Supplement LNG History

A SIGTTO NewsletterSupplement

September 2004

BULK LIQUEFIED GAS BY SEA:THE EARLY YEARS

by Robin Gray

Much has been written about the carriage of the first cargoes of liquefiednatural gas (LNG) onboard the Methane Pioneer in 1959. But what ofliquefied petroleum gas (LPG), a gas ship cargo which predates LNG? Whenwere the pioneering LPG cargoes carried and how did this importantseaborne trade develop?

In this tribute to the first gas carriers, Robin Gray, former SIGTTO GeneralManager, sheds light on the early days of the less well-known part of the gasshipping industry and on the role played by one particular shipyard in theNorth East of England.

The Society of International GasTanker and Terminal Operators Ltd

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MAIN OFFICE: BERGEHUS, DRAMMENSVEIEN 106, P.O.BOX 2800 SOLLI, N-0204 OSLO, NORWAY

TELEPHONE: +47 22 12 05 05, TELEFAX: +47 22 12 05 00, E-MAIL: [email protected]

www.bergesen.no

gas

Bergesen is the world’s leading owner and operator of LPG carriers,

and we aim to become the leading independent LNG player by 2010.

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Agnita - the first purpose-built gas carrier, showing the domed heads of the cylindrical cargo tanks protruding above deck

In his book “Oil Tanker Cargoes”, published in 1954,John Lamb, the then technical director of Shell Tankers,described ships able to carry butane and propane gas inChapter 17. He stated that the Shell oil tanker Megarawas the first ship to carry LPG in bulk. Megara may havebeen the first ship to physically transport LPG but shewas not the first able to do so.

The Dutch-flag Megara was built by the Le Traitshipyard at Rouen in France for Petroleum Maatschappij”le Coruna“, part of the Shell Group‘s Anglo SaxonPetroleum, in 1928 as an oil tanker.

However, the 7,931 gross ton (gt) ship did not becomea gas carrier until 1934 when she was specially convertedto enable the carriage of LPG, as well as oil, by theWerkspoor yard in the Netherlands.

The conversion work entailed the installation of 20cylindrical pressure vessel tanks totalling 1,305 m3 forthe transport of butane and four tanks totalling 158 m3

for propane. Each butane tank had a capacity ofapproximately 65 m3 while the propane tanks, at about40 m3 each, had smaller diameters to compensate forthe much higher vapour pressure of propane.

All the cylindrical gas tanks, which were positionedvertically, were fitted in several of the ship’s centre tankspaces. When engaged in the carriage of gas, thebutane tanks were filled to 95 per cent of the cylinder’scapacity while the propane tanks were filled to 91 percent. This provided Megara with the ability to carry upto a maximum of 780 tonnes of LPG cargo.

Purpose-built AgnitaThe cylindrical LPG tanks for Megara were built byWerkspoor to a design by R & W Hawthorn Leslie, ashipyard located at Hebburn on the south bank of theRiver Tyne. Shipbuilding had come to Hebburn in 1853when Andrew Leslie, the son of a dispossessed Shetlandcrofter, arrived on Tyneside from Aberdeen to takeadvantage of new opportunities and launch hisenterprising project.

The UK yard’s LPG tank design was chosen for Megarabecause Hawthorn Leslie had designed and constructedthe first purpose-built gas carrier a few years earlier.This was the 3,552 gt Agnita, delivered in 1931, also toAnglo Saxon Petroleum. Agnita was a unique vessel inthat she was designed to carry three different types ofcargo - gas oil, sulphuric acid and LPG.

For the carriage of oil Agnita was provided with sixsets of cargo tanks divided by a centreline, longitudinalbulkhead. For the carriage of LPG and acid, the ship had12 large cylindrical pressure vessel tanks. Built to a 4.14bar gauge working pressure, each was 5.26 metres indiameter and 9.91 metres high, providing Agnita witha total pressure vessel capacity of 2,100 m3.

Agnita’s cylindrical tanks were built of 24 mm thickboiler plate in the engineering works of R & W HawthornLeslie. The tanks had butt straps inside and out, with theclose-butted pressure vessel shell plates being doublerow-riveted on each side. The hemispherical ends were

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constructed in petals with double riveted overlap joints.In addition, end capping plates of 3.60 metres in diameterwere double-riveted outside the petal plates.

In installing the cylindrical cargo tanks onboard ship,each was supported on substantial angle bar sections,radiused and riveted back to back to the longitudinaland transverse ship girders, with a short section rivetedthrough the pressure vessel bottom petal plates servingas a holddown bracket. The top of the hemisphericalend of each tank protruded 1.83 metres above Agnita’supper deck.

Victim of warBecause of her unique cargo-carrying capabilities andher distinctive appearance, with the domed cylinderheads visible above the main deck, Agnita became quitewell known in shipping circles following her delivery inMarch 1931. The ship construction project had presentedconsiderable challenges for both the tank manufacturerand the shipbuilder.

Later in 1931 the ship was provided with two additionalcylindrical tanks for the carriage of propane. Located inthe forward oil tanks, the new cylinders had a workingpressure of 13.8 bar gauge and a total capacity of 100m3.

