STRUCTURAL INSULATION

There are two main purposes of structural insulation on a ship :

a)  THERMAL INSULATION : A ship’s steel structure will conduct heat very well . In way of 

heated tanks , refrigerated spaces and exposed accommodation spaces some form of insulation is

necessary to reduce the heat flow to an acceptable level .Thermal insulation is also provided on A & B class fire divisions to delay the temperature rise of 

unexposed side in case of fire .

 b)  ACOUSTIC INSULATION : Sound results from the movement of air particles and travels in theform of waves away from the source . There are many sources of sound onboard ship , such as

 propulsion and auxiliary engines , ventilation fans etc. These would have a cumulative disturbing

effect on the personnel if allowed to continue unchecked . Additionally insulation may be required against transmission of vibration apart from sound . Steel structure is a good transmitter of sound and 

vibration .

INSULATING MATERIALS : Rockwool , Glasswool , Stonewool , Cork , Ceramic fibre & Plastic

foam are some of the materials which can be used for thermal insulation of ship’s structure .

Insulating material is available in the form of slabs ,wired mats and wired mats or slabs reinforced 

with dustproof or vapour barrier sheets . These slabs/mats have to be cut to the desired sizes for fixingthem onto the structure . The thickness and quality of insulation fitted in a compartment is decided by

the acceptable temperature within the compartment or the temperature rise criteria on the unexposed 

side , for a fire division .

FIXING OF THE INSULATION :Fastening of insulation is usually done by pinning it to the bulkhead , but there are examples where

the insulation slabs may be glued to the bulkhead or deck . In case of fastening of the insulation on

the steelwork the following steps are involved :

a)  WELDING OF PINS TO THE BULKHEAD/DECK : A stud gun/welding gun is used to weld 

 pins to the steelwork . The pins are of 3mm in diameter and either made up of stainless steel or of mild steel and coated with copper to prevent corrosion and give increased life . The length of the pins

are chosen in such a way that after allowing it to pierce through the insulation and putting the lock 

(spring) washer it will project out by about 10mm . The welding of the pins is carried out at a distance

of not more than 300 mm to ensure that insulation slab placed is firmly secured and remains incontact with surface without bulging out .

 b)  PAINTING THE STEEL WORK : After welding all the pins on the steelwork it is required to be

 painted over by a corrosion protection paint . It is to ensure that the steelwork remains protected against corrosion , which normally will not be visible and accessible for the duration insulation stays

in place .

c)  CUTTING OF INSULATION : The insulation slabs/mats can be cut using special knife/scissorsor in case of large quantities even a power saw can be used . Normally insulation is cut approximately

2-5 mm oversize so as to get a tight fitting between adjacent insulation layers .

d)  INSTALLATION OF INSUALTION : 1)depending on the construction it is recommended tostart with the insulation of the stiffeners , first by filling out the spaces in between the stiffeners and 

the steel plating .The insulation should fit exactly the profile structure . 2) Next insulate around the

stiffener with the required thickness . 3) Next insulate the plating in between the stiffeners . The joints

 between the insulation should be tight and air gaps should be found . NOTE : In case more than one

 

layer of insulation is required , the second layer should be placed on the first layer in such a way thatthe joints should be staggered by at least 150 mm ( so that joints are not sitting one on top of other )

e)  SECURING/FIXING OF INSULATION : Spring lock washers are pushed into the projecting

 portions of the pins for securing the insulation in place . The pins will remain projection out by about1 mm after placing the washer . The spring washers are of stainless steel or mild steel galvanized to

 prevent corrosion .

f)  COVERING OF STEEL WASHERS : A plastic cap may be fitted on the projecting pin surfacefor covering up the steel spring washer to give a nice appearance .

VAPOUR BARRIER /LINING/FACING : Normally the insulation material is fibrous in nature and 

can absorb moisture , liquids and vapours which leads to deterioration in quality as well as leads to a problem of spontaneous combustion in case of oil getting soaked on the insulation of a hot surface .(if 

insulation material on a hot surface gets soaked with oil , the oil soaked into the material may ignite

spontaneously due to heat ) . In case of liquid/moisture/vapour absorption the quality and insulationdeteriorates and sometimes insulation may be required to be renewed completely . Additionally

 physical damage to the insulation may also take place .

Sometime insulation material comes covered with vapor barrier and reinforced with wired mat .Where it is not , an aluminium foil or glass cloth sheet may be used as a vapour barrier to cover the

insulation after installation stage ( stage d) mentioned above) and then both the insulation as well as

the vapour barrier are fixed by means of steel spring washers as described in e) above .

In accommodation spaces , insulation will be placed behind decorative panels . In places where it is

exposed to damage , a protective lining in the form of galvanized mild steel sheet may be provided.