Constructional requirements of chemical tankers

CONSTRUCTIONAL REQUIREMENTS

OF CHEMICAL TANKERS

by Dr. Giuliano PATÎOFA1TO Technical Bulletin N. 104 Genova, December 1989.

An abstract of this paper was presented at the 10th International Symposium on the Transport of Dange-rous Goods by Sea and Inland Waterways held in Hamburg on 25-27 September 1989

CONTENTS

Page

Summary

_i

i

- Foreword 2

2 - Rules and regulations 3

3 - Ship survival capability and location of cargo tanks 5

4 - Ship arrangements 7

5 - Cargo containment ₉

6 - Materials of construction

il

7 - Cargo tank vent systems ₁₄

8 - Electrical installations ₁₆

9 - Fire protection and fire extinction ₁₈

10 - Additional measures for the protection of the marine

environment ₂₀

SUMMARY

Alter an introduction, in which a brief historical hiflt is given

and the scope of the paper is underlined, section 2 lists the most

important rules governing chemical tanker design.

The remaiiirgr

_{sections deal with thé chapters of IBC Code in}

which constructional requirements are. given. Whilst trying t'o keep to

a minimum the quoting of the Codes' requirements, in the few pages

of this paper

it has been attempted to 'highlight sorné

partioülàr aspects of said requirements Cand to point Out thé relating amendments developed by 1MO.

Section 3 deals with survival ôapability and loçation _of cargo tanks and gives a cömparison with oil tankers. Thé importance of the compliance with minimum dhnensióhs Of openings for access to

spaces. in cargo area is stressed in section 4 "Ship arrangements", in which it is à]so shown how said compliance can influence, the ship design. The stifi unresolved problem of calculating the stresses due to sloshing in partially filled tanks is mentioned in section 5 "Cargo containment".. Section 6 gives a brief review _{of materials of} construction and of their development. The amendments to chapter 8 of the Code "Cargo tank vent systems" recently approved by MSC are illustrated. in section 7. Section 8, dealing with electrical installations,

stresses the problem of missing data relating to electrical equipmént

for products listed in the Code. Section 9 introduces the amendments 'to Reg. 11-2/55.5 of SOLAS 74 dealing with the requirements of_'inert

gas systems for cargo tanks and section 10 deals with the additional measures for the prOtection of 'the mariné environment.

_{Section ii}

contains the. reference to the major items uÌider development.

in the

present paper,

where not expressly mentioned, by

- FOREWORD

Dealing with constructional requirements of chemical tankers, in

a sufficiently complete

way and

in few pages, is practically

impossible., due to the complexity of the matter.

Since their first

appearance in the ports of the world immediately after the end of the

second World War, up to now, the progress has been continuOus.

Thus,

step by step,

national regula ions were developed in the

countries whose Administrations were, as first,

to cope with the

problems of construction f tanlçs and systems for the simultaneous

carriage of dangerous and often mutually non-compatible products.

In 1971 the first 1MO Code was finalized, whose aliti was to

consolidate the various national regulations for'. chemical tankers and reconcile the differences between them, which gave rise to problems for ships trading world-wide.. Although the Code was developed as a

recommendation, it' Soon appeared to have gained universal approvai. Since then 1MO has constantly worked in improving the Code and

in 983 the Code, called International Code, became part f. the 1983

Amenthnents of SOLAS 74, as amended.

Registro Italiano Navale has been active, since the beginning,

both in the development of national regulations and in the

participation in international works. This in support of requests for

classification,

practically continuous during the years, of chemical

tankers at the service of a òhemical industry which, in Italy and

abroad, is very active.

By the present paper it has been attempted to:

give a brief hint

at the fundamental points of the Codes'

requirements, keeping to a minimum their repetition;

highlight certain aspects of said requirements Which may present

particular problems; this on the basis of the. experléncé gained

by the activity peculiar to a Classification Society;

adopted by 1MO or are under development, with a

hint at theiì

background.

In other words,

it

has been tried

to give Some impression,

additional to the text of the Codes, which may be beneficial to all who

are interested in the field

of chemical tankerS or may represent a

starting-point for discussions and clarifications; this with the aim at

achieving a greater and greater

ütijfornilty

in the application

of international regulations in order to insure a uniform safety standard

and not tó cause troubles tò ships trading worldwide.

2 - RULES AND REGULATIONS

The most important rules governing chemical tanker design are: (i) the International Code for the Construction and Equipment of

Ships Carrying Dangerous Chemicals in Bulk (ÏBC Code),

adopted by the 1MO

Márithne Safety Committee (MSC) by

Res. 4(48), on 17 June 1983, and by the 1MO Marine

Environment Protection Committee (MEPC) by Res. 19(22) on 5

December 1985;

(il) the Code. for the Construçtion and Equipment of Ships Carrying

Dangerous Chemicals in Bulk (BCH Code) adopted by MSC by

Res. 9(53), on 17 September 1986,

and by MEPC by Res.

20(22), on 5 December 1985. The BCH Code was originally adopted by the 1MO Assembly by Res. A.212(VII) in 1971. The

COde referred to above, in respect to the one adopted in 1971,

contains 11 Sets óf amendments developed from 972 to 1985; ffl) Annex I to MARPOL 73/78,

as amended by MEPC by Res.

16(22), which entered into force on 6April 1987.

With Annex II to MARPOL, which is relating, to the prevention of

the pollution of marine environment by noxious liquid substances

carried in bui by ships, 1MO Codes for chemical tankers become an

Whilst, to the aim of safety, -only IBC Code is part of SOLAS, as provided by chapter VII of SOLAS itself, and the BCH Code remains as a recommendation, to the aim of pollution prevention, both Codes, BCH and. IBC, become compulsory under MARPOL, for ships built before or after 1 July 1986, respectively.

