Wallace & Tiernan SERIES V-2000, Manual

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WT.025.000.001.UA.IM.0614
CHLORINE HANDLING MANUAL
PAGE 12
EVOQUA W3T98244
4.7 PRESSURE RELIEF DEVICES
There are two types of pressure relief devices in use in chlorine
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 expansion of the
liquid chlorine. It consists of a rupture disc that ruptures be-
fore the pipe line itself can rupture, an expansion chamber
that allows for relief of the over-pressure condition 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.
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 PERSON-
NEL, SUCH AS WORK AREAS OR PATHWAYS, NOR NEAR
WINDOWS OR VENTILATION SYSTEM INTAKES. IF AN
AREA MEETING THESE REQUIREMENTS IS NOT AVAIL-
ABLE, REFER TO THE CHLORINE INSTITUTE’S CHLORINE
MANUAL AND PAMPHLET 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 therefore
essential that all piping be thoroughly cleaned and dried
prior to exposure to chlorine.
WARNING: INCOMPLETE CLEANING CAN RESULT IN
VIOLENT REACTIONS BETWEEN CHLORINE 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
maximum 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 hydrostatic testing must be removed and replaced
with new packing 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 NORMALLY EXPOSED
TO DRY CHLORINE ONLY. WHILE DRY CHLORINE IS NON-
CORROSIVE, MOIST CHLORINE IS EXTREMELY CORRO-
SIVE 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, SUBSEQUENT 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 pressure applies.
WARNING: TO AVOID SEVERE PERSONAL INJURY, BEFORE
PLACING THE PIPING SYSTEM INTO SERVICE, PRESSURE
TEST WITH CHLORINE GAS, NOT LIQUID. EACH VOLUME
OF CHLORINE LIQUID THAT LEAKS AND THEN EVAPO-
RATES RESULTS IN APPROXIMATELY 460 VOLUMES OF
CHLORINE GAS.
The chlorine container valve should be opened only slightly
during this phase of testing or preferably closed again after
pressurizing the system. The piping should be tested in the
smallest sections permitted by the existing valves to minimize
Figure 17 – Evaporator Pressure Relief System