Guidelines for Installation and Maintenance of Sea Water Heat Exchangers, Strainers, and Fuel Coolers{1379, 3319} Caterpillar

Engine:Marine 3500 Series

Introduction

Do not perform any procedure in this Special Instruction until you read this information and you understand this information.

The purpose of this Special Instruction is to raise dealer and customer awareness of proper installation and maintenance practices for copper nickel type sea water heat exchangers.

Sea Water Strainers

Purpose

Strainers protect the sea water pump, the heat exchanger and other cooling system components from foreign material in the sea water. The foreign material can plug or coat heat transfer surfaces, causing overheating of the engine. Abrasive, foreign material will erode pump impellers and soft metal parts, reducing their effectiveness.

Location

Install strainers below the boat's water line. Install the strainers as close to the sea water intake or to the sea chest as possible, (adjacent to the sea cock). The strainer must be installed so the strainer can be easily cleaned, even in the worst weather conditions.

Type

While simple strainers, which require a shutoff of the sea water flow, are adequate to protect the engine, greater protection will result from using duplex strainers, which can be cleaned without interrupting sea water flow or engine power.

Size

Properly sized strainers will impose no more than 9 kPa (36 inch of H₂O) restriction to flow at conditions of full sea water flow. Suppliers can help in the proper selection of strainer size by providing the flow restriction of each size of strainer at varying conditions of water flow.

Mesh Dimensions

The strainer screen should not pass solid objects that are larger than 1.600 mm (0.0625 inch) in diameter. Plate type heat exchangers require a mesh that is less than 3.000 mm (0.1181 inch). Tube type heat exchangers require a mesh that is less than 5.000 mm (0.1969 inch).

Differential Pressure Switch for the Strainer

Schools of small fish, floating debris, or ice chips can plug a clean strainer in a few seconds. When the differential pressure across the connections of a strainer goes too high, the strainer needs to be cleaned. A differential pressure switch will provide early warning of the strainer being plugged, which could result in loss of cooling. The switch will also provide the precise location of the problem. A hightemperature of the fluid that is cooled by the sea water may indicate a loss of sea water flow.

Marine Growth

Marine plants and animals will enter sea water piping and take up residence there. Many forms of sea life are very comfortable in the piping of an engine cooling system. The sea life can grow to a size that will threaten adequate flow. Darkness and the abundance of suspended food particles combine to create prime growth conditions for sponges, barnacles, and similar creatures. Strainers are no protection against creatures which are microscopic in size during their infant stages of life. Periodic operation of the vessel in fresh water will rid boats of salt water life infestation. In any case, it will be necessary to clean the corpses from the piping and from the passages of the heat exchanger.

The use of high temperature alarms, pressure switches for the sea water pump, and other instrumentation are recommended. These devices will warn of a gradual loss of sea water flow. Periodic chemical treatment resists marine growth. Chemical type and concentration must be controlled to prevent deterioration of the sea water cooling system components. Contact a knowledgeable chemical supplier. Continuous low concentration chemical treatment via either bulk chemical or self-generating electrical processes are offered by various manufacturers.

Corrosion

Piping System Materials

Electromotive series - A list of metals whose order indicates the relative tendency to be oxidized.

An excellent material for piping carrying sea water is the copper-nickel alloys. The cost makes the use of this piping unusual for all but the most critical systems. Whenever practical, use the same type of material for all the sea water piping. Piping that is made from different metals should not make contact with each other. One of the metals can corrode at a rapid rate.

The materials will corrode according to their position in the electromotive series. Refer to Table 1 for corrosion rates of various metals in sea water.

Black iron pipe is often used in sea water service. Replacement should be planned every two or three years. If it is necessary to use pipe or other cooling system components of more than one material, avoid allowing the dissimilar metals to touch, even by mutual contact with an electrically conductive third material. Corrosion will be much more severe if a flow of electrons is able to pass freely from one of the metals to the other.

Galvanic Corrosion in Sea Water

Noble metal - A metal or alloy, such as gold, that is highly resistant to oxidation and to corrosion.

