LPG Piping

LPG Training Course – Korea May 2007LLOYD’S REGISTER EMEA

LPG Gas Carriers

Cargo Piping

Robbie SillarsLead Specialist – Refrigeration

London Design Support Services

Busan Korea - May 2007

LPG Training Course – Korea 2007LLOYD’S REGISTER EMEA

Piping Functions – Cargo operations

• Cargo tank inerting

• Line inerting

• Loading

• Venting

• Reliquefaction

• Heating


Piping Functions – ancillary systems

• Initial loading

• Tank drying (low dew point air)

• Inerting and gassing up

• Changing cargo or gas freeing

• Stripping and puddle heating

• Inerting and gas freeing

• Other systems

• Emergency discharge

• Hold drainage

• Methanol


Typical Layout of an LPG Tanker

Cargo Machinery Room

Water Ballast Tanks Cofferdam

Ballast Pump RoomGas Dangerous area

Gas Safe Area

ForePeak

Engineroom

Cargo Pump


Typical Layout of an Oil Tanker

Water Ballast Tanks CofferdamPump Room

Gas Dangerous areaGas Safe

Area

Cargo TanksForePeak

EngineRoom


Oil Tanker Pumping Arrangements

Pump room Cargo tanks

Manifold


Mast Riser

Cargo Pumps

Cargo Heater

Booster Pumps

Relief Valves

Manifold

Sea Water

Cargo Tank

Dome

Gas Carrier Pumping Arrangements


Reliquefaction Plant - Simple System

ExpansionDevice

Vapour

Liquid Gas Return Oil-lessCompressors

CargoCondenser

LiquidSump

CargoTank

Sparge Pipe

Intercooler

Single stageconnections

Seawater

KO Pot


Deck Tanks

• Dependant on proposed cargoes to be carried

• Reduced time alongside at terminal

• Sufficient liquid to ‘gas up’ and cool down one system

• Size depending on cargoes

• Standard arrangement - 1 large and 1 small deck tank

• Ammonia main reason – Propane butane compatible


LPG Cargo Piping System – Piping requirements

• Material as per Tables 6.1 & 6.4 of the IGC Code

• Stainless steel

• Thin wall – large sizes schedule 10

• ‘L’ Grades (low low-carbon) to allow welding

• Design pressure – IGC Code 10 bar (Boosters more)

• Design Temperature – LPG warmer than minus 55 deg C

• Class II system

• Guidance notes available


LPG Cargo Pipe Fittings

• Type testing not required due to design temperature

• Isolation arrangements

• Removable spool pieces

• ‘Block and bleed’

• Seut valves

• Bellows pieces (EJMA)

• Ball and Butterfly valves

• Remote control valves – closing time critical


Hold Drainage Arrangements

Hold void space Ballast tanks

Duct keel / Pipe tunnel

Wateroverboard

Cargo tank(Type A tank)

Machinery space

Cargoto tank

Ballast wateroverboard

Dome


Why Use Inert Gas?

Gas Free

Inert

Cargo


Inert Gas Non-return Devices

Oil tanker Gas Carrier

Deck water seal

+N.R. Valve

Two N.R. valvesbleed valve between valves

(no liquid, no ice)(Back flow from hold

spaces only)


Filling Limits Requirements

• IGC Code filling limit states a limit of 98% at the reference temperature

• Type ‘C’ tanks may be loaded to a level higher than their relief valve set pressure, but never greater than 98%

• SIGTTO document covers how to calculate ‘highest voyage temperature’

• Dispensation of 98.5% now common on Type A LPG carriers

• Dispensation to be acceptable to the administration

• SIGTTO overfill protection guidelines to be followed


Filling Limits - Type C

• The difference for Type ‘C’ tanks is that the relative density can now be taken at the highest temperature the cargo will reach at design conditions, IGC Code paragraph 15.1.5

• This can only be applied where the venting system has been approved and shown to be suitable for two phase flow.

• Savings are not so great for low pressure tanks where the loading and reference temperatures are close.

• High level alarms are still to be fitted for 98%


Pressure Relief Arrangements

• The setting of the second pressure relief valve can be at 5%

above MARVS.

• Reduces the amount of cargo vented during short periods

of pressure rise (not fire condition)

• Relief valve vent exit is to be 6 m above the deck storage

tanks and the cargo liquid lines.

• Low melting point materials (< 925C) such as aluminium and

neoprene could be accepted for use as internal parts of relief

valves.


Pressure Relief Arrangements

• The setting of the second pressure relief valve can be at 5%

above MARVS.

• Reduces the amount of cargo vented during short periods

of pressure rise (not fire condition)

• Low melting point materials, less than 925OC such as

aluminium and neoprene can be accepted for use as internal

parts of relief valves. Neoprene diaphragms being common.

• Relief valve vent exit is to be 6 m above the deck storage

tanks and the cargo liquid lines.


Relief Valve Pressure Drop Calculations

• Pressure drop calculation s need to be undertaken and

submitted for approval

• Inlet pressure drop, from tank to relief valve, to be < 3%

• Outlet pressure drop is dependant on type of relief valve

fitted.

• For Type A tanks with pilot operated relief valve <

50%

• For Type C tanks with coiled spring < 10%

• Vent mast to be fitted with grill but not flame arrester

CHANGE TITLE IN SLIDE MASTERLLOYD’S REGISTER (amend as req.)

The Lloyd’s Register Group works to enhance safety and approve assets and systems at sea, on land and in the air –because life matters.

Services are provided by members of the Lloyd’s Register Group Lloyd’s Register, Lloyd’s Register EMEA and Lloyd’s Register Asia are exempt charities under the UK Charities Act 1993.

For more information please contact:

Robbie SillarsLead Specialist - RefrigerationEngineering SystemsLondon Design Support ServicesLloyd’s Register EMEADirect Tel No. +44 (0) 20 7423 1921Direct Fax No. +44 (0) 20 7423 1824Email [email protected]

LPG Piping

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