CONSTRUCTIONAL REQUIREMENTSOF 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 marineenvironment 20

11 - Items under development 21

SUMMARY

Alter an introduction, in which a brief historical hiflt is givenand the scope of the paper is underlined, section 2 lists the mostimportant rules governing chemical tanker design.

The remaiiirgr sections deal with thé chapters of IBC Code inwhich constructional requirements are. given. Whilst trying t'o keep toa minimum the quoting of the Codes' requirements, in the few pagesof this paper it has been attempted to 'highlight sorné partioülàraspects of said requirements Cand to point Out thé relating amendmentsdeveloped by 1MO.

Section 3 deals with survival ôapability and loçation ofcargo tanks and gives a cömparison with oil tankers. Thé importanceof the compliance with minimum dhnensióhs Of openings for access tospaces. in cargo area is stressed in section 4 "Ship arrangements", inwhich it is à]so shown how said compliance can influence, the shipdesign. The stifi unresolved problem of calculating the stresses dueto sloshing in partially filled tanks is mentioned in section 5 "Cargocontainment".. Section 6 gives a brief review of materials ofconstruction and of their development. The amendments to chapter 8of the Code "Cargo tank vent systems" recently approved by MSC areillustrated. in section 7. Section 8, dealing with electrical installations,stresses the problem of missing data relating to electrical equipméntfor products listed in the Code. Section 9 introduces the amendments'to Reg. 11-2/55.5 of SOLAS 74 dealing with the requirements of 'inertgas systems for cargo tanks and section 10 deals with the additionalmeasures for the prOtection of 'the mariné environment. Section iicontains the. reference to the major items uÌider development.

in the present paper, where not expressly mentioned, by"Code!', the "IBC Codee is meant.

- FOREWORD

Dealing with constructional requirements of chemical tankers, ina sufficiently complete way and in few pages, is practicallyimpossible., due to the complexity of the matter. Since their firstappearance in the ports of the world immediately after the end of thesecond World War, up to now, the progress has been continuOus.Thus, step by step, national regula ions were developed in thecountries whose Administrations were, as first, to cope with theproblems of construction f tanlçs and systems for the simultaneouscarriage of dangerous and often mutually non-compatible products.

In 1971 the first 1MO Code was finalized, whose aliti was toconsolidate the various national regulations for'. chemical tankers andreconcile the differences between them, which gave rise to problemsfor ships trading world-wide.. Although the Code was developed as arecommendation, it' Soon appeared to have gained universal approvai.

Since then 1MO has constantly worked in improving the Code andin 983 the Code, called International Code, became part f. the 1983Amenthnents of SOLAS 74, as amended.

Registro Italiano Navale has been active, since the beginning,both in the development of national regulations and in theparticipation in international works. This in support of requests forclassification, practically continuous during the years, of chemicaltankers at the service of a òhemical industry which, in Italy andabroad, 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 presentparticular problems; this on the basis of the. experléncé gainedby the activity peculiar to a Classification Society;mention amendments to the Codes which have already been

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adopted by 1MO or are under development, with a hint at theiìbackground.

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 astarting-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 standardand 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 5December 1985;

(il) the Code. for the Construçtion and Equipment of Ships CarryingDangerous Chemicals in Bulk (BCH Code) adopted by MSC byRes. 9(53), on 17 September 1986, and by MEPC by Res.20(22), on 5 December 1985. The BCH Code was originallyadopted by the 1MO Assembly by Res. A.212(VII) in 1971. TheCOde 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 ofthe pollution of marine environment by noxious liquid substancescarried in bui by ships, 1MO Codes for chemical tankers become anintegral part of MARPOL Convention itself.

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

The connectiOns between MARPOL and Codes are stated underReg. 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 withthe provisions of the IB C Code, chemical tankers constructed before iJuly 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, alsobecome means to minimize the risk of accidental pollution of sea bychemical 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 marinepollution aspects and are briefly dealt with in section Ï0 of the

- present notes.

In additiOn to the above mentioned Codes, chemical tankers haveto comply with the applicable SOLAS requirements and with the Rulesof Classification Societies for the areas not covered by the Codes,such as ship's strength and scantlings, fire protection inaccomodation spaces, lifesaving appliances (Ch. III of SOLAS with theparticular requirement of lifeboats with a self-contained air supportsystem), steering gear (with particular requirements for chemicaltankers, new and existing,, of 10,000 tons gross tonnage and

úpwards) etc.

