LinkedIn Discussion

Which Is better for Cooling Tower Use: Schedule 80 or Schedule 40 Piping?

Compiled by Mike Henley and James McDonald

COOLING TOWERS CORROSION HEAT EXCHANGERS MATERIALS OF CONSTRUCTION ORP PIPING PVC TROUBLESHOOTING

Abstract

 (Editor’s note: This article is based on recent discussions in the LinkedIn Industrial Water Treatment group. This column seeks to accurately reflect comments from each contributor. On occasion, there may be the need to edit contributor commentary for clarity or length. An important purpose of each group is to provide a forum for practical examination of issues facing endusers of high-purity and industrial water.)

 

Industrial Water Treatment Discussions

Compiled by James McDonald, PE

(Senior Corporate Engineer, Chem-Aqua)

 

Cooling Tower Piping Choice?

James: When Schedule 40 piping can meet the pressure and temperature requirements of a cooling tower application, why might one still choose Schedule 80 piping? Which do you use and why?

Alnie: “Cooling water becomes fouled. The use of Schedule 80 yields to a greater pipe thickness, thus giving: 1. increased allowance against corrosion; and 2. increased cooling water velocity, resulting in a decreased fouling rate.”

Ahmad: “For cooling system pipes, sometimes designers go with Schedule 80 for corrosion allowance, especially for the circulating water side (open side). On the other hand, for polyvinyl chloride (PVC) pipes, there is no need to increase the thickness because thicker materials mean more expensive piping and more money spent for stronger supports (this is also true for the cooling system pipes, but the advantages/disadvantages have to be weighed).

By the way, the open side of cooling water is usually treated against scaling and fouling, but not against corrosion.”

David: “Long-term durability and aesthetics are probably my main reasons (for selecting Schedule 80), but I have used Schedule 40 as well.”

Mitchell: “If you are referring to PVC for the chemical system, I personally try to avoid PVC. I never sell PVC coupon racks. Somebody always cracks a fitting and causes a flood. PVC will sag when the temperature gets too high. When I do use PVC, I always go with Schedule 80.”

Glen: “If PVC is the appropriate material, I prefer Schedule 80 simply for the structural rigidity, even if Schedule 40 would be acceptable for the pressure rating.”

Frank: “Schedule 80 all the way all the time. Schedule 40 cracks too easily with age.”

Drew: “”In an industrial application, I specify Schedule 80. Hands down there is less likelihood of early failures. This works at my site.”

Kevin: “I use Schedule 80 because we have to feed acid to maintain the cycles required by the city. The Schedule 80 can withstand the potential temperatures better than Schedule 40. And as already stated, it looks better.”

Darren: “Schedule 80 for sure. Not only does the installation look better, but if installed correctly, it will be more rigid and less susceptible to embrittlement and UV degradation. Schedule 80 will also have much better chemical resistance than Schedule 40.”

Daniel: “I find Schedule 80 to be more durable in heavy industrial applications. Yes, Schedule 40 might meet the requirements, but it is more prone to damage from unforeseen circumstances.”

Heat Exchanger Troubleshooting Tips

James: How can you tell if a heat exchanger is leaking without taking the unit offline to physically inspect?

Marc: “PTSA dye. Put it in the high-pressure side (closed loop) and test for it in the open loop.”

Steven: “Pressure drops, temperature profiles, mass balance, chemical oxygen demand (COD), fluorescein dye.”

Jan: “If water comes in the product or if product comes into the water…it depends on pressure. Or, if a water/water exchanger, look at the consumptions or make-up. Indeed, you can also put a tracer like Marc mentions.”

Debjyoti: “Here are some possible problems:

  1. Increase in pressure drop in the lower pressure side (shell/tube). 
  1. Abnormal temperature profiles.
  1. Abnormal lab analysis of the low-pressure stream like in the air preheaters.
  1. If there's water ingress, then increase in downstream separator levels.”

Varshan: “All of the earlier comments as mentioned. But also note this: your heat exchanger (regardless of the type) is used to cool or heat a fluid, and that fluid is going somewhere (be it into a storage tank, directly to a process…). If you have a flow-measuring device on your storage tank or process line that is fed from the outlet flows of the heat exchanger, you will immediately notice drops in flowrate, which could mean you have a leak in the piping or the heat exchanger itself.”

Matt: “Cross contamination will change water quality.”

Magesh: “At present, using radio tracer techniques have proven to detect leaks in heat exchangers. However, the process parameters should fit the prerequisites of the radio element to be used.”

Hitesh: “Normally, the leakage in a heat exchanger takes place by the process fluid mixing with water stream. Hence, to identify the leakage, check the pH of the water at the inlet and outlet of the heat exchanger. The difference will immediately indicate the leak.”

Keith: “You can also find a hydrocarbon (or other reducing process side material) leak into a halogenated cooling water flow in an exchanger by evaluating the oxygen reduction potential (ORP) values in and out of the exchanger. Any reducing material will react with the halogen and cause the ORP to drop. The larger the leak, and/or the more reducing the material, the greater the impact on ORP.”

The Ultrapure Water and Industrial Water interest groups may be accessed at www.linkedin.com.

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