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Piping systems for cargo ship's machinery spaces

A ship's machinery space contains hundreds of metres of piping and fittings. The various systems are arranged to carry many different liquids at various temperatures and pressures. The influences of operational and safety requirements, as well as legislation, result in somewhat complicated arrangements of what are a few basic fittings. Valves, strainers, branch pipes, etc., are examples of fittings which are found in a pipe system.

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Pipes: Machinery space pipework is made up of assorted straight lengths and bends joined by flanges with an appropriate gasket or joint between, or very small-bore piping may use compression couplings. The piping material will be chosen to suit the liquid carried and the system conditions. Some examples are shown below .

Where piping is to be galvanised, the completed pipe with all joints fully welded is to be hot dipped galvanised. The pipes are supported and held in by hangers or pipe clips in such a way as to minimise vibration. Steam pipes or pipes in systems with considerable temperature variation may be supported on spring hangers which permit a degree of movement. An alternative to spring hangers is the use of expansion loops of piping or an expansion joint.

Machinery spaces piping system - various fittings

Mud boxes: Mud boxes are fitted into the machinery space bilge suction piping. The mud box is a coarse strainer with a straight tailpipe down to the bilge . To enable the internal perforated plate to be cleaned when necessary, the lid of the mud box is easily removed without disconnecting any pipework.

Suction pipes

Suction pipes in tanks should be arranged with a bell mouth or foot. The bell end or foot should provide an inlet area of about one-and-a-half times the pipe area.

It should also be a sufficient distance from the bottom plating and nearby structure to provide a free suction area, again about one-and-a-half times the pipe area.

Mud box

Fig:Mud box

Steam traps

Steam trapFig:Steam trap

A steam trap does as its name implies and permits only the passage of condensed steam. It operates automatically and is situated in steam drain lines. Various designs are available utilising mechanical floats which, when floating in condensate, will enable the condensate to discharge . Other designs employ various types of thermostat to operate the valve which discharges the condensate.

Expansion pieces

Expansion bellows pieceFig:An Expansion bellows piece

An expansion piece is fitted in a pipeline which is subject to considerable temperature variations. One type consists of a bellows arrangement which will permit movement in several directions and absorb vibration . The fitting must be selected according to the variation in system temperatures and installed to permit the expansion and contraction required in the system.


Drains are provided in pipelines and usually have small cocks to open or close them. It is essential that certain pipelines are drained regularly, particularly in steam systems. When steam is admitted to a pipeline containing a reasonable surface of water it will condense and a partial vacuum occur: the water will then be drawn along the pipe until it meets a bend or a closed valve. The impact of the moving water in the pipework will create large forces known as 'water hammer', which can result in damage to pipework and fittings.

Connection to pumps

Pipes are connected to pumps by flanges. Flanges are a potential weak point in a piping system. Occasionally, and to provide the correct pressure from a pump, a calibration orifice is fitted in the delivery piping. This can result in turbulent fluid flow and cause abrasive corrosion or erosion. Welded flanges are prone to accelerated corrosion in the weld metal or in the heat-affected zone. Pipes in wet areas where corrosion is likely need to be examined at regular intervals (six-monthly).

Pipe joints

The preferred method for connecting two lengths of steel pipe, whether a straight, elbow or tee joint, is with a flange. With the possible exception of small-bore pipes in low-pressure systems, pipes are not normally connected by threaded joints.

Mechanical, expansion or sliding joints are fitted in longitudinal pipes to allow the pipe to move when a ship bends and flexes, or to cater for thermal expansion. Expansion joints are not fitted where there is regularly high stress, nor are they used inside cargo holds or tanks. Expansion joints should never be used as a permanent connection for corroded pipes after a temporary repair. Classification society rules define which piping systems to use and the positions where expansion joints can be fitted. Only approved expansion joints are allowed.

Clips and supports

Clips and supports are used to hold pipes in position and to prevent movement or vibration. A vibrating pipe can ‘work harden’ and fail. Pipes can fracture when there is insufficient support.

There are no hard and fast rules about the number of clips required in a length of pipe as this will depend on the pipe’s diameter, length, its position and the density of fluid conveyed. The contact area at the surface of the pipe requires protection. Failures often occur as a result of mechanical wear when the clip loosens, allowing the pipe to move. Inspection procedures must be designed to ensure that all clips are checked regularly, including those hidden from sight behind insulation or under engine room floor plates. Special attention should be paid to clips in concealed places.


Valves are fitted to isolate sections of pipe and will typically be found at suction points, crossovers, feed lines, delivery lines and where pipes need to be removed. Valves connected to the shell are flanged and made of steel or other ductile material. Grey or nodular cast iron cannot be used for boiler blow-down valves, for valves fitted to fuel oil or lubricating oil tanks, or for shell valves. Shell valves should be tested regularly, on a monthly basis, by opening them. Marking valve handles with high-visibility paint will help with identification during an emergency.

Cast iron valves have a service life shorter than those made from cast steel. Consequently, they need careful examination during a special survey.

Machinery space pipework material

Waste steam :Carbon steel to BS 3601

SW circulating :Aluminium brass

Wash deck and firemain :Carbon steel to BS3601 — galvanised

Bilge and ballast :Carbon steel to BS3601 - galvanised

Control air :Copper

Starting air :Carbon steel to BS 3602

All system pipework throughout the vessel is to be periodically inspected for condition and security in a systematic manner and be reported upon in the PMS. It is of utmost importance to include in these inspections the pipework located in those spaces that are remote, poorly lit and may be difficult to access.

Particular attention should be paid to sea water pipework which may be subject to corrosion and wastage on both internal and external surfaces, and opportunity should be taken whenever possible, and certainly during drydocking periods, to establish pipewall condition by hammer testing and visual inspection of internal surfaces in locations where valves or pipe sections have been removed for routine maintenance, repair or replacement. Defective pipework is to be replaced at the earliest convenient opportunity.

Classification societies have specific requirements with regard to ships’ piping systems that follow the general survey criteria. The survey involves extensive examinations and checks to show that all piping systems are in satisfactory condition to allow the ship to operate and for the new period of class to be assigned (provided proper maintenance and required interim surveys are carried out).

Machinery and all piping systems used for essential services are examined and tested under working conditions, as considered necessary by the surveyor.

Steam pipes are specially examined. Superheated steam pipes with a steam temperature exceeding 450°C require additional tests.

Piping systems for fuel or lubricating oil are carefully examined.

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