Ship Vetting and its Application to LNG, 2nd Edition

This revised edition of SIGTTO’s book describes the importance of the vetting of LNG ships as a risk assessment tool. Laid out as a specialised guide it incorporates an overview of the trade of LNG by sea, covers technical aspects of LNG ships relevant to vetting and describes the current vessel clearance processes. It also details the use of the SIRE vessel inspection questionnaire for assessing risk and includes up to date industry best practices and recommendations.

Published June 2020

ISBN 9781856098816


Inspections and vetting carried out by charterers, buyers, terminal operators and sellers has been an integral part of ship operations in both oil tankers and LPG carrier operations for more than 25 years and has improved the operating standards. As LNG ships have tended to operate under long-term contractual arrangements they have not been exposed to vetting.


Recent changes in trading patterns have resulted in short-term freight contracts, involving vessels trading to new ports. As a result charterers, buyers, terminal operators and sellers must be sure that the condition, operation and ownership of the vessels are of an acceptable standard, by applying ship inspection and vetting systems to LNG shipping.


This publication draws on information learned from the oil industry and passes it on to all concerned parties involved in vetting LNG ships. It also contains information about the practices of some individual companies and these examples are purely for guidance only.



The Author



Purpose and Scope  

The Need to Vet Ships  

Section 1: The Trading of LNG by Sea  

1.1 Overview

1.1.1 History of the natural gas and LNG industry

1.1.2 The LNG industry in numbers

1.1.3 The macro-economic trends affecting LNG supply and demand

1.2 Sales and Purchase Agreements  

1.3 The LNG Supply Chain

1.4 Production Projects

1.5 Major Exporters of LNG

1.6 Major Importers of LNG

1.7 The LNG Shipping Business

1.7.1 Demand  

1.7.2 Supply  

1.7.3 Charter parties  

1.7.4 Fleet utilisation strategies  

1.7.5 FSRUs/FLNG  

1.7.6 LNG bunkering  

1.7.7 LNG to power  

1.8 The LNG Terminals  

1.9 Ship to Ship Transfer

Section 2: The LNG Fleet in 2020. A Technical Overview  

2.1 LNG Carriers  

2.1.1 Small scale LNG carriers

2.2 Floating Storage Regasification Units (FSRU)  

2.2.1 FSRU regasification system: Closed loop with steam heating  

2.2.2 FSRU regasification system: Combined open/closed loop with seawater and steam heating  

2.2.3 FSRU regasification system: Closed loop with steam heating and intermediate water/glycol loop  

2.2.4 FSRU regasification system: Open loop with seawater heating and intermediate propane loop

2.3 Surveys and Certification. Certificate of Fitness

2.4 Cargo Containment Systems  

2.4.1 Construction materials  

2.4.2 Tank insulation

2.4.3 Types of cargo containment systems  

2.5 Main Propulsion Systems on LNG Carriers  

2.5.1 Steam  

2.5.2 Dual fuel diesel electric (DFDE)

2.5.3 Slow-speed 2-stroke diesel engines  

2.5.4 Slow speed 2-stroke dual fuel engines  

2.5.5 STaGE propulsion plants

Section 3: Vetting on LNG Carriers

3.1 The SIRE Programme

3.2 The Elements of Vetting

3.2.1 The technical approval process. Ship/shore compatibility  

3.2.2 Assessing ship quality

3.2.3 Assessment for use  

Section 4: The SIRE Vessel Inspection Questionnaire as a Risk Assessment Tool  

4.1 Chapter 8 of the VIQ 7 and its Application to LNG Carriers

4.2 Policies, Procedures and Documentation

4.2.1 Maximum loading rates

4.2.2 Reference temperature, saturated vapour pressure and cargo tank filling and temperature limits  

4.2.3 Cargo and ballast system mimics and diagrams  

4.2.4 Cargo plans for partial cargoes and unusual cargo operations

4.3 Stability and Cargo Loading Limitations  

4.3.1 Loading computer/program

4.3.2 Verification of inherent intact stability issues  

4.3.3 Cargo operations manual and its contents

4.3.4 Carriage requirements and emergency procedures for LNG  

4.4 Cargo Operations and Related Safety Management

4.4.1 Records of cargo operations and adherence to cargo planning  

4.4.2 Emergency procedures for dealing with cargo leakage, spillage or fire involving the cargo

4.4.3 Requirements to isolate the electrical supply of the submerged cargo pump motors during gas freeing operations and verification of the pump protection systems (shut down in case of low liquid level)

4.4.4 Condition of the cargo, ballast and stripping pumps, eductors and their associated instrumentation and controls, where fitted, and evidence of regular testing

4.4.5 Cargo pump performance curves and the requirements for cargo lines and vapour on the system

4.4.6 Cargo and ballast system valve’s condition and evidence of testing

4.4.7 Cargo system remote and local tank pressure, temperature and level sensors and gauges, and evidence of regular testing  