Even if not directly connected with the ship design, it is deemeduseful to mention the following rules and guidelines, which, for

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different aspects, are anyhow fundamental for people operating in thefield of chemical tankers:

the 1MO "Standards for the Procedures and Arrangements for theDischarge of Noxioüs Liquid Substances" called for by Annex II toMARPOL 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 underAnnex 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 besthighlights the close connection between the cargo intended to becarried and the constructional characteristics of the ship.

Depending on the hazards associated with diffèrent chemical

products (health hazard, fire hazard, pollution hazard, reactivityhazard, corrosion hazard) the Code provides for three types of shipsand namely Type 1, Type 2 and Type 3. Such classification is basedon the ship's ability to survive degrees of damage and not to

present,, or at least to limit, cargo release. Each type of ship isassociated 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 theship type and length.

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

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In Figure 3 the damaged condition stability diagrams of two Type2 áhemical tankers are shown.

The first diagram of Figure 3 is relating to a chemical tanker, of132 m in length, having a deadweight of 11750 t, subdivided into 22cargo tanks. The second diagram refers to a chemical tanker of 85 min length, having a deadweight of 3400 t, subdivided into 22 cargotanks.

Chemical tankers have in general, on accrnit't of operationalpurposes, a high degree of subdivision, and therefore stability andsurvival requirements are generally easily met.

An important role may be played by the way in which the doublebottom is subdivided, which may give rise, in case of collision, to asymmetrical or non-symmetrical flooding; but also the cases of

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

Situations which aré to be carefully examined are the.: loadingconditions with products having a high density, also because in sucha case it may be necessary to keep some cargó tanks empty. Forsulphuric acid, for example, a further reason fr keeping wing tanksempty is that the ship shell plating should not form any boundaries Ofthe tanks, to the purpose of preventing possible contact with water.In such a. case, specially in cases of flooding of the forward shipzone, 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 whiçhcompletes the deadweight) and due to excessive trim. The stabilitydiagrams 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, asfor oil tankes.

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If we cOmpare the requirements relating to survival capability ofchemical tankers with the ones of oil tankers as per Reg. 25 ofAnnex I of MARPOL 73/78, it appears that the survival requirementsañd 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 notexceeding 225 m in length (two compartment . ships except formachinery space);oil tankérs of less than 150 m in length are 'dealt with, byMARPOL as single compartment ships with relaxations for theengine room. FOr tankers of 100 rn in length or less, where suchrequirement cannot be. fulfilled without impairing the operationalqualities of the ship, Administrations may allow relaxations..This lead to dealirg with oil tankers in a remarkably lesssevere '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 cOmpartmentships, 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 anparticúlar, it contains requirements in connection with:'- cargo segregation: segregation of cargo taflkS from 'accomodtiOn,

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

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location of accomodation, servce and machinery spaces and contrólstations in respect to cargo area. It contains requirements similar tothe 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 themportance of the compliance with minimum dimensions of openings foraccess to spaces in the cargo area (paragraph 3.4), which is veryimportant and may remarkably affect the ship structure.

Such dimensions are 600 mm by 600 mm for horizontal openingsand 600 mm by 800 mm for vertical openings.

The compliance with said dimensions is important in order toallow a sifficiént acceSS to persons wearing a self -containedairbreathing apparatus. and. protective equipment or to provide, a clearopening tO facifitate the hoisting of an injured person frOm the bottomof the space.

The compliánce with such dimensions turns out to be a seriousproblem, specially for double bottoms of small or middle size units,and requires a careful study of the ways of access to the varioúszones in which the double bottom is subdivided, taking also intoacçount the presence of bilge and general service piping whichfurther reduces the available space.

As a matter of fact, the Code provides for the possibility ofaccepting access openings having lower dimensions, in the case wherethe possibility of passage is demonstrated, however, accidentsoccurred should discourage the acceptance of such lower dimensions.

8

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 therequirements.

In fact, if we consider the space occupied by top and bottomlongitudinais

f the double bottom, in general having a height ofabout 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 withshear, and it is thérefOre necessary tO move, when possible, the

opening to sections having a lower shear stress level, and toproblems of constructional details due to the location of longitudinaisvery close to the opening.