The connectiOns between MARPOL and Codes are stated under

Reg. 13 of Annex II and in chapters 16A and VA of IBC and BCH.

Codes, respectively.

Under the provisions of Reg. 13 of Annex II of MARPOL 73/78, chemical tankers constructed on or after 1 July 1986 must comply with the provisions of the IB C Code, chemical tankers constructed before i

July 1986 must comply with the provisions of

the BCH Code.

Therefore the constructional requirements provided by the Codes, which until 6 April 1987 were only a matter interesting safety, also become means to minimize the risk of accidental pollution of sea by

chemical tankers carrying Category A, B or C substances.

-Chapters iA and VA, of IBC Code and BCH Code, respectively,

are the main part of the extension of the Codes to cOver the marine

pollution aspects and are briefly dealt with in

section Ï0 of the

- present notes.

In additiOn to the above mentioned Codes, chemical tankers have to comply with the applicable SOLAS requirements and with the Rules

of Classification Societies for the areas not covered by the Codes,

such as ship's strength and scantlings, fire protection in

accomodation spaces, lifesaving appliances (Ch. III of SOLAS with the

particular requirement of lifeboats with a self-contained air support

system), steering gear

(with particular requirements for chemical

tankers,

new and

existing,, of 10,000 tons gross tonnage and

úpwards) etc.

Even if not directly connected with the ship design, it is deemed

different aspects, are anyhow fundamental for people operating in the

field of chemical tankers:

the 1MO "Standards for the Procedures and Arrangements for the

Discharge of Noxioüs Liquid Substances" called for by Annex II to MARPOL 73/78, adopted by MEPC by Res. 18(22);

the 1MO "Guideline on the PrQvisions of Adequate Réception

Facilitiès in Ports";

the 1MO "Guldélifle for Surveys under Annex II to MARPOL 73/78"

adopted by MEPC with Res. 25(23);

the 1MO "Procedures for the Control of Ships and Discharges under

Annex II to MARPOL 73/78", adopted by MEPC with Res. 26(23);

the ÏCS Tanker Safety Guide (Chemicals).

3 - SHIP SURVIVAL CAPABILITY AND LOCATION OF CARGO TANKS

Chapter 2 of IB C. Code IS

certainly the chapter which best

highlights the close connection between the cargo intended to be

carried and the constructional characteristics of the ship.

Depending on the hazards associated with diffèrent

chemical

products (health hazard, fire hazard,

pollution hazard, reactivity

hazard, corrosion hazard) the Code provides for three types of ships

and namely Type 1, Type 2 and Type 3. Such classification is based

on the

ship's ability to survive degrees

of damage and not

to

present,, or at least to limit,

cargo release.

Each type of ship is

associated with certain damage assumptions and tank location

requirements as schematically represented in Figure 1.

As it may be noted, a two compartment standard is iequired,

with a certain relaxation in way of the engine room, depending on the

ship type and length.

The survival requirements associated with the damage conditions specified in the Code are schematically shown in Figure 2.

In Figure 3 the damaged condition stability diagrams of two Type

2 áhemical tankers are shown.

The first diagram of Figure 3 is relating to a chemical tanker, of 132 m in length, having a deadweight of 11750 t, subdivided into 22 cargo tanks. The second diagram refers to a chemical tanker of 85 m in length, having a deadweight of 3400 t, subdivided into 22 cargo tanks.

Chemical tankers have in general, on accrnit't of operational

purposes, a high degree of subdivision, and therefore stability and

survival requirements are generally easily met.

An important role may be played by the way in which the double

bottom is subdivided, which may give rise, in case of collision, to a symmetrical or non-symmetrical flooding; but also the cases of

non-symmetrical flooding rarely may give rise to problems because, in this case, according to the Codes, a maximum angle of heel of 25° iS allowed, which may be increased to 30° if no deck immersion occurs.

Situations which aré to be carefully examined are the.: loading conditions with products having a high density, also because in such

a case it may be necessary to keep some cargó tanks empty. For

sulphuric acid, for example, a further reason fr keeping wing tanks

empty is that the ship shell plating should not form any boundaries Of

the tanks, to the purpose of preventing possible contact with water.

In such a. case, specially in cases of flooding of the forward ship

zone, the situation may turn out to be critical due to the weight

of

intàken water (the weight of which is in excess of the one whiçh

completes the deadweight) and due to excessive trim. The stability

diagrams may then turn out to be not sufficient.

For what intact stability and freeboard are concerned, Rés.

A.267(VIII) and Load Line Convention 1966, respectively, apply, as

for oil tankes.

If we cOmpare the requirements relating to survival capability of

chemical tankers with the ones of oil tankers as per Reg.

25 of

Annex I of MARPOL 73/78, it appears that the survival requirements

añd the damage assumptions are the same, but different are. the

criteria of such damage along the length of the ship. It may be: said, also mAking reference to Figure 4, that:

(i)

the requirements for Type 1 ships correspond to. those of oil

tankers of more than 225 m in length (two compartment ships);

(il) the requirements for Type 2 ships of less than 150 rn in length

correspond to those of oil tankers of more than 150 .m but not

exceeding 225 m in length (two compartment .

ships except for

machinery space);

oil tankérs of less than 150 m in

length are 'dealt with, by

MARPOL as single compartment ships with relaxations for the

engine room. FOr tankers of 100 rn in length or less, where such requirement cannot be. fulfilled without impairing the operational

qualities of the ship, Administrations may allow relaxations..

