Blog · Sourcing guide · 2026-07-24
Marine cooling water system spare parts — a sourcing guide for heat exchangers, sea water pumps and thermostatic valves
A commercial vessel's cooling-water circuit combines gaskets, plates, pumps, valves and instrumentation whose materials and duties must be matched carefully. Two things make this circuit different from the others on board. The first is that most of it has sea water on one side, so material is not a preference but the whole specification: the same exchanger frame is built with stainless plates for a fresh-water duty and with titanium for a sea-water one, and the two are not told apart by looking at them. The second is that the circuit is a loop, so a symptom appears a long way from its cause. A jacket temperature that will not come down can be a fouled exchanger, a thermostatic element that has failed open, or a pump that is no longer delivering, and the three are three different orders. This guide covers frequently encountered OEM families, four recurring spare-part groups, the data needed to identify each unit and the supply-route context considered at RFQ stage. It does not quote lead times or prices — those depend on the specific unit, vessel schedule and supply route confirmed during quotation.
Which OEM families are common on commercial vessels
Several OEM families recur across marine cooling-water component groups. Correctly identifying the family and exact unit is the first step for any RFQ, and on this circuit the unit is more often identified from the frame than from a part number, because plates and gaskets are consumed and reordered while the frame stays for the life of the vessel.
- Plate heat exchangers — Alfa Laval (M and T gasketed frames, AlfaNova, WideGap), SWEP (B/F/V, brazed and gasketed), APV / SPX Flow (ParaFlow), Kelvion (formerly GEA PHE, NT and NX series), Sondex, Tranter, Funke, Hisaka. An Alfa Laval JWP in the same engine room is a freshwater generator, not a cooler: its plate pack is identified from the generator's own type designation and plate count, not from a cooler frame.
- Shell-and-tube heat exchangers (fresh water and lube oil coolers) — Bloksma, Alfa Laval, Bowman, Serck Como, Kelvion, and coolers supplied with the engine by the engine builder (MAN B&W, Wärtsilä, MaK).
- Sea water pumps — Naniwa, Shinko, DESMI (NSL and DSL in-line centrifugal series), Iron Pump, Allweiler, Taiko Kikai. Imo is not on this list: it builds rotary three-screw and gear pumps for oil and fuel duties. See our marine pumps guide for the full pump-family breakdown.
- Thermostatic (three-way) valves — engine-builder OEM valves and specialist valve makers. Take the valve maker from the plate on the valve housing, because the engine documentation may list the valve only under the engine builder's own part number.
- Expansion tank fittings, sight glasses, air vents and drains — Klinger, Georg Fischer (GF), Danfoss, and vessel-specific OEM specifications.
Plate heat exchangers — plate and gasket identity is the RFQ challenge
Plate heat exchangers are identity-sensitive because the plate pattern, plate material (SS 316, titanium, SMO 254, nickel-based alloys) and gasket compound (NBR, EPDM, HNBR, FKM) all affect the correct spare. How the type code on the frame is read is set out frame by frame for Alfa Laval M-series and Kelvion NT and NX coolers. Send the following with the RFQ:
- Nameplate photo — with the manufacturer, model designation and serial number. On Alfa Laval M-series the model looks like "M10-BFG" or "M15-MFG". SWEP nameplates give the type as "B25" or "V80THx". Kelvion plates read like "NT100M". Photograph the plate itself as well as the frame plate where the pack is open: the plate pattern is stamped on the plate and it is what a supplier matches, while the frame designation only narrows the family.
- Plate count — the number of plates in the pack. Often stamped on the frame or in the vessel documentation. Send the tightening dimension alongside it. A gasketed pack is closed to a dimension between the frame plates rather than to a torque, so that figure and the plate count together say whether the pack is complete and correctly closed, and a pack that has lost plates over the years reads immediately in the comparison. It is also worth noting that plates hang in complementary patterns, so a pack is not simply a number of identical parts.
- Plate material and gasket compound — confirm these against the original duty and vessel documentation. Titanium or another corrosion-resistant grade is often specified for sea-water service, while fresh-water duties may use stainless steel. In a central cooler the same plate has sea water on one face and the closed fresh-water circuit on the other, so its material is set by the sea-water side; do not infer the material from appearance alone. Titanium and stainless look alike in a frame, and a titanium plate fitted where stainless was specified is mainly a cost question, while stainless fitted where titanium was specified is exposed on the sea-water side to chloride pitting and to crevice corrosion under the gasket. The gasket compound carries the same weight: a compound chosen for a jacket-water temperature is not the compound for a hot-oil duty, and the two are the same colour more often than not.
- Service side and duty — sea water / fresh water / lube oil / jacket cooling. Some plate patterns are optimised for high viscosity, others for low pressure drop. Where the exchanger has been re-plated before, say so and say with what, because a pack that was changed to a different pattern at some point is no longer described by its original documentation.
- Old order or part-book reference — if the vessel has a spare-plate history, the previous order is a strong anchor.