For these reasons, instead of passages in the floor plates, oftentransverse passages àre chosen, cutting the 800 mm x 600 mmopenings in the girders, which, being intaót, offer a better usefulheight, but this solution does not allow the presence of watertightgirders except for the central girder (see Figure 5).

The two solutions imply a different layout of the double bottomand therefore a big impact on the design of hull and on the capacityplaìi of the ship.

Similar accessibility problems, with iritluelice on the structure.,may be found in cofferdams, but, obviously, with better possibilitiesof solution.

5 - CARGO CONTAINMENT

Chapter 4 of the Code lists the various types of cargocóntainment, differentiating between tanks the sides of which form, ordo not form, part of the ship's hull and tanks having design pressurebelow or above 0.7 bar gauge.

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For tanks of the gravity type (design pressure not greater than0.7 bár gauge), no major difference is encountered, for whatstructural strength is concerned, in respect of oil tankers, except forthe problems arising from sloshing loads.

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

In case of bad weather this leads to large motions of the liquidcargo which induce high transient pressures on longitudinal andtransverse bulkheads. -.

The matter of liquid sloshing motions has been extensivelyinvestigated in the last decade, both theoretically and experimentally,but unfortunately most of the work done is relevant to single caseswhere 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 largeamplitudes quite easily, but the pressure variation varies smoothlywith the natural periOd of the tank. On the contrary, when there is adeck closing the tank, it interferes with the liquid motion, byreducing the sloshing amplitude, but each time the mternai sloshingwave hits the deck, high shock pressures are generated, which mayinduce high transient stresses on the deck itself and on thesurrounding bulkheads.

A theoretical solution to the problem is still missing, although,in the last few years, numerical methods have been developed, whichseem to reproduce guite closely the sloshing motions in closed tanks.In particular, extension of these new methods is needed, in order to

10

include the effects of random motions of the ship in a. seaway,correlation of liquid motions, shock pressures and transient stressesin the structure, calibration of numerical methOds on the basis ofexperience at sea. All these items are still matter for futuredevelopment.

For the tiñe being, the only viable way to prevent structuraldamages in partially filled tanks at sea, without requiring unjustified

heavy Strengthening of the structures, seems to be á carefulextrapolation of èxisting practice.

Particulàx care is to bè taken in any case to preserveredundancy and. toughness of deck and bulkhead structures,particularly in double shell tanks without interilal stiffénerS, whichare expected to. offer reduced damping. (to sloshing motions) withrespect tò traditional tanks.

As an example, Figure 6 shows the distribution of pressures dueto sloshing motions calcúlated for a tank which osôiiltes around the.centre-line of the lower base. The calculated values may be comparedwith. the . hydrostatic head indicated for easy reference at the fourvertices of the tank.

6 - MATERIALS OF CONSTRUCTION

Chapter 6 of the Códe, whilst specifically indicates the types ofmatérial not suitable for specific products, does nOt go into detail onthe general suitability of structural materials uséd for tankconstruction, together with associated piping, pumps, valves, ventsand their jointing materials. There is only a general sentence Statingthat materialsare tò be suitable at thé temperature ánd pressure forthe cargo to be carried to the satisfaction of the Administration.

The type of material is therefore depending on carried, productsand on economic reasons and, for what the characteristics andscantlings are concerned, Classification Societies' rules apply!

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Although mild steel is acceptable for the majority of chemftalscarried by sea; stainless steel Is generally used both to ensurequality control of the product and containment of certain cargoeswhich may have corrOSive properties.

Versatility and flexibility certainly are two major factors in thefIeld of chemical transportation and it is in these respects that theuse of appropriate grades öf stainless steel offers outstandingadvantages. Versatility stems from the ability of stainless steel tañksto be suitable for a range of cargoes,; flexibility results from therelative ease with which stainless Steel cargo taflks, properlydesigned, can be çleaned, so reducing cleaning time and costs.

The selection of a particUlar grade of stainless steel from thewide variety available will be influenced by the cost nd the desireddegree of corrosion resistance. For a vessel intendéd to carry one ortwo specific cargoes the choice of grade will be rather simple, whilefor a multi-parcel chemical taflker a grade that is compatible with asmany different types of cargo as possible must be selected.