This lead to dealirg with oil

tankers in a remarkably less

severe 'way than with cherniáal tankers having the, same length, even if of Type 3.

If we refer to the cargo area,

it may be. therefore said that,

irrespective of their length,. che ical tankers are ,,.two cOmpartment ships, whilst oil tankers are such only if exceeding 150 m in length.

Below Such length oil

triloers are

one compartment ships, With.

possibility of relaxation below 100 metres.

4

-

SHIP ARRANGRMRNTS

Chapter 3 of the Code deals with ship arrangements an

particúlar, it contains requirements in connection with:'

- cargo segregation: segregation of cargo taflkS from 'accomodtiOn,

service and machinery Spaces and segregation of cargoes from Other cargoes when dangerous reaction may occur;

location of accomodation, servce and machinery spaces and contról stations in respect to cargo area. It contains requirements similar to

the ones of SOLAS Regí II-2/56;

- cargo pump rooms (location, arrangement, instrumentation, etc.);

- access to

spaces in

the cargo area,

dealt with more in

detail

hereinafter;

- bilge and ballast arrangements; .

- pump and pipeline identification;

- bow or stern loading and unloading arrangements.

It is deemed useful, among the above points,

to stress the

mportance of the compliance with minimum dimensions of openings for

access to spaces in the cargo area (paragraph 3.4), which is very

important and may remarkably affect the ship structure.

Such dimensions are 600 mm by 600 mm for horizontal openings

and 600 mm by 800 mm for vertical openings.

The compliance with said dimensions is important in order to

allow a sifficiént acceSS to persons wearing a self -contained

airbreathing apparatus. and. protective equipment or to provide, a clear opening tO facifitate the hoisting of an injured person frOm the bottom of the space.

The compliánce with such dimensions turns out to be a serious problem, specially for double bottoms of small or middle size units,

and requires a careful study of the ways of access to the varioús

zones in which the double bottom is subdivided, taking also into

acçount the presence of bilge and general service piping which

further reduces the available space.

As a matter of fact, the Code provides for the possibility of

accepting access openings having lower dimensions, in the case where

the possibility of passage is demonstrated, however, accidents

For a ship of, e. g., about 120 rn in length, with

longitudinal

structure, for which a normal doubie bottom height could be 1200 mm,

it is clear how difficult is

it to realize openings according to the

requirements.

In fact,

if we consider the space occupied by top and bottom

longitudinais f

the double bottom, in general having a height of

about 240 mm, and the clear space of slits for their passage,

the

cuttiflg of an 800 mm x 600 mm opening practically causes the floor

plate to

disappear,

giving rise both to problems connected with

shear, and it

is thérefOre necessary tO move, when possible, the

opening to

sections having a lower shear

stress level, and to

problems of constructional details due to the location of longitudinais very close to the opening.

For these reasons, instead of passages in the floor plates, often

transverse passages àre chosen,

cutting

the 800 mm x 600 mm

openings in the girders, which, being intaót, offer a better

useful

height, but this solution does not allow the presence of watertight

girders except for the central girder (see Figure 5).

The two solutions imply a different layout of the double bottom and therefore a big impact on the design of hull and on the capacity

plaìi of the ship.

Similar accessibility problems, with iritluelice on the structure.,

may be found in cofferdams, but, obviously, with better possibilities

of solution.

5 - CARGO CONTAINMENT

Chapter 4 of the Code lists the various types of cargo cóntainment, differentiating between tanks the sides of which form, or

do not form, part of the ship's hull and tanks having design pressure

For tanks of the gravity type (design pressure not greater than

0.7

bár gauge),

no major difference is encountered,

for what

structural strength is concerned, in respect of oil tankers, except for

the problems arising from sloshing loads.

The prOblem of sloshing is mainly connected to eases where tanks are used tO carry a cargo denser than the design one, and the, filling is therefore reduced to maintáin the design static pressure on

the bottom.

In case of bad weather this leads to large motions of the liquid

cargo which induce high transient pressures on longitudinal and

transverse bulkheads. -.

The matter of

liquid sloshing motions

has been extensively

investigated in the last decade, both theoretically and experimentally,

but unfortunately most of the work done is relevant to single cases

where two main aspects are neglected:

(i) the damping effect of floors and internal girders in single shell

tanks;

(il) the effect of the deck over the tank.

This secOnd effect is of paramount importance in real tankers.

When the tank top

is missing, the sloshing motion reaches large

amplitudes quite easily, but the pressure variation varies smoothly

with the natural periOd of the tank. On the contrary, when there is a

deck closing the tank,

it

interferes with the

liquid motion, by

reducing the sloshing amplitude, but each time the mternai sloshing wave hits the deck, high shock pressures are generated, which may

induce high transient stresses on the deck itself

and on

the

surrounding bulkheads.

A theoretical solution to the problem is still missing, although,

in the last few years, numerical methods have been developed, which seem to reproduce guite closely the sloshing motions in closed tanks.

include the effects of random motions of the ship in

a. seaway,

correlation of liquid motions, shock pressures and transient stresses

in the structure, calibration of numerical methOds on the basis of

experience at sea. All these items are still matter for future

development.

For the tiñe being, the only viable way to prevent structural

damages in partially filled tanks at sea, without requiring unjustified

heavy Strengthening of the structures, seems to

be á

careful

extrapolation of èxisting practice.

Particulàx care is to bè taken in any case to preserve

redundancy and. toughness of deck and bulkhead structures, particularly in double shell tanks without interilal stiffénerS, which are expected to. offer reduced damping. (to sloshing motions) with respect tò traditional tanks.

