T.U.T.O.R

the discharge tubing. An anti-syphon valve is basically a one-way valve that prevents liquid from syphoning through a pump after it shuts off. Anti-syphon valves are required if the point of chemical injection is below the chemical pump discharge.

The evening after the new inhibitor chemical feed was initiated, the service representative arrived home and used his laptop to access the controller. He noticed an alarm for high PTSA. He checked the controller inhibitor pump relay to determine if it was energized and discovered that it had been off for several hours. He then looked at the controller PTSA trend graph and noticed it was continuing to increase! At that point, he realized the inhibitor was syphoning through the pump since there was no anti-syphon valve on the inhibitor pump discharge tubing. A call was placed to the plant operator to remove the inhibitor feed line from the tower basin location and to temporarily place it in the minibulk tank. When the hose was removed from the tower basin, this “broke” the syphon, and the feed of corrosion inhibitor stopped.

The service rep visited the plant the next day with the correct fittings and injection nozzle in order to feed the inhibitor chemical into the CPVC controller bypass line downstream of the controller sensors. No further incidents involving inhibitor chemical overfeed have occurred.

If it was not for the PTSA alarm callout features and remote monitoring capability of the controller, the entire 110 gallons of inhibitor could have been added to the system in less than 24 hours. Not a good way to start a new program with a new customer! Closing Thought The use of PTSA and remote monitoring are excellent applications for cooling tower water systems. This story illustrates the value of these technologies. As a word of caution, there is always a chance of controller sensor failure, sensor fouling, and damage to controller electronics caused by power surges and other unforeseen conditions. Controller sensor calibration should be checked on a routine basis, preferably at least monthly. In addition, chemical actives should be checked (in this case zinc) and compared to PTSA values.

Table A: New Monitoring System Parameters Sensor Purpose Range

pH Acid feed 7–7.4

Conductivity Blowdown 1,800–2,000

PTSA Inhibitor feed 60–80 ppb

ORP Bleach feed 600–650 mV

Free chlorine* Bacteria/algae control 0.15–0.30 ppm *The controller does not directly monitor free-chlorine level.

Gene Tonetti, CWT, is the founder of Water Systems Management. He has worked in the water treatment field for more than 41 years and has expertise in wastewater and high-purity, boiler, and cooling tower water. His experience in treating water includes treatment chemicals, chlorine dioxide, reverse osmosis, and process controllers. Tonetti is a 1973 graduate of RoseHulman Institute of Technology with a B.S. in biological engineering.

Why Do Materials of Construction Matter?

By Mike Henley

Corrosion. Leaching. Safety. These are three of many concerns one might list that will drive decisions when engineers and other decision-makers select the materials used for a plant’s water treatment system. The purpose of this short article is to provide initial background as to why materials of construction are important. The nature of this discussion is general, but at the close of the article, we will provide a list of resources for those wishing to learn more specifics about this important area.

Normally, materials of construction are primarily associated with piping, valves, and gaskets. However, another area of concern can be system components such as storage tanks, pumps, and filters. It should be noted that some materials are critical to ensuring the water purity or protecting the operations of the end-user that needs the treated water. These two aspects will be the focus of the remainder of this discussion.

Wetted Parts

Ultrapure Water

Particularly within the high-purity water world, the choice of materials of construction used in the treatment equipment and for piping systems is critical. Besides piping and valves, other areas where attention may be given to the use of specialty materials include pumps, pressure vessels, gaskets, heat exchangers, instrument sensors, ultraviolet sleeves, and even filters and membranes, among others.

One concern is that the chosen material not accidentally become the source of contaminating the treated water. For example, in a semiconductor plant, great care is given to ensure that piping systems and pump surfaces do not leach ionic contaminants back into the water or shed particles.

It is for those reasons that, at least in the microelectronics industries, polyvinylidene fluoride (PVDF) is widely used for valves and distribution systems for ultrapure water. PVDF is considered an inert material that will maintain the purity of the high-purity water because it does not leach out contaminants nor shed particles. This is particularly important in the semiconductor industry where plant operators are concerned that particles or dissolved solids in the water can either precipitate or land on a chip line and later lead to defective products. Figure 1 shows an example of PVDF piping at a photovoltaic (solar) panel manufacturing plant near Portland, Oregon.

Figure 1: Example of PVDF piping in a microelectronics plant. The smaller diameter pipes on the left are used to carry hot ultrapure water, while the two pipes on the right side carry deionized water.

In the microelectronics world, PVDF is widely used— particularly in the ultrapure loop. Not only is it considered an inert material that will not contaminate the

water, but one that can withstand sanitization by ozone and other chemical agents like hydrogen peroxide.

However, in areas not requiring the highest purity water, piping made from polyvinyl chloride (PVC) can also be found in plants. Metallic piping (e.g., stainless steel, steel, copper) is not used because it will leach ionic contaminants, shed particles, and can corrode.

Other Factors Impacting Choices

Besides material purity, other reasons to select a particular material used in water can be the ability to withstand higher temperatures, structural strength, or compatibility with other materials used in the facility. Cost can also be a factor but is often a lesser concern, especially if the cheaper piping, valves, or other items can negatively impact plant operations.

Pharmaceutical-Grade Waters

Generally, pharmaceutical plants will have stainless steel for their water distribution systems and tanks. A key reason is that this material does not contribute contaminants to the treated water. It can withstand hot water temperatures such as found in Water for Injection (WFI) loops, where distillation is widely used. To control formation of microorganisms, WFI loops circulate, and the temperature is normally maintained at 80 °C. WFI is a type of pharmaceutical water that is considered to be microbial free and is used to manufacture products such as IV fluids and other products that must meet particular sterility requirements because the final product may be injected into the human body.

Pharma plants normally have chosen stainless steel because it can be used with hot water and can withstand sterilization with hot water or steam and retain its structural integrity. Please note that PVDF is also used to carry hot ultrapure water, but that at high temperatures, the piping will sag and must have additional structural support.

There is some movement to using thermoplastics in pharmaceutical plants, but this trend is still limited. Historically, distillation has been the prescribed treatment technology for WFI production, so this production method has required piping capable of withstanding hot water/steam sterilization temperatures as well as carrying the hot water flows during normal loop operations. Stainless steel has easily met those needs. However, in recent years, the major pharmacopeias have been amended to also allow the use of reverse osmosis (RO) to produce WFI. RO systems use ambient temperature water, which opens the possibility of using thermoplastic piping for these applications. Note: A pharmacopeia is a document that provides guidelines on different aspects of pharmaceutical manufacturing, including water quality requirements.

Figure 2 shows stainless steel piping in a pharmaceutical plant, and Figure 3 is an example of stainless-steel tanks, such as might be found in a pharmaceutical plant.

Figure 2: Stainless steel piping in a pharmaceutical plant.

Figure 3: Stainless steel tanks such as may be found in a

pharmaceutical plant. Photo courtesy of Joe Manfredi, GMP Systems, Inc. (Fairfield, New Jersey).