The austenitic stainless steels have the' widest range ofcompatibility with chemicals. The molybdenum-free grades (AISI 3Ó4,321 and 304L) are satisfactory only for mildly corrosive cargoes. Type316L is the most widely used stainless steel, being compatible with awide range of cargoes. Type 317L is a more highly alloyed materialthan 316L and its greater molybdenum content gives it a higherresistance to pitting, which is of use in phosphoric acid service.

One disadvantage of stainless steel is that normal stainless steelgrades exhibit a yield strength (200 MPa) lower than that of mildsteels, which implies a heavier structure. An important developmenthas 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 theyield strength and a moderate improvement in the ultimate tensilestrength are obtained.

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A further improvement in mechanical and corrosion resistanceproperties is offered by a new type of stainless steel which has beendeveloped in the recent years and which has a duplex structurecontaining approximately the same content of austenite and ferrite.This steél offers a minimum specified yield strength (460 MPa) about50% higher than for the standard austemtic N grades.

For what the yield strength is concerned, it therefore increasedfrom 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 corrosionresistance.

In this regard it is however to be pointed out that highermechanical properties do not allow in general a proportional reductionin the scantlings, since also the fatigue resistance of the weldedjoints is to be takén into account, which does not increase inproportion to the mechanical properties of the steel.

In any case, for reasons of elastic stability and of resistance tolocal loads , the thicknesses are not allowed to decrease below minimumvalues, properly fixed for the different structures.

As usually done for new materials, the jnterventions ofClassification Societies for duplex steel are relating to the approval ofSteel, through tests performed at the steel manufacturer's works, andthe approval of the welding procedures, whiçh, for duplex steel, areparticularly important due to the strong influence of heat.

In fact, owing tÓ the particular duplex microstructure, care is tobe taken to limit the heat input specific to values as recommended bythe manufacturer. Heat input has a strong influence on the austeniteferrite balancé and therefore much attention is to be paid to selectthe correct: welding parameters. In particular, severe thermal cyclesincrease the ferrite content beause high cooling rates do not allowthe transformation into aústenite of the ferrite phase which is stableat high temperature. On the contrary, high heat input produces lower

13

ferrite content but a wider heat affected zone with coarsening offerrite grains. The ferrite content in both weld metal and heataffected zone is to be limited because increased ferrite reduces theCharpy V values and corrosion resistance properties. The ferritecontent should be limited to 70 - 75%.

- CARGO TANK VENT SYSTEMS

Chapter 8 of the Code deals with the différent types of tankvent systems (open or controlled) and their characteristics. The opentype, i.e. a system which offers no restriction to the free flow ofcargo vapour from cargó tanks during normal operation, should onlybe 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 Committeeapproved the revised chapter 8 of the Code as an acceptablealternative to the appropriate sections of Regs. 11-2/59.1 and 59.2 ofSOLAS, and agreed to it as a future amendment to thé Code, to be.adopted at an appropriate time. The requirements of the revisedchapter 8, suitable for the carriage of flammable chemicals are equallyacceptable 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 suitablealternative venting requirements could be developed, chemical tankersintended to carry chemicals and, petroleum products sho1d continue tobe, 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 beindependent of venting systems of other ship compartments;requirements concerning drainage of venting systems are moredetailed (self-draining back to cargo tank is required,' as far aspracticable);

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15

factors to be taken into account for determining the size of theventing 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 ofthe controlled type venting systems has been increased from 4 m

to 6 rn and it has been clarified that the 10 m distance from airintakes 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 hasbeen 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 certaincharacteristics assoôiated with a flame-arresting device fitted atthe 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 arrangementshave been déveloped with full participation of the Sub-Committee

on Fire Protection over many sessions and with extensivediscussion of technical considerations, laboratory testing and thepractical experience of Members to substantiate the requirementsof the circular and therefore confirmed the proposed

amendments;a paragraph has been added to draw the attention to the.

possibility of the blockage of thé devices to prevent the passageof flame into cargo tanks by, for example, the freezing of cargovapour, polymer build up, atmospherk dust or icing up inadverse weather conditions.In this respect it was several times pointed out that regularmaintenance was an essefltiái feature to be associated with saiddevices;

(viii) the procedure for cargo tank gas freeing has been added, whichwas developed on thé basis of Reg. uI_2159..2 of SOLAS 74(83).