As an example, Figure 6 shows the distribution of pressures due

to sloshing motions calcúlated for a tank which osôiiltes around the.

centre-line of the lower base. The calculated values may be compared

with. the . hydrostatic head indicated for easy reference at the four vertices of the tank.

6 - MATERIALS OF CONSTRUCTION

Chapter 6 of the Códe, whilst specifically indicates the types of matérial not suitable for specific products, does nOt go into detail on

the general suitability of structural materials uséd for tank

construction, together with associated piping, pumps, valves, vents and their jointing materials. There is only a general sentence Stating

that materialsare tò be suitable at thé temperature ánd pressure for

the cargo to be carried to the satisfaction of the Administration.

The type of material is therefore depending on carried, products

and on economic reasons and,

for what the

characteristics and

Although mild steel is acceptable for the majority of chemftals

carried by sea;

stainless steel Is

generally used both to

ensure

quality control of the product and containment of certain cargoes

which may have corrOSive properties.

Versatility and flexibility certainly are two major factors in the

fIeld of chemical transportation and it is in these respects that the

use of appropriate grades öf stainless steel offers outstanding

advantages. Versatility stems from the ability of stainless steel tañks

to be suitable for a range of cargoes,;

flexibility results from the

relative ease with which stainless Steel cargo taflks, properly

designed, can be çleaned, so reducing cleaning time and costs.

The selection of a particUlar grade of stainless steel from the

wide variety available will be influenced by the cost nd the desired degree of corrosion resistance. For a vessel intendéd to carry one or two specific cargoes the choice of grade will be rather simple, while for a multi-parcel chemical taflker a grade that is compatible with as

many different types of cargo as possible must be selected.

The austenitic stainless steels have the' widest range of

compatibility with chemicals. The molybdenum-free grades (AISI 3Ó4, 321 and 304L) are satisfactory only for mildly corrosive cargoes. Type 316L is the most widely used stainless steel, being compatible with a

wide range of cargoes. Type 317L is a more highly alloyed material

than 316L and its

greater molybdenum content gives it

a higher

resistance to pitting, which is of use in phosphoric acid service.

One disadvantage of stainless steel is that normal stainless steel

grades exhibit a yield strength (200 MPa) lower than that of mild

steels, which implies a heavier structure. An important development

has been obtained with the addition of 0.10

- 0. 20% of nitrogen

(grades 316 LN, 317 LN) ; by which an increase by about 5Ó% of the

yield strength and a moderate improvement in the ultimate

tensile

A further improvement in mechanical and corrosion resistance properties is offered by a new type of stainless steel which has been

developed in the recent years and which has a duplex structure

containing approximately the same content of austenite and ferrite.

This steél offers a minimum specified yield strength (460 MPa) about 50% higher than for the standard austemtic N grades.

For what the yield strength is concerned, it therefore increased from values of about 200 MPa, e.g. for 304L, to values of 460 MPa,

which allow the use of thinner plates and grant a higher corrosion

resistance.

In this regard it

is however to be pointed out that higher

mechanical properties do not allow in general a proportional reduction

in the scantlings, since also the fatigue resistance of the welded

joints is

to be takén into account,

which does not increase

in

proportion to the mechanical properties of the steel.

In any case, for reasons of elastic stability and of resistance to

local loads , the thicknesses are not allowed to decrease below minimum

values, properly fixed for the different structures.

As usually done for new materials, the jnterventions of

Classification Societies for duplex steel are relating to the approval of

Steel, through tests performed at the steel manufacturer's works, and the approval of the welding procedures, whiçh, for duplex steel, are

particularly important due to the strong influence of heat.

In fact, owing tÓ the particular duplex microstructure, care is to

be taken to limit the heat input specific to values as recommended by

the manufacturer. Heat input has a strong influence on the austenite

ferrite balancé and therefore much attention is to be paid to select

the correct: welding parameters. In particular, severe thermal cycles

increase the ferrite content beause high cooling rates do not allow

the transformation into aústenite of the ferrite phase which is stable at high temperature. On the contrary, high heat input produces lower

ferrite content but a wider heat affected

zone with coarsening of

ferrite grains. The ferrite

content

in both weld metal and heat

affected zone is to be limited because increased ferrite reduces the

Charpy V values and corrosion resistance properties. The ferrite

content should be limited to 70 - 75%.

- CARGO TANK VENT SYSTEMS

Chapter 8 of the Code deals with the différent types of tank

vent systems (open or controlled) and their characteristics. The open

type, i.e.

a system which offers no restriction to the free flow of

cargo vapour from cargó tanks during normal operation, should only

be used for cargoes having a flashpoint above 60°C (closed cup test)

and not offering a significant inhalation health hazard.'

During its

57th session, the. 1MO Maritime Safety Committee

approved the revised chapter 8

of the

Code as _{an acceptable}

alternative to the appropriate sections of Regs. 11-2/59.1 and 59.2 of SOLAS, and agreed to it as a future amendment to thé Code, to be.

adopted at an appropriate time. The requirements of the revised

chapter 8, suitable for the carriage of flammable chemicals are equally acceptable when the. vessel is carrying oil products.

It is worth while remembering the previous decision of the MSC

(MSC 51/21, paragraph 7.14) that, until such time as suitable

alternative venting requirements could be developed, chemical tankers intended to carry chemicals and, petroleum products sho1d continue to

be, allowed to comply with .the BCH and IBC Codes.

