IGS Ballast Tanks Guide_e-May12

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G u i d e f o r I n e r t G a s S y s t e m f o r B a l l a s t T a n k s

GUIDE FOR

INERT GAS SYSTEM FOR BALLAST TANKS

JUNE 2004 (Updated May 2012 see next page)

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


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ABS GUIDE FOR INERT GAS SYSTEM FOR BALLAST TANKS.2004 iii

F o r e w o r d

Foreword

The main purpose of this Guideis 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 canbe sent electronically [email protected].
mailto:[email protected]:[email protected]:[email protected]:[email protected]


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iv ABS GUIDE FOR INERT GAS SYSTEM FOR BALLAST TANKS.2004

T a b l e o f C o n t e n t s

GUIDE FOR

INERT GAS SYSTEM FOR BALLAST TANKS

CONTENTS

SECTION 1 General Conditions ................................................................................ 11 Application........................................................................................... 13 Objective ............................................................................................. 15 Definitions ........................................................................................... 17 Plans and Data to be Submitted ......................................................... 29 Class Notation ..................................................................................... 2

SECTION 2 System Design ........................................................................................ 31 Inert Gas System ................................................................................ 3

1.1 General ............................................................ ................................ 31.3 Dedicated Inert Gas System for Ballast Tanks ................................ 31.5 Common Inert Gas Systems for Ballast Tanks and Cargo

Tanks ............................................................................................... 31.7 Basic Requirements ................................................................ ......... 31.9 Inert Gas Quality ..................................................................... ......... 41.11 Source of Inert Gas ................................................................. ......... 41.13 Flue Gas Isolating Valves ................................................................ 41.15 Flue Gas Scrubber .................................................................. ......... 41.17 Blowers ............................................................ ................................ 51.19 Flue Gas Leakage .................................................................. ......... 51.21 Gas Regulating Valve ............................................................. ......... 51.23 Non-return Devices ................................................................. ......... 61.25 Branching of Inert Gas Main ............................................................ 71.27 Venting for Large Gas Volumes ....................................................... 71.29 Inerting, Purging or Gas-freeing of Empty Tanks ............................. 71.31 Pressure/Vacuum-breaking Devices................................................ 81.33 Instrumentation at Gas Blower Outlets ............................................ 81.35 Monitoring of Inert Gas ........................................................... ......... 81.37 Portable Detectors .................................................................. ......... 81.39 Calibration of Instruments ................................................................ 81.41 Alarms and Shutdowns ........................................................... ......... 91.43 Nitrogen Generator Inert Gas Systems .......................................... 10

3 Ballast Tanks Venting ....................................................................... 123.1 General Principles .................................................................. ....... 123.3 Venting Capacity............................................................................ 123.5 Vent Piping ................................................................. ................... 123.7 Self-draining of Vent Piping ........................................................... 12


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ABS GUIDE FOR INERT GAS SYSTEM FOR BALLAST TANKS.2004 v

3.9 Protection for Tank Overpressurization and Vacuum .................... 133.11 Position of Pressure/Vacuum Valves ............................................ 133.13 Pressure/Vacuum Valve Bypass ................................................... 133.15 Vent Outlets for Large Flow Volumes ............................................ 13

5 Ballast Tank Gas Detection System ................................................. 145.1 Portable Gas Measuring Detectors ............................................... 14

5.3 Fixed Gas Sampling System ......................................................... 14

5.5 Piping of Gas Sampling Lines ....................................................... 14

5.7 Gas Sampling System Installation ................................................. 14

7 Ballast Tank Level Gauging .............................................................. 157.1 Tank Overfill Protection ................................................................. 15

9 Ballast Pump Operation .................................................................... 15

11 Operating Manuals ............................................................................ 15

SECTION 3 Survey Requirements .......................................................................... 16

1 New Construction .............................................................................. 163 Annual Survey ................................................................................... 16

3.1 Inert Gas Systems ............................................................... .......... 165 Special Periodical Survey ................................................................. 18

5.1 General................................................................................ .......... 185.3 Separate Inert Gas Generator System .......................................... 195.5 Gas Stored in Bottles System ........................................................ 19

APPENDIX 1 Examples of Inerting/Gas Freeing Analysis of Ballast Tank ............ 201 Introduction ....................................................................................... 203 Description of the Ballast Tank ......................................................... 20

3.1 Dimensions ............................................................... ..................... 203.3 Transverse Bulkheads and Frames ............................................... 213.5 Stringers ........................................................................................ 213.7 Girders........................................................................................... 213.9 Discharge Pipe and Gas Outlet ..................................................... 223.11 Simulation Model ........................................................................... 22

5 Results .............................................................................................. 225.1 Inerting ..................................................................... ..................... 22

5.3 Gas-freeing ................................................................ .................... 257 Conclusions ...................................................................................... 29TABLE 1 Composition of Gases ............................................................. 22FIGURE 1 Ballast Tank with Discharge Pipe ........................................... 21FIGURE 2(a) Inerting at 0.5 hr (1800 seconds), 0.33 Atmosphere

Changes ................................................................................. 23FIGURE 2(b) Inerting at 1.0 hr (3600 seconds), 0.67 Atmosphere

Changes .................................................................................. 23FIGURE 2(c) Inerting at 1.5 hr (5400 seconds), 1.0 Atmosphere

Change .................................................................................... 24


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vi ABS GUIDE FOR INERT GAS SYSTEM FOR BALLAST TANKS.2004

FIGURE 2(d) Inerting at 2.25 hr (8100 seconds), 1.5 AtmosphereChanges .................................................................................. 24

FIGURE 2(e) Inerting at 3.0 hr (10800 seconds), 2.0 AtmosphereChanges .................................................................................. 25

FIGURE 3(a) Gas-freeing at 0.5 hr (1800 seconds), 0.33 Atmosphere

Changes .................................................................................. 26FIGURE 3(b) Gas-freeing at 1.0 hr (3600 seconds), 0.67 Atmosphere

Changes .................................................................................. 26FIGURE 3(c) Gas-freeing at 1.5 hr (5400 seconds), 1.0 Atmosphere

Change .................................................................................... 27FIGURE 3(d) Gas-freeing at 2.25 hr (8100 seconds), 1.5 Atmosphere

Changes .................................................................................. 27FIGURE 3(e) Gas-freeing at 3.0 hr (10800 seconds), 2.0 Atmosphere

Changes .................................................................................. 28FIGURE 4 Averaged Oxygen Concentrations .......................................... 28

APPENDIX 2 Pump Certification (4-6-1/7.3 of the ABS Rules for Building andClassing Steel Vessels) ....................................................................... 30


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ABS GUIDE FOR INERT GAS SYSTEM FOR BALLAST TANKS.2004 1

S e c t i o n 1 : G e n e r a l C o n s i d e r a t i o n s

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, asspecified 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, ora 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 levelof 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 tankhas 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 gasto cargo and ballast tank systems.

Inert Gas Distribution System: The inert gas distribution system pertains to all piping, valves and associatedfittings to distribute inert gasfrom the inert gas generating plantto cargo and ballast tanks, to vent gasesto atmosphere and to protect against excessive pressure or vacuum.

Inert Gas System: The inert gas system is the inert gas generating plantand inert gas distribution system

together with means for preventing backflow of gases to the machinery spaces, fixed and portable measuringinstruments and control devices.

Inerting: Inerting refers to the process of the introduction of inert gasinto a tank with the object of attainingthe inert condition.

Gas-freeing: Gas-freeing is the introduction of fresh air into a tank with the object of removing toxic,flammable and inert gasesand 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 gasinto a tank already in the inert conditionwith 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 gasinto a tank which is already in the inert conditionwith the object of raising the tank pressure to prevent any ingress of air.


