8/2/2019 DNV Casualty Info 2011 #3

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8/2/2019 DNV Casualty Info 2011 #3

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www.dnv.com/maritime

Casualty Information is published by Det Norske Veritas,

Classification Support.

Det Norske Veritas

NO-1322 Hvik, Norway

Tel: +47 67 57 99 00

Fax: +47 67 57 99 11

The purpose of Casualty Information is to provide the maritime

industry with lessons to be learned from incidents of ship damage

and more serious accidents. In this way, Det Norske Veritas AS hopes

to contribute to the prevention of similar occurrences in the future.

The information included is not necessarily restricted to cover ships

classed with DNV and is presented, without obligation, for information

purposes only.

Queries may be directed to

Det Norske Veritas, Classification Support, NO-1322 Hvik, Norway.

Fax: +47 67 57 99 11, e-mail: experience.feedback@dnv.com

Det Norske Veritas AS. This publication may be reproduced

freely on condition that Det Norske Veritas AS (DNV) is always

stated as the source. DNV accepts no responsibility for any errors or

misinterpretations.

We welcome your thoughts!

12-2011

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Casualty Information No. 3-11 November 2011

A general reference is made to the Casualty Information published on the Internet:

http://exchange.dnv.com/ServiceExperience/CasualtyInformation/CasualtyInfoTable.asp

makes the vent head cheaper but also requires a more frequent

maintenance programme to replace corroded floats and guiding

pins.

Some vent heads are also equipped with a wire mesh as a

spark arresting screen on top of the tank (it is a requirement to

have the wire mesh for e.g. heated fuel oil tanks, or if there are

anodes in a tank with a single air pipe, or if there are specificnational requirements). In reality, our surveyors often see the

wire mesh covered with paint. This will of course reduce the air

flow through the vent head substantially and shall be avoided. We

have seen a number of tanks, predominantly ballast tanks but also

fresh water tanks damaged due to over-pressurisation. We recom-

mend that the wire mesh is removed on fresh water tanks and bal-

last tanks were anodes are not fitted.

Lessons to be learnedn Malfunctioning air vent heads are a common finding, for both

the Class surveyor and the Port State Control inspector. Each

vent head is an essential safety feature on board and should be

kept in good condition. A broken air vent head will most prob-

ably result in a PSC deficiency which must be rectified beforeleaving port.

n The ship manager should ensure that there is a regular inspec-

tion and maintenance programme in place for the air vent

heads on board its vessels. Since we see vent heads broken after

only a few years in operation, we recommend inspecting each

vent head annually. Such a programme should include the gen-

eral condition (rust, dirt, functionality) and especially the con-

dition of the float/ball/disc, guiding pin, seat and wire mesh

(if installed). A vent head replacement shall be of an approved

type and any replacement parts shall be of the original or an

equivalent quality.

n Special attention shall be paid to air pipes and air vent heads

located in the fore deck (1/4 L) due to green seas and the

ships movement.

n A cheap air vent head can become an expensive experience.

The trend seems to be to buy the least expensive vent heads

for newbuildings. This often means stainless steel type 304 as

an accepted material quality for the floats according to present

requirements (Load Line and IACS UR P3). However, this does

not mean that such stainless steel is maintenance free. Manufac-

turers, ship designers, yards and ship managers are encouraged

to consider the implications for air vent heads during a ships

life of maybe 20 years.

n Air vent heads made out of aluminium or other grades of stain-

less steel have become increasingly popular in the last few years.

Such materials are options to be considered in order to achieve

a more maintenance-free vent head.