As it can be noted, chapter 18 has been deeply revised Therévision took a long time at 1MO to adapt, to chemical tankers, thestandards already developed for oil tankers.

8. - ELECTRICAL INSTALLATIONS

As already said, chapter 10 of the Code has been deeply revisedand, in particular, specific requirements for electrical equipment havebeen introduced.

Where electrical equipment is installed in hazardous locations, itshould be certified by the relevant authorities recognized by theAdministration .fòr operation in the flammable atmosphere concerned, asindicated in column "i" in the table of chapter 17. In this column, forflammable products, temperature classes and apparatus groups, asdefined 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 temperatureaccördirig to IEC Publication 79-8.

The determination of the group is based on the maximumexperimental safety gap (MESG) fOr explosion proof enclosures and onthe minimum ignition current (MIC) for intrinaically safe electricalequipment, and the. test procedures are contained in lEG Publiçatións79-lA and 79-3, respectively.

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What above certainly represents an improvement for safety inrespect to B CH C öde, but the remarkable thing is that for manyproducts 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 electricalequipment, 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 shipis strictly linked to the eleötrical equipment installed for the productscarried, and Administrations have difficulties when they have to decidewhat to do without any indication in the Code.

When it is inten4ed to carry products without data fOr eleçtricalequipment, one possibility is to chOose an equipment having thehighest apparatus group lIC and the highest temperature class T6, butthis is obviously particularly onerous both due to the higher costinvolved 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 manyproducts, but which may not bó Sufficient for some other chemicalproducts.

The problem of drawing up a complète table of chemiôal productsand suitable électrkal equipment was discussed within IEC in thecourse of the revision of the TC 18 Publication Nô. 92-502 Tankers.The TC 18, during its November 1988 meeting in Dubrovnik, dèémednot to introduce said table into the Official requirements, taking intoconSidération the difficulty in issuing añd updating such a completeList of products.

1MO, recognizing the importance of the missing. parameters,should make any effórt. tó solve this problem b stressing to

Administrations the necessity òf having said data for the new products

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

9 - FIRE PROTECTION AND FIRE EXTINCTION

Chapter 11 of the Code deals in particular with fire protection Ofcargo 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 systemand a halogenated hydrocarbon (halon) system. For the two systemsreference is made to the applicable requirements of Reg. II-2/5 ofSOLAS 74(83).

For cargo area a fixed deck foam system is required and theparameters 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 offoam concentrates"! it is really hoped that the guidelines will bedeveloped so that a uniform standard in this important field can beapplied. Also lACS and ISO are working on this subject.

As far as the requirements for inert gas systems in cargo tanksare concerned, Reg. 11-2/55.5 of SOLAS 74(83) Specifies that Reg. 60need not be applied to chemical tankers, provided that alternativearrangements, to be developed by the Organization, are fitted. ¡MOdeveloped and adopted by Res. A. 473(XII) the "Interim Regulations forInert Gas Systems on Chemical Tankers Carrying Petroleum Products".

The problem of carrying flammable chemicals was therefore leftopen and, in fact, the same resolution urged the MSC to develop finalrequirements for chemical tankers carrying chemical fhìmmible cargoesand specified that compliance with, additional provisions which will becontained in the final requirements should not be required to beapplied to ships the keel of which is laid before the date of coming

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into force of the final requirements.

1MO continued to work according to what above and good resultswere 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 concludedthat, in case of tanks not exceeding 3000 m3 capacity andwashing machines having individuai nozzle capacity not exceeding17.5 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 ofSOLAS need not therefore be applied;

(li) on the basis of experience and researches carried out by theindustries involved, it was concluded that, apart from fewmodifications, the interim Res. A.473(XII) can also cover thecarriage of flammable chemicals. The new resolution was adoptedby the Assembly at its. 14th session as Res. A. 567(14) andprovides the final requirements for inert gas systems on chemicaltankers carrying petroleum and chemical products.

On the, basis of the above results, Reg. 11-2/55.5 was amendedand its new requirements, depending on thé . date of conStruction ofthe chemical tanker and On the products carried, are summprized inthe following table. Said amendments were adopted by the expandedMSC during its 57th session and, they will enter into force on the istFebruary 1992, together with other important amendments to SOLAS.