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Section 1 Class Notation

2 ABS GUIDE FOR INERT GAS SYSTEM FOR BALLAST TANKS.2004

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 ABSRules for Building and Classing Steel Vessels (Steel Vessel Rules).

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 excessof 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 foundto 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 theRecordwith the class notation IGS Ballast.


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S e c t i o n 2 : S y s t e m D e s i g n

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 followingare 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% ofthe 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 cannotbe 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 containinstructions that the inert gas main for ballast tanks is to be blanked off when the ballast tanks arein a gas free condition. See also 2/1.25.2(b).

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% byvolume 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 sucha tank to be gas free


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Section 2 System Design


iii) Eliminating the need for air to enter a tank during normal operations, except when it is necessaryfor 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 SO 2content of not more than 2 ppm inthe inert gas supply main to the ballast tanks at any required rate of flow. This may require theinstallation 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 from one or more separate gas generators or other sources or any combination thereof maybe accepted, provided that an equivalent standard of safety is achieved. All flue gas plants are to

be fitted with automatic control so that inert gas of suitable volume and quality can be deliveredupon demand under all service conditions. Systems using stored carbon dioxide are not permitted

unless the risk of ignition from the generation of static electricity by the system itself is minimized.

1.11.2 Fuel Oil Pumps for Inert Gas Generators

Two fuel oil pumps are to be fitted to the inert gas generator. Only one fuel oil pump may be

permitted on condition that sufficient spares for the fuel oil pump and its prime mover are carriedonboard to enable any failure of the fuel oil pump and its prime mover to be rectified by the vessels

crew.

1.11.3 Pump Certification

The fuel oil pumps serving the boiler or inert gas generator are to be certified in accordance with

the requirements of Appendix 2.

1.13 Flue Gas Isolating Valves

Flue gas isolating valves are to be fitted in the inert gas supply mains between the boiler uptakes and the

flue gas scrubber. These valves are to be provided with indicators to show whether they are open or shut, andprecautions are to be taken to maintain them gastight and to keep the seatings clear of soot. Arrangements

are to be made to ensure that boiler soot blowers cannot be operated when the corresponding flue gas valveis open.

1.15 Flue Gas Scrubber

1.15.1 General

A flue gas scrubber is to be fitted which will effectively cool the volume of gas specified in2/1.3.1 or 2/1.5, as applicable, and remove solids and sulfur combustion products. The cooling waterarrangements are to be such that an adequate supply of water will always be available without

interfering with any essential services on the vessel. Provision is also to be made for an alternativesupply of cooling water.

Scrubbers, blowers, non-return devices, scrubber effluent and other drain piping which may besubjected to corrosive action of the gas and liquid are to be either constructed of corrosion-resistantmaterial or lined with rubber, glass epoxy resin or equivalent coating. See the ABSGuidance

Manual for Material Selection and Inspection of Inert Gas Systems1980.


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1.15.2 Filters

Filters or equivalent devices are to be fitted to minimize the amount of water carried over to theinert gas blowers.

1.15.3 Scrubber Location

The scrubber is to be located aft of all cargo tanks, cargo pump rooms and cofferdams separatingthese spaces from machinery spaces of category A.

1.15.4 Pump Certification

The cooling water pumps serving the flue gas scrubber are to be certified in accordance with the

requirements of Appendix 2.

1.17 Blowers

1.17.1 Number of Blowers

At least two blowers are to be fitted which together are to be capable of delivering to the ballast

tanks at least the volume of gas required by 2/1.5. Where two blowers are fitted, the total requiredgas capacity is preferably to be divided equally between the two blowers. In no case is one blower

to be less than 1/3of the total required gas capacity.

In the system with a gas generator only, one blower may be permitted if that system is capable ofdelivering the total volume of gas required by 2/1.5 to the protected ballast tanks, provided that

sufficient spares for the blower and its prime mover are carried onboard to enable any failure ofthe blower and its prime mover to be rectified by the vessels crew.

1.17.2 Blower Piping

The inert gas system is to be so designed that the maximum pressure which it can exert on anyballast tank will not exceed the test pressure of any ballast tank. Suitable shut-off arrangements are

to be provided on the suction and discharge connections of each blower. Arrangements are to beprovided to enable the functioning of the inert gas plant to be stabilized before commencing ballast

discharge. Oil-fired inert gas generators are to be provided with arrangements to vent off-specificationinert gas to the atmosphere (e.g., during startup or in the event of equipment failure). If the blowersare to be used for gas freeing, their air inlets are to be provided with blanking arrangements.

1.17.3 Blower Location

The blowers are to be located aft of all cargo tanks, cargo pump rooms and cofferdams separatingthese spaces from machinery spaces of category A.

1.19 Flue Gas Leakage

1.19.1 General

Special consideration is to be given to the design and location of scrubbers and blowers with relevantpiping and fittings in order to prevent flue gas leakage into enclosed spaces.

1.19.2 Leakage During Maintenance

To permit safe maintenance, an additional water seal or other effective means of preventing flue

gas leakage is to be fitted between the flue gas isolating valves and scrubber or incorporated in the

gas entry to the scrubber.

1.21 Gas Regulating Valve

1.21.1 Gas Flow Regulation

A gas regulating valve is to be fitted in the inert gas supply main. This valve is to be automaticallycontrolled to close, as required in 2/1.41.3 and 2/1.41.4. It is also to be capable of automatically

regulating the flow of inert gas to the ballast tanks unless means are provided to automaticallycontrol the speed of the inert gas blowers required in 2/1.17.


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1.21.2 Location of Gas Regulating Valve

The gas regulating valve is to be located at the forward bulkhead of the forwardmost gas safespace through which the inert gas supply main passes. A gas safe space is a non-hazardous space(see 5C-1-7/1.3.8 of the Steel Vessel Rules).

1.23 Non-return Devices

1.23.1 General

At least two non-return devices, one of which is to be a water seal, are to be fitted in the inert gassupply main in order to prevent the return of hydrocarbon vapor to the machinery space uptakes or

to any gas safe space under all normal conditions of trim, list and motion of the vessel. They are tobe located between the gas regulating valve required by 2/1.21 and the aftermost connection to

any ballast tank.

1.23.2 Location of Non-return Devices

The non-return devices referred to in 2/1.23.1 are to be located in the cargo area on deck.

1.23.3 Water Supply to Water Seal

The water seal is to be capable of being supplied by two separate pumps, each of which is to becapable of maintaining an adequate supply at all times.

1.23.4 Function of Water Seal

The arrangement of the seal and its associated fittings is to be such that it will prevent backflow ofinert gas or hydrocarbon vapors and will ensure the proper functioning of the seal under operatingconditions.

1.23.5 Anti-freeze Arrangement for Water Seal

Provisions are to be made to ensure that the water seal is protected against freezing in such a waythat the integrity of the seal is not impaired by overheating.

1.23.6 Water Loop Protection for Gas Safe SpacesA water loop or other approved arrangement is also to be fitted to each associated water supply anddrain pipe and each venting or pressure-sensing pipe leading to gas safe spaces. Means are to be

provided to prevent such loops from being emptied by vacuum.

1.23.7 Hydrostatic Head of Water Seal and Water Loop

The deck water seal and all loop arrangements are to be capable of preventing return of inert gas

or hydrocarbon vapors at a pressure equal to the test pressure of the ballast tanks.

1.23.8 Non-return Valve

The second device is to be a non-return valve or equivalent capable of preventing the return ofvapors or liquids and fitted forward of the deck water seal. It is to be provided with a positive

means of closure. As an alternative to a positive means of closure, an additional valve having suchmeans of closure may be provided forward of the non-return valve to isolate the deck water seal

from the inert gas main to the ballast tanks.

1.23.9 Venting Arrangement

As an additional safeguard against the possible leakage of water or gas back from the deck main,

means are to be provided to permit the section of the line between the valve having positive meansof closure referred to 2/1.23.8 and the gas regulating valve referred to in 2/1.21 to be vented in a

safe manner when the first of these valves is closed.