The author contacted Shell Transport and Trading in1965, enquiring about Agnita. Shell advised that recordsfor the tanker had been lost, probably during WorldWar II, but she had carried five LPG cargoes, most likelyfrom the Caribbean to Malta.

Agnita had emerged unscathed after a tangle with aHeinkel bomber while running up the Channel toRotterdam in December 1939, thus becoming the firsttanker to be attacked from the air in World War II.However, the ship was not so fortunate on March 22,1941, when she was sunk in the mid-Atlantic near theEquator, by the surface raider Kormoran while enroutefrom Freetown to Caripito in Venezuela. Anglo SaxonPetroleum lost 10 tankers in 1941.

Special cargo secretsThe author has a copy of a Lloyd’s Register of Shippinginternal note dated May 17, 1935 and headed “Motorvessels Megara and Agnita“ which concerns theirpublished class notation. The note reads:

“The owners desire to avoid any reference in theRegister Book to the fact that these two vessels havebeen specially constructed for the carriage ofsulphuric acid and high-pressure petroleum products.They state that they have spent a great deal ofmoney in constructing these vessels for a specialtrade and it is essential in their interests not toadvertise their special features. They, therefore, askthat the notation in the Register Book be limited to“Carrying Petroleum in Bulk” and point out that, in

making this request, the vessels are not insured inthe open market and in consequence no outsideinterests will be adversely affected by the recordbeing made as suggested. In these circumstancesno objection is seen to omitting from the records inthe Register Book the purpose for which thecylindrical tanks are to be used …… These tanksoccupy a large proportion of the volume of theordinary oil compartments ……. Some reference tothe cylindrical tanks should be made.”

As a result, the notation “100A1 Carrying Petroleum inBulk” and “Fitted with Cylindrical Tanks” was agreedby Lloyd’s Register and Anglo Saxon Petroleum for thetwo vessels.

Carefully to carryIn his “Oil Tanker Cargoes” book John Lamb describesthe operating procedures to be followed when carryingcargoes of butane, i.e.:

“Prior to loading, all containers and lines arecompletely filled with water. This should be doneduring the ballast voyage when well clear of land inorder to prevent sediment entering the containerswhich might choke the test and pressure gaugevalves … The tanks are topped up through thesounding opening” (this opening was at the topdead centre of Agnita’s tanks) “by a hose connectedto the wash deck line. By opening the appropriatevalve, the vapour line and all its branches can befilled simultaneously with water …. thus ….eliminating the possibility of any air being present inthe system which could form an explosive mixturewith butane or propane.“When the system is completely filled with waterthe sounding openings in the tanks are then closedand the containers and pipelines tested on eachoccasion by restarting the ship’s pumps until thevapour relief valves on the masts lift and water isejected at the tops of the vapour lines. All pipelinesand joints should then be inspected for leakages.“Butane and propane can then be loaded in variousways. One method is by ‘gassing’ the containers …by admitting a small quantity of liquid butane. Thebutane entering the containers through the topvapour line gasifies and ejects the water via the 150mm loading line led down to 150 mm above thebottom of the container and overboard through alength of flexible hose coupled to the outboardloading line connection. The discharge of wateroverboard is continued until a rushing sound isheard in the loading line which indicates that butanevapour has entered this line. The loading line controlvalve is then closed and the balance of waterremaining in the containers drained off through thebottom 50 mm drain line.“The test valve is then opened and at first water only

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will be ejected. When gas only emerges, this indicatesthat all water has been ejected. For measuring thequantity of ‘oil’ and observing the liquid level whenfilling or emptying the butane containers, an internalpipe extends into the container to a predeterminedfixed level. For butane this level is fixed at 95% full,so that when loaded to this level 5% of the totalvolume of the container is available for expansion ofthe liquid butane … vapour will emerge from thispipe until liquid has reached the lower end of it,when liquid will emerge showing that the tank is95% full. The expansion coefficient of liquid propaneis higher than that of liquid butane and, consequently,in propane containers the internal ullage pipe extendsto the ‘91%’ line, allowing for an ullage of 9% of thetotal capacity of the container.“The discharge of LPG is affected by pumping seawater into the bottom of the containers anddisplacing the LPG through the 100 mm gas linefrom the top of the tanks.”

Post-war developmentsThe interfacing of LPG with salt water described in theprevious paragraph is practised today in undergroundsalt caverns used for LPG storage. Such facilities includethe caverns operated by Warren Petroleum at MontBelvieu, Texas and those on Teesside in the UK.

The author had the privilege of meeting Rex Phelps ofWarren Petroleum during a visit to the USA in 1964 atwhich time he was shown models of the huge saltstorage facilities then being planned for Mont Belvieu.

Rex Phelps had also been closely involved in thedevelopment of the fully pressurised gas carrier NatalieO Warren on behalf of Warren Petroleum in 1947.Natalie O Warren was a converted cargo ship and thefirst vessel able to carry propane in large volumes. The68 vertical, cylindrical tanks, positioned in the ship’s fiveholds, were able to withstand working pressures of upto 17.6 bar g and provided a total capacity of 6,050 m3.The ship was used to carry propane from Houston toNew York.