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Product carriedShip constructed

Before, 1 July 1986 After1

July 1986

Crude Oil orpetroleum products

IGS as perRes. A.473(XII), or

Res. A.567(14)IGS as per

es. Af567(14)

F1Rmrnble chemicalsCh. 17 of IBC CodeCh. VI of BCH Code

No IGS

-IGSas perRes. A.567(i4)

- No IGS if theconditions un-der previous(i) are met

lo - ADDITIONAL MEASURES FOR THE PROTECTÏÖN F THEMARINE ENVIRONMENT

In addition to the requirements of Reg. 13 mentioned undersection 2 of the present paper, Annex II and 1MO Standards forProcedures and Arrangements called for by said Annex II require theinstallation of new plants or affect the design of already foreseenplants. 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 acertain diameter depending on its distance from the forwardperpendicular and on the rate to be discharged so as to limit theflow velocity in order to maintain the flow within the ship layerand the ship wake. In addition, the location of said outlet has totake into account the location of sea. intakes located aft, in orderto avoid intakes of polluted waters (see Figure 8);

(fi) the dimensions of suction wells in the cargo tank and unloadingpiping are affected. They should be reduced as much as possibleto keep to a minimum the tank residues and in any case not toexceed the maximum quantity of residues fixed by Reg. 5A ofAnnex II, What above taking into account that súbmerged ordeepwell pumps (centrifugal type) are generally installed andthat the amount of residues left in the tank and in the relatingunloading piping increases with the dimensions of suction wellsand discharge piping. Additional small diameter stripping pipingor other arrangements are often installed to comply with saidReg. 5A;the cargo tank heating system is to be designed as to guarantee,for certain cate gory B and C substances, an unloadingtemperature such as to consider them "non-solidifying" or "lowviscosity";the cargo tank washing system is to have dimensions and to bepositioned in order to comply with the requirements of AppendixB to the above menUoned Standards, i. e a minimum temperatureOf 60°C has to be assured for the required flow rate of washing

20

water (in case Of solidifying and/or high viscosity substances)and the position and characteristics of the washing machineshave to be sucth that all tank bound5ries are washed.

Il - ITEMS UNDER DEVELOPMENT

It is deemed useful to conclude the présent paper by mentioningthe items under discussion at 1MO in connection with which possiblefuture amendments to the present constructional requirements of theCode will be made.

111 - Recycling techiiiques of chemical tnnkers

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

The adequacy of the prewash procedures presently contained inthe standards for procedures and arrangements for the discharge ofnoxious li4uid substances (NLSs) was discussed with the aim atsuggesting ways to improve the procedures in order to follow upsatisfactorily the objective of Annex II to MARPOL 73/78.

It. was outlined a possible way of modifying the prewashprocedure based on a number of cycles so as to take account of theactual amount of residues in a tank, and specifying minimum

quantities of washwater.

In regard to the potential hazards associated with recycling ofwas hwater in a flammable tank atmosphere, the use of inert gas onchemical tankers needs to be considered in connection with specificlimitations related to cargo tank size and tank washing throughputs.It was also pointed out that previous research had shown increasedgeneration of static electricity if additives were used. or if thewas hwater was contaminated with cargo residues as will be the casewhen recycling.

21

Some delegations were inclined to consider thé reasons forexempting chemical tankérs from inertirig requirements Subject to tanksize and washing machines throughput limitations also valid for thiscase. Other delegations disagreed. However, the matter should bemore deeply examined.

It was therefore decided by the Sub-Committee to coñsidêr thematter further before any firm decisiöns could be taken.

11.2 -. Vapour emission oentrol systms (VECSs)

This item was started during the 19th session of theSub-Committee on Bulk Chemicals with the aim at improving the airquality in areas already polluted and to prevent deterioration of airquality in clean areas.

It was therefore decided thAt design standards should bedevelOped fr VECSs to cover transfer operations and. particularlyloading and bafiRsting of cargo tanks It was alsó agreed thAt thedesign standards would not be intended to mandate the use of vapouremission contro!, but rather standàrds would be fóllowed if vapouremission control is mandated by a State or a local Authority.

The examinatiOn of the hazards connected with VECSs wasstarted and such, examination will continue during the next session.

