1、 Guide for Hydrocarbon Gas Blanket System GUIDE FOR HYDROCARBON BLANKET GAS SYSTEM JULY 2014 American Bureau of Shipping Incorporated by Act of Legislature of the State of New York 1862 Copyright 2014 American Bureau of Shipping ABS Plaza 16855 Northchase Drive Houston, TX 77060 USA ii ABSGUIDE FOR
2、HYDROCARBON GAS BLANKET SYSTEM .2014 Foreword Foreword ABS has been requested by the industry and regulatory bodies to provide guidelines to address the arrangements where hydrocarbon produced gas is used as a blanketing gas to maintain a non-explosive atmosphere inside the cargo storage tanks of AB
3、S Classed floating production units. This Guide has been written for worldwide application and as such, compliance with individual requirements may require comprehensive data, analyses and plans to be submitted to demonstrate the adequacy of the system. ABS acknowledges that there is a wide range of
4、 documents that may be required for submittal to satisfy this type of blanketing system. It is not the intention of this Guide to impose requirements or practices in addition to those that have previously proven satisfactory in similar situations. ABS currently has requirements for tank blanketing s
5、ystems using produced gas in 3-5/5.3 of the ABS Rules for Building and Classing Facilities on Offshore Installations. Design and installation requirements presented in this Guide are based on existing industry practice and criteria employed by ABS in the review of such systems that are deemed to pro
6、vide an adequate level of safety equivalent to traditional “Inert Gas Systems”. The application of this Guide by ABS will not seek to inhibit the use of any technological approach that can be shown to produce an acceptable level of safety. With the use of hydro carbon blanketing systems, oxygen is e
7、liminated from cargo tanks via the use of produced gas, forming an atmosphere within the tank, saturated with hydrocarbon to a level above the UEL, at which combustion cannot be supported (too “rich” to burn). Advantages to a HC blanketing system are (1) using a medium which is readily available in
8、large volumes which can continuously protect a multitude of large tanks, (2) evaporation in the cargo tank is minimal and the displaced gas from the tanks can be easily recovered resulting in a safe closed system which enable substantial reduction in volatile organic compound (VOC) emissions to the
9、atmosphere. However, one of the disadvantages of using a HC blanketing system is that an Inert Gas (IG) blanket system must be kept as backup to the HC blanketing system, should the supply of the HC blanketing medium become unavailable Currently more than 20 offshore production platforms world-wide
10、are using hydrocarbon gas for tank blanketing and ABS expects more to come as this system is becoming a standard in the industry. This Guide is to be used in conjunction with other ABS Rules and Guides, as specified herein. This Guide becomes effective on the first day of the month of publication. U
11、sers are advised to check periodically on the ABS website www.eagle.org to verify that this version of this Guide is the most current. We welcome your feedback. Comments or suggestions can be sent electronically by email to rsdeagle.org. ABSGUIDE FOR HYDROCARBON GAS BLANKET SYSTEM .2014 iii Table of
12、 Contents GUIDE FOR HYDROCARBON BLANKET GAS SYSTEM CONTENTS SECTION 1 General 1 1 Scope and Applicability . 1 3 Plans and Data to be Submitted . 1 3.1 Documents Required for Review . 1 3.3 Supporting Documentation 1 5 Governmental Authority 2 SECTION 2 Definitions, References, Acronyms and Abbreviat
13、ions 3 1 Definitions . 3 3 References 4 3.1 ABS Referenced Rules 4 3.3 References 4 5 Acronyms and Abbreviations 5 SECTION 3 Recognition of Risk Based Techniques to Justify Alternatives . 6 1 General . 6 3 Application 6 5 Submittals . 7 7 Risk Evaluation Methodology . 7 9 Identification of Hazards .