While Natalie O Warren was the first ship to carry LPGin bulk in the immediate post-Second World War years,she did not remain the only one for long. Again, ownersinitially turned to the conversion of existing ships becausethe work could be carried out more quickly and at lesscost than the construction of a new, purpose-built gascarrier. Also, the trade in LPG was at a comparativelyearly stage of its evolution and conversions representedless of a commercial risk should the market fail todevelop as envisaged.

Major conversionsThe oil and gas majors Esso and Shell modified a numberof their tankers in the immediate post-War years toprovide them with the ability to carry LPG. Esso fittedsome pressure vessel tanks for propane onboard the T2

tanker Esso Sao Paulo, while on Teesside in the UKSmith’s Dock built Genota (later renamed Shell Manaure)for Shell in 1951, installing 34 pressure vessels tankswith a total gas capacity of 950 m3. The same yardconverted Rebecca, also in 1951, by providing 10 pressurevessel tanks totalling 245m3 in capacity. In 1960 Smith’sDock converted the 7,900 dwt oil tanker Gyrotoma(later renamed Shell Murachi) for the carriage of up to1,643 m3 of propane in 22 pressure vessel tanks.

In the 1950s the seaborne movement of LPG developedslowly. Some notable trades were the carriage of LPGfrom the US to Italy in large horizontal pressure vesseltanks strapped onto oceangoing barges and the transportof LPG and ammonia on the Mississippi River in tankbarges towed by tug boats.

Hebburn yard returns to gasBy the early 1960s, when the author was working atHawthorn Leslie and the size of crude oil carriers wasbeginning to exceed the 50,000 dwt maximum capacityof the yard, management looked at gas carriers onceagain. In April 1961 the yard purchased plans and aspecification prepared by J J Henry Inc, the New Yorknaval architecture firm that had carried out the designwork for the Methane Pioneer conversion, in order totender for two 7,500 dwt fully refrigerated LPG carriersfor the British Coal Board for service between the USGulf and the UK.

In the event the Coal Board did not go ahead with theorder because the project was competing with a BritishGas Council scheme to import LNG from Algeria.Hawthorn Leslie continued with the development of aslightly modified fully refrigerated LPG carrier designfor approval in principle by Lloyd’s Register of Shippingand the US Coast Guard by the end of 1961.

As this precedent-setting LPG carrier projectprogressed, Hawthorn Leslie had to deal with severalissues that were new to shipyards. The major issues,which are described below, can be itemised as follows:

(a) construction rules and patents;(b) liability Insurance;(c) cargo tank and secondary barrier steel; and(d) tank insulation.

Rules and patentsBecause fully refrigerated gas carrier design developmentwas only in its early stages at this time, the variousclassification societies had no firm rules for theconstruction of such ships. Their requirements were“tentative” or “provisional” in nature. Classificationsocieties, as well as shipyard designers, were operatingunder frustrating conditions because many features offully refrigerated gas carrier designs were protected bypatents.

Most of the patented designs were based on a double-hull tanker configuration but Hawthorn Leslie was able

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Mercury-filled U-tube manometers with electric contacts at tank highand low level alarm settings

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to design out this liability by developing a single-hulldesign in which the side shell and containment spaceboundary were constructed using cargo tank qualitysteel and welding procedures.

Amusingly, the yard was pursued by an Italian patenteein 1967 who had interpreted the ghostline depicting theoffset bulb frame to stiffen the single-skin side shell asdepicting a “double-hulled tanker”.

Having taken the morning of our meeting to establishthat this sole point was the cause of our allegedinfringement, we broke for lunch and provided thevisiting Italian delegation with high-class Italian cuisinein Newcastle’s new Ristoranti Roma. After lunch weopened the classification society’s stamped midshipsection to reveal that we had not built a double-hulltanker! Others had more of a struggle to stave off theclaims of this early designer.

Liability insuranceAs shipbuilders entering a new technical trade, involvinghazardous and difficult-to-handle cargoes, we requestedliability insurance from Lloyd’s underwriters in case ourgas carrier failed to carry gas. We estimated the cost ofconverting our purpose-built gas carrier into a dry cargovessel and a distressed sale price to establish a reasonablelimit of liability.

Subsequently, we heard that the cargo tank membraneof a pilot project LPG carrier had been so badly corrodedthrough maloperation of her inert gas generator on thefirst voyage that she was converted to a dry cargovessel. This sensible contractual precaution benefitedus in an unexpected way. Insurance was granted for ourship on the condition that “Owners operate the gascargo handling system strictly in accordance with theshipbuilders’ Operating Manual throughout theguarantee period”.

Cargo familiarityThis requirement did not conform with accepted practice,as shipbuilders generally know, or are required to know,remarkably little about the nature of the cargoes carriedby the ships they build. The details of cargo handlinghad traditionally been considered the exclusive provinceof the shipowner.

It thus became essential that Hawthorn Leslie considerall the operating procedures and the components of thecargo-handling system from first principles and acquirea basic working knowledge of the physical and chemicalcharacteristics of the commercial gas cargoes to becarried. The McGraw-Hill handbook “Butane-PropaneGases” and our good friends at ICI Teesside, recognisingtheir potential interest in competently designed shipsfor their export cargoes, provided this basic knowledge.