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1.25 Branching of Inert Gas Main

1.25.1 General

The inert gas main may be divided into two or more branches forward of the non-return devicesrequired by 2/1.23.

1.25.2 Branch Piping Isolation

1.25.2(a) Valves.The inert gas supply mains are to be fitted with branch piping leading to eachballast tank. Branch piping for inert gas is to be fitted with either a stop valve or an equivalent means

of control for isolating each tank. Where stop valves are fitted, they are to be provided with lockingarrangements, which are to be under the control of a responsible officer of the vessel. The control

system is to provide positive indication of the operational status of such valves.

1.25.2(b) Spectacle Flanges.Branch piping to ballast tanks is to be arranged with spectacle flangesinstalled at each ballast tank. The operating manual, see Subsection 2/11, is to contain instructionsthat the branch lines are to be blanked off when the corresponding ballast tanks are in a gas free

condition.

1.25.3 Overpressure and Vacuum Protection of Isolated Tanks

Means are to be provided to protect ballast tanks against the effect of overpressure or vacuum caused

by thermal variations when the ballast tanks are isolated from the inert gas mains. See also 2/3.5.

1.25.4 Self-draining of Piping

Piping systems are to be so designed as to prevent the accumulation of water in the pipelines under

all normal conditions. See also 2/3.7.

1.25.5 External Supply Connection

Suitable arrangements are to be provided (International Inert Gas Connection) to enable the inert

gas main to be connected to an external supply of inert gas. The arrangements are to consist of a250 mm (10 in.) nominal pipe size bolted flange, isolated from the inert gas main by a valve andlocated forward of the non-return valve referred to in 2/1.23.8.

1.27 Venting for Large Gas Volumes

The arrangements for the venting of all vapors displaced from the ballast tanks during ballasting are to

comply with 2/3.15 and are to consist of either one or more mast risers or a number of high velocity vents.The inert gas supply mains may be used for such venting.

1.29 Inerting, Purging or Gas-freeing of Empty Tanks

The arrangements for inerting, purging or gas freeing of empty tanks, as required in 2/1.7, are to be suchthat the accumulation of air in pockets formed by the internal structural members in a tank is minimized.

Effectiveness of the arrangement is to be confirmed by means of experiment or computer simulation and

submitted to ABS for review.See Appendix 1 for examples of inerting/gas freeing analysis.

1.29.1 Position of Gas Outlet Pipe

On individual ballast tanks, the gas outlet pipe, if fitted, is to be positioned as far as practicable fromthe inert gas/air inlet and in accordance with Subsection 2/3. The inlet of such outlet pipes may be

located either at deck level or at not more than 1 m (3.3 ft) above the bottom of the tank.

1.29.2 Size of Gas Outlet Pipe

The cross sectional area of such gas outlet pipe is to be such that an exit velocity of at least 20 m/s

(66 ft/s) can be maintained when any three tanks are being simultaneously supplied with inert gas.Their outlets are to extend not less than 2 m (6.6 ft) above deck level.

1.29.3 Blanking of Gas Outlet Pipe

Each gas outlet is to be fitted with suitable blanking arrangements.


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1.31 Pressure/Vacuum-breaking Devices

1.31.1 General

One or more pressure/vacuum-breaking devices are to be provided on the inert gas supply main toprevent the ballast tanks from being subject to:

i) A positive pressure in excess of the test pressure of the ballast tank if the ballast were tobe loaded at the maximum specified rate and all other outlets were left shut; or

ii) A negative pressure in excess of 700 mm (27.5 in.) water gauge if ballast was to be discharged

at the maximum rated capacity of the ballast pumps and the inert gas blowers were to fail.

Such devices are to be installed on the inert gas main unless they are installed in the venting systemrequired by 2/3.1 or on individual ballast tanks.

1.31.2 Location and Design

The location and design of the devices are to be in accordance with Subsection 2/3.

1.33 Instrumentation at Gas Blower Outlets

Means are to be provided for continuously indicating the temperature and the pressure of the inert gas atthe discharge side of the gas blowers, whenever the gas blowers are operating.

1.35 Monitoring of Inert Gas

1.35.1 Instrumentation at Inert Gas Supply Main

Instrumentation is to be fitted for continuously indicating and permanently recording when the

inert gas is being supplied:

i) The pressure of the inert gas supply mains forward of the non-return devices required by2/1.23.1

ii) The oxygen content of the inert gas in the inert gas supply mains on the discharge side of

the gas blowers.

iii) The SO2content of the inert gas in the inert gas supply mains on the discharge side of thegas blowers.

1.35.2 Cargo Control Room Displays

The devices in 2/1.35.1 are to be placed in the cargo control room, where provided. However, where

no cargo control room is provided, they are to be placed in a position easily accessible to the officerin charge of the ballast operations.

1.35.3 Navigation Bridge and Machinery Control Room Displays

In addition, displays are to be fitted:

i) In the navigation bridge to indicate at all times the pressure referred to in 2/1.35.1i)

ii) In the machinery control room or in the machinery space to indicate the oxygen contentreferred to in 2/1.35.1ii)

iii) In the machinery control room or in the machinery space to indicate the sulfur contentreferred to in 2/1.35.1iii)

1.37 Portable Detectors

Suitable arrangements are to be made on each ballast tank such that the condition of the tank atmosphere

can be determined using portable detectors required in 5-1-7/25.33 of the Rules for Building and ClassingSteel Vessels.

1.39 Calibration of Instruments

Suitable means are to be provided for the zero and span calibration of fixed gas concentration measurementinstruments, referred to in 2/1.35.


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1.41 Alarms and Shutdowns

1.41.1 Alarms for Flue Gas Type Systems

For inert gas systems of the flue gas type, audible and visual alarms are to be provided to indicate:

i) Low water pressure or low water flow rate to the flue gas scrubber, as referred to in 2/1.15.1

ii) High water level in the flue gas scrubber, as referred to in 2/1.15.1

iii) High gas temperature, as referred to in 2/1.33

iv) Failure of the inert gas blowers, as referred to in 2/1.17

v) Oxygen content in excess of the limit specified in 2/1.9.1, as referred to in 2/1.35.1ii)

vi) Failure of the power supply to the automatic control system for the gas regulating valve

and to the indicating devices, as referred to in 2/1.21 and 2/1.35.1

vii) Low water level in the water seal, as referred to in 2/1.23.1

viii) Gas pressure less than 100 mm water gauge, as referred to in 2/1.35.1i)

ix) High gas pressure, as referred to in 2/1.35.1i)x) SO2content in excess of the limit specified in 2/1.9.2, as referred to in 2/1.35.1iii)

1.41.2 Inert Gas Generator Type Systems

For inert gas systems of the inert gas generator type the relevant requirements for control of firedburners in 4-4-1/11.5 of the Steel Vessel Rules are applicable. In addition,audible and visual alarms

are to be provided in accordance with 2/1.41.1, and the following:

i) Insufficient fuel oil supply

ii) Failure of the power supply to the generator (This condition is to also automatically shut

down the gas-regulating valve.)

iii) Failure of the power supply to the automatic control system for the generator

In addition, fuel oil supply to the gas generator is to be automatically shut down in the event of a)low water pressure (or flow) to scrubber and b) high gas temperature.

1.41.3 Automatic Shut-down of the Inert Gas Blowers and Gas Regulating Valve

Automatic shut-down of the inert gas blowers and gas regulating valve is to be arranged on

predetermined limits being reached in accordance with 2/1.41.1i), 2/1.41.1ii) and 2/1.41.1iii).

1.41.4 Automatic Shut-down of the Gas Regulating Valve

Automatic shut-down of the gas regulating valve is to be arranged in accordance with 2/1.41.1iv).

