ABS-131-2004.pdf

GUIDE FOR INERT GAS SYSTEM FOR BALLAST TANKS JUNE 2004 American Bureau of Shipping Incorporated by Act of Legislature of the State of New York 1862 Copyright 2004 American Bureau of Shipping ABS Plaza 16855 Northchase Drive Houston, TX 77060 USA Copyright American Bureau of Shipping Provided by IHS under license with ABS Licensee=Boeing Co/5910770001 Not for Resale, 08/07/2008 20:27:44 MDTNo reproduction or networking permitted without license from IHS -,-,- This Page Intentionally Left Blank Copyright American Bureau of Shipping Provided by IHS under license with ABS Licensee=Boeing Co/5910770001 Not for Resale, 08/07/2008 20:27:44 MDTNo reproduction or networking permitted without license from IHS -,-,- ABS GUIDE FOR INERT GAS SYSTEM FOR BALLAST TANKS . 2004 iii Foreword The main purpose of this Guide is to provide vessel Owners with design criteria for inerting ballast tanks on double hull tankers. The ballast tanks are to be inerted for the following reasons: To minimize risk of explosion in ballast tanks To minimize corrosion ABS welcomes comments and suggestions for improvement of this Guide. Comments or suggestions can be sent electronically to rddeagle.org. Copyright American Bureau of Shipping Provided by IHS under license with ABS Licensee=Boeing Co/5910770001 Not for Resale, 08/07/2008 20:27:44 MDTNo reproduction or networking permitted without license from IHS -,-,- This Page Intentionally Left Blank Copyright American Bureau of Shipping Provided by IHS under license with ABS Licensee=Boeing Co/5910770001 Not for Resale, 08/07/2008 20:27:44 MDTNo reproduction or networking permitted without license from IHS -,-,- ABS GUIDE FOR INERT GAS SYSTEM FOR BALLAST TANKS . 2004 v GUIDE FOR INERT GAS SYSTEM FOR BALLAST TANKS CONTENTS SECTION 1 General Conditions1 1 Application .1 3 Objective1 5 Definitions 1 7 Plans and Data to be Submitted2 9 Class Notation2 SECTION 2 System Design .3 1 Inert Gas System.3 1.1 General .3 1.3 Dedicated Inert Gas System for Ballast Tanks3 1.5 Common Inert Gas Systems for Ballast Tanks and Cargo Tanks .3 1.7 Basic Requirements4 1.9 Inert Gas Quality.4 1.11 Source of Inert Gas.4 1.13 Flue Gas Isolating Valves .4 1.15 Flue Gas Scrubber5 1.17 Blowers .5 1.19 Flue Gas Leakage.6 1.21 Gas Regulating Valve .6 1.23 Non-return Devices.6 1.25 Branching of Inert Gas Main .7 1.27 Venting for Large Gas Volumes8 1.29 Inerting, Purging or Gas-freeing of Empty Tanks8 1.31 Pressure/Vacuum-breaking Devices.8 1.33 Instrumentation at Gas Blower Outlets9 1.35 Monitoring of Inert Gas9 1.37 Portable Detectors 9 1.39 Calibration of Instruments .9 1.41 Alarms and Shutdowns .9 1.43 Nitrogen Generator Inert Gas Systems.11 Copyright American Bureau of Shipping Provided by IHS under license with ABS Licensee=Boeing Co/5910770001 Not for Resale, 08/07/2008 20:27:44 MDTNo reproduction or networking permitted without license from IHS -,-,- vi ABS GUIDE FOR INERT GAS SYSTEM FOR BALLAST TANKS . 2004 3 Ballast Tanks Venting13 3.1 General Principles.13 3.3 Venting Capacity.13 3.5 Vent Piping13 3.7 Self-draining of Vent Piping.14 3.9 Protection for Tank Overpressurization and Vacuum14 3.11 Position of Pressure/Vacuum Valves 14 3.13 Pressure/Vacuum Valve Bypass.15 3.15 Vent Outlets for Large Flow Volumes15 5 Ballast Tank Gas Detection System15 5.1 Portable Gas Measuring Detectors .15 5.3 Fixed Gas Sampling System.15 5.5 Piping of Gas Sampling Lines .15 5.7 Gas Sampling System Installation.16 7 Ballast Tank Level Gauging.16 7.1 Tank Overfill Protection.16 9 Ballast Pump Operation.17 11 Operating Manuals.17 SECTION 3 Survey Requirements19 1 New Construction.19 3 Annual Survey19 3.1 Inert Gas Systems.19 5 Special Periodical Survey22 5.1 General22 5.3 Separate Inert Gas Generator System22 5.5 Gas Stored in Bottles System22 APPENDIX 1 Examples of Inerting/Gas Freeing Analysis of Ballast Tank.23 1 Introduction 23 3 Descriptions of Ballast Tank 24 3.1 Dimensions of Ballast Tank.24 3.3 Transverse Bulkheads and Frames.24 3.5 Stringers25 3.7 Girders.25 3.9 Discharge Pipe and Gas Outlet.25 3.11 Simulation Model.25 5 Results.25 5.1 Inerting 26 5.3 Gas-freeing29 7 Conclusions .32 TABLE 1 Composition of Gases26 Copyright American Bureau of Shipping Provided by IHS under license with ABS Licensee=Boeing Co/5910770001 Not for Resale, 08/07/2008 20:27:44 MDTNo reproduction or networking permitted without license from IHS -,-,- ABS GUIDE FOR INERT GAS SYSTEM FOR BALLAST TANKS . 