROXIMATELY 460 VOLUMES OF
CHLORINE GAS.
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