Seawater-Resistant Pumps

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 Pumps Lineup

  • KTZ Seawater-Resistant Pumps
  • KRS Seawater-Resistant Pumps
  • LH Seawater-Resistant Pumps LH-W Seawater-Resistant Pumps

Seawater-Resistant Kit

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

Catalogue Download

Mechanism of Metal Corrosion

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 >

Corrosion of Stainless Steel

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)

without galvanic anode
with galvanic anode installed

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)

High-chromium cast iron
Seawater-resistant special cast iron