The revised chapter 8, as per Annex 13 to BCH 18 Repört,

contains the following main modifications:

it has been specified that cargo tank venting systems should be

independent of venting systems of other ship compartments;

requirements concerning drainage of venting systems are more detailed (self-draining back to cargo tank is required,'

as far as

factors to be taken into account for determining

the size of the

venting system have been added;

it has béen specified that the master

should be provided with

the value of maximum allowable loading/unloading rates;

(y) the minimum height of the vent outlets On the weather deck of

the controlled type venting systems has been increased from 4 m

to 6 rn and it has been clarified that the 10 m distance from air intakes has to be measured horizontally

(as required by Reg.

II-2/59 SOLAS 1974(83) in case of openings for free flow

discharge);

the requirement of devices to prevent the passage of flame has been added for products having a flashpoint of less than 60°C. To this purpose, a proposed amendment to MSCI Circ.406 (see

BCH 18/16, Annex 12) gives the details of a venting

arrangement which may be accepted as providing a level

of

protection equivalent to that required. by SOLAS Reg.

11-2/59.1.5 and contained in the Annex t MSCICirc.373IRev.1

"Revised Standard for the design, testing and location of devices

to prevent the passage of flame into cargo tanks in tankers" This alternative arrangement consists of a p/v valve with certain characteristics assoôiated with a flame-arresting device fitted at

the pipe outlet

which has been tested

for flashback (see

Figure 7).

During the 57th session of MSC, difficulties have been mentioned

with the required flow velocity of 10 rn/s of the outlet and the

matter has been therefore further discussed at the Sub-Committee on Bulk Chemicals during its 19th session.

The SbCommittee recalled that the alternative

arrangements

have been déveloped with full participation of the Sub-Committee

on Fire Protection

over many sessions and with

extensive

discussion of technical considerations, laboratory testing and the practical experience of Members to substantiate the requirements

of the circular and therefore confirmed the proposed amendments;

possibility of the blockage of thé devices to prevent the passage

of flame into cargo tanks by, for example, the freezing of cargo

vapour, polymer build up, atmospherk dust or icing up in

adverse weather conditions.

In this respect it was several times pointed out that regular

maintenance was an essefltiái feature to be associated with said

devices;

(viii) the procedure for cargo tank gas freeing has been added, which

was developed on thé basis of Reg. uI_2159..2 of SOLAS 74(83).

As it can be noted, chapter

18 has been deeply revised The

révision took a long time at 1MO to adapt, to chemical tankers, the

standards already developed for oil tankers.

8. - ELECTRICAL INSTALLATIONS

As already said, chapter 10 of the Code has been deeply revised and, in particular, specific requirements for electrical equipment have

been introduced.

Where electrical equipment is installed in hazardous locations, it

should be certified by the

relevant authorities recognized by the

Administration .fòr operation in the flammable atmosphere concerned, as

indicated in column "i" in the table of chapter 17. In this column, for flammable products, temperature

classes and apparatus groups,

as defined in the International Electrotechnical Commiasion Publication 79, should be indicated.

The temperature class corresponds to the classification of. electrical equipment depending on its maximum surface temperature

accördirig to IEC Publication 79-8.

The determination of the group is

based on

the maximum

experimental safety gap (MESG) fOr explosion proof enclosures and on

the minimum ignition current (MIC) for intrinaically safe electrical

What above certainly represents an improvement

for safety in

respect to B CH C öde, but the

remarkable thing is

that for many

products said data are not available.

About 50% of the products listed in chapter 17 of the Code having

a flashpoint less than

60°C have no data at all relating to electrical

equipment,

or one

of the two parameters (temperature class or

apparatus group) is missing.

The lack of such data is a serious problem; the safety of the ship

is strictly linked to the eleötrical equipment installed for the products carried, and Administrations have difficulties when they have to decide what to do without any indication in the Code.

When it is inten4ed to carry products without data fOr eleçtrical

equipment, one possibility is to

chOose an equipment having the

highest apparatus group lIC and the highest temperature class T6, but

this is obviously particularly onerous both due to the higher cost

involved and tó the difficultiès in finding such equipment,

A àórnmon practice is to use equipmént belonging to lIB explosion

group and tO T4 temperature class, which is suitable for oil ànd many

products, but which may not bó Sufficient for some other chemical

products.

The problem of drawing up a complète table of chemiôal products

and suitable électrkal equipment was discussed within IEC in the

course of the revision of the TC 18

Publication Nô. 92-502 Tankers.

The TC 18, during its November 1988 meeting in Dubrovnik, dèémed

not to introduce said table into the Official requirements, taking into conSidération the difficulty in issuing añd updating such a complete

List of products.

1MO, recognizing the importance

of the

missing. parameters,

should make any

effórt. tó solve this problem b stressing to

submitted for approval and by completing the data of products already in the Code or in the adopted amendments.

9

-

FIRE PROTECTION AND FIRE EXTINCTION

Chapter 11 of the Code deals in particular with fire protection Of

cargo pump-rooms and cargo area.

For cargo pump-rooms a

fixed fire extinguishing system is

required and the alternative is given between a çarbon dioxide system and a halogenated hydrocarbon (halon) system. For the two systems

reference is made to the applicable requirements of Reg. II-2/5 of

SOLAS 74(83).

For cargo area a fixed deck foam system is required and the

parameters for designing such system are given. It is. reminded that,

up to now, there are no internationally agreed standards

for foam.

The 1MO Sub-Committee on Fire Protection has in its agenda the item

"Guidelines for the performance and testing criteria, and surveys of

foam concentrates"! it is

really hoped that the

guidelines will be

developed so that a uniform standard in this important field can be

applied. Also lACS and ISO are working on this subject.