Electrochemical series - A list of metals that have been arranged in order of their standard electrode potentials.

When two dissimilar metals are electrically connected and both are submerged in saltwater, the metals form a battery and an electrochemical reaction takes place. In this process, one metal is eroded. The rate of deterioration is proportional to a number of factors:

• The differential potential between the two metals on the electrochemical series.

• The relative areas of the two metals: If there is a small area of the more noble metal relative to the less noble metal, the deterioration will be slow and relatively minor. If there is a large area of the more noble metal such as copper sheathing on a wooden hull, and a much smaller area of the less noble metal, such as iron nails holding the copper sheathing to the wood, the wasting away of the iron nails will be violent and rapid.

• Stray electrical currents will accelerate the electrochemical reaction. Proper grounding and isolation from all electrical sources is required.

Dissimilar Metal Combinations to Avoid

• Bronze propeller on steel shaft

• Mill scale on hull plate (internal or external)

• Aluminum fairwaters fastened to a steel hull

• Steel bolts in bronze plates

• Bronze unions and elbows used with galvanized pipe

• Bronze sea cocks on iron drain pipes

• Brass bilge pumps on boats with steel frames

• Brass, bronze, or copper fasteners in steel frames

• Stainless steel pennants on steel mooring chains

• Bronze or brass rudder posts with steel rudders

• Bronze rudders with steel stopper-chains

• Steel skegs (rudder shoes) fastened with bronze or brass leg screws

• Steel and brass parts in the same pump

Rule of Thumb

Do not put iron or steel close to or connected with alloys of copper under salt water.

The Protective Role of Zinc

If alloys of copper (bronze, brass), iron (steel), and zinc are all connected together and submerged in salt water, the zinc will be eaten away, protecting the iron (steel). It is necessary to have a metallic electrical connection to the metals to be protected. This is usually easy to accomplish on a steel hull. It is more difficult on a fiberglass hull, since a special electrical connection may be required unless the zincs are connected directly to one of the metals, preferably the copper alloy.

The zinc must never be painted. When electrical contact is made through the fastening studs, it's desirable to put galvanized or brass bushings in the holes in the zincs so that contact will be maintained as the zincs corrode. Zinc anode rods should be initially inspected after the first 50 hours of operation. The condition of the zinc rod will determine how often the zinc rods should be inspected for possible replacement. As they work, a white, crust-like deposit of zinc oxides and salts form on the surface. This is normal. If the deposits do not form and the zincs remain clean and like new, they are not protecting the structure.

Electrochemical Series

• Corroded End - Least Noble

• Magnesium

• Magnesium alloys

• Zinc

• Beryllium

• Aluminum alloys

• Cadmium

• Mild steel or iron

• Cast Iron

• Low Alloy Steel

• Austanitic cast iron

• Aluminum bronze

• Naval brass

• Yellow brass

• Red brass

• 18-8 stainless steel (active)

• 18-8-3 stainless steel (active)

• Lead-tin solders

• Lead

• 70-30 copper nickel

• Tin

• Brasses

• Copper

• Bronzes

• Copper-nickel alloys

• Monel

• Admiralty brass, aluminum brass

• Manganese bronze

• Silicon bronze

• Tin bronze

• Silver solder

• Nickel (passive)

• Chromium-iron (passive)

• 18-8 stainless steel (passive)

• 18-8-3 stainless steel (passive)

• Silver

• Ni-Cr-Mo alloy 8

• Titanium

• Ni-Cr-Mo alloy C

• Gold

• Platinum

• Graphite

• Protected End - Most Noble

General Corrosion

A protective film is produced on the surface of copper-nickel if fresh clean oxygenated sea water continuously flows at a minimum rate of one meter per second. If long stagnant conditions are expected, blow-drying the system is recommended.

Flow rates greater than three and one-half meters per second can cause the protective film to be eroded.

Polluted water containing sulphides is especially corrosive to copper alloys. Avoid this water, if possible.

Erosion

Flow rates should not exceed two meters per second if the sea water contains sand or debris.

Install pressure taps front and back of the sea water heat exchanger to allow for flow measurement.