However, we failed to adequately recognise the liabilityfrom subcontracted items which may result in theinability to carry gas or cause costly delays in shipcompletion and system testing. Tank cargo liquid level

gauging, overfill shutdown trips, low pressure gaugesand alarm pressure switches all had to be replaced onHawthorn Leslie’s first fully refrigerated LPG carrier.

We made good use of the inherent pressure accuracyof the U-tube manometer, with platinum contactsfused through the glass and mercury for electricalswitches for low and high pressures in the intrinsicallysafe electrical alarm systems.

The cargo tank overfill switches were standard stall-speed alarm switches from the Aerocommander lightaircraft of the type used by the chairman of the companythat owned the ship.

All these ingenious provisions were replaced at theguarantee drydocking.

We developed our own cargo-handling system designteam to specify and manage the complete cargo systemfor our second and subsequent gas carriers.

Cargo tank steelHawthorn Leslie was fortunate to find a locally producedmodified carbon steel suitable for use with cargoes atcarriage temperatures of -50°C to replace the 3 per centnickel steel plate which had been specified by J J HenryInc. Such nickel steels were not then made in the UK.The modified carbon steel used on this and subsequent

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The test tank used to demonstrate viability of polyurethane foam insulationand secondary barrier system at -104°C on Emiliano Zapata

fully refrigerated ships built at the yard was known asArctic D steel.

Our shipyard was fully aware of the problemsexperienced by two shipyards which had called inwelding teams from Chicago Bridge & Iron Inc to meetthe stringent low-temperature welding quality controlstandards. It took us three years and 150 weld proceduretests to qualify all position manual welding proceduresand another year to qualify submerged arc twin filletwelding of stiffeners and submerged arc, butt weldingof plate panels for our production lines. Low-temperaturecargo piping, in 3 per cent nickel steel, was easilywelded with consumables used for the fabrication of 9per cent nickel steel.

Tank insulationPerlite powder insulation had been specified for thecomplete filling of the void spaces between the cargotank and its secondary barrier. Our reservations on thepracticality of this material for the service life of the shipwere determined when we saw that perlite, floating onwater in a large glass container, became perlite sludgewhen the container was inverted!

Various alternatives were considered. The shipyardobtained quotations for four million ping-pong balls; forglassfibre slabs to fill the void spaces; and for factory-made polyurethane slabs pinned onto the cargo tank.We concluded that polyurethane was the most practicalsolution and developed shipyard application procedureswith an expert local insulation contractor.

For another design project, for an ethylene gas carrier,we had specified a ‘proven’ proprietary polyurethane

for –104°C service for application to the ship’s inner hullwith an epikote resin sealed glassfibre secondary barrier.This foam developed random through-cracking undertest when the secondary barrier was cooled to –104°C.

Newcastle University undertook a three-dimensionalstress analysis to confirm that cracking must be expectedbased on the ‘proven’ foam’s mechanical properties!We had to rapidly develop a modular polyurethanesystem with deliberate Z cracks for stress relief of thefoam applied by our local contractor using an ICI

polyurethane formulation for deep-freeze applications.No random cracks occurred under test and we were justin time for the shipbuilding programme.

Conversion projectIn 1963 Hawthorn Leslie converted a 1956-built coasterto enable the carriage of LPG and chemical gases forStephenson Clarke, the company that managed MethanePioneer during the time when the historic trial cargoesof LNG were transported from Lake Charles in the US toCanvey Island in the UK.

The LPG carrier conversion project proved to be anexcellent small contract for our shipyard, especially inhelping us to develop our understanding of gas cargooperating procedures and pump and compressorperformance calculations. The semi-refrigerated gascarrier was the first such ship in the UK to be equippedwith a reliquefaction plant.

Cargo was carried in two large horizontal, cylindricaltanks, each 16.3 metres long and 6.0 metres in diameter,providing a total capacity of 734 m3, at a maximumpressure of 7 bar g and with a minimum servicetemperature of -10°C. A memorable moment waslifting the tank pressure relief valves at 4:00 AM tosound off the largest organ pipe ever heard on the RiverTyne. Blowdown seemed to take forever!

The first cargo carried by the converted ship, whichwas renamed Abbas, was isobutylene. A sample wastaken upon completion of cargo loading by opening the50 mm tank bottom drain line, after water had beenpurged to form a sheet of ice over the tank canopy anda golf ball size sample of polymer hung off the valveflange.

Just as the loading operation was being completed,the ship’s master, fresh from a voyage on MethanePioneer, was suddenly convinced that our system, ofpressurising one tank to press cargo liquid into the deck-mounted cargo pump with vapour from the adjacenttank, would not work due to rapid condensation of theoverpressure.

As a result, we used the cargo compressors to providea 2 bar overpressure in one tank and closed all valves.Three days later, after fog delays on passage, we wererelieved to find the 2 bar overpressure was still holdingon arrival at the port of discharge. It was our firstexperience of gas carrier folklore!

The Danish contributionThis is an appropriate point at which to acknowledgethe pioneering contribution of the Tholstrup brotherstowards the development of transporting liquefied gasesby sea in the early 1950s.

