If you’ve ever been on the floor of a refinery, a petrochemical plant, or a midstream pipeline terminal, you know API 610 isn’t just another set of guidelines—it’s the backbone of pump reliability when every second of downtime costs tens of thousands of dollars. As a pump supplier that’s spent the last 12 years delivering API 610-compliant centrifugal pumps to heavy industries, I get more questions about cooling systems than any other component. Operators and engineers don’t just want to check a box; they want to know why a cooling system is built a certain way, what failure modes the standard is designed to prevent, and how to avoid the costly mistakes that come from cutting corners. API610 Pump
Let’s start with what API 610 actually defines for cooling systems. First, the standard applies to pumps rated for continuous service at 500 horsepower or higher, operating at temperatures above 350°F (175°C) on the pumped fluid, or in services where thermal buildup can damage internal components. Cooling systems in these pumps serve two core jobs: they remove excess heat generated by mechanical friction (from the shaft seal, bearings, or fluid shear in the pump casing) and prevent the internal temperature of the pump from exceeding the material limits of parts like bearings, seal faces, and impeller hubs. Skimp on the cooling, and you’re looking at seal failure, bearing seizure, or a total pump outage—no exaggeration.
A common misconception I run into is that cooling systems are “one-size-fits-all” across all API 610 pump types. They’re not. API 610 splits pumps into two primary categories: OH (overhung) pumps and BB (between-bearings) pumps, and the cooling requirements shift dramatically between them. For OH pumps, which have overhung impellers and are more compact, the bearing housing is typically cooled via a jacket that wraps around the housing itself. API 610 mandates that this jacket be constructed from carbon steel or corrosion-resistant alloy (CRA) material matched to the process fluid, with a minimum wall thickness of 0.125 inches (3.175 mm) to handle pressure differences between the cooling media and the process side. What many suppliers miss here is the jacket’s pressure rating: it has to handle a minimum of 150 psig (10.3 bar) unless the process requires a higher rating, and all connections to the jacket must have bolted flanges, not threaded fittings—welded connections are only allowed if they’re code-compliant and radiographed, a detail that’s saved more than one customer from a leaky cooling system.
For BB pumps, which have impellers supported between two bearing sets and are used for higher-pressure, higher-temperature services, cooling is often more complex. API 610 allows for three primary cooling methods here: jacketed bearing housings (same as OH pumps), circulating water systems, or external heat exchangers tied to the bearing lube oil system. The key rule here is that regardless of the method, the maximum bearing operating temperature can’t exceed 200°F (93°C) for babbitted bearings, or 300°F (149°C) for sleeve bearings made of other CRA materials. I’ve seen BB pump failures where the bearing ran at 240°F because the supplier undersized the heat exchanger and used city water that plugged with scale—API 610 requires that the cooling system be sized for a 10°F (5.5°C) maximum temperature rise across the cooling media, so that’s a hard limit, not a suggestion.
Next, let’s talk about cooling media, because this is where half the arguments between operators and suppliers come from. API 610 doesn’t mandate a specific cooling fluid, but it does set strict qualification requirements. For most onshore applications, cooling water is the go-to, but the standard requires that it be treated to prevent fouling, corrosion, or biological growth in the jacket or lines. If a customer tries to use raw water without treatment, API 610 requires the supplier to add features like strainers with 100-mesh (150-micron) elements to prevent debris from clogging the jacket—we had a customer once who skipped that and ended up with the cooling line plugged after three months, leading to a bearing failure that cost them $120,000 in downtime. For offshore or remote sites where water is scarce, oil cooling is common. API 610 specifies that if you’re using lube oil as the cooling media, the oil must meet the viscosity and temperature requirements outlined in ISO VG grades, and the heat exchanger has to be designed to handle the same lube oil flow rate as the bearing system. We recently delivered a set of BB3 pumps to an offshore rig where oil cooling was required, and we had to test the system at 150% of the design flow rate to ensure it could handle peak load without overheating—something a lot of smaller suppliers skip, leading to underperforming systems.