Sea water pumps — identity from nameplate and driven-end configuration
Marine sea water cooling pumps are single-stage centrifugal pumps, and in many engine rooms they are vertical in-line units with the motor carried above the casing; larger duties also use double-suction in-line builds. The main identity fields are pump maker, model as cast or stamped on the plate (e.g. Shinko SVA, DESMI NSL or DSL), impeller diameter as fitted rather than nominal, casing material and mechanical seal specification.
For gasket kits and mechanical seal sets the identity evidence is the same as for the general pump guide — refer to marine pumps sourcing guide. What is specific to sea water service is the material specification: bronze / gunmetal / super duplex for wetted parts, ceramic / carbon / silicon-carbide face pairing for the seal, and the specific corrosion allowance. Add whether the pump has been running dry or intermittently. A sea-water pump that sits stopped in a warm engine room with sea water in it corrodes differently from one that runs continuously, and that history explains why a wet end is being renewed sooner than the hours suggest.
Thermostatic valves — element vs housing distinction
Thermostatic valves may be ordered as a complete valve or as a replacement thermostatic element. The element is a calibrated cartridge with a specific temperature set point, and the correct value must come from the installed unit or its documentation. Which of the two is being asked for is worth deciding before the enquiry rather than during it. A valve that is passing, hunting or holding the wrong temperature is an element question first: the element is what carries the set point and what fails with age, while the housing usually outlives several elements. A valve that is leaking externally or has a damaged flange face is the opposite case. Send the following:
- Valve maker and model, as stamped on the valve plate.
- Set point temperature (stamped on the element, on the housing, or in the vessel documentation).
- Whether the replacement is the full valve, the element cartridge, or a gasket / seal set. On a multi-element valve say how many elements the housing carries and whether all are being renewed, since elements age together and a single new one against several old ones does not restore the control the valve had.
- Line size, flange standard and rating for full-valve replacement, read from the body casting or the flange itself. Name the standard (EN/DIN PN, JIS or ASME class) as well as the size: flanges built to different standards are generally not interchangeable, and a valve body ordered to the wrong one will not bolt to the existing pipework.
OEM route vs verified alternative
For plate heat-exchanger plates and gaskets, a documented third-party option may be considered when geometry, material, gasket compound, warranty conditions and class requirements have been confirmed. Vessel Core records the proposed route for each RFQ line. For sea-water pump wet-end components such as impellers, wear rings and casings, casting tolerances and corrosion allowances must match the specific pump family. The casing material belongs in that assessment as well as the component material, because on sea-water duty the two are selected as a pair and a wet-end part in a more noble alloy than the casing moves the corrosion into the casing instead of solving it.
Thermostatic elements are factory-calibrated components. Whether the route is OEM or an alternative, confirm the element model, set point, fit and documented calibration for the exact valve.
What we cannot promise before the RFQ is reviewed
Vessel Core does not quote cooling-water spare-part prices, lead times or supply route before the specific unit, application and identification data are confirmed. A shell-and-tube bundle quoted without saying which side carries sea water, and a pump wet-end part quoted without the casing material, are in the same position: the right part depends on information the unit designation does not carry. A plate heat-exchanger quotation remains preliminary until the plate count, material and gasket specification are known. The same applies to a thermostatic element quoted without its set point, since the set point is the element rather than a setting made on installation.
How to send the RFQ
Use the RFQ form. Attach a clear nameplate photo and include the duty, plate count, material and gasket specification where relevant. Use the RFQ evidence checklist to review the fields item by item.
Frequently asked questions
What is the critical identity evidence for plate heat exchangers?
Nameplate photo (Alfa Laval M/T series, SWEP B/F/V, APV ParaFlow, Kelvion NT/NX), plate count, plate material (SS316 / titanium / SMO 254), gasket compound (NBR / EPDM / HNBR / FKM), and service side (sea water / fresh water / lube oil / jacket cooling).
Why does the plate material matter so much?
Plate material must match the original duty, chloride exposure, temperature and approved specification. Titanium or another corrosion-resistant grade is often specified for sea-water service, while some fresh-water duties use stainless steel. A mismatch can accelerate corrosion and lead to premature leakage.
What identity evidence does a thermostatic valve need?
Send the maker and model as stamped on the valve plate, the set-point temperature stamped on the element, whether the requirement is a complete valve or element cartridge, and the exact line size and flange rating. The set point has to come from the installed element or the vessel documentation.
Are aftermarket plate heat exchanger plates safe?
A documented alternative may be considered only after plate geometry, material grade, gasket compound, duty and applicable warranty or class requirements are confirmed. For sea-water service, verify the exact material specification rather than relying on appearance or nominal dimensions.
How does the sea water side differ from fresh water side at RFQ time?
Sea-water service often uses more corrosion-resistant plates, tubes and wetted components, while fresh-water duties may use different stainless grades and gasket compounds. Confirm the original material, gasket, corrosion allowance and duty data for the exact exchanger rather than applying a generic sea-water or fresh-water rule.