11.3 - Halons as fi e-extinguishing agents

Following the recent measures taken internatiOnally, aimed atlimiting the use of chlorouluórocarbons (CFCs), the 1MO Assembly,during its 16th session (in October 1989), adopted a Resolution bywhich 1MO decides not to develop further requirements which couldencourage an increased use of halons and to draw up a plan for thegradual total elimination of hAlOnS on board ships in a short time.

22

- 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. IExcept here if L<125 m

Figure i - Damage Assumptions

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

No exception

23

/ 15

B/i 5

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- 132mA-5.92°

Case 2

A - 5.250B - 0.045 m.radC - 0.244 mD-37°

85m

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

24

e (e)

B 0,034 m.rad

C - 0.118mD - 25.5°

() if Ls 100 m Adminitrathns may allow relaxatiöns

Figure 4 - Companson between damage survival

capabilities of oil tankérs and chemical tankers

25

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

ooc'J

200x loo

o

Figure 5 - Ship arrangements

Ship type? L120m

0250

26

8

L

Girder 3240 mm from C.L.

.»;

s

13

100x10

[A)1

I 1t__

Web frame 2OOx15

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

- rolling amplitude=8°

- forcing frequency = 1.1 rad/s

p (calculated values)

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') in accordance with MSC/Circ. 373/Rev. i

28

I--

le I

I I I I

I I I II 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

29

discharge piping

5L

ULTIMI BOLLE'PrINI TECNICI PUBBLICATILAST PUBLISHED TECHNICAL BULLETINS

BT 74 - Febbraio 1981 / Pittaluga, ZiliottoUna procedura per la valutazione della robustezza trasversale dellenavi peril traspOrto di merci alla rinfusaA procedure for the transverse strength asséssment of large bulkcarrier ships

BT 75 - Novembre 1981 / FerroMetodi e problemi nell'analisi dell'affidabil.itá' déllè trutturenavali

Methods and problems in reliability analysis of ship structures

BT 76 - Dicembre 1981 / Bisagno, Marchesi, ValentinGIPSY - Un post-processor per l'analisi ad elementi finitiGIPSY - A post-processor for finite element analysis

BT 77 - Gennaio 1982 / FerroApplicabilita' delle tecniche affidabilistjche alla progettazionenavale

Applicability of reliability concept to ship design

BT 78 Febbraio 1982 / SelvaggiProblemi di progettazione per navi adibite al trasporto di gasliquefatti. a bassa tempetaturaDesign problems for ships carryng low temperature liquefiéd gases

HT 79 - AprIle 1982 / SpinelliConvenzione MARPOL 1973, come emendata dal protocollo 1978- interpretazione della normativa controlli RINA per il rilascio didichiarazioni di corrispondenza alle norme della convenzione(seconda edizione)

HT 80 - Maggio 1982 / Ferro,. ZiliottoApplicazione di una procedura diretta per il calcolo dei carichid'onda per le analisi di robustèzza trasversaleApplication of a direct procedure to the assessment of wave loadsfor the transverse strength analysis of ships

B'2 81 - Aprile 1983 / MicilloApplicazione dei procedimenti speciali di. saldatura nelle costruzioninavali

BT 82 Novembre 1983 / Marchesi, ZiiiàttoComportamento post-critico di pannelli nervati-].cônfronti trarisultati. numerici e prove sperimentali

HT 83 - Dicembre 1983 / AlimentoI materiali per la costruzione degli scafi- Note sulle caratteristiche e prove de:i materiali secOndo là

normativa dei RINAMaterials for hull structures- Review of the properties and tests of the materials accordinglywith RINA requirements

PAG. i

ULTIMI BOLLETfiNI TECNICI PUBBLICATILAST PUBLISHED TECHNICAL BULLETINS

BT 84 - Gennaio 1984 / FerroAdvances in the calculation of the maxima of ship responsesPaper presented at the Euromech Colloquium 155, reliability theör.yof st:r.ucturai engineering systems, Jüne 15-17, 1982, EnginéeringAcademy of Denmark - reprinted from Dialog 6-82

BT 85 - Gennàio 1984 / Ferro, CrvéttôReliability of marine structures under dynamic loadingsPaper presented at the International Workshop on stochasticmethods in structural mechanics, June 9-12, 1983, Universityof Pavia - reprinted from the proceedings.