As far as the requirements for inert gas systems in cargo tanks

are concerned, Reg. 11-2/55.5 of SOLAS 74(83) Specifies that Reg. 60

need not be applied to chemical tankers, provided that alternative

arrangements, to be developed by the Organization, are fitted. ¡MO

developed and adopted by Res. A. 473(XII) the "Interim Regulations for

Inert Gas Systems on Chemical Tankers Carrying Petroleum Products".

The problem of carrying flammable chemicals was therefore left open and, in fact, the same resolution urged the MSC to develop final

requirements for chemical tankers carrying chemical fhìmmible cargoes and specified that compliance with, additional provisions which will be

contained in

the final requirements should not be required to be

into force of the final requirements.

1MO continued to work according to what above and good results

were reached in the twO following areas:

(i) electrostatic field and risk of electröstatic charges in cargo tanks:

studies have been developed and. discussed and it was concluded

that, in case

of tanks

not exceeding 3000 m3 capacity and

washing machines having individuai nozzle capacity not exceeding 17.5 m3/ h and a combined total capacity not exceeding 110 m3 / h,

there is no electrostatic hazard. For tanks having dimensions and

washing machines complying with what above, Reg. II-2/60 of

SOLAS need not therefore be applied;

(li)

on the basis of experience and researches carried

out by the

industries involved, it was concluded that, apart from few

modifications,

the interim Res. A.473(XII) can also cover the

carriage of flammable chemicals. The new resolution was adopted

by the Assembly at

its. 14th session as Res. A. 567(14)

and

provides the final requirements for inert gas systems on chemical tankers carrying petroleum and chemical products.

On the, basis of the above results, Reg. 11-2/55.5 was amended and its new requirements, depending on thé . date of conStruction of the chemical tanker and On the products carried, are summprized in

the following table. Said amendments were adopted by the expanded

MSC during its 57th session and, they will enter into force on the ist

February 1992, together with other important amendments to SOLAS.

Product carried Ship constructed

Before, 1 July 1986 After 1 July 1986

Crude Oil or petroleum products IGS as per Res. A.473(XII), or Res. A.567(14) IGS as per es. Af567(14) F1Rmrnble chemicals Ch. 17 of IBC Code Ch. VI of BCH Code No IGS

-IGSas per

Res. A.567(i4) - No IGS if the conditions un-der previous (i) are met

lo - ADDITIONAL MEASURES FOR THE PROTECTÏÖN

F THE

MARINE ENVIRONMENT

In addition to the requirements of Reg.

13 mentioned under

section 2

of the present paper, Annex II and 1MO Standards for

Procedures and Arrangements called for by said Annex II require the

installation of new plants or affect the design of already foreseen

plants. The thai new requirements are the following:

(i) the installation of an underwater discharge outlét arrangement

for residue/water mixtures is required. The outlet is to have a

certain diameter depending on its

distance from the forward

perpendicular and on the rate to be discharged so as to limit the flow velocity in order to maintain the flow within the ship layer and the ship wake. In addition, the location of said outlet has to

take into account the location of sea. intakes located aft, in order to avoid intakes of polluted waters (see Figure 8);

(fi) the dimensions of suction wells in the cargo tank and unloading

piping are affected. They should be reduced as much as possible

to keep to a minimum the tank residues and in any case not to exceed the maximum quantity of residues fixed by Reg. 5A of

Annex II,

What above taking into account that súbmerged or

deepwell pumps (centrifugal type) are generally installed and

that the amount of residues left in the tank and in the relating

unloading piping increases with the dimensions of suction wells and discharge piping. Additional small diameter stripping piping

or other arrangements are often installed to comply with said

Reg. 5A;

the cargo tank heating system is to be designed as to guarantee,

for certain cate gory B and C substances, an unloading

temperature such as to consider them "non-solidifying" or "low

viscosity";

the cargo tank washing system is to have dimensions and to be

positioned in order to comply with the requirements of Appendix

B to the above menUoned Standards, i. e a minimum temperature

water (in case Of solidifying

and/or high

viscosity substances)

and the position and characteristics of the washing machines

have to be sucth that all tank bound5ries are washed.

Il

- ITEMS UNDER DEVELOPMENT

It is deemed useful to conclude the présent paper by mentioning the items under discussion at 1MO in connection with which possible

future amendments to the present constructional requirements of the

Code will be made.

111 - Recycling techiiiques of chemical tnnkers

The matter was started during the 19th session of the Sub-Committee on Bulk Chemicals in September 1989.

The adequacy of the prewash procedures presently contained in the standards for procedures and arrangements for the discharge of

noxious li4uid substances (NLSs) was discussed with the aim at

suggesting ways to improve the procedures in order to follow up

satisfactorily the objective of Annex II to MARPOL 73/78.

It. was outlined a possible

way of

modifying the prewash

procedure based on a number of cycles so as to take account of the

actual amount of residues in a tank, and specifying minimum

quantities of washwater.

In regard to the potential hazards associated with recycling of was hwater in a flammable tank atmosphere, the use of inert gas on chemical tankers needs to be considered in connection with specific limitations related to cargo tank size and tank washing throughputs. It was also pointed out that previous research had shown increased

generation of static

electricity if

additives were used. or

if the

was hwater was contaminated with cargo residues as will be the case

Some delegations were inclined to consider

thé reasons

for exempting chemical tankérs from inertirig requirements Subject to tank

size and washing machines throughput limitations also valid for this

case. Other delegations disagreed. However, the matter should be

more deeply examined.

