Bulletin 1003: Cooling Tower LayUp Procedure

Sep 21, 2015

Cooling Tower LayUp Procedure

Columbus, OH – Why is it important to lay up my cooling tower? Most cooling towers and condenser water piping systems require chemical treatment to protect against corrosion. Chemical treatment also prevents microbiological growth from promoting biofilms which can reduce heat transfer, restrict flow and harbor potentially dangerous bacteria. Throughout the cooling season, your equipment is protected by Chardon’s treatment program, but what about during the off season? If left full of water and untreated, chiller end bells, tube sheets and condenser water pipes will develop corrosion problems that will lead to mill scale, pitting and ultimately failure. Mill scale builds up and eventually flakes off and collects in tower distribution pans as rust chips. These rust chips can cause cooling tower distribution pans to overflow resulting in reduced cycles of concentration, increased water usage, accelerated corrosion rates, and ultimately shorter equipment life.

Another problem facing cooling towers when not properly laid up is underdeposit corrosion. Sediment brought in by air pulled through by the tower fan accumulates in the tower sump. This is part of the normal operation of a cooling tower and the quantity deposited depends on the air quality, location of the tower, load and run time of your equipment. As deposits accumulate in the tower sump, they create electrolytic corrosion cells and barriers to chemical passivation that can accelerate the corrosion rate and decrease the life cycle of the cooling tower.
When water is left in the system, microbiological activity continues even though the system is no longer circulating. If left unchecked, bacteria will multiply and begin forming biofilm. Biofilm creates even more heat transfer problems than calcium scale. Biofilm can harbor Legionella and other potentially harmful species. Microbiologically influenced corrosion, or MIC, can attack tube sheets, end bells, and other system components that are protected during normal tower operation.
Cooling tower systems that operate intermittently during the cooler months have similar problems. While Chardon’s treatment products remain active in the system even when it is not circulating, all biocides have a certain half-life and even scale inhibitors can lose their effectiveness over time. Condensers and other heat exchangers that remain full of water for weeks or months will experience bacterial growth that can result in biofilm formation and corrosion. Systems using wet lay up techniques require attention throughout the off season.

Okay, so how do I protect my cooling system?

The cooling tower lay up procedure must be done at the end of each cooling season and coordinated with your shutdown date. The procedure is simple and the treatment is inexpensive. In the two weeks prior to tower shutdown and draining, reduce cycles by 50% to allow the tower to bleed out solids and suspended matter. In the days before shut down, add 5 gallons of CT Lay-up and 10 ounces of Mayosperse 7700-15 into the cooling system for every 1,000 gallons of condenser water. Allow the system to circulate for 24 to 48 hours, then drain and clean as usual. After shut down, drain and clean the tower sump to remove any remaining solids. OSHA guidelines indicate that cooling tower sumps should be cleaned twice each operating year. All tower and piping surfaces will be passivated and protected against further corrosion during the off-season.

Why do I have to drain the tower?

The tower must be drained to prevent the water from freezing and rupturing the tower sump and associated piping systems. Anti-freeze measures are not effective because evaporation reduces the effectiveness within weeks. Glycol-based products should not be discharged to your sewer system.

How about if I just drain the piping to my roofline to protect from freezing?

Draining to the roofline can protect exposed piping from freezing damage, but the system must be circulated at least once a week to keep inhibitor and biocide fresh and at the right concentrations. Stagnant water is always a problem and the lack of inhibitor and biocide makes the situation worse. Anaerobic species like SRB can gain a foothold that will cause long term problems even when the system comes back on line.

Is it okay if I start the system up for a few warm days?

If you plan to use a wet lay up for the off season, or if your system must remain ready for operation, work with your Chardon Service Technician to reduce cycles by 50% and make the necessary adjustments to the inhibitor and biocide feed rates for this period. You should also work with your Service Technician and Energy Management Program to turn on the tower circulation pump in coordination with the biocide feed schedule. This will ensure that the system receives an adequate amount of biocide to prevent the formation of biofilm.

Is there anything else I need to do?

If the system has an outside water meter or the meter is located in an unheated area, it must be removed because water can accumulate in the meter and associated piping and cause the meter to rupture. Water meter removal should be a routine part of the tower lay-up procedure.

So then I can button it back up?

Whenever the system is drained it is best to open the chiller heads and piping to the air to avoid a moist environment that will promote attack on steel. If there is not time to punch the tubes until spring, it is even more important to let the system dry out. It may seem like keeping water in the system makes it easier to punch tubes, but the consequences of corrosion always outweigh the potential benefit of keeping deposits “soft.”

What do I do before startup?

The CT Lay-up and Slimex B program does not interfere with your startup procedure. Simply fill the tower as usual and begin your usual operation. Mill scale problems will be reduced and your equipment life cycle will improve.
If you have questions about this or any other technical matter, call one of our Technical Support Team Members at 800-848-9526.