BT 86 - Gennaio 1984 / Rôbino,. ZiliottoWave. torsional moments in ships with large hatch openingsPaper presentedat the VI Italian - Polishseminar Genoa,Ñovember 1983.

ET 87 - Marzo 1984 / SpinelliConvenzione 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 / PasiniLa saldatura subacquea - Statò dell'arte

BT 89 - Giugno 1984 / FerroStochastic models for low-frequency, springing and impact loads onships

BT 90 - GennaiO 1985 / Pittaluga, BisagnoModerne tecniche di analisi dei comportamento in mare

ST 91 - Gennaio 1985. / Cazzulo, ZiliottoApplicazione della meccanica della frattura nelle verifiche a fatica

BT92 - Gennaio 1985 / Ferro, MeregaProspettive della progettazione affidabilistica delle strutture marine

BT 93 - Gennaio 1985 / MarcheSi, ZiliöttòAnalisi di un'avaria di una portarinfùse

ET 94 - Maggio 1985 / CazzùloPanoramica sui fondamenti teorici delle meccanica della frattura

ET 95 - Luglio 1985 / Cervetto, FerroAffidabilita' e ridondanza nelle fondazioni offshoreSystem reliability of offshore foundations

PAG.

BT 96 - Aprile 1986 / AlimentoMezzi di salvataggio - Le nuove norme della convenzione SOLAS 1974 (83)

ULTIMI BOLLETTINI TECNÏCI PUBBLICATILAST PUBLISRED TECHNICAL BULLETINS

BT 97 Settembre 1986 / PittálûgaSimilarities and differences in thin-walled beams theories

BT 98 - Novembre 1986 / Pittaluga, Dog ianiSecOnd order non-linear effects In marine s'sterns

ST 99 - Dicembre 1986 / PattofattoL'Annesso II allá MARPOL 73/78 e connessa normativa

BT 100 - Ottöbre 1981 / PittalugaReliability based ship design in the 90'sRealistic scenario or a dream?

ST 101 - Maggio 988 / SpinelliLe frontiere della progettazione di strutture navali

BT 102 - Agosto 1988 / Osborne DoglianiSecond-order non linear effects in random oceañ surface. wáves

ST 103 - Aprile 1989 / DoglianiStochastic modelling of quadratic wave components

PAG. 3

ULTIMI RESEARCH REPORTS PUBBLICATILAST PUBLISHED RESEARCH REPORTS

KR 211 - Agosto 1981 / Pittaluga, Sciacca, ZiliottoAlcune note sulle vibrazioni flessionali degli alberi porta elica

RE 212 Agosto 1981 / Ferro, PittalugaInfluenza delle previsioni metereologiche sul calcolo della rispostadelle navi.

KR 213 - Dicembre 1981 / FerroInfluenza della larghezza di banda sulla distribuzione dei picchiin un processo stocastico stazionario

RK 214 Márzo 1982 / Alberti, Robino, ZiliottoAnalisi del comportamento strutturale di navi portacontenitorisoggette a torsione

KR 215 - Giugno 1982 /CarettiNon-linear, frequency domain analysis of motions and loads ofships in irrêgula± waves

KR 215 - Aprile 1983 / CazzuloUn programma di verifica globale delle temperature dello Scafo

RK 2Ï7 Agosto 1983 / Albert, BerrinóVerifica sperimentale di un metodo di calcolo del comportamentodelle chiatte in mare

RK 218 - Marzo 1984 / FerroFoundamentals of a procedure för reliability analysis of jacketstructures

RK 219 - Dicembre 1984 / CaZzuloRecenti aspetti della teoria delle travi a parete sottile

KR 220 - Marzo 1985 / Ferro, CarettiMetôdi per l'analisi del comportamento non-lineare dellenavi in mare confuso

RK 21 Maggio 1985 / Càsciati, FerroReliabIlity based code format for marine cranksháfts

KR 222 - Aprilé 1988 / Dogliani SalzaOnde regolari e periodiche domini di applicabilita' delle teorieanalitiche.

KR 223 -. Máy 1988 / Cazzulo DoglianiStochastic wave loads for reliability analysis of jacket structuresBRITE P 1270 Task 1.1

KR 224 - Agosto 1989 / Ferrando Dogliani C8zzuloMaxima of mooring forces: an approach based on outcroSsing methods

PAG. 1