It was therefore decided by the Sub-Committee to coñsidêr the

matter further before any firm decisiöns could be taken. 11.2 -. Vapour emission oentrol systms (VECSs)

This item was started during the 19th session of the

Sub-Committee on Bulk Chemicals with the aim at improving the air

quality in areas already polluted and to prevent deterioration of air

quality in clean areas.

It was therefore decided thAt design standards should be

develOped fr VECSs to cover transfer operations and. particularly

loading and bafiRsting of cargo tanks

It was alsó agreed thAt the

design standards would not be intended to mandate the use of vapour

emission contro!, but rather standàrds would be fóllowed if vapour

emission control is mandated by a State or a local Authority.

The examinatiOn

of the

hazards connected with VECSs was

started and such, examination will continue during the next session. 11.3 - Halons as fi e-extinguishing agents

Following the recent measures taken internatiOnally, aimed at

limiting the use of chlorouluórocarbons (CFCs), the 1MO Assembly,

during its 16th session (in October 1989), adopted a Resolution by

which 1MO decides not to develop further requirements which could

encourage an increased use of halons and to draw up a plan for the

- type 1 ships - type2shipsifL>150m - type3shipsifL>225m - type2shipsifLstSOñ, - type 3 ships if 125 s L s225 m - type 3 ships ¡f L<125 m Except here if Ls 150 m

t.

I Except here if L<125 m

Figure i - Damage Assumptions

Ship type Colìision or stranding damage anywhere except: Tank oc tion

No exception

/ 15

Figure 2 - Sctiematic representation of survival assumptions assOciated with damage condition specified n the lBC Coae

A - max angle of heel 25°

(increasab'e to 30° if rio deck immersiOn occurs)

B righting lever area aO.0175 mrad

C = residuai righting lever 0.1 m

D range of stability 20° Casel L- 132m A-5.92° Case 2 A - 5.250 B - 0.045 m.rad C - 0.244 m D-37° 85m

Fïgure 3 - Damaged condition stability diagrams of two type 2 chemical tankers

e (e)

B 0,034 m.rad

C - 0.118m D - 25.5°

() if Ls 100 m Adminitrathnsmay allow relaxatiöns

Figure 4 - Companson between damage survival capabilities of oil tankérs and chemical tankers

The ship should substain damage: Oil tanker Chemical tanker

M.S. - L>225m - pe 1 - type2shipsdL>150m - type3shipsitL>225m

-t

anywhere M.S. 150<Ls225m - type2shipsifLs150rn - type3shipsif 125sLs225m

/

-anywhere except M.S. bulkheads

M.S. L si o m () - t,pe3ShipsifL<i25m .-I--anywhere except MS. bulkheads MS.

íIiÍi.

adjacent excepts anywhere between

o o

c'J

200x loo

o

Figure 5 - Ship arrangements

Ship type? L120m 0250 8 L Girder 3240 mm from C.L. .»; s 13 100x10

[A

)1

I

1t

__

H

Figure 6 - Pressure due to sloshing motions

- tank dimensions 60 x 60 x 60

- hs = 45 height of still water

- H = hydrostatic head

- p = pressure due to slashing motions

- C = rolling centre

Fgure 7 - Venting systems

Alternative arrangement for Chemical Tankers:

cw velocity 10 rftls

flame arrestin device tested fbr flashback

o O0 mm

p/v valve - opening pressure0.l8 bar

- vacuum side protécted by â flame screen ()

I--le

I

I I I I

I I I I

I I I I

Figure 8 - Additional measures for the protection of the marine environment

Underwater discharge outlet

J-Section A-A

D = minimum diameter of the discharge outlet, m

Q0 = maximum selected discharge rate, me/h

L = distance from forward perpendicular, m

discharge piping

ULTIMI BOLLE'PrINI TECNICI PUBBLICATI LAST PUBLISHED TECHNICAL BULLETINS

BT 74 - Febbraio 1981 / Pittaluga, Ziliotto

Una procedura per la valutazione della robustezza trasversale delle

navi peril traspOrto di merci alla rinfusa

A procedure _{for the transverse strength asséssment of large bulk} carrier ships

BT 75 - Novembre 1981 / Ferro

Metodi e problemi nell'analisi dell'affidabil.itá' déllè _trutture navali

Methods and problems in reliability analysis of ship structures BT 76 - Dicembre 1981 / Bisagno, Marchesi, Valentin

GIPSY - Un post-processor per l'analisi ad elementi finiti

GIPSY - A post-processor for finite element analysis BT 77 - Gennaio 1982 / Ferro

Applicabilita' delle tecniche affidabilistjche alla _{progettazione} navale

Applicability of reliability concept to ship design BT 78 _{Febbraio 1982 / Selvaggi}

Problemi di progettazione per navi adibite _{al trasporto di gas} liquefatti. a bassa tempetatura

Design problems for ships carryng low temperature _{liquefiéd gases} HT 79 - AprIle 1982 / Spinelli

Convenzione MARPOL 1973, come emendata dal protocollo 1978

- interpretazione della normativa controlli RINA _{per il rilascio di} dichiarazioni di corrispondenza alle _{norme della convenzione}

(seconda edizione)

HT 80 - Maggio 1982 / Ferro,. Ziliotto

Applicazione di una _{procedura diretta per il calcolo dei carichi} d'onda per le analisi di robustèzza _trasversale

Application of a direct procedure to the _{assessment of wave loads} for the transverse strength analysis of ships