14、 7 11 Other Requirements 8 SECTION 4 System Design . 9 1 Basic Requirements 9 3 Hydrocarbon Gas for Tank Blanketing 9 3.1 Oxygen Content 9 5 Materials 9 7 Inert Gas System 9 9 Tank Blanketing-Venting Capacity and Arrangement . 9 9.1 General 9 9.3 System Capacity and Calculations 10 9.5 Hydrocarbon B
15、lanket Gas Recovery/Disposal . 10 iv ABSGUIDE FOR HYDROCARBON GAS BLANKET SYSTEM .2014 11 Piping System . 10 11.1 General 10 11.3 Piping Specification Breaks . 10 11.5 Pressure Control Valves (PCVs) . 11 11.7 Shutdown Valves (SDVs) . 11 11.9 Interlocked Key Operated Valves 11 13 Instrumentation . 11
16、 13.1 Electrical Installations in Hazardous Areas 11 13.3 Instrumentation and Control System 11 SECTION 5 Special Considerations for Single Tanks Fitted in the Hull and Containing Low Flash Point Flammable Liquids Flash Point of 60C (140F) or less 13 1 Application . 13 3 Tank Arrangement Considerati
17、ons . 13 5 Tank Blanketing System Considerations 13 SECTION 6 Fire Protection 14 1 Fire Suppression System 14 3 Fire and Gas Detection . 14 SECTION 7 Manuals . 15 1 Operating Manuals 15 ABSGUIDE FOR HYDROCARBON GAS BLANKET SYSTEM .2014 1 Section 1: General SECTION 1 General 1 Scope and Applicability
18、 This Guide applies to floating production installations equipped for storage of liquid hydrocarbons, where hydrocarbon gas is used for tank blanketing as permitted in 3-5/5.3 of the ABS Rules for Building and Classing Facilities on Offshore Installations (Facilities Rules). Blanketing systems emplo
19、yed in crude storage tanks and slop tanks are to comply with the requirements in Section 4 of this Guide. Blanketing systems employed in a single tank containing low flash point flammable liquid flash point of 60C (140F) or less, such as methanol tanks built as a hull or integral tanks are to comply
20、 with the special considerations in Section 5 of this Guide. 3 Plans and Data to be Submitted 3.1 Documents Required for Review i) Document showing standard construction details for piping systems. ii) Arrangement showing the location of the liquid hydrocarbon storage hull tanks. iii) Process and in
21、strumentation diagrams of the hydrocarbon gas blanket system clearly indicating connection to: a) Cargo tanks system, b) Inert Gas system, c) Venting System; and, d) Cargo tank vents recovery system, as applicable iv) Cargo tank venting system, purging and gas freeing systems, including details and
22、setting of the pressure/vacuum valves (relief valves). v) Cause and Effect matrix and Safety Analysis Function Evaluation (S.A.F.E.) charts for the system. vi) Since the hydrocarbon blanket gas system is a part of the topside process system, the same is to comply with safety system requirements in 3
23、-3/13.3, “Safety System” and Chapter 3, Section 7, “Instrumentation and Control Systems” of the Facilities Rules and API 14C, regardless of the Class Notation of the unit. Applicable process P or, ii) Purging and gas-freeing operations The cargo tanks are to be previously purged with inert gas when
24、hydrocarbon gas is used for tank blanketing. 9 Tank Blanketing-Venting Capacity and Arrangement 9.1 General The Hydrocarbon blanket gas system is to be interconnected to the tank venting system and the inert gas system. The following conditions are to be complied with: i) The hydrocarbon blanket gas
25、 system is not to interfere with the proper operation of the tank venting system. ii) The tank venting system is to be designed and constructed in accordance with 5C-1-7/11 of the Steel Vessel Rules. See also 3-5/5.5ii) of the Facilities Rules. Section 4 System Design 10 ABSGUIDE FOR HYDROCARBON GAS
26、 BLANKET SYSTEM .2014 iii) The hydrocarbon blanket gas system may be considered as the primary means for tank venting. The setting of the pressure control valves (PCVs) required in 4/11.5 is to be less than the pressure setting of the venting arrangements required in 5C-1-7/11 of the Steel Vessel Ru
27、les. iv) Release of the hydrocarbon blanket gas through the Pressure/vacuum relief valves fitted on the tanks is to be connected to the low-pressure flare header, or vented to a safe location as required in 5C-1-7/11.13 of the Steel Vessel Rules. See also 3-5/5.5i) of the Facilities Rules. v) Releas
28、e to the atmosphere of the hydrocarbon blanket gas through the cargo vent mast in 5C-1-7/11.17 of the Steel Vessel Rules may be considered acceptable provided the vent outlet is located at a height and horizontal distance that allow safe dispersion of the hydrocarbon gases. The vent outlet location
29、is not to be less than 5C-1-7/11.17iii) of the Steel Vessel Rules and is to be justified in a gas dispersion analysis. Worst-case atmospheric conditions are to be used for gas dispersion calculations. Dispersion calculations are normally to assume still air and low vent velocity as worst-case condit
30、ion. vi) The hydrocarbon blanket gas system is to be isolated from the inert gas piping when the inert gas system is in operation and vice versa. Interlocked key operated valves are to be provided to ensure proper alignment and complete isolation between the two systems. 9.3 System Capacity and Calc
31、ulations 9.3.1 Capacity The hydrocarbon gas blanket system is to be capable of delivering the blanket gas to the tanks at a rate of at least 125% the maximum rate of discharge capacity of the facility expressed as a volume flow rate. 9.3.2 Calculations Hydraulic calculations are to be submitted to s
