Above-ground proprietary prefabricated oil storage tank systems

Transcription

1 CIRIA C535 London 2002 Above-ground proprietary prefabricated oil storage tank systems Teekaram A J H Sterne S Abel B Elliott C R N 6, Storey s Gate, Westminster, London, SW1P 3AU TELEPHONE FAX enquiries@ciria.org.uk WEBSITE

2 Above-ground proprietary prefabricated oil storage tank systems Teekaram A J H, Sterne S, Abel B, Elliott C R N Construction Industry Research and Information Association CIRIA 2002 C535 ISBN: Keywords environmental good practice, pollution prevention, regulation, water quality Reader interest environmental regulators and policy makers, standards producing organisations, local authorities, site operators, oil tank manufacturers, oil suppliers, contractors, tank ancillary equipment suppliers, property owners, managers Classification AVAILABILITY CONTENT STATUS USER Unrestricted Guidance based on good practice Committee guided Environmental agencies, oil tank manufacturers, oil companies specifiers and owners of oil storage tanks Published by CIRIA, 6 Storey s Gate, Westminster, London SW1P 3AU. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, including photocopying and recording, without the written permission of the copyright-holder, application for which should be addressed to the publisher. Such written permission must also be obtained before any part of this publication is stored in a retrieval system of any nature. This publication is designed to provide accurate and authoritative information in regard to the subject matter covered. It is sold and/or distributed with the understanding that neither the author(s) nor the publisher is thereby engaged in rendering a specific legal or any other professional service. While every effort has been made to ensure the accuracy and completeness of the publication, no warranty or fitness is provided or implied, and the author(s) and publisher shall have neither liability nor responsibility to any person or entity with respect to any loss or damage arising from its use. 2 CIRIA C535

3 Summary The Environment Agency report Water Pollution Incidents in England and Wales (1998) concludes that oil is a major cause of pollution in the UK, accounting for approximately 30 per cent of all water pollution incidents. In 1998 there were 5308 substantiated pollution incidents involving oil. Agency data indicate that at least 60 per cent of the major and significant incidents could have been prevented if oil storage tanks were adequately bunded. This CIRIA publication provides detailed guidance on the design, construction and use of proprietary prefabricated above-ground bunded oil storage tank systems for use in domestic, agricultural and industrial applications. Oil storage tank systems of steel or plastic construction up to litres are reviewed. The use of mobile oil storage bowsers is also included. The report also assesses the level of environmental protection offered by these types of systems against common causes of oil pollution and the preventative measures that can be taken to avoid them. It offers good practice recommendations, which are designed to minimise the risk of oil pollution. The report concludes by identifying several objectives that the oil storage industry needs to pursue. These include legislative requirements governing the manufacture of oil storage tank systems and fitting of overfill protection devices. Recommendations are also made for the development of manufacturing standards, test procedures and performance standards for overfill prevention devices. CIRIA C535 3

4 Acknowledgements This report was produced under CIRIA Research Project RP603 Above ground proprietary prefabricated oil storage tank systems. The detailed research work carried out as part of this study was undertaken by BSRIA with guidance from CIRIA. Following CIRIA s usual practice, the research was also guided by a steering group, which comprised: Mr Gordon Rose (chairman) Mr Peter Annabring Ms Carol Bowman Mr Reginald Brown Mrs Teresa Brown Mr David Campbell Mr Lawrence Coey Mr Tim Cope Miss Elspeth George Mr Simon Kernick Mr John Lovesay Mr Richard Lowry Dr Julia McDaid Mr Bob Miles Mr Bryan Ribbans Mr Jeff Spencer Mr Colin Sutherland Mr John Thomson Mr Mike Terry Mr Murray Leflaive Rose Associates Eurogauge Co Ltd Kingscourt (CAPITB Trust through the European Social Fund) BSRIA Environment Agency SEPA (SNIFFER) Harlequin Oil Tanks Ltd Joseph Ash Storage Tanks Ltd Balmoral Tanks Ltd Garnic Plant Barton Petroleum Ltd Titan Environmental Ltd The Plastics Development Centre Ltd Ledbury and Engineering Ltd Terence Barker Ltd OFTEC OFTEC WS Hunts s Oil Co Ltd CTS Western Trailers Corresponding members of the project steering group: Mr Mark Atterbury Mr C Drake Mr G Edwards Ms Susan Hancock Mr Robert Shenton Mr Mick Tye The Polymer Development Centre Neston Tank Cleaners Ltd British Standards Institute (BSI) Federation of Petroleum Suppliers Fuel Energy Services Ltd Barton Plant Ltd CIRIA s research manager for this project was Mr Craig Elliott. 4 CIRIA C535