1.41.5 Suspension of Ballast Tank Operations

In accordance with 2/1.41.1v), when the oxygen content of the inert gas exceeds 8% by volume,immediate action is to be taken to improve the gas quality. If the quality of the gas does not improve

and a flammable vapor is detected within a ballast tank, the ballast tank operation is to be suspendedso as to avoid air being drawn into the tank and the isolation valve referred to in 2/1.23.8 is to be

closed.

1.41.6 Alarms in Cargo Control Room and Machinery Space

The alarms required in 2/1.41.1v), 2/1.41.1vi) and 2/1.41.1viii) are to be fitted in the machineryspace and cargo control room, where provided, but in each case, in such a position that they are

immediately received by responsible members of the crew.


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1.41.7 Dry Water Seal Water Supply

As per the intent of 2/1.41.1vii), an adequate reserve of water is to be maintained at all times andthe integrity of the arrangements to permit the automatic formation of the water seal when the gasflow ceases is also to be maintained. The audible and visual alarm on the low level of the water in

the water seal is to operate when the inert gas is not being supplied.

1.41.8 Additional Low Inert Gas Pressure Protection

An audible alarm system independent of that required in 2/1.41.1viii) is to be provided to operate

on predetermined limits of low pressure in the inert gas mains being reached.

1.43 Nitrogen Generator Inert Gas Systems

1.43.1 Application

The requirements of 2/1.43 apply where inert gas is produced by separating air into its component

gases by passing compressed air through a bundle of hollow fibers, semi-permeable membranes orabsorber materials. Where such systems are provided in place of the boiler flue gas or oil-fired inert

gas generators, the following requirements are also applicable for the piping arrangements, alarmsand instrumentation downstream of the gas generator:

2/1.21.1 2/1.21.2 2/1.25 2/1.27 2/1.29

2/1.31 2/1.35.1i) 2/1.35.2 2/1.35.3 2/1.37

2/1.39 2/1.41.1vi) 2/1.41.1viii) 2/1.41.1ix) 2/1.41.3

2/1.41.4 2/1.41.6 2/1.41.8 2/1.43

1.43.2 Nitrogen Generator

1.43.2(a) Capacity. A nitrogen generator consists of a feed air treatment system and any number

of membrane or absorber modules in parallel necessary to meet the required capacity specified in2/1.3.1 and 2/1.5.2, as applicable.

1.43.2(b) Gas Specification. The nitrogen generator is to be capable of delivering high puritynitrogen with oxygen content not exceeding 5% by volume. The system is to be fitted with automaticmeans to discharge off-specification gas to the atmosphere during start-up and abnormal operation.The block and bleed arrangement indicated in 2/1.43.4 is not to be used for this purpose.

1.43.2(c) Air Compressors. The system is to be provided with two air compressors. The total

required capacity of the system is preferably to be divided equally between the two compressors,and in no case is one compressor to have a capacity less than 1/3of the total capacity required.

Only one air compressor may be accepted, provided that sufficient spares for the air compressor

and its prime mover are carried onboard to enable their failure to berectified by the vessels crew.

1.43.2(d) Feed Air Treatment. A feed air treatment system is to be fitted to remove free water,particles and traces of oil from the compressed air, and to preserve the specification temperature.

1.43.2(e) Nitrogen Receiver. Where fitted, a nitrogen receiver/buffer tank may be installed in a

dedicated compartment or in the separate compartment containing the air compressor and the generatoror may be located in the cargo area. Where the nitrogen receiver/buffer tank is installed in anenclosed space, the access is to be arranged only from the open deck and the access door is to open

outwards. Permanent ventilation and alarm are to be fitted as in 2/1.43.3.

In order to permit maintenance, means of isolation are to be fitted between the generator and thereceiver.

1.43.2(f) Enriched Gases. The oxygen-enriched air from the nitrogen generator and the nitrogen-

product enriched gas from the protective devices of the nitrogen receiver are to be discharged to asafe location on the open deck.


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1.43.3 Location of Installation

The air compressor and the nitrogen generator may be installed in the engine room or in a separatecompartment. Where a separate compartment is provided, it is to be:

i) Treated as other machinery spaces with respect to fireprotection

ii) Positioned outside of the cargo area

iii) Fitted with an independent mechanical extraction ventilation system providing at least six(6) air changes per hour

iv) Fitted with a low oxygen alarm

v) Arranged with no direct access to accommodation spaces, service spaces and control stations

1.43.4 Non-return Devices

At least two non-return devices are to be fittedin the inert gas supply main. One of the non-return

devices is to be of the double block and bleed arrangement (two shut-off valves in series with aventing valve in between) for which the following conditions apply:

i) The operation of the valve is to be automatically executed. Signal(s) for opening/closingare to be taken from the process directly (e.g., inert gas flow or differential pressure).

ii) Alarm for faulty operation of the valves is to be provided (e.g., the operation of blower

stop and supply valve(s) open is an alarm condition).

iii) Upon loss of power, the block valves are to automatically close and the bleed valve is toautomatically open.

The second non-return device is to be equipped with positive means of closure.

1.43.5 Instrumentation

1.43.5(a) Compressed Air. Instrumentation is to be provided for continuously indicating thetemperature and pressure of air:

i) At the discharge side of the compressor

ii) At the entrance side of the nitrogen generator

1.43.5(b) Inert Gas. Instrumentation is to be fitted for continuously indicating and permanentlyrecording the oxygen content of the inert gas downstream from the nitrogen generator when inert

gas is being supplied. This instrumentation is to be placed in the cargo control room and in themachinery control room (or in the machinery space).

1.43.5(c) Alarms. Audible and visual alarms are to be provided to indicate:

i) Low air pressure from compressor, as referred to in 2/1.43.5(a)i)

ii) High air temperature, as referred to in 2/1.43.5(a)i)

iii) High condensate level at automatic drain of water separator, as referred to in 2/1.43.2(d)

iv) Failure of electrical heater, if fitted

v) Oxygen content in excess of that specified in 2/1.43.2(b)

vi) Failure of power supply to the instrumentation, as referred to in 2/1.43.5(b)

These alarms are to be fitted in the machinery space and cargo control room, where provided, but ineach case, in such a position that they are immediately received by responsible members of the crew.

1.43.6 Automatic Shutdown

Automatic shutdown of the system is to be arranged for alarm conditions in 2/1.43.5(c)i) through

2/1.43.5(c)v).


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3 Ballast Tanks Venting

3.1 General Principles

The venting systems are to be designed so as to maintain the inert condition in the ballast tanks, except

when the tanks are required to be gas free. The venting systems of inerted ballast tanks are to be entirely distinctfrom the vent pipes of the other compartments of the vessel. The arrangements and position of openings in

the ballast tank deck from which emission of inert gas can occur are to be such as to minimize the possibilityof gases being admitted to enclosed spaces, or collecting in the vicinity of deck machinery and equipment,

which may constitute a hazard during operation. In accordance with this general principle, the criteria in2/3.3 to 2/3.15 will apply.

3.3 Venting Capacity

The venting arrangements are to be so designed and operated as to ensure that neither pressure nor vacuum

in ballast tanks is to exceed design parameters and be such as to provide for:

i) The flow of the small volumes of air or inert gas mixtures caused by thermal variations in a ballasttank in all cases through pressure/vacuum valves.

ii) The passage of large volumes of air or inert gas mixtures during ballasting or during deballasting.iii) A secondary means of allowing full flow relief of air or inert gas mixtures to prevent overpressure

or underpressure in the event of the failure of the arrangements in ii). Alternatively, pressuresensors may be fitted in each tank protected by the arrangements required in ii), with a monitoring

system in the vessels cargo control room or the position from which ballast operations are normallycarried out. Such monitoring system is also to provide an alarm facility which is activated bydetection of overpressure or underpressure conditions within a tank.