32、ubstantiate the adequacy of the tank blanketing-venting system. The calculations are to consider possible failure scenarios in the system and undesirable events in the hydrocarbon blanket source (process system), such as gas blow-by. 9.5 Hydrocarbon Blanket Gas Recovery/Disposal The excess of hydroc
33、arbon blanket gas and the gas coming from the boil off and/or loading of crude oil are to be led to: i) The topside process system for gas recovery; and/or, ii) The low pressure flare system (LP Flare) for gas disposal. Gas recovery to topside process system is strongly encouraged as it provides env
34、ironmental protection against the release of Volatile Organic Compound (VOC) to the atmosphere and hydrocarbon gas recycling. 11 Piping System 11.1 General i) The hydrocarbon blanket gas piping is not to be routed through gas safe areas or enclosed spaces. ii) The hydrocarbon blanket gas piping is t
35、o be grounded in accordance with the requirements of 4-6-2/9.15 of the Steel Vessel Rules. iii) Additional requirements may be necessary as a result of the HAZOP studies at the discretion of ABS and the Governmental Authorities. 11.3 Piping Specification Breaks The design criteria of the hydrocarbon
36、 blanket gas inlet piping starting from, and including, the SDV to the tanks is considered part of the marine system and are to meet the Part 4, Chapter 6 of the Steel Vessel Rules or Part 4, Chapter 2 of the MODU Rules, as applicable. Please also refer to 3-5/5.1 of the Facilities Rules. Likewise,
37、hydrocarbon blanket gas outlet piping is considered part of the marine system up to, and including, the SDV. Section 4 System Design ABSGUIDE FOR HYDROCARBON GAS BLANKET SYSTEM .2014 11 11.5 Pressure Control Valves (PCVs) The pressure of the hydrocarbon blanket gas supply and tank outlet is to be re
38、gulated by pressure control valves to maintain the design pressure of the hydrocarbon blanketing gas in the tanks. 11.7 Shutdown Valves (SDVs) i) A fast closing shutdown valve is to be provided at the hydrocarbon blanket gas supply piping, located upstream and next to the PCV, in order to provide is
39、olation of the tanks from the hydrocarbon blanket gas supply source. ii) A fast closing shutdown valve is to be provided at the hydrocarbon blanket gas release/recovery required in 4/9.5, located downstream and next to the PCV, in order to provide isolation between the tank and downstream process eq
40、uipment. 11.9 Interlocked Key Operated Valves The hydrocarbon blanket gas is to be isolated from the inert gas piping when the inert gas is in operation by means of interlocked key operated valves, as required in 4/9.1vi). 13 Instrumentation 13.1 Electrical Installations in Hazardous Areas All instr
41、umentation and electrical equipment are to be suitable for the hazardous areas where they are located. 13.3 Instrumentation and Control System 13.3.1 Monitoring Devices Means are to be provided to automatically monitor and control the following parameters: i) The pressure in each individual tank ii)
42、 The pressure in the hydrocarbon blanket gas header iii) The oxygen content at the hydrocarbon blanket gas header 13.3.2 Alarms and Shutdowns i) Audible and visual alarms are to be provided to indicate failure of the PCVs required in 4/11.5. ii) The monitoring devices in 4/13.3.1 are also to provide
43、 an audible and visual alarm in the cargo/process control rooms. The set point of the monitoring devices is to be clearly identified. The operating points are to be arranged such that the alarm is activated earlier than the safety action (shutdowns). iii) A warning alarm is to sound when the oxygen
44、analyser in 4/13.3.1iii) detects oxygen content exceeding 5% by volume. Cargo offloading operations (shutdown of cargo offloading or transfer pumps) are to be suspended when the oxygen analyzer detects oxygen content exceeding 8% by volume so as to avoid air being drawn into the tanks. Guidance or p
45、rocedures to be followed are to be included in the operating manual. See 7/1vi). iv) Automatic shutdown is to be provided for the SDV in the hydrocarbon blanket gas supply piping required in 4/11.7i) and for the hydrocarbon blanket gas system when predetermined high pressures limits are reached in p
46、ressure transmitters required in 4/13.3.1ii). v) Automatic shutdown is to be provided for the SDVs required in 4/11.7 and for the hydrocarbon blanket gas system upon actuation of the Process Emergency Shutdown (ESD) system of the facility. See 3-3/13.3.4 of the Facilities Rules. vi) A drop in pressu
47、re in the hydrocarbon blanket gas header sensed by the pressure monitoring device required by 4/13.3.1ii) is to shut down the cargo pumps and the hydrocarbon blanketing system, and the inert gas system is to be put in operation to supply inert gas into the tanks, per 4/13.3.2viii). Section 4 System
48、Design 12 ABSGUIDE FOR HYDROCARBON GAS BLANKET SYSTEM .2014 vii) Failure of the recovery system in 4/9.5i) is to automatically shut down the hydrocarbon blanket gas. viii) The inert gas system, or any other acceptable back-up blanket gas sources (i.e., gas buy back), is to be put in operation when t
49、he hydrocarbon blanket gas is shutdown. Instructions to manually start the inert gas system and change-overs procedures (inter-locked valves, etc.) in the venting system necessary to bring inert gas into the tanks are to be included in the operating manual. Refer to 7/1vi). ix) Additional requirements may be necessary as a result of the HAZOP studies at the discretion of ABS and/or the Governmental Authorities. 13.3.3 Cargo/Process Control Room Displays The monitoring devices in 4/13.3.1 and alarms and shutdowns in 4/13.3.2 are to be placed in the cargo/process control room. How