5 The research leading to the publication of this report was funded by: Balmoral Tanks Ltd Building Services Research and Information Association (BSRIA) CAPITB Trust through the European Social Fund Construction Industry Research and Information Association (CIRIA) The Environment Agency Harlequin Oil Tanks Ltd Joseph Ash Storage Tanks Ltd Ledbury Welding and Engineering Ltd The Scottish and Northern Ireland Forum For Environmental Research (SNIFFER) Terence Barker Ltd Titan Environmental Ltd CIRIA and the authors gratefully acknowledge the support of these funding organisations and the technical help and advice provided by the members of the steering group. Contributions do not imply that individual funders necessarily endorse all views expressed in published outputs. CIRIA C535 5

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7 Contents List of figures List of tables INTRODUCTION Background Scope Structure of the report DEFINITIONS Proprietary tank systems and prefabricated bunds Primary containment Secondary containment Integrally bunded tank Mobile bunded bowsers Equipment cabinet Petroleum fuel oil classes A, C, D, E, F, G and H Head Valves Tank system capacities Puddle flange Twin-skinned construction Tank system foundation/base PREFABRICATED BUNDED STEEL OIL STORAGE TANK SYSTEMS Open bunded steel tanks General description Application Fabrication Bunds Structural support of primary tank within bund Fill pipes and connections Draw-off pipes and connections Vent pipes Tank drain Inspection hatch Enclosed bunded steel tanks General description Application Fabrication Fill pipes and connections Draw-off pipes and connections Vents CIRIA C535 7

8 3.2.7 Tank drain Inspection hatch Compartment-bunded steel tanks General description Application Fabrication Fill pipes and connections Draw-off pipes and connections Vent pipes Tank drain Inspection hatch Gravity draw-off bunded steel tanks General description Applications Fabrication Fill pipes and connections Draw-off pipes and connections Vent pipes Tank drain Inspection hatch Multi-compartment bunded tanks General description Application Fabrication Fill pipes and connections Draw-off pipes and connections Vent pipes Tank drain Inspection hatch Tanks for specialist applications Refurbished tank systems Tank system cleaning Tank system testing Tank system modification Regulations for cleaning and waste disposal INTEGRALLY BUNDED PLASTIC OIL STORAGE TANK SYSTEMS General description Application Fabrication Design and construction of plastic tanks Quality control CIRIA C535

9 5 MOBILE BOWSERS General description Application Construction Bunds Vents Baffles Fill port Inspection hatch Bowser drain Selecting a bowser Siting a bowser Dispensing fuel from bowsers Refilling of bowsers Gauges Security Manufacturing standards Maintenance OIL STORAGE TANK ANCILLARY EQUIPMENT Simple non-mechanical contents indicators The dip-stick The sight gauge Direct-reading float gauges Side-mounted floats Top tank-mounted direct-reading float gauges Remote-reading contents gauges Hydrostatic bubbler gauges Continuous-reading hydrostatic gauge Electronic contents gauges and alarms Float-operated alarms Electronic multi-level gauges and multi-level gauge and alarm systems Overfill protection alarms Ultrasonic level measurement Remote reading and radio transmission Tank management systems and distant reading Other protective devices Valves Oil filters Strainers Oil separators Tank system marking and manuals Tank system markings Tank system instruction manuals CIRIA C535 9