B'2 81 - Aprile 1983 / Micillo

Applicazione dei procedimenti speciali di. saldatura nelle costruzioni navali

BT 82 _{Novembre 1983 / Marchesi, Ziiiàtto}

Comportamento post-critico di pannelli nervati-].cônfronti tra risultati. numerici e prove sperimentali

HT 83 - Dicembre 1983 / Alimento

I materiali per la costruzione degli _scafi

- Note sulle caratteristiche e prove de:i materiali _{secOndo là} normativa dei RINA

Materials for hull structures

ULTIMI BOLLETfiNI TECNICI PUBBLICATI LAST PUBLISHED TECHNICAL BULLETINS

BT 84 - Gennaio 1984 / Ferro

Advances in the calculation of the maxima of ship responses

Paper presented at the Euromech Colloquium 155, reliability theör.y

of st:r.ucturai engineering systems, Jüne 15-17, 1982, Enginéering Academy of Denmark - reprinted from Dialog 6-82

BT 85 - Gennàio 1984 / Ferro, Crvéttô

Reliability of marine structures under dynamic loadings Paper presented at the International Workshop on stochastic methods in structural mechanics, June 9-12, 1983, University of Pavia - reprinted from the proceedings.

BT 86 - Gennaio 1984 / Rôbino,. Ziliotto

Wave. torsional moments in ships with large hatch openings

Paper presentedat the VI Italian - Polishseminar Genoa, Ñovember 1983.

ET 87 - Marzo 1984 / Spinelli

Convenzione MARPOL 73, come emendata dal protocollo 78

- Interpretazione della normativa controlli RINA per ii rilascio di dichiarazioni di corrispondenza alle norme della convenzione

(terza edizione)

BT 88 Maggio 1984 / Pasini

La saldatura subacquea - Statò dell'arte BT 89 - Giugno 1984 / Ferro

Stochastic models for low-frequency, springing and impact loads on ships

BT 90 - GennaiO 1985 / Pittaluga, Bisagno

Moderne tecniche di analisi dei comportamento in mare ST 91 - Gennaio 1985. / Cazzulo, Ziliotto

Applicazione della meccanica della frattura nelle verifiche a fatica

BT92 - Gennaio 1985 / Ferro, Merega

Prospettive della progettazione affidabilistica delle strutture marine BT 93 - Gennaio 1985 / MarcheSi, Ziliöttò

Analisi di un'avaria di una portarinfùse ET 94 - Maggio 1985 / Cazzùlo

Panoramica sui fondamenti teorici delle meccanica della frattura ET 95 - Luglio 1985 / Cervetto, Ferro

Affidabilita' e ridondanza nelle fondazioni offshore System reliability of offshore foundations

PAG.

BT 96 - Aprile 1986 / Alimento

ULTIMI BOLLETTINI TECNÏCI PUBBLICATI LAST PUBLISRED TECHNICAL BULLETINS

BT 97 _{Settembre 1986 / Pittálûga}

Similarities and differences in thin-walled beams theories

BT _{98 - Novembre 1986 / Pittaluga, Dog iani}

SecOnd order non-linear effects In marine _s'sterns ST 99 - Dicembre 1986 / Pattofatto

L'Annesso II allá MARPOL 73/78 e connessa normativa BT 100 - Ottöbre 1981 / Pittaluga

Reliability based ship design in the 90's Realistic scenario or a dream?

ST 101 - Maggio 988 / Spinelli

Le frontiere della progettazione di strutture navali BT 102 - Agosto 1988 / Osborne Dogliani

Second-order non linear effects in random oceañ surface. wáves ST 103 - Aprile 1989 / Dogliani

Stochastic modelling of quadratic wave components

ULTIMI RESEARCH REPORTS PUBBLICATI LAST PUBLISHED RESEARCH REPORTS

KR 211 - Agosto 1981 / Pittaluga, Sciacca, Ziliotto

Alcune note sulle vibrazioni flessionali degli alberi porta elica RE 212 Agosto 1981 / Ferro, Pittaluga

Influenza delle previsioni metereologiche sul calcolo della risposta

delle navi.

KR 213 - Dicembre 1981 / Ferro

Influenza della larghezza di banda sulla distribuzione dei picchi in un processo stocastico stazionario

RK 214 Márzo 1982 / Alberti, Robino, Ziliotto

Analisi del comportamento strutturale di navi portacontenitori soggette a torsione

KR 215 - Giugno 1982 /Caretti

Non-linear, frequency domain analysis of motions and loads of ships in irrêgula± waves

KR 215 - Aprile 1983 / Cazzulo

Un programma di verifica globale delle temperature dello Scafo RK 2Ï7 Agosto 1983 / Albert, Berrinó

Verifica sperimentale di un metodo di calcolo del comportamento delle chiatte in mare

RK 218 - Marzo 1984 / Ferro

Foundamentals of a procedure för reliability analysis of jacket structures

RK 219 - Dicembre 1984 / CaZzulo

Recenti aspetti della teoria delle travi a parete sottile KR 220 - Marzo 1985 / Ferro, Caretti

Metôdi per l'analisi del comportamento non-lineare delle navi in mare confuso

RK 21 Maggio 1985 / Càsciati, Ferro

ReliabIlity based code format for marine cranksháfts KR 222 - Aprilé 1988 / Dogliani Salza

Onde regolari e periodiche domini di applicabilita' delle teorie analitiche.

KR 223 -. Máy 1988 / Cazzulo Dogliani

Stochastic wave loads for reliability analysis of jacket structures BRITE P 1270 Task 1.1

KR 224 - Agosto 1989 / Ferrando Dogliani C8zzulo

Maxima of mooring forces: an approach based on outcroSsing methods