Their innovation was the so-called “semi-refrigerated”gas carrier. Such ships were able to refrigerate their gascargoes to reduce their carriage pressure. Because thecargoes did not have to be fully pressurised to liquefy

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Liquid nitrogen storage tank and steam vaporiser on Clerk Maxwell, withaft end of reliquefaction house at right

them, the shells of the pressure vessel tanks on a semi-refrigerated tanker did not have to be as thick as thoseof the tanks on a fully pressurised ship.

The Tholstrup brothers put their first gas tanker, the127 m3 Kosangas, into service as early as 1951. This wasa converted ship fitted with a pressure vessel for thecarriage of gas in the fully pressurised mode. By 1960they had built up a fleet of 10 fully pressurised gascarriers, with an average capacity of 500 m3 per ship andthe primary focus of operations in Northern Europe.

Then, between 1961 and 1963 the Tholstrups addedsix semi-refrigerated gas carriers to their operation.These were larger ships, with an average capacity of912 m3 and improved cargo-handling flexibility. By thistime the Tholstrup brothers had experience of handling16 different liquefied gas cargoes, including a range ofchemical gases.

Integrated gas distributionThe Tholstrups provided a fully integrated bottled gasdistribution service for domestic and commercialcustomers, backing up their ships with bottling plants,bulk storage facilities and a gas bottle pick-up anddelivery service. The hulls of the company ships sporteda distinctive, bright yellow colour, as those of thesuccessor company Lauritzen Kosan still do, while thecompany’s gas road vehicles were distinguished by theslogan “KOSANGAS – The housewives’ burning desire”painted across them in bright blue.

For deliveries of limited quantities to remote islandcommunities, the company’s smaller, 175 m3 gas carrierswere used to refill domestic LPG bottles directly onboardship.

As part of the Tholstrups’ network of gas distributionactivities and full customer service package, companyengineers also tested new domestic and commercialappliances at the in-house research station.

I met one of the Tholstrup brothers in 1962 inCopenhagen. He was busy developing his Danish bluecheese spread for sale in a tube! They were innovativepeople and, besides being masters of their gas marketniche, always seeking to promote technologicaladvances!

New departure with ClerkMaxwellThe first fully refrigerated gas carrier to be ordered atHawthorn Leslie, and the first such ship to be built in theUK, was the 11,750 m3 Clerk Maxwell, a ship contractedin 1965 by Ocean Gas Transport Ltd, a joint venturebetween Houlder Brothers and Gazocean. The ordermarked the realisation of our fully refrigerated gascarrier design project commenced four years earlier.

We had built many ships for Houlder Brothers in thepast, although this particular newbuilding was to takeus into new territory. The French company Technigaz,

the technical affiliate of Gazocean, brought itsexperience of gas carrier technology to bear in itsappraisal of our design and cargo equipment selection.

The basic ship became more complex when it wasdecided to provide the ability to carry butadiene cargoes.This necessitated the use of nitrogen as inert gas,indirect reliquefaction and chemical seals on cargo tankpressure instruments.

A storage tank for 36 tonnes of liquid nitrogen wasmounted on deck at the front of the accommodation.This tank clunked from side to side inside its vacuum-insulated enclosure during the crash stop and full astern

trials when the completed ship underwent sea trials in1966. The experience prompted the installation of 100mm of insulation on deck with an overside chute portand starboard to protect the hull structure!

Propane loading problemsThe gas trials on Clerk Maxwell were dogged by propanehydrate blockages. The blockages were attributed tothe fact that the trial propane cargo had been loadedfrom an underground salt cavity storage facility withoutmethanol dosing having been carried out. The blockagesoccurred first in the refrig-drier which was used toremove water vapour from the cargo tanks beforeinerting, and then later during tank cooldown at theloading port.

When the watch was changed at the terminal, aspreparations were made to load the gas cargo onboardClerk Maxwell, the loading pump was restarted withoutreference to the ship after a four-hour stoppage topurge the cooldown spray lines with methanol. A quantityof propane liquid in the 1,500-metre long loading linehad vaporised during the stop period and the pressuresurge on refilling the line liquid full exceeded the testpressure of the liquid filter of 38 bar g, with consequentleakage through all the joints and liquid relief valves.

This potential hazard, equivalent to the rapid shutdownof cargo transfer operations through the quick closureof power-operated valves, was only properly addressedby “Recommendations for Linked Ship-Shore ESD” Philips

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Liquid crossover on Clerk Maxwell, with liquid filter on left

Pemex followupThanks to a sterling currency loan by a London banker,Hawthorn Leslie received an order for a sister ship toClerk Maxwell from Petroleos Mexicanos (Pemex) inmid-1966. We repeated the hull, cargo tanks andpropulsion machinery but the cargo-handling systemon the Mexican ship, which was to be christenedMariano Escobedo, was much simplified. Simplicity isgood engineering; it lowers initial capital andmaintenance costs and simplifies operations.