3.5 Vent Piping

3.5.1 Venting Arrangement

The venting arrangements in each ballast tank may be independent or combined with other ballast

tanks and may be incorporated into the inert gas piping.

3.5.2 Combined Venting System

Where the arrangements are combined with other ballast tanks, either stop valves or other acceptable

means are to be provided to isolate each ballast tank. Where stop valves are fitted, they are to beprovided with locking arrangements, which are to be under the control of the responsible vessels

officer. There is to be a clear visual indication of the operational status of the valves or otheracceptable means. Where tanks have been isolated, it is to be ensured that relevant isolation valves

are opened before ballasting or deballasting of the tanks is commenced. Any isolation must continueto permit the flow caused by thermal variations in a ballast tank, in accordance with 2/3.3i).

Additionally, combined vent pipes from ballast tanks are to be arranged with spectacle flanges installed

at each ballast tank. The operating manual (see Subsection 2/11) is to contain instructions that thevent lines are to be blanked off when the corresponding ballast tanks are in a gas free condition.

3.5.3 Isolation from Common Venting System

Where it is intended to ballast or deballast a ballast tank or a ballast tank group while it is isolated

from the common venting system, such ballast tank or ballast tank group is to be fitted with meansof overpressure and underpressure protection, as in 2/3.3iii).

3.7 Self-draining of Vent Piping

The venting arrangements are to be connected to the top of each ballast tank and are to be self-draining to

the ballast tanks under all normal conditions of trim and list of the vessel. Where it may not be possible toprovide self-draining lines, permanent arrangements are to be provided to drain the vent lines to a ballasttank.


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3.9 Protection for Tank Overpressurization and Vacuum

3.9.1 Liquid Rising in Vent Pipes

Provision is to be made to guard against liquid rising in the venting system to a height whichwould exceed the design head of ballast tanks. This is to be accomplished by:

i) High level alarms or overflow control systems or other equivalent means

ii) Gauging devices

iii) Ballast tank filling procedures

In the event that protection is by means of an overflow control system, an analysis is to be submittedto indicate that, in the worst overflowing condition, the tanks will not be overpressurized.

3.9.2 Pressure/Vacuum Valve Setting

The pressure-vacuum valves of ballast tanks are not to be set at a pressure in excess of the pressureappropriate to the length of the vessel, as per the table below:

Vessel size Pressure/Vacuum setting

a) 103 m (337 ft) in length or more P0.21 bar (0.21 kgf/cm2, 3 psi)

V0.07 bar (0.07 kgf/cm2, 1 psi)

b) 61 m (200 ft) in length or less P0.12 bar (0.12 kgf/cm2, 1.7 psi)

V0.07 bar (0.07 kgf/cm2, 1 psi)

c) Vessels of intermediate lengths Interpolate between (a) and (b)

P= Pressure above atmospheric; V= Pressure below atmospheric

3.11 Position of Pressure/Vacuum Valves

Openings for pressure release required by 2/3.3i) are to:

i) Have as great a height as is practicable, but in no case less than 2 m (6.6 ft), above the cargo tankdeck to obtain maximum dispersal of gases

ii) Be arranged at the furthest distance practicable, but not less than 5 m (16.5 ft), from the nearest airintakes and openings to enclosed spaces containing a source of ignition and from deck machinery

and equipment which may constitute an ignition hazard

3.13 Pressure/Vacuum Valve Bypass

Pressure/vacuum valves required by 2/3.3i) may be provided with a by-pass arrangement when they arelocated in a vent main or masthead riser. Where such an arrangement is provided, there are to be suitable

indicators to show whether the bypass is open or closed.

3.15 Vent Outlets for Large Flow VolumesVent outlets for ballasting and deballasting required by paragraph 2/3.3ii) are to:

i) Permit the free flow of gas or permit the throttling of the discharge of the gases to achieve a

velocity of not less than 30 m/s (100 ft/s).

ii) Be so arranged that the gas is discharged vertically upwards.

iii) Where the method is by free flow of gas, be such that the outlet is to be not less than 6 m (19.7 ft)above the cargo tank deck or fore and aft gangway, if situated within 4 m (13.2 ft) of the gangway

and located not less than 10 m (33 ft) measured horizontally from the nearest air intakes andopenings to enclosed spaces containing a source of ignition and from deck machinery and

equipment which may constitute an ignition hazard.


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iv) Where the method is by high velocity discharge, be located at a height not less than 2 m (6.6 ft)above the cargo tank deck and not less than 10 m (33 ft) measured horizontally from the nearest air

intakes and openings to enclosed spaces containing a source of ignition and from deck machineryand equipment which may constitute an ignition hazard. These outlets are to be provided with high

velocity devices of an approved type.

v) Be designed on the basis of the maximum designed ballasting rate multiplied by a factor of at least1.25 in order to prevent the pressure in any ballast tank from exceeding the design pressure. The

master is to be provided with information regarding the maximum permissible ballasting rate foreach ballast tank and, in the case of combined venting systems, for each group of ballast tanks.

5 Ballast Tank Gas Detection System

The water ballast tanks are to be fitted with fixed or portable means to detect hydrocarbon gas, being capable

of operation in a low-oxygen (inert) environment.

5.1 Portable Gas Measuring Detectors

Suitable portable detectors for measuring oxygen and flammable vapor concentrations are to be provided.See 2/1.37 regarding the required number of detectors. In selecting these detectors, due attention is to be

given to their use in combination with the fixed gas-sampling-line systems referred to in 2/5.3.

5.3 Fixed Gas Sampling System

Where the atmosphere in ballast tanks cannot be reliably measured using flexible gas sampling hoses, suchspaces are to be fitted with permanent gas sampling lines. The configurations of such line systems are to beadapted to the design of such tanks.

5.5 Piping of Gas Sampling Lines

The materials of construction and the dimensions of gas sampling lines are to be such as to prevent restriction.

Where plastic materials are used, they are to be electrically conductive.

5.7 Gas Sampling System Installation

Gas sampling systems with gas-analyzing/measurement units not certified safe for installation in a hazardousarea may have such units installed in a safe area, such as the cargo control room or the navigation bridge,

provided that the following installation details are complied with:

i) The gas-analyzing unit is to be mounted on the forward bulkhead of the safe space, except as

specially permitted in vi).

ii) The sampling lines are not to run through safe spaces, except where specially permitted in vi).

iii) Bulkhead penetrations of sampling pipes between safe and hazardous areas are to be of approvedtypes and have the same fire integrity as the division penetrated. An isolation valve is to be fitted

in each of the sampling lines at the bulkhead on the safe side.

iv) The gas sampling pipes are to be equipped with flame arresters. Sample gas is to be exhausted tothe atmosphere with outlets away from sources of ignition.

v) The gas detection equipment, including sampling piping, sampling pumps, solenoids, analyzing

units, etc., are to be located in a reasonably gas-tight steel cabinet (e.g., fully enclosed steel cabinetwith gasketed door) which is to be monitored by its own sampling point. At a gas concentrationabove 30% of the lower flammable limit inside of the steel cabinet, the entire analyzing unit is to

be automatically shut down. Shutdown of the unit is to be alarmed at both the cargo control roomand the navigation bridge.

vi) Where the cabinet cannot be mounted directly on the forward bulkhead, sampling pipes are to be

of steel or other equivalent material and without detachable connections, except for the connectionpoints for isolating valves at the bulkhead and for the analyzing units. Runs of the sampling pipes

within the safe space are to be as short as possible.


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7 Ballast Tank Level Gauging

A closed remote control tank gauging system capable of measuring the full height of the tank is to be fitted. A

tank level display is to be provided at each cargo transfer control station.

