Page 213 - Facility Piping Systems Handbook for Industrial, Commercial, and Healthcare Facilities

WATER TREATMENT AND PURIFICATION

WATER TREATMENT AND PURIFICATION 4.49

Storage
Storage of water will reduce the size of the purification equipment. Storage tanks are con-
structed from FRP, PP, and SS. The bottom of the tank is dished or conical to aid in com-
plete drainage. It is an established fact that high-purity water degrades in storage. The four
major sources of this degradation are:
1. Water will extract contamination from any container.
2. Bacteria will grow and secrete waste products.
3. Organics from solvents and shedding of clothing can diffuse through the air and dis-
solve in the water.
4. Laboratory personnel secrete urea in perspiration and respiration that can cause the
formation of ammonia in stored laboratory water.
The tank for USP water should be airtight and equipped with a nonshedding, 0.2-μm
hydrophobic filter for venting. For WFI systems, the tank should be type 304L or 316L
stainless steel, pressure rated to a minimum of 35-psig pressure, 30-in Hg vacuum, 180 grit,
and electropolished. It is common practice to have a nitrogen gas blanket in the vapor space
above the water in the storage tank to reduce the possibility of airborne contamination. The
tank should have a jacket to maintain a temperature of 80°C and be insulated and provided
with a rupture disk.
The discharge from the tank should be from the center bottom of the tank to allow com-
plete circulation of the stored water. The water return should be at the top of the tank and be
equipped with a spray ball or spray ring. This minimizes microbial growth by continuously
washing the upper areas of the tank.
Sterilization. It is common practice to provide an in-line UV sterilization device to reduce
microorganisms that may be present in the water. Another common method is to heat puri-
fied water to a temperature of 80°C (177°F) to prevent microorganism growth, and circulate
it to maintain the sterile condition. Another possibility is installation of a filter that will
remove any organic particulates.

Piping Distribution Network

The piping material for USP water should be fabricated from virgin PP, PVDF, or SS.
Plastic pipe should be buttjoint heat-fused and SS pipe should be orbital welded. Piping
material for WFI water should be SS, 180 grit and electropolished. Fittings must have
extended ends for orbital welding. All couplings must be sanitary triclamp. Insulation
must be nonchloride bearing and designed for a temperature of 80°C. Velocity in the
system should be approximately 6 to 9 ft/s for supply from the storage tank to the system
and 3 to 6 ft/s in the return leg. This is accomplished by the installation of a back-pressure
regulator. These velocities are recommended to scour the pipe interior and prevent the
formation of biofilm.
The pipe should be sloped at a 1/8-in pitch to allow complete drainage of the network.
Dead legs of more than six pipe diameters are not permitted by cGMP requirements. To
prevent future plastic pipe sagging from interfering with drainage, continuous support is
recommended. Using PP as a baseline, PVDF is twice the cost and SS 4 times the cost
installed.
Valves must be consistent with the piping materials. Prior to the RO or DI units, full
bore ball valves are recommended. In the purified loop, SS diaphragm valves with an
EPDM or Teflon diaphragm and a backing ring should be used. Sample valves (usually
needle type) should be provided in areas of the system to allow samples to be taken at
strategic points.

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