Water & Wastewater Asia Mar/Apr 2018

WATER & WASTEWATER ASIA March / April 2018 54 / TECH ROUND UP Tsurumi has spent decades improving their pumps’ durability and maintainability. With their submersible pumps, users can once again be assured of quality, reliability and safety. S ince its founding in 1924 in Japan, Tsurumi Manufacturing Co., Ltd. has been manufacturing, purchasing and selling va r i ous pumps and re l a t ed equipment. A key product in its line-up is the submersible pumps, which is ideal for difficult-to-handle liquids, such as seawater, corrosive and high-temperature liquids, as well as general wastewater. Why Tsurumi submersible pumps? To prevent corrosion on the metal parts, titanium is used for Tsurumi submersible seawater pumps. This includes the plugs, and bolts and nuts; parts that come in contact with liquid. While titanium is a suitable material for handling seawater, it is an expensive material. 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, hence, the issues of corrosion and cost are resolved. Harsh liquid with TM- series Seawater can cause corrosion and deterioration of pump performance, or in a worst-case scenario, pump failure, if not handled properly. In conventional a p p l i c a t i o n s , stainless steel and submersible pumps with coated castings a r e u s e d . C a s t pumps corrode as the coating peels off while stainless-steel pumps suffer from localised corrosion in the forms of crevice and pitting corrosion — leading to a relatively short service life for these pumps. The corrosion with stainless steel pumps, which may eventually cause insulation failures due to water intrusion into the motor in a short period of time can result in unexpected costs. Stainless steel only provides high resistance to corrosion when a protective film of chromium oxide is applied onto the surface. However, if the protective film is affected by shortage in oxygen, the resistance will reduce considerably. For example, if packing or marine organisms (barnacles, etc.) adhere to the chromium oxide film, there will be a shortage of oxygen under the adhering substances. If the pump continues to run under this condition, localised corrosion will occur. Hence, caution is required even with stainless steel pumps. This is proven with our field test whereby the crevice corrosion occurred in the stainless-steel motor frame, bolts, nuts and washers after about six months of operation. In fact, the motor shaft was extremely damaged by heavy corrosion. Results from field test The following depicts the condition of a VANCS-series pump (made of 304 stainless steel and resin) and the TM-series pump (made of titanium and resin) after six months of operation in the seawater. The results reflect the resistance to corrosion of the TM-series pump to seawater. The TM-series pumps are suitable for handling seawater.