7.1 Tank Overfill Protection7.1.1 High Level and Overfill Alarms

Each cargo tank is to be fitted with a high level alarm and an overfill alarm, which are to be

independent of each other. The overfill alarm is at least to be independent of the tank gauging system.The alarm systems are to be self-monitoring (or fitted with other means of testing) and provided

with alarms for failure of tank level sensor circuits and power supply. All alarms are to have visualand audible signals and are to be given at each cargo transfer control station. In addition, overfill

alarms are also to be given in the cargo deck area in such a way that they can be seen and heardfrom most locations.

7.1.2 Level Alarm Setting

The high level alarm is to be set at no less than that corresponding to 95% of tank capacity, and

before the overfill alarm level is reached. The overfill alarm is to be set so that it will activateearly enough to allow crew in charge of the transfer operations to stop the transfer before the tank

overflows.

7.1.3 Operational Checks

Each alarm system is to have a means of checking locally at the tank to assure proper operation

prior to the cargo transfer operation. This is not required if the system has a self-monitoring feature.

9 Ballast Pump Operation

Emergency stop arrangements of the ballast pump prime movers are to be provided at the location(s) where

the ballast system is normally controlled.

11 Operating Manuals

Detailed operating manuals are to be provided onboard, covering the operations, safety and maintenancerequirements and occupational health hazards relevant to the inert gas system and its application to theballast tank system. The manuals are to include guidance on procedures to be followed in the event of a

fault or failure of the inert gas system. Also, the manuals are to include detailed requirements for gas freeingoperation. Reference is to be made to the IMO document MSC/Circ.353 and 387Guidelines for Inert Gas

Systems.


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S e c t i o n 3 : S u r v e y R e q u i r e m e n t s

S E C T I O N 3 Survey Requirements

1 New Construction

The inert gas generating plant, inert gas distribution system, alarms, shutdowns and control equipment are

to be installed and tested under working conditions to the satisfaction of the Surveyor. The fuel oil pumpsand cooling water pumps are to be provided with certificates (see 2/1.11.3 and 2/1.15.4).

3 Annual Survey

3.1 Inert Gas Systems

At each Annual Survey Machinery (see the ABSRules for Survey After Construction (Part 7))the inertgas system for the cargo and ballast tanks is to be generally examined in so far as can be seen and placed in

satisfactory condition. The survey is also to include the following, as applicable:

3.1.1 General

3.1.1(a) External Examination. External examination of all components and piping, including

scrubber, fans, valves, stand pipe and screens.

3.1.1(b) Inert Gas Blower. Confirmation of proper operation of inert gas blowers. In the gas

generator type system with one inert gas blower and/or one fuel oil pump, sufficient spares for the

blower and/or fuel oil pump and its prime mover are to be verified onboard.

3.1.1(c) Air Compressor. Confirmation of proper operation of air compressors and feed air

treatment system for nitrogen generator system. In the system with one air compressor, sufficientspares for the air compressor and its prime mover are to be verified onboard.

3.1.1(d) Scrubber Room Ventilation System. Observation of the operation of the scrubber room

ventilation system.

3.1.1(e) Air Compressor, Nitrogen Generator and Nitrogen Receiver/Buffer Tank Room. Observationof the operation of the ventilation system and low oxygen alarm system for the compartment

3.1.1(f) Non-return Device. Deck seals or double block and bleed assemblies, and non-returnvalves are to be examined externally and proven to be in operation. Automatic filling and draining

of the deck seal, operation of non-return valves and double block and bleed assemblies, and thewater carryover are to be checked.

3.1.1(g) Control Valves. Verify the operation of all remotely operated or automatically controlledvalves and, in particular, the flue gas isolating valves.

3.1.1(h) Interlocking Feature. Verify the operation of the interlocking feature of soot blowers.

3.1.1(i) Gas Pressure Regulating Valve. Verify the automatic operation of the gas pressure-

regulating valve.

3.1.1(j) Operation and Maintenance Records. The Surveyor is to examine the permanent recordsto verify the operation and maintenance of the system. Consideration may be given by the Surveyor

for the crediting of certain items that have been properly documented and recorded.


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Section 3 Survey Requirements


3.1.2 Alarm and Safety Device

Verify the operation of the following alarms and safety devices, using simulated conditions where

necessary:

3.1.2(a) Flue Gas Systems

i) Low water pressure or low water flow rate to the flue gas scrubber, including automaticshutdown of the inert gas blowers and gas regulating valve.

ii) High water level in the flue gas scrubber, including automatic shutdown of the inert gasblowers and gas regulating valve.

iii) High gas temperature at IGS blower discharge, including automatic shutdown of the inert

gas blowers and gas regulating valve.

iv) Failure of the inert gas blowers, including automatic shutdown of the gas regulating valve.

v) Oxygen content in excess of 5% by volume.

vi) SO2content in excess of 2 ppm.

vii) Failure of the power supply to the automatic control system for the gas regulating valveand to the oxygen content and gas pressure indicating devices.

viii) Low water level in the water seal.

ix) Gas pressure less than 100 mm water gauge.

x) Additional low gas pressure audible alarm system independent of alarm system for gaspressure less than 100 mm water gauge, if fitted.

xi) Manual emergency shutdowns of ballast pump prime movers located where the ballastsystem is normally controlled.

xii) High gas pressure.

xiii) Accuracy of fixed and portable oxygen measuring equipment by means of a calibration gas.xiv) Accuracy of fixed and portable SO2measuring equipment by means of a calibration gas.

3.1.2(b) Gas Generating Systems

i) Low water pressure or low water flow rate to the flue gas scrubber, including automatic

shutdown of the inert gas blowers, gas regulating valve and fuel oil supply to the gasgenerator.

ii) High water level in the flue gas scrubber, including automatic shutdown of the inert gasblowers and gas regulating valve.

iii) High gas temperature at IGS blower discharge, including automatic shutdown of the inertgas blowers, gas regulating valve and fuel oil supply to the gas generator.

iv) Failure of the inert gas blowers, including automatic shutdown of the gas regulating valve.

v) Oxygen content in excess of 5% by volume.

vi) SO2content in excess of 2 ppm.

vii) Failure of the power supply to the automatic control system for the gas regulating valveand to the oxygen content and gas pressure indicating devices.

viii) Low water level in the water seal.

ix) Gas pressure less than 100 mm water gauge.

x) Additional low gas pressure audible alarm system, independent of alarm system for gaspressure less than 100 mm water gauge, if fitted.

xi) Manual emergency shutdowns of ballast pump prime movers located where the ballast system

is normally controlled.


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xiii) Insufficient fuel oil supply.

xiv) Failure of the power supply to the generator, including automatic shutdown of the gasregulating valve.

xv) Failure of the power supply to automatic control system for the generator.

xvi) Accuracy of fixed and portable oxygen measuring equipment by means of a calibration gas.

xvii) Accuracy of fixed and portable SO2measuring equipment by means of a calibration gas.

3.1.2(c) Nitrogen Generating Systems

i) Low air pressure, including automatic shutdown of the system.

ii) High air temperature, including automatic shutdown of the system.

iii) High condensate level at automatic drain of water separator, including automatic shutdownof the system.

iv) High gas temperature, including automatic shutdown of the gas regulating valve.

v) Failure of electrical heater, if fitted, including automatic shutdown of the system.

vi) Failure of inert gas pressure, including automatic shutdown of the gas regulating valve.

vii) Oxygen content in excess of 5% by volume, including automatic shutdown of the system.

viii) Failure of the power supply to the automatic control system for the gas regulating valveand to the oxygen content and gas pressure indicating devices.

ix) Gas pressure less than 100 mm water gauge

x) Additional low gas pressure audible alarm system independent of alarm system for gaspressure less than 100 mm water gauge, if fitted.

xi) Manual emergency shutdowns of ballast pump prime movers located where the ballastsystem is normally controlled.


xiii) Accuracy of fixed and portable oxygen measuring equipment by means of a calibration gas.

