Seawater-Resistant Pumps

DEWATERING
SEWAGE

Seawater pumps are indispensable to waterfront development projects and aquaculture facilities. Japan is a maritime nation with the sixth longest coastline in the world. Tsurumi has performed field tests in various marine construction projects under severe conditions over many years, in collaboration with general contractors, and applied the obtained know-how to developing submersible seawater-resistant pumps. Tsurumi also considers economic efficiency important and, therefore, designs pumps with "as many standardized materials as possible."
Tsurumi's standard pumps can be combined with a seawater-resistant kit (optional) that adds a "galvanic anode" and "seawater-resistant special cast iron impeller," to solve both problems of long service life and cost efficiency.

Seawater-Resistant Kit
Mechanism of Metal Corrosion
Corrosion of Stainless Steel

Tsurumi's standard pumps can be combined with a seawater-resistant kit (optional) that adds a "galvanic anode" and "seawater-resistant special cast iron impeller," and enables about two years of service. (The service period depends on operating conditions.) If your pump is to be used for a longer period, contact your dealer.

Galvanic Anodes (with Fittings, Seal Putty)
Seawater-Resistant Special Cast Iron Impeller
304 Stainless Steel Eye Bolts*

*Applicable only with models having steel eye bolts

KTZ33.7
KRS815
LH311W

If seawater-resistant measures are not taken in seawater applications, metal parts corrode, which causes performance drop that can result in pump failure. One suspected cause of corrosion in metallic parts by seawater is the "metal corrosion potential".
In seawater, a metal's resistance to corrosion can be seen clearly. As shown in the illustration of <Bimetallic Corrosion in Seawater>, when metals of different potential contact one another, only the metal of lower potential will corrode while the metal of higher potential is protected from corrosion.
The table of <Potentials of Various Metals in Seawater> shows the corrosion strength/weakness of various metals. As the potential difference increases, the metal of lower potential corrodes faster. For example, with a cast iron impeller and stainless steel shaft, only the impeller will corrode. With a 316 stainless steel impeller and 420 stainless steel shaft, corrosion attacks the shaft first. This is the most important point to be considered in handling seawater.
Based on this principle, a galvanic anode is provided for Tsurumi's submersible seawater-resistant dewatering pumps to protect the pump body against corrosion. To prevent corrosion of the motor shaft, which may not be fully protected by only the galvanic anode, a seawater-resistant special cast iron impeller was developed exclusively by Tsurumi.

< Bimetallic Corrosion in Seawater >

< Potentials of Various Metals in Seawater >

Stainless steel pumps are not absolutely resistant to seawater. After test-running a Tsurumi VANCS-series pump made of stainless steel and resin in seawater for one month, remarkable corrosion occurred in isolated areas of the pump.
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 formed due to an oxygen shortage, that corrosion resistance is considerably reduced.

Crevice corrosion is a phenomenon whereby corrosion concentrates in a crevice that oxygen cannot readily reach, as shown in the pictures of <Example of Crevice Corrosion>. Pitting corrosion looks like a hole and occurs only in areas where marine organisms (barnacles, etc.) attach and consequently deprive the spot of oxygen. Even with stainless steel, localized corrosion will occur, so great caution is required.

< Example of Crevice Corrosion >

Galvanic Anode

The galvanic anode is an electrolytic protective measure used with metals of differing corrosive potentials. Metals of a potential lower (aluminium and zinc) than the pump body (cast iron and steel) are brought into contact with the body via the galvanic anodes and allowed to corrode in order to protect the body. However, the full effect cannot be obtained unless the anodes are installed in the proper positions.
Tsurumi mainly utilizes aluminium because of its superior anticorrosive performance per unit weight, while utilizing zinc for only the strainer stand that is liable to be worn by water current.
Since the galvanic anodes are worn by corrosion, they need to be replaced every two years. They can be replaced easily and used immediately after replacement.

Corrosion Test (in seawater / 1 year)

Seawater-Resistant Special Cast Iron Impeller

While the pump is running, the galvanic anode does not protect rotating parts. In seawater applications, the materials of the shaft and impeller must be carefully matched to avoid shaft corrosion and expensive repairs. After long years of research, Tsurumi developed an exclusive "seawater-resistant special cast iron impeller" suited to protect the shaft against corrosion by seawater.
This material is made by specially treating chromium cast iron. Because its electric potential is slightly lower than that of the shaft, the impeller corrodes gradually, which helps to prevent the shaft from corroding. The impeller needs to be replaced every few years to 10 years, depending on operating conditions. However, the impeller costs far less than the shaft to replace.

Potentials of Various Metals in Seawater

Motor Shaft Corrosion Test (in seawater / 1 year)

A cast 304 stainless steel impeller was mounted on 403 stainless steel shaft.
(The shaft was heavily corroded.)

A seawater-resistant special cast iron impeller was mounted on 403 stainless steel shaft.
(The shaft was protected against corrosion.)

