Skip to content 
Submersible seawater pump
To prevent corrosion of metal parts, Tsurumi’s submersible seawater pumps use titanium for all metal parts, including plugs, bolts and nuts, that come in contact with liquids. Titanium is suitable for handling seawater, but it is extremely expensive, which can make it disadvantageous in terms of material costs. To counter this problem, the TM-series pumps use titanium in combination with the same highly-functional resin that Tsurumi has adopted in its VANCS-series of resin pumps, so both problems — resistance to seawater and cost — are solved.
Difficulty in handling seawater
Seawater is difficult to handle with general pumps if the pumps are not provided with countermeasures, because seawater causes corrosion, resulting in pump performance deterioration and, in the worst case, pump failure. In conventional applications for handling seawater, stainless steel pumps and submersible pumps with coated castings are used. However, stainless steel pumps suffer localized corrosion in the form of crevice corrosion and pitting corrosion, while cast pumps corrode as the coating peels off. The truth of the matter is that the service-life of these pumps is relatively short because of corrosion.
Corrosion of stainless steel
In seawater handling applications, stainless steel pumps are generally used. However, stainless steel parts still suffer localized corrosion that eventually causes insulation failures due to water intrusion into the motor in a short period of time, which may result in unexpected cost increases. Stainless steel provides high corrosion resistance when a protective film of chromium oxide is formed on the surface. However, if the protective film is not maintained due to an oxygen shortage, corrosion resistance will be considerably reduced. For example, if packing or marine organisms (barnacles, etc.) adhere to the chromium oxide film, an oxygen shortage occurs under the adhering substances, so the chromium oxide film is not integral. If the pump is kept running in such a condition, localized corrosion occurs in the form of crevice corrosion and pitting corrosion. Therefore, even with stainless steel pumps, thorough caution is required. What this means is that stainless steel pumps are not absolutely resistant to seawater. As a result of our field tests using seawater, crevice corrosion occurred in the stainless steel motor frame, bolts, nuts and washers after about 6 months of operation. And, in particular, the motor shaft was extremely damaged by heavy corrosion.
