These are scenes of avoidable and expensive disasters did they occur due
to bad design inadequate maintenance or incorrect operational procedures
experience shows that a large number of machinery breakdowns occur due to a
mistake in operation or maintenance of the alarm systems and the protection
devices yes engines generators boilers compressors
do break down sometimes fatally damaged because the alarm systems and the
protection devices monitoring them have been prevented from working sometimes
deliberately disconnected sometimes clogged up with paint and forgotten
abandoned without checking for long periods of time
this of course is asking for trouble when only a little attention to detail
by duty engineers could avoid an unforeseen incident resulting in
possible injuries of people major machine breakdowns upsetting the
commercial operation of the vessel leading to extra workload for ship's
personnel
once are less than meticulous checking and maintenance regime of the alarm
systems is allowed to develop onboard ship things can go wrong at any time the
ship's systems cease to be reliable because no one can be sure which alarm
is working and which is not
now what a blackened
this can occur as a direct consequence of neglecting the alarm system and
protection devices now the search begins what caused the blackout how long will
it take to get things going again why isn't the standby generator or the
emergency generators starting how long will it take to find the answer an
unscheduled event like this can cause consequential breakdowns as well let's
hope it's not too bad
unfortunately a ship cannot run on the basis of hope alone the engineers on
board ship must be sure that the alarm systems work properly at all times there
is no other way
let's leave this nightmare scenario now and look at a typical schematic view of
an alarm and protection system and its function a typical alarm circuit has a
censoring device such as a level sensor a thermocouple or pressure sensor these
are normally connected to display devices
which may have minimum and maximum values marked on them when these values
are reached a switch is activated and an electrical
or pressure signal is sent to the ship's alarm panels and audio-visual warning
devices the light on the panels will remain on or continue flashing until the
alarm has been acknowledged by the duty engineer and the condition which has
caused the alarm to activate is removed if it is a protection circuit as well as
a warning circuit the activation of the limit switch also initiates a shutdown
procedure of the affected machines that is the protection circuit activates one
or more switches or valves causing the protective machine to come to an
unscheduled halt but in a controlled manner this is how the system looks
using internationally recognized symbols
a typical example of this system operates on a main engine or on a
generator diesel the sensor may be a lube oil temperature or pressure sensor
or cylinder liner temperature sensor any one of these may indicate action devices
as well as some less important circuits
do you know which circuits on your ship are very important than which a less sir
if you came across a faulty sensor would you know if it was part of a
top-priority circuit or a relatively less critical one you need to know
all alarm and protection devices would protect the main propulsion engine and
the steering system are of top priority as are those on the power generation
plant and steam boilers these plants are vital components of ship's control any
breakdown or serious loss of these functions can be catastrophic for the
ship and its crew
still very important but not top priority are the alarms and protection
devices monitoring the air compressors air conditioning systems and
refrigeration systems they may not be as critical in the North Sea as they are in
the Gulf other systems such as cargo pump alarms or bow thruster alarms may
be low or high priority depending on the ship's working condition there are
warning only alarm systems which do not protect but warn of
potentially hazardous conditions arising these are normally level indicators or
temperature sensors in tanks and heating or cooling systems
now let's look at census starting with level indicators these monitor liquid
levels in fuel tanks lube oil tanks boilers and the like the simplest
systems are activated by the liquid itself the device is activated by the
level of the fuel rising or sinking a bath or below the set safety levels when
this occurs a sensor sends a signal to the warning devices coupled usually with
an indicator one of the most important level alarms onboard ship monitors the
boiler water level it is critical to maintain the right water level in
pointers especially in high pressure water tube boilers to ensure safe
operation a very dangerous situation can rapidly arise if the water quantity
inside the boiler is not maintained at the correct level there are visual level
indicators as well as alarm sensors monitoring the water level to check that
it is within set safety limits whilst we're dealing with boilers we must
mention a unique sensor and alarm circuit known as the flame out alarm
system a sudden loss of flame inside the boiler can lead to many undesirable
consequences therefore optical sensors flame eyes provide continuous monitoring
of the presence of flame and will give instant warning should the flame go out
the main propulsion engines alarm and protection devices can be looked at as
the most important ones onboard ship
on a typical diesel unit these employ temperature and pressure sensors which
monitor operational conditions to ensure optimum operation and effective
lubrication
for example the temperature sensors check the jacket cooling freshwater
outlet the lube oil inlet the fuel oil inlet and the reduction gear lube oil
inlet these are all of primary importance the pressure sensors monitor
the main lube oil inlet the reduction gear lube oil inlet the turbocharger
lube oil inlet and the cooling fresh water inlet among others these are all
part of the main engines protection system as well as providing warning
signals identical systems operate on other diesel engines such as those
driving the generators
because of their critical function these sensors must be tested regularly in
accordance with the ship's maintenance or test schedules ensuring accurate
function only sensors supplied with a valid certificate or assurance of
calibration should be installed and only calibrated test instruments must be used
for testing
here a temperature sensor is tested at both the minimum and maximum limits of
its operation
the quality control is on the measuring device attached to the testing
instrument
this one is using an oil bath with a controlled heating device and calibrated
thermometer
details of the test are recorded for future reference
the alarm setting can usually be read from the central monitoring system
provided that it can be demonstrated as operational this is done by resetting
the alarm to a normal value or by simulating an alarm value
but the most convenient method for this test is the use of a test pump and gauge
here a lube oil Inlet pressure sensor is tested with a precision testing
instrument
testing level alarms sometimes involves activating the alarm manually in this
case a builds well alarm and monitoring the response in accordance with the set
parameters
the test results should then be recorded for future reference
all these tests are most important to ensure that the monitoring system is
reliable at all times
the ship's manual will provide the necessary details for each test
applicable to the system's onboard
each engineer on board must know the alarm and protection systems thoroughly
including their relative importance to the ship's proper function each time an
alarm activates the duty engineer must be able to answer a number of critical
questions what does not alarm signify how important is the system to which it
relates what measures must be taken to eliminate the cause of the alarm
condition in what order should the countermeasures be executed
in conclusion it is essential that you know your ship's alarm system and
protection devices let you pay special attention to the critical alarm circuits
onboard ship that you always follow the alarm systems maintenance schedule and
ensure that all sensors and display systems are fully functional when an
alarm condition arises never press the reset without noting the cause of the
alarm if an adjustment must be made to temperature or pressure switches it is
essential that a calibrated instrument is used and direction of change is taken
into account for example when setting the starting pressure of a compressor
the setting should be the design figure with the pressure dropping when an
adjustment has been made always repeat the tests at different values no
adjustment should be permitted without checking at least two values afterwards
when an automatic restart circuit is involved in machine control it should
always be switched to manual and off before pressing reset to avoid the
machines starting automatically when reset equipment should never be
restarted or put back into service without rectifying the cause of the
alarm trip any abnormal run indication should always be investigated even if
the equipment is apparently running smoothly
the engineer on watch must have confidence in the alarm system and
protection devices in the engine room
he must be short all times that he will be given timely warning of any changing
condition which may lead to a breakdown so that he can take remedial action this
confidence is an essential component of good engineering practice