2004 vii FIGURE 1 Ballast Tank with Discharge Pipe 24 FIGURE 2(a) Inerting at 0.5 hr (1800 seconds), 0.33 Atmosphere Changes.26 FIGURE 2(b) Inerting at 1.0 hr (3600 seconds), 0.67 Atmosphere Changes.27 FIGURE 2(c) Inerting at 1.5 hr (5400 seconds), 1.0 Atmosphere Change.27 FIGURE 2(d) Inerting at 2.25 hr (8100 seconds), 1.5 Atmosphere Changes.28 FIGURE 2(e) Inerting at 3.0 hr (10800 seconds), 2.0 Atmosphere Changes.28 FIGURE 3(a) Gas-freeing at 0.5 hr (1800 seconds), 0.33 Atmosphere Changes29 FIGURE 3(b) Gas-freeing at 1.0 hr (3600 seconds), 0.67 Atmosphere Changes30 FIGURE 3(c) Gas-freeing at 1.5 hr (5400 seconds), 1.0 Atmosphere Change30 FIGURE 3(d) Gas-freeing at 2.25 hr (8100 seconds), 1.5 Atmosphere Changes31 FIGURE 3(e) Gas-freeing at 3.0 hr (10800 seconds), 2.0 Atmosphere Changes31 FIGURE 4 Averaged Oxygen Concentrations.32 APPENDIX 2 Pump Certification (4-6-1/7.3 of the Rules for Building and Classing Steel Vessels)33 Copyright American Bureau of Shipping Provided by IHS under license with ABS Licensee=Boeing Co/5910770001 Not for Resale, 08/07/2008 20:27:44 MDTNo reproduction or networking permitted without license from IHS -,-,- This Page Intentionally Left Blank Copyright American Bureau of Shipping Provided by IHS under license with ABS Licensee=Boeing Co/5910770001 Not for Resale, 08/07/2008 20:27:44 MDTNo reproduction or networking permitted without license from IHS -,-,- ABS GUIDE FOR INERT GAS SYSTEM FOR BALLAST TANKS . 2004 1 S E C T I O N 1 General Conditions 1 Application The requirements in this Guide apply to vessels equipped with inert gas systems designed to continuously inert the ballast tanks. Application of the requirements of this Guide is optional. When a vessel is designed, built and surveyed in accordance with this Guide, and when found satisfactory, a classification notation, as specified in Subsection 1/9, will be granted. 3 Objective The objective of this Guide is to provide requirements which will: i) Prevent the risk of explosion in ballast tanks caused by the ignition of hydrocarbon gas leaking in from adjacent cargo tanks ii) Reduce corrosion in ballast tanks This is achieved by means of replacing the atmospheric content of the tanks with a gas such as nitrogen, or a mixture of gases such as flue gas, containing reduced levels of oxygen. 5 Definitions The following definitions are applied to the terms used in this Guide: Inert gas: Inert gas is a gas such as nitrogen or a mixture of gases such as flue gas, containing a reduced level of oxygen, which will decrease corrosion rate and is insufficient to support the combustion of hydrocarbons. Inert condition: An inert condition exists when the oxygen content throughout the atmosphere of a tank has been reduced to 5% or less by volume by addition of inert gas. Inert gas generating plant: An inert gas generating plant pertains to all equipment specially fitted to supply, cool, clean, pressurize, monitor and control delivery of inert gas to cargo and ballast tank systems. Inert gas distribution system: The inert gas distribution system pertains to all piping, valves and associated fittings to distribute inert gas from the inert gas generating plant to cargo and ballast tanks, to vent gases to atmosphere and to protect against excessive pressure or vacuum. Inert gas system: The inert gas system is the inert gas generating plant and inert gas distribution system together with means for preventing backflow of gases to the machinery spaces, fixed and portable measuring instruments and control devices. Inerting: Inerting refers to the process of the introduction of inert gas into a tank with the object of attaining the inert condition. Copyright American Bureau of Shipping Provided by IHS under license with ABS Licensee=Boeing Co/5910770001 Not for Resale, 08/07/2008 20:27:44 MDTNo reproduction or networking permitted without license from IHS -,-,- Section 1 Class Notation 2 ABS GUIDE FOR INERT GAS SYSTEM FOR BALLAST TANKS . 2004 Gas-freeing: Gas-freeing is the introduction of fresh air into a tank with the object of removing toxic, flammable and inert gases and increasing the oxygen content to 21% by volume. Off specification inert gas: Inert gas which quality exceeds the limits specified in 2/1.9 of this Guide. Purging: Purging is the introduction of inert gas into a tank already in the inert condition with the object of: (1) further reducing the existing oxygen content; and/or (2) reducing the existing hydrocarbon gas content to a level below which combustion cannot be supported if air is subsequently introduced into the tank. Topping up: Topping up is the introduction of inert gas into a tank which is already in the inert condition with the object of raising the tank pressure to prevent any ingress of air. 7 Plans and Data to be Submitted The following plans and data specific to ballast tank inerting and venting systems are to be submitted: i) Booklet showing standard construction details for piping systems, as applicable. See 4-6-1/9.5 of the Rules for Building and Classing Steel Vessels. ii) Arrangement showing the location of ballast tanks. iii) Ballast tank venting and gas freeing systems, including details of the pressure/vacuum valves. iv) Calculations showing that the ballast tanks will not be subjected to a pressure or vacuum in excess of the P/V valve setting. v) Inert gas system servicing the ballast tanks, including inert gas generating plant, all control and monitoring devices and inert gas distribution piping. vi) Inert gas system operating manual. vii) Results of analysis for Inerting, Purging and Gas-Freeing effectiveness. See 2/1.29. 