Butadiene was not a specified cargo on the Pemexnewbuilding, so an oil-burning inert gas generatorreplaced the liquid nitrogen tank and vaporiser.Simpletests had demonstrated that liquefied propane, with atleast 3 bar g saturated vapour pressure, will flashthrough a 3 mm orifice to a fine aerosol to generate adirectional flow of cold vapour to precool the cargotanks. A single spray line each side of the centrelinebulkhead to give a flow of cold vapour across the top ofthe tanks enabled a satisfactory cooldown.

U-tube manometers enabled accurate cargo tankpressures to be read at each tank hatch and a low-pressure transmitter allowed tank pressure changes tobe monitored in the cargo control room.

Float-operated tape gauges were used to determinetank liquid levels as well as for high and low liquid levelalarms. These level alarms were tested on every voyage.Afloat overfill level switch, based on aircraft fuel tanktechnology, was fitted in each tank, port and starboard.

Local gas trialsPemex had also ordered a 3,500 m3 non-propelled,oceangoing LPG barge from Hawthorn Leslie at aboutthe same time.

The demonstration of successful inerting, gas purgingand precooling of at least one cargo tank at a safe berthon the River Tyne was commercially essential beforethese Pemex vessels entered service across the Atlanticin Mexican coastal service.

The Pemex contract for the LPG barge, which wasnamed Petroquimico I, called for its handover beforedelivery of Mariano Escobedo. After a short trial of thevessel’s cargo features on the Tyne, we towed the bargeto Felixstowe for the gas trials. There we loaded a fullcargo of propane from Philips Petroleum’s new gas jettyand fully refrigerated propane storage into one of thebarge’s tanks up to overfill and automatic shutdownlevel.

The deepwell pumps were to be used to transfer thecargo from tank to tank and then for the discharge ofthe propane back to the shore tank. At least, that wasthe plan. Unfortunately, we could not get started becausethe heat from the summer sun, shining down on the500-metre liquid export line, was generating propanevapour at a higher rate than we could reliquefy it!

After two hours we returned to our hotel for an earlynight and returned at 0400 hours the next morning.

published by SIGTTO in 1987, some 21 years followingthe incident described.

More valuable lessonsIn addition, the reliquefaction compressor lubricatingoil was contaminated during this first loading operation,causing seizure of the compressors. Compressed butanevapour condensed in the cold discharge line into cold oilseparators when the reliquefaction plant was first startedup. These oil separators had float-operated drain valvesto return separated oil from the discharge gases to thecompressor oil sumps. Liquefied butane was returnedinitially in sufficient quantity to vaporise in the compressorbearings to expel the lubricant!

This was a problem which was experienced throughoutthe 1960s and was only satisfactorily solved whenspecialised oils were developed and operating proceduresestablished to control gas contamination of thecompressor lubricating oil to tolerable levels.

We had also experienced equipment problems due togalling and seizure of stainless steel components, as

well as deepwell pump shaft bearing failures duringthose early days with Clerk Maxwell.

I will never forget a Sunday visit to the Chantiers duHavre repair yard by Rene Boudet, the much-reveredfounder and chairman of Gazocean. Surveying thecargo deepwell pumps, reliquefaction compressors andcargo line valves in pieces on the upper deck of ClerkMaxwell, he put his arm round me and said “I don’tknow who is going to pay for all this damaged equipmentbut I do admire and thank you for staying with us to sortit out.”

This very human action ensured maximum effort fromall his team, outsiders like myself included. John Houlder,chairman of Houlder Brothers, commanded a similarloyal response with his innovative thinking and 100 percent back-up in awkward situations. But that is anotherstory!

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The short ethylene purge and tank cooldown trials on Emiliano Zapata

Robin Gray in 1970 as Emiliano Zapata takes shape in the background; hewon a NatWest Bank Young Exporter award that year for gas carrier salesto Mexico

had vented the liquid in the line to reduce the liquidtemperature and, with a little assistance from thefourth compressor (the vent mast for those unfamiliarwith LPG carrier language), we loaded the cargo andcompleted the trials.

Ethylene is differentPemex had also ordered the 3,344 m3 ethylene carrierEmiliano Zapata from Hawthorn Leslie. Upon completionof the ship, we were fortunate to be able to arrange thedelivery of a supply of this liquefied gas cargo byinsulated road tanker from ICI’s nearby Teessidepetrochemical complex. This enabled short gas trials tobe conducted at the Tyne Tanker Cleaning Berth.

A few parts per million of ethylene gas in air are usedin commercial horticulture to ripen tomatoes. Ethylenein excess of this small dose kills vegetation. This fact isused when underground ethylene pipelines areoverflown by air to check for leakage!

We were fortunate that the local press were notaware of this property of the cargo when we conductedour short ethylene gas trials. We were aware of thehazards and ensured that no ethylene was vented. Thequarter tank volume of nitrogen-ethylene mixture from

the gas purge of the trial tank was contained in theadjacent cargo tank.

These short gas trials on all our gas carriers enabled usto confirm the performance calculations we hadestimated for both the time and quantity of liquid cargoneeded to purge and cool down the tanks, and thestratification achieved in purging the relatively lightammonia vapour with relatively heavy propane vapour.

Oh, for the simplicity of designing and operating a gascarrier for just one cargo - LNG - on a liner tradebetween nominated export and import terminals withcustom-designed jetty facilities!