4.4.8 Procedures for addressing the emergency discharge method in the event of cargo pump failure

4.5 Cargo Handling and Monitoring Equipment

4.5.1 Condition of tank domes and associated fittings

4.5.2 Insulation on cargo or vapour lines and evidence of inspection routines  

4.5.3 Electrical bonds on cargo and vapour line joints  

4.5.4 Cargo and vapour line expansion arrangements. Liquid/vapour line clamps and sliding supports

4.5.5 Cargo line and system relief valves

4.5.6 Screwed-in connections and cargo pipelines  

4.5.7 Cargo tank high level alarm systems

4.5.8 Records of calibration of key cargo instrumentation (including temperature and pressure gauges)

4.5.9 Cargo measurement and custody transfer system

4.5.10 Cargo tank high level and overflow alarms

4.6 LNG Cargo Machinery Rooms

4.6.1 Bulkhead seals between the compressor room and the motor room  

4.6.2 Electrical fittings and lighting in cargo machinery rooms  

4.6.3 Compressor room ventilation system

4.6.4 Airlock alarms and their operation

4.6.5 Cargo equipment in the compressor room and gas leaks

4.6.6 Fixed gas detection equipment and operation and requirements

4.6.7 Officers’ awareness of the requirements for setting gas detector sample points

4.7 Cargo Reliquefaction Systems (if fitted)

4.7.1 Cargo reliquefaction plant and associated machinery and instrumentation

4.7.2 The ESD system and the gas supply to the engine room

4.7.3 Emergency shutdown control to the cargo ESD system fitted on the reliquefaction plant  

4.8 Gas Combustion Systems (applicable to ships fitted with a reliquefaction system or other cargo system that requires a gas combustion unit to be fitted)  

4.8.1 GCU unit  

4.8.2 Testing of alarms associated with the GCU in accordance with the planned maintenance system  

4.8.3 Gas fuel piping protection system  

4.8.4 Automatic gas shut-off system and evidence of regular testing  

4.9 Void and Interbarrier Spaces and Seals (applicable for all types of cargo containment)  

4.9.1 Interbarrier spaces N2 purging system  

4.9.2 Monitoring of pressure and oxygen content in the interbarrier spaces  

4.9.3 Relief valves for hold spaces and primary and secondary barriers

4.9.4 Means to sample for ingress of water into the insulation space  

4.9.5 Glycol heating system in the void spaces between cargo tanks  

4.10 Inert Gas Systems

4.10.1 Inert gas system and/or storage and associated pipework

4.10.2 Arrangements to prevent backflow of cargo vapour into the inert gas system

4.11 Pressure Relief and Venting Systems

4.11.1 Testing for the cargo tank safety relief valves

4.11.2 Vent outlet arrangements and protective flame screens

4.11.3 Liquid sensors on systems where the pressure relief lines vent directly through a mast riser

4.11.4 Fixed fire-fighting systems on the vent masts, where such systems are fitted  

4.11.5 Automatic mode operation for the forward vent mast

4.11.6 Procedures and authorisation for changing settings and inhibiting alarms

4.12 Emergency Shutdown (ESD) System

4.12.1 Emergency shutdown (ESD) systems

4.12.2 ESD and auxiliary equipment shutdown points

4.12.3 Requirements for closing of the manifold valves and tank filling valves if they form part of the ESD system

4.12.4 Fusible plugs on the liquid domes and in the vicinity of the manifolds  

4.12.5 Reliquefaction plant trip in the event of activation of the ESD (where a plant is fitted)

4.12.6 Secondary tank pressure management systems in use at sea  

4.12.7 Override procedure for the alarms and ESD trips  

4.13 Manifold Arrangements

4.13.1 Manifolds, associated valves, blank flanges and pressure gauges

4.13.2 Safe access for connection and disconnection of cargo lines and restricted access to the manifolds during cargo operations

4.13.3 Checking of offshore manifolds during cargo transfer for manifold valve leakage

4.13.4 Flange connections

4.13.5 Manifold strainers

4.13.6 LNG spill arrangements

4.13.7 Liquid spill and manifold drip tray arrangements

4.13.8 Draining and purging prior to disconnection of the MLAs

4.14 Safety Equipment

4.14.1 Protective equipment

4.14.2 Safety equipment and donning of safety equipment  

4.14.3 Firemen’s outfits

4.14.4 Chemical dry powder systems  

4.14.5 Water spray systems

4.14.6 Fixed fire-fighting and extinguishing systems installed within enclosed spaces containing cargo handling equipment

4.15 Cargo Hoses

4.16 Cargo Lifting Equipment

4.17 Ship to Ship Transfer Operations (applicable if the ship is utilised for regular commercial ship to ship cargo transfer)  

4.17.1 Procedures and equipment for LNG cargo transfers

4.17.2 Risks and requirements during ship to ship operations

4.17.3 Person in overall advisory control (POAC)/STS Superintendent

4.17.4 Ship to Ship transfer checklists

4.17.5 CDI/ICS/OCIMF/SIGTTO ‘STS Transfer Guide’ recommendations  

Section 5: Assessing Risk

5.1 Observations

5.2 The Role of the Vetter in Assessing Risk

5.3 Continuous Improvement  


Appendix A – Contains a list of the full LNG carrier fleet (listed by size) >65 km3 as of the beginning of 2020, including FSRUs

Appendix B – Contains the list of the LNG fleet ordered by ship age, oldest to newest

Appendix C – Contains LNG fleet ordered alphabetically, by ship name

Appendix D – Shows the orderbook of LNG carriers >65 km3 as of the beginning of 2020, including FSRUs

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