Impeller Corrosion Test (in seawater / 11 months)

Handling seawater with submersible pumps for a long term period is not an easy task. When pumps are not equipped with adequate specifications for use in seawater, corrosion in metal sections may cause the pumps to become worse in terms of performance, or in the worst case scenario, suffer a breakdown.
Supported by demonstrative experiments using seawater over a long time, Tsurumi has continued unremitting research into submersible seawater-resistant pumps, combining both corrosion resistance and durability. As a result, by giving the maximum possible consideration to economy, reliability and dependability, Tsurumi has successfully developed its original submersible seawater-resistant sewage pumps, which have achieved the upgrading of pumps to a level that allows them to withstand even the seawater.
Tsurumi offers a product lineup comprising two series: B-series pumps equipped with channel impeller and C-series pumps equipped with cutter impeller, with the motor output varying from 0.75 up to 15 kW depending on the model. As part of the seawater-resistant specifications, these pumps are provided with a Duplex stainless steel shaft, a frame and a casing made of FC250 cast iron, 3-layered Epoxy resin paint coating, and a Galvanic anode (optional), with a choice of either 316 stainless steel (DS version) or FC250 (DF version) as the impeller material. In addition, these pumps are equipped with an anti-wicking cable, motor protector, dual inside mechanical seals with silicon carbide faces, Oil Lifter and the like, as in the case with standard Tsurumi products.
Submersible seawater-resistant sewage pumps have a wide range of uses including sewage drainage mixed with seawater, transfer of sewage/wastewater from water treatment facilities in plants and commercial buildings, water intake/discharge at pumping stations and shipyards in coastal areas, desalination plants and the like.

The B-series is a submersible channel impeller pump designed for handling raw sewage, wastewater and heavy-duty industrial applications, where the pump is subject to complete submersion and requires maximum reliability.
The C-series is a submersible cutter pump for sewage and wastewater, which is made of casting and equipped with cutting mechanism. Featuring a combination of impeller vane with brazed sintered tungsten carbide alloy edge and a suction cover of serrated shape, the C-series pumps enable smooth pumping, while cutting solid and fibrous matter during suction.

For 60 Hz models, please contact your dealer.

Selection Table

		DS version Example Model 100B43.7-DS	DF version Example Model 100B43.7-DF
Applicable Series		B-series (Channel Impeller) C-series (Cutter Impeller)
Discharge Bore (mm)		50 - 150
Motor Output (kW)		0.75 - 15
Materials	Shaft	Duplex Stainless Steel (JIS Grade SUS329J4L)
	Cast Iron Grade	FC250
	Suction Cover	FC250 Cast Iron (B-series) High-chromium Cast Iron (C-series)
	Impeller	316 Stainless Steel Casting	FC250 Cast Iron
Surface Painting		Epoxy Resin Paint
Galvanic Anode		Option

If seawater-resistant measures are not taken in seawater applications, metal parts corrode, which causes performance drop that can result in pump failure. One suspected cause of corrosion in metallic parts by seawater is the “metal corrosion potential.”
In seawater, a metal’s resistance to corrosion can be seen clearly. As shown in the illustration of <Bimetallic Corrosion in Seawater>, when metals of different potential contact one another, only the metal of lower potential will corrode while the metal of higher potential is protected from corrosion.
The table of <Potentials of Various Metals in Seawater> shows the corrosion strength/weakness of various metals.
When the metal of higher electrode potential, duplex stainless steel, SUS329J4L is in contact with a metal of lower electrode potential, 316 stainless steel or cast iron, duplex stainless steel is protected from corrosion. Weaker metal, common stainless steel or cast iron, corrodes away.
Therefore, when shaft material is SUS329J4L and the impeller is made of 316 stainless steel or cast iron, shaft is eventually protected from corrosion and the impeller acts as a galvanic anode. The impeller needs to be replaced every few years depending on operating conditions. However, replacement of the impeller costs far less and is easier than that of the shaft. Hence the material combination brings notable benefits to reduce repairing cost and enhance maintainability for pump usage in a long time.

< Bimetallic Corrosion in Seawater >

< Potentials of Various Metals in Seawater >

Duplex Stainless Steel - JIS Grade SUS329J4L (EN 1.4481) -

Shaft Material

Duplex stainless steel SUS329J4L is a 25% chromium duplex ferritic-austenitic stainless steel designed to provide a superior combination of high strength and excellent corrosion resistance for a wide variety of applications, especially in corrosive seawater usage.
This alloy consists a microstructure of a balanced mixture of austenite and ferrite. The combination of these phases develops the unique combination of strength and resistance for chloride stress-corrosion cracking of this alloy.

FC250

Cast Iron Material

Cast iron components are made of FC250 grade gray cast iron. FC250 cast iron has higher resistance under tension and is also harder than FC200 cast iron material.

Epoxy Resin Paint

Surface Painting

3 layers of epoxy resin provide extra protection to the metallic components of the pump from direct exposure to corrosive medium.
180μm of minimum thickness has been maintained throughout the painted components. Epoxy layer preventing direct exposure of metallic components to corrosive medium acts as an electrical resistance between metal and the medium, and hence improves corrosion resistance.

Galvanic Anode (Option)

Cathodic Protection

The galvanic anode is an electrolytic protective measure used with metals of differing corrosive potentials. Metals of a potential lower (aluminium and zinc) than the pump body (cast iron and steel) are brought into contact with the body via the galvanic anodes and allowed to corrode in order to protect the body. However, the full effect cannot be obtained unless the anodes are installed in the proper positions.
Tsurumi mainly utilizes aluminium because of its superior anticorrosive performance per unit weight, while utilizing zinc for only the strainer stand that is liable to be worn by water current. Since the galvanic anodes are worn by corrosion, they need to be replaced every two years. They can be replaced easily and used immediately after replacement.

Corrosion Test (in seawater / 1 year)

Seawater Pumps | TM-series

Tsurumi also offers
submersible seawater pumps, the TM-series.

All the wetted parts of this pump are made of titanium and resin, which provides the highest corrosion resistance to seawater. The TM-series is available in 0.25 to 3.7kW motor output, and both single-phase and three-phase models.