Officer trainingIf we were to achieve a guarantee operating period freeof guarantee claims on the shipbuilder, it was obviouslyessential that the Pemex officers were familiarised withthe liquefied gas cargoes and operation and maintenanceof all the cargo-handling equipment on their vessels.

Pemex operated a modest fleet of oil tankers andreadily agreed to pay for training of their gas carrierpersonnel. We rewrote the cargo operating manualprepared for Clerk Maxwell to make it more concise.We also provided some worked examples to illustratehow we calculated time to inert; time to gas purge; timeto cool down the tanks and establish a liquid reading onthe float gauge; time to load using full reliquefactioncapacity, etc, etc.

The Pemex officers attended instruction courses atNewcastle University’s Chemical EngineeringDepartment to understand the physical characteristicsof ammonia and commercial propane-butane mixturesand appropriate cargo reliquefaction and R22 unitoperating conditions.

They also visited the reliquefaction plant makers forinstruction in the operation and maintenance of thecompressors and protection instruments.

To Pemex must go great credit; they were fullycommitted to the safe and reliable operation of theships we had built. We had no major guarantee claimson their three gas carriers and developed lifelongfriendships with the Mexican officers.

Bibby and WiltshireThe yard ensured continued involvement with this shiptype when an established shipowner, already operatinga fleet of smaller capacity gas carriers, ordered a fullyrefrigerated gas ship. At 15,500 m3, this was to be thelargest size LPG carrier in the company’s fleet. Also,because a long-term charter had been negotiated,substantial bank finance was forthcoming.

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Deck storage tanks at forward end of Faraday

The “traffic lights” just below the wheelhouse on Faraday; the compressorhouse ventilation ducting is shown below and the swimming pool in leftforeground

However, when the charterer defaulted halfwaythrough construction of the ship, Hawthorn Leslie soughtout a new owner for the vessel.

At this juncture, it can be pointed out that few LPGcarriers operate in the trade for which they were originallyordered. Such ships need to be flexible in their operation,e.g. they need to be able to change cargoes, say, fromLPG to ammonia and back again to LPG. They shouldalso be able to discharge fully refrigerated propanethrough a cargo heater into semi-refrigerated shorestorage or into rail tank cars.

All such operations were commonly encounteredduring the course of normal LPG carrier operations.Because these features were fitted onboard our latestnewbuilding, we felt confident that alternativeownership arrangements could be found.

Bibby Brothers of Liverpool were keen to enter the gasshipping business. After discussions, the company agreedto finance the construction of the ship, which waschristened Wiltshire. It was Hawthorn Leslie’s fourthpurpose-built gas carrier and was constructed withoutany difficulties or delays.

Wiltshire proved to be the yard’s most profitablecontract, a reward for its established lead technology.Bibby arranged a long-term charter to ICI Australia forthe ship at a good rate, so both parties were satisfied.

Faraday featuresThe Hawthorn Leslie yard at Hebburn next built twofully refrigerated gas carriers that were twice the size ofWiltshire, the sisterships Faraday and Lincolnshire, thelatter ship also being constructed for Bibby Brothers.

The 31,300 m3 LPG carrier Faraday was ordered byOcean Gas Transport Ltd in 1969 and incorporatedmany novel features at the request of her owners. Thecargo-handling system was operated locally on deck, ateach of three cargo tank hatches and in the cargocompressor room on deck aft and 1 metre clear of theaft accommodation house front.

The cargo supervision room was a corner of thewheelhouse, an arrangement which enabled the officerof the watch to monitor cargo tank pressures andreliquefaction plant alarms at sea.

Cargo line ball valves were arranged so that theposition of their operating handles, open or shut, could

be checked from the wheelhouse with binoculars.Sixred traffic lights were mounted on the accommodationhouse front so that, if the alarm klaxon sounded overthe cargo deck, the cargo officer could see if attentionwas required in either the wheelhouse, the cargocompressor room, the R22 compressor room or at No 1,No 2 or No 3 tank hatch.

The electric motors for all compressors and the R22reliquefaction system were mounted at upper decklevel on a flat within the engine room for supervision bythe engineer officer on watch. The cargo compressorswere driven by shafts extended from the engine room,across the 1 metre open cofferdam into the compressorhouse.

Fire protection testsA high expansion (hi-ex) foam system discharged throughthe house ventilation ducts provided fire protection forthe compressor house. A swimming pool was fitted onthe upper deck just forward of No 3 tank hatch and thisreceptacle was used to receive the hi-ex foam during itsperformance test. So voracious was its output that,following the test, a 500-metre slick of foam wasobserved proceeding sedately down river to the sea!

A similar story was told about the hi-ex foamdemonstration by the Glamorgan Fire Brigade. In thisexercise the hose-drying tower was used to demonstratethe height of foam which could be supported by itscellular structure. Unfortunately, a lower window in thetower had been left open so that the foam neverappeared at the top of the tower but, instead, coveredthe VIP car park and all the cars therein. The fire brigadehad to respond with the well-rehearsed drill of blowingaway the foam with water spray!