Another critical area is seal cooling, which is often lumped in with bearing cooling but has its own separate requirements under API 610. Mechanical seals in API 610 pumps operate in a very specific temperature range, and the heat from the seal interface can add 50–100°F to the surrounding components if not managed. API 610 requires that for single mechanical seals operating above 400°F (204°C), either a seal flush plan that includes cooling (like Plan 21 or Plan 23) or an external seal cooling jacket is used. For dual seals, API 610 mandates that the barrier fluid be cooled to a maximum of 180°F (82°C) to prevent seal face degradation. I’ve had customers ask why we can’t just use a lower-cost seal without cooling, and the answer is simple: API 610 will reject the pump if it doesn’t meet the seal temperature requirements, and more importantly, the seal will fail within months instead of years.
Let’s get into the verification and documentation side, because this is what makes API 610 requirements enforceable. As a supplier, we’re required to provide a full data sheet for the cooling system that includes design temperature, pressure rating, flow rate, cooling media type, and material specifications. API 610 also requires that we perform a thermal performance test on every pump above 1000 horsepower, or any pump operating above 500°F, to confirm that the cooling system keeps bearing and seal temperatures within limits. This test isn’t just a paper exercise—we use thermal imaging and RTD (resistance temperature detector) probes mounted directly on the bearing housing and seal chamber to take readings during factory acceptance testing (FAT). I remember a few years back, we had a pump that passed all pressure tests but failed the thermal test, because the cooling jacket had a thin spot that meant water flowed unevenly across the housing. We had to re-manufacture the jacket, and the client appreciated that we caught it before shipment, instead of them dealing with it on-site. That’s the difference between a supplier that checks boxes and one that actually understands API 610’s intent.
Common mistakes I see in cooling system design, even from other “API 610” suppliers, boil down to cutting corners on materials or sizing. For example, using a 0.100-inch wall jacket instead of the required 0.125-inch doesn’t sound like a big deal, but when the pump is cycling between ambient and 500°F, the thinner wall can warp, leading to cooling media leaks into the bearing housing or process fluid. Another mistake is undersizing the cooling lines: API 610 requires that the velocity of cooling water in the lines be between 3 and 10 feet per second to prevent erosion on one end and sediment buildup on the other. Too slow, and sediment plugs the line; too fast, and the line erodes, leading to leaks. We always size our lines with a 15% safety factor, per API 610’s allowance for operating variances, which means our customers rarely have issues with cooling system performance.
What about special services? API 610 has additional requirements for pumps operating in cryogenic services (below -50°F or -46°C) or high-temperature services (above 600°F or 315°C). For cryogenic pumps, the cooling system has to be designed to handle thermal contraction—jackets have to have expansion joints, and materials have to be matched to prevent embrittlement. For high-temperature services above 600°F, API 610 requires that the cooling system be designed for continuous operation at the maximum process temperature, not just a peak load. We recently delivered pumps to a coal gasification plant operating at 750°F, and we had to use Inconel 625 for the cooling jacket instead of carbon steel, because carbon steel would lose strength at that temperature. That’s the kind of detail that only comes from years of working with API 610, not just memorizing the standard’s clauses.
At the end of the day, API 610’s cooling system requirements aren’t just red tape—they’re built on decades of industry experience with pump failures that cost millions in downtime. As a pump supplier that’s been in this game long enough to see those failures firsthand, I don’t look at API 610 as a set of rules to follow. I look at it as a guide that keeps our customers’ pumps running reliably, year after year. If you’re in the market for an API 610 pump, and you want to make sure the cooling system is designed to handle your specific service, not just meet the minimum code requirements, reach out to discuss your application needs. We can walk through the data, the test results, and the design choices that will keep your pump online when you need it most.
Fire Pump References
API Standard 610, 11th Edition (2020), Petroleum, Petrochemical and Natural Gas Industries — Centrifugal Pumps for Heavy-Duty Applications
ISO 10438-2:2017, Petroleum and natural gas industries — Lube systems for general purpose machinery — Part 2: Centrifugal pumps
American Society of Mechanical Engineers (ASME) B31.3, Process Piping
Hunan Sanchang Pump Co., Ltd.
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