9 Class Notation Where requested by the Owner, an inert gas installation, supplying inert gas to ballast tanks, which is found to comply with the requirements specified in this Guide and which has been constructed and installed under survey by the Surveyor, will be assigned and distinguished in the Record with the class notation IGS Ballast. Copyright American Bureau of Shipping Provided by IHS under license with ABS Licensee=Boeing Co/5910770001 Not for Resale, 08/07/2008 20:27:44 MDTNo reproduction or networking permitted without license from IHS -,-,- ABS GUIDE FOR INERT GAS SYSTEM FOR BALLAST TANKS . 2004 3 S E C T I O N 2 System Design 1 Inert Gas System 1.1 General The inert gas system is to be so designed and operated as to render and maintain the atmosphere of the ballast tanks as specified in 2/1.9 at all times, except when such tanks are required to be gas free. 1.3 Dedicated Inert Gas System for Ballast Tanks For vessels equipped with a dedicated inert gas system for ballast tanks only, the following is also required, as applicable, in addition to the requirements of 2/1.7 through 2/1.43: 1.3.1 Inert Gas System Capacity The inert gas system is to be capable of delivering the inert gas at a rate of at least 125% of the maximum discharge rate of the ballast tanks. 1.5 Common Inert Gas Systems for Ballast Tanks and Cargo Tanks For vessels equipped with an inert gas system that services both ballast tanks and cargo tanks, the following are also required, as applicable, in addition to the requirements of 2/1.7 through 2/1.43: 1.5.1 Inert Gas Main Connection Connection of the inert gas main for the ballast tanks with the inert gas main for the cargo tanks is permitted only upstream of the cargo tanks gas-regulating valve or valves. 1.5.2 Inert Gas System Capacity i) The inert gas system is to be capable of delivering the inert gas at a rate of at least 125% of the combined maximum rate of discharge of the cargo tanks and the ballast tanks, or ii) The inert gas system is to be capable of delivering inert gas at a rate of at least 125% of the maximum rate of discharge of the cargo tanks or the ballast tanks, whichever is greater. The gas regulating valves are to be interlocked so that cargo tanks and ballast tanks cannot be supplied with inert gas simultaneously. 1.5.3 Spectacle Flange for Ballast Inert Gas Main The inert gas main for ballast tanks is to be arranged with a spectacle flange installed at the connection with the inert gas main for cargo tanks. The operating manual (see Subsection 2/11) is to contain instructions that the inert gas main for ballast tanks is to be blanked off when the ballast tanks are in a gas free condition. See also 2/1.25.2(b). Copyright American Bureau of Shipping Provided by IHS under license with ABS Licensee=Boeing Co/5910770001 Not for Resale, 08/07/2008 20:27:44 MDTNo reproduction or networking permitted without license from IHS -,-,- Section 2 System Design 4 ABS GUIDE FOR INERT GAS SYSTEM FOR BALLAST TANKS . 2004 1.7 Basic Requirements The system is to be capable of: i) Inerting ballast tanks by reducing the oxygen content in any part of any ballast tank to 5% by volume of the atmosphere in each tank ii) Maintaining the atmosphere in any part of any ballast tank at the 5% by volume oxygen content level and at a positive pressure at all times in port and at sea, except when it is necessary for such a tank to be gas free iii) Eliminating the need for air to enter a tank during normal operations, except when it is necessary for such a tank to be gas free iv) Purging empty ballast tanks of hydrocarbon gas, should a cargo leak occur, so that subsequent gas freeing operations will at no time create a flammable atmosphere within the ballast tanks 1.9 Inert Gas Quality 1.9.1 Oxygen Content The system is to be capable of delivering inert gas with an oxygen content of not more than 5% by volume in the inert gas supply main to the ballast tanks at any required rate of flow. 1.9.2 Sulfur Content The system is to be capable of delivering inert gas with an SO2 content of not more than 2 ppm in the inert gas supply main to the ballast tanks at any required rate of flow. This may require the installation of two or more scrubbers in series or a multistage scrubber. 1.11 Source of Inert Gas 1.11.1 Acceptable Sources The inert gas supply may be treated flue gas from main or auxiliary boilers. Systems using flue gases fro