Cooldown tanksThree large, horizontal pressure vessels were fitted ondeck on Faraday and Lincolnshire forward of No1 cargotank hatch. These tanks contained sufficient ammoniaand propane to enable either commissioning andcooldown of all cargo tanks or a change of cargo in athree-day operation.

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With the freshwater scrubber in rear, the water droplet separator leadsinto the refrig-drier in foreground onboard Faraday

Robin Gray today - with abit more time to reminisceabout those pioneeringdays of gas carrierconstruction

When commissioning one of the cargo tanks intoammonia service, for example, air in the tank wasexpelled from the tank bottom gas pipeline system byproviding warm ammonia vapour through the tankupper gas pipeline system. In this operation the purgecommenced slowly until the ammonia-air interface wassome three metres below the top of the tank (shown by100 per cent ammonia from a fixed sample pipe at thislevel).

Following that, the ammonia supply rate was increased.A total of 1.05 tank volumes of ammonia achieves a 100per cent ammonia sample from the bottom of the tank.Ammonia-air mixtures are flammable in the relativelynarrow range of 16-28 per cent by volume ammonia,requiring an ignition energy of 680 millijoules at 651°C.Propane-air mixtures, by comparison, have a flammabilityrange of 2.1-9.5 per cent, requiring an ignition energyof approximately 1 millijoule at 460°C.

As the air purge of the cargo tank was carried outeither underway or at a safe anchorage, and the volumeof flammable mixture was very small, the shipownersconsidered it to be a safe procedure.

If propane was the cargo to be loaded, the ammoniawas displaced by relatively heavy propane vapouradmitted through the tank bottom gas line and tankpressure was controlled by reliquefying the ammoniaand returning the condensate to the deck storage tankdedicated to ammonia.

Finally, the ammonia contamination of the propanevapour was removed in a fresh water scrubber and thewet propane vapour refrig-dried by the R22 system at 5bar g and returned to the tank with a dew point of -18°Cor lower. The tanks were then precooled to establish aliquid puddle of propane and the condensate dosedwith methanol to prevent hydrate formation.

Design and specification of the cargo-handling systemreally required a chemical engineer but the yard’scargo-handling design team rose to the challenge.

Awkward weld problemThere was a worldwide shortage of nickel in 1969-70due to a prolonged strike at one of the major oresuppliers. As a result, the suppliers of the specified

Nicrex 9 welding electrode had properly warned ourcargo pipework subcontractor that they may be unableto provide this item.

The subcontractor qualified another electrode used inthe fabrication of land storage tanks for a minimumservice temperature of -20°C. The welding proceduretests of this subcontractor apparently met the Lloyd’sRegister as well as the US Coast Guard (USCG) standardsfor a -45°C minimum service temperature.

The subcontractor’s quality assurance documentationwas submitted to the USCG some two months beforedelivery, as the ship would require entry to US portswhen in service.

The USCG metallurgists questioned the chemistry ofthese electrodes, particularly as to whether they wouldbe capable of achieving their requirements at -50°C.

We undertook another weld procedure test and, sureenough, the results were below specification. When thetest was repeated, the test result was once again sub-specification. I personally then had the awful task oftelephoning the chairman of the owners to request thatthe ship be returned to the shipyard for correction.

He immediately agreed and requested that the USCGbe kept updated on the proposed correction procedures.These procedures entailed either cutting out andrewelding some 100 butt welds or heat-treating theexisting weld metal to enhance its low temperaturetoughness. This latter technique was described in atechnical paper published in the Steelmakers’ InstituteTransactions.

The latter procedure demonstrated a significantincrease in toughness and was accepted by the USCG.Faraday was out of service for some eight weeks.Although it was an unpleasant experience for us asshipbuilders, the situation was mitigated by the 100 percent back-up afforded us by the shipowner.

End of an eraBy the time Hawthorn Leslie built Faraday andLincolnshire, the writing was on the wall for shipbuildingin the UK. Shipyards elsewhere in Europe and,increasingly, in Japan could build ships more efficiently

than their counterparts in Britain.On the Tyne some rationalisation

of shipbuilding capacity had beencarried out and Swan Hunter hadtaken over the Hawthorn Leslieyard in Hebburn prior to the deliveryof Faraday and Lincolnshire.

One more gas carrier was to beconstructed at this facility, the22,700 m3 fully refrigerated LPG/ammonia carrier Gandara for theP&O Group. Built with four cargotanks in Arctic D steel, Gandarawas handed over to her owners inMarch 1976.

NewsletterSupplement

SIGTTO News is the Newsletter of the Societyof International Gas Tanker and TerminalOperators Ltd and is published in March andAugust each year.

Web site: www.sigtto.orgEditor:Mike CorkhillSIGTTO Contact:Jenny Neeves, Business Support AssistantPrinting:Orion Print Services, LU2 7EB, UK

Society of International Gas Tanker and TerminalOperators Ltd (SIGTTO)17 St Helen’s PlaceLondon EC3A 6DG,UK

Tel: +44 20 7628 1124Fax: +44 20 7628 3163E-mail: [email protected]

Copyright: ©SIGTTO 2004 The contents may not be reproduced without permission of the authors