5 Special Periodical Survey

In conjunction with the Special Periodical Survey Machinery (see the ABS Rules for Survey After

Construction (Part 7))the following items of the Inert Gas System for the cargo and ballast tanks are to beexamined and placed in satisfactory condition:

5.1 General

All valves, including valves at boiler uptakes, air seal valves at uptakes, scrubber isolating valve, fans inletand outlet isolating valves, main isolating valve, re-circulating valve (if fitted), pressure/vacuum breaker

and cargo tank isolating valves, are to be examined.

i) Scrubber(s) is to be examined.

ii) Fans (blowers), including casing drain valves, are to be examined.

iii) Fan (blower) drives, either electric motor or steam turbine, are to be examined.

iv) Bellows expansions pieces are to be examined.

v) Sea water pumps, valves and strainers for scrubbers and water seals together with piping connectionsat the scrubber, water seals, shell plating and the remainder of the sea water piping are to be examined.

vi) Stand pipe, where fitted, for purging in each cargo tank is to be examined.

vii) Deck seals or double block and bleed assemblies, and non-return valves are to be examined externallyand internally.


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5.3 Separate Inert Gas Generator System

Surveys for separate inert gas generator systems are to comply with all applicable requirements for Special

Periodical Surveys given in Section 7-6-2 of the ABSRules for Survey After Construction (Part 7), togetherwith the following:

i) Automatic combustion control system is to be examined and tested, as necessary.ii) Combustion chamber and mountings are to be examined internally and externally.

iii) Forced draft fan is to be examined.

iv) Fuel oil service pumps are to be examined.

5.5 Gas Stored in Bottles System

Systems using inert gas stored in bottles are to comply with all applicable requirements for SpecialPeriodical Surveys given in Section 7-6-2 of the ABSRules for Survey After Construction (Part 7), together

with the following:

i) Bottles are to be examined internally and externally. If they cannot be examined internally, they are

to be thickness measured. When considered necessary by the Surveyor, they are to be hydrostaticallytested. Relief valves are to be proven operable.

ii) Where an alkali (or other) scrubber is fitted in the system, the scrubber, circulating pump, valves

and piping are to be examined internally and externally.


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A p p e n d i x 1 : E x a m p l e s o f I n e r t i n g / G a s F r e e i n g A n a l y s i s o f B a l l a s t T a n k

A P P E N D I X 1 Examples of Inerting/Gas Freeing Analysis ofBallast Tank

1 Introduction

There are two reasons for replacing the atmosphere in a ballast tank:

To inert the atmosphere, which prevents explosion of any hydrocarbon gas leaking in from adjacentcargo tanks and reduces tank corrosion.

To gas-free the tank so as to allow safe personnel entry.

The IMO Guidelines for Inert Gas Systems (1990 Edition) proposes two theories regarding the replacementof the atmosphere in a cargo tank: dilution theory and replacement theory. The dilution theory assumesthat the incoming gas mixes with the original gas to form a homogeneous mixture throughout the tank, resulting

in the concentration of the original gas decreasing exponentially. The replacement theory requires a stablehorizontal interface between lighter gas entering at the top of the tank and heavier gas at the bottom, and

results in the heavier gas being displaced from the bottom of the tank through some suitable piping arrangement.

However, a ballast tank structure is unlike a cargo tank in that it is subdivided into smaller interconnected

compartments by the transverse webs and longitudinal girders in the double bottom, and stringer platforms

in the sides. This complex arrangement makes the theories proposed by IMO inappropriate.

The purpose of the analysis required by 2/1.29 of this Guide is to establish the time required to effectively

inert or gas-free the ballast tanks. Gas-freeing, for example, should be carried out when it is necessary for

personnel entry into a ballast tank, and it should be certain that 21% oxygen by volume is achieved throughoutthe tank. Any pockets of gaseous mixtures with an oxygen level below 21% by volume should be removed.

One method that may be used to confirm the effectiveness of inerting or gas freeing as required by 2/1.29is to apply numerical simulation using the principles of fluid dynamics, heat and mass transfer with proper

approximations. The example analysis in this Appendix investigates gas replacement inside a typical ballasttank, and estimates the required number of atmosphere changes for satisfactory inerting and gas-freeing,

including the removal of any air or inert gas pockets.

There are a number of commercially available computational fluid dynamics (CFD) software packages that

may be used to predict the distribution of multiple gas species (i.e. oxygen, carbon dioxide and nitrogen)inside of a ballast tank. Such programs should be carefully evaluated before being used.

In this analysis, a suitable CFD software package was chosen to simulate the flow patterns inside of a ballast

tank. By solving the complex governing equations of the flows with multiple species, the software providessteady and transient analysis of turbulent flows with complex boundary conditions in the tank.

3 Description of the Ballast Tank

3.1 Dimensions

The geometry of the ballast tank in the computer model was taken from a typical ULCC with the following

principal dimensions:

Length: 58.70 m

Depth: 34.00 m

Breadth: 34.00 m


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Appendix 1 Examples of Inerting/Gas Freeing Analysis of Ballast Tank


The analyzed ballast tank has a volume of 14,267 m3. All of the surfaces of the ballast tank in the model

were assumed to be adiabatic, i.e., no heat transfer between the gases and the surfaces is considered. Also,no structural deformation was assumed in the model. Appendix 1, Figure 1 shows the schematic diagram

of the ballast tank with discharge pipe in this analysis.

FIGURE 1Ballast Tank with Discharge Pipe

Discharge

pipe inlet Gas

outlet

y

x

z

Discharge

pipe outlet

3.3 Transverse Bulkheads and Frames

Between the transverse bulkheads, there are nine transverse frames with 5.87 m spacing.

Fourteen ballast vent holes of 800 mm by 600 mm on each frame are represented in the model. The manholeadjacent to the turn of the bilge is modeled as a polygon shape with its area equivalent to the actual area of7.52 m2.

3.5 Stringers

Three stringers are located at 9.6 m, 16.6 m and 24.6 m above the base line (A/B), respectively. There are

two access holes of 750 mm by 1800 mm on every stringer, one located at the aft end and the other at theforward end. Between transverse frames on each stringer, at the sides of the longitudinal inner skin bulkhead

and side shell plating, there are four drain holes of 120 mm by 240 mm with 1.468 m of spacing.

3.7 Girders

One side girder is located 13.00 m off the centerline, and another side girder under the longitudinal bulkhead islocated 25.35 m off the center line. On each side girder, there is one access manhole of 1200 mm by 800 mmat the aft end and two of 1000 mm by 800 mm at the forward end.

Between transverse frames on each girder, there are four drain holes of 150 mm by 300 mm at the side ofthe bottom shell plating and two of 100 mm by 200 mm at the side of the inner bottom plating.


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3.9 Discharge Pipe and Gas Outlet

The discharge pipe is of 300 mm ID, installed in the middle of the aft bulkhead and the adjacent transverse

web frame. The open end of the pipe is located halfway between the centerline longitudinal bulkhead andthe adjacent side girder. The position of the gas outlet is located at the forward end of the ballast tank on

the deck level.

3.11 Simulation Model

Numerous openings on girders and stringers provided a unique challenge to numerical simulations in thisanalysis. Since a non-structure meshing scheme was used, the cell size ranged from 0.01 m to 0.70 m,depending on sizes of the openings. The basic philosophy of meshing was that for each opening at least

three cells should be assigned in each direction. As a result, up to 1.97 million nodes and 1.88 millionhexagonal cells were generated in the numerical models. The numerical calculations were carried out on a

UNIX server with two CPUs and up to 4 GB memory. Due to the large sizes of the models, it took about30 CPU hours to complete the calculation of a three-hour real time simulation.

A complete set of continuity and momentum equations were solved for every species of oxygen, carbon

dioxide and nitrogen. Among various turbulent models (i.e., indoor zero equation, zero equation, two equation,

RNG, etc.) featured in the software package, the two-equation k-

turbulent model was applied to capturethe turbulent dissipation and kinetic energy, especially in the areas with intensified turbulent mixing and large

velocity gradients.

5 Results

Full-scale, 3D simulations were carried out for inerting and gas-freeing, respectively. Each numericalsimulation resulted in determining if and when the applicable threshold value was reached. For inerting

operation, the threshold value of oxygen was 3% by volume (3.2% by mass), whereas for gas-freeing thethreshold value of oxygen was 21% by volume (23.3% by mass).

The compositions of inert gas and fresh air used throughout this analysis are listed in Appendix 1, Table 1:

TABLE 1Composition of Gases

Inert gas Fresh air

By volume

%

By mass

%

By volume

%

By mass

%

Oxygen 3 3.2 21 23.3

Carbon dioxide 14 20.3 0 0

Nitrogen 87 76.5 79 76.7

During the full-scale 3D simulations, the flow velocity and the concentrations of oxygen, carbon dioxideand nitrogen inside of the ballast tanks were recorded. The recorded data were written out to graphic andtext files.

5.1 Inerting

The inert gas was discharged into the ballast tank with a flow rate of 9500 m 3/hr. At the initial stage, theballast tank was filled with air. To illustrate the timeline distribution of gases during the inerting operation,

two plane cuts were made in the ballast tank model: one horizontally through the middle of the tank bottom,and the other vertically through the middle of the tank side. Appendix 1, Figures 2(a) to 2(e) show the

oxygen concentration by mass on both planes at intervals 0.5, 1.0, 1.5, 2.25 and 3.0 hours, respectively.

After three hours (two atmosphere changes) of inerting, the results of the model calculations show that the

air inside the ballast tank was completely replaced by the inert gas [see Appendix 1, Figure 2(e)].


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FIGURE 2(a)Inerting at 0.5 hr (1800 seconds), 0.33 Atmosphere Changes

FIGURE 2(b)Inerting at 1.0 hr (3600 seconds), 0.67 Atmosphere Changes


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FIGURE 2(c)Inerting at 1.5 hr (5400 seconds), 1.0 Atmosphere Change

FIGURE 2(d)Inerting at 2.25 hr (8100 seconds), 1.5 Atmosphere Changes


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FIGURE 2(e)Inerting at 3.0 hr (10800 seconds), 2.0 Atmosphere Changes

5.3 Gas-freeing

In the gas-freeing operation, a flow rate of 9500 m3/hr of fresh air was discharged into the ballast tank initiallyfilled with inert gas.

As per the inerting simulation, two plane cuts were made in the ballast tank model: one horizontally through

the middle of the tank bottom, and the other vertically through the middle of the tank side. Appendix 1,Figures 3(a) to 3(e) show the oxygen concentration by mass on both planes at intervals 0.5, 1.0, 1.5, 2.25and 3.0 hours, respectively.

After three hours of simulation, the results show that the inert gas inside of the ballast tank was completelyreplaced by fresh air [see Appendix 1, Figure 3(e)].


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FIGURE 3(a)Gas-freeing at 0.5 hr (1800 seconds), 0.33 Atmosphere Changes

FIGURE 3(b)Gas-freeing at 1.0 hr (3600 seconds), 0.67 Atmosphere Changes


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FIGURE 3(c)Gas-freeing at 1.5 hr (5400 seconds), 1.0 Atmosphere Change

FIGURE 3(d)Gas-freeing at 2.25 hr (8100 seconds), 1.5 Atmosphere Changes


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FIGURE 3(e)Gas-freeing at 3.0 hr (10800 seconds), 2.0 Atmosphere Changes

Appendix 1, Figure 4 shows the averaged oxygen concentrations by mass during the inerting and gas-freeing

operations in the ballast tank. The values in Appendix 1, Figure 4 were obtained by averaging the oxygenconcentration at every discrete cell over the entire ballast tank at each time step.

FIGURE 4Averaged Oxygen Concentrations

0.00

0.05

0.10

0.15

0.20

0.25

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Time of discharge, (hour)

Oxygenmas

sfraction

Gas-freeing

Inerting

0.233

0.032


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7 Conclusions

Using a computational fluid dynamics (CFD) software package, two sets of simulations were performed:

one for the inerting and one for gas-freeing in a ballast tank. Despite the complex structures and boundaryconditions of the tank, the full-scale 3D simulations provided the timeline concentrations of gaseous

compositions for any location in the ballast tank. For gas-freeing, the simulation results showed that threehours of operation were sufficient to replace the atmosphere inside of the ballast tank with fresh air.

Similar results were also found for the inerting operation, in which the air was completely replaced by theinert gas after three hours of operation.

The simulation results can be used to confirm whether or not the arrangement of the discharge pipe and the

system capacity are effective for gas replacement. In this analysis, the arrangement of the discharge pipeprevented the creation of pockets of gases which may be difficult to replace during the inerting or gas-freeing operation. In any case, the operating manual should indicate that portable oxygen detectors are to

be used to verify the condition of the tank atmosphere prior to personnel entry.


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Appendix 2: Pump Certification (4-6-1/7.3 of the ABS Rules for Building and Classing Steel Vessels)

A P P E N D I X 2 Pump Certification(4-6-1/7.3 of the ABS Rules for Building and

Classing Steel Vessels)

The requirements in this Appendix are reprinted verbatim from 4-6-1/7.3 of the Steel Vessel Rulesfor theconvenience of users of this Guide.

The latest requirements in 4-6-1/7.3 of the Steel Vessel Ruleswill take precedence over requirements inthis Appendix.

7.3 Pumps

7.3.1 Pumps Requiring Certification

The pumps listed below are to be certified by a Surveyor at the manufacturers plants:

i) Pumps for all vessels (500 gross tonnage and over):

Fuel oil transfer pumps

Hydraulic pumps for steering gears (see also 4-3-4/19.5), anchor windlasses, controllablepitch propellers

Fire pumps, including emergency fire pumps

Bilge pumps

Ballast pumpsii) Pumps associated with propulsion diesel engine and reduction gears (for engines with

bores > 300 mm only):

Fuel oil service pumps, booster pumps, etc.

Sea water and freshwater cooling pumps

Lubricating oil pumps

iii) Pumps associated with steam propulsion and reduction gears:

Fuel oil service pumps

Main condensate pumps

Main circulating pumps

Main feed pumps

Vacuum pumps for main condenser


iv) Pumps associated with propulsion gas turbine and reduction gears:

Fuel oil service pumps



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Appendix 2 Pump Certification (4-6-1/7.3 of the ABS Rules for Building and Classing Steel Vessels)

v) Cargo pumps associated with oil carriers, liquefied gas carriers and chemical carriers.

vi) Pumps associated with inert gas systems:

Fuel oil pumps for boilers/inert gas generators

Cooling water pumps for flue gas scrubber

7.3.2 Required Tests

The following tests are to be carried out at the manufacturers plant in the presence of the Surveyor.

7.3.2(a) Hydrostatic Tests. The pumps are to be hydrostatically tested to a pressure of at least1.5P, where P is the maximum working pressure of the pump. If it is desired to conduct thehydrostatic test on the suction side of the pump independently from the test on the discharge side,the test pressure on the suction side is to be at least 1.5Ps, where Ps is the maximum pressureavailable from the system at the suction inlet. In all cases, the test pressure for both the suction andthe discharge side is not to be less than 4 bar.

7.3.2(b) Capacity Tests. Pump capacities are to be checked with the pump operating at designconditions (rated speed and pressure head). For centrifugal pumps, the pump characteristic (head-

capacity) design curve is to be verified to the satisfaction of the Surveyor. Capacity tests may bewaived if previous satisfactory tests have been carried out on similar pumps.

Documents

IGS Ballast Tanks Guide_e-May12