10 7 POLLUTION FROM OIL STORAGE TANKS - CAUSES AND PREVENTATIVE MEASURES Bund design General leakage Leaks from primary tanks and bunds Leaks from fill point connections, faulty and open valves and pumps, gravity draw-offs and pipework Leakage from sight gauges, dispensing pumps and nozzles Overfilling Lack of care exercised during refilling Unsupervised deliveries Inadequate illumination Poor location of overfill vent, contents gauge oil level indicators Poor reliability of contents gauges/oil level indicators Absence of tank overfill or bund alarm Absence of overfill cut-out valve Impact damage Vandalism Fire Rainwater accumulation and disposal Poor siting and installation Misuse TANK SELECTION, SITING, INSTALLATION, INSPECTION AND MAINTENANCE, REFILLING Selection of oil storage tank systems Location and size of site Application Siting of oil storage tank systems Above-ground oil storage tank systems Bunding of oil storage tanks Oil supply pipework General considerations Vehicular access Installation Installation instruction Tank system foundations, supports and treatments Testing tank systems post-installation Commissioning Connecting pipework Multiple storage tank installations Storage temperatures Inspection and maintenance Painting Repairing leaks Refilling CIRIA C535

11 9 PROPRIETARY PREFABRICATED BUNDED OIL STORAGE TANK SYSTEMS GOOD PRACTICE RECOMMENDATIONS Tank system design and construction General requirements Secondary containment systems Pipework and connections Fill pipes and connections Draw-off pipes and connections Vent pipes Tank drain Inspection hatch Overfill protection General requirements Sight gauges Float gauges Electronic gauges Security Tank markings Testing Siting Installation and commissioning Dispensing fuel Refilling Inspection and maintenance Inspection Maintenance User information Tank disposal MOBILE BUNDED BOWSERS GOOD PRACTICE RECOMMENDATIONS Bowser design and construction Pipework and connections Fill ports and connections Draw-off pipes and connections Vents Drains Overfill protection Security Tank markings Testing Siting Dispensing fuel Refilling Inspection and maintenance Annual inspection and maintenance CIRIA C535 11

12 Preventative maintenance User information Bowser disposal LONG-TERM RECOMMENDATIONS REFERENCES APPENDICES A1 FILL POINT PROTECTION A2 PIPEWORK SIZES CIRIA C535

13 Figures Figure 2.1 Detail of a common form of twin-skinned construction for steel tanks 23 Figure 3.1 Example of an open bunded rectangular storage tank Figure 3.2 Example of an open bunded horizontal cylindrical storage tank Figure 3.3 Example of an open bunded vertical cylindrical storage tank Figure 3.4 Example of a totally enclosed bunded storage tank for direct connection to fixed surfaces eg boiler plant Figure 3.5 Example of a totally enclosed bunded storage tank for vehicle refuelling applications Figure 3.6 Example of a partially enclosed bunded storage tank Figure 3.7 Example of a partially enclosed bunded storage tank Figure 3.8 Example of a gravity draw-off partially enclosed bunded storage tank 37 Figure 3.9 Example of a gravity draw-off totally enclosed rectangular bunded storage tank Figure 3.10 Example of a partially enclosed multi-compartment bunded storage tank Figure 3.11 Example of a custom-built storage tank system Figure 4.1 Example of a plastic totally enclosed bunded storage tank Figure 4.2 Schematic of the major components of a rotational moulding rig Figure 4.3 Example of a plastic, slimline, totally enclosed bunded oil storage tank showing typical strengthening of the primary tank (sectional view).. 49 Figure 5.1 Example of a bowser system specifically designed for transportation in an excavator bucket Figure 5.2 Example of the above bowser system in transit Figure 5.3 Example of an all-steel bunded bowser system ( litres) Figure 5.4 Example all-steel bunded bowser system ( litres) Figure 5.5 Example steel bunded bowser system with a plastic primary tank ( litres) Figure 5.6 Example steel bunded plastic primary tank bowser ( litres) 56 Figure 6.1 Example of sight gauges Figure 6.2 Example combined vent and float gauge Figure 6.3 Example of an ultrasonic gauge Figure 6.4 Example of an overfill cut-out valve Figure 6.5 Further example of an overfill cut-out valve Figure 7.1 Example of a failure that may occur during the bund overflow test (this type of failure would not occur in an OFTEC-approved tank) Figure 7.2 Fill point connection to tanker, example of bad practice Figure 7.3 Fill point connection to tanker, example of good practice Figure 7.4 Example of a standard brass gate valve illustrating areas where leaks commonly occur Figure A1.1 Fill point protection: source BS 799 Part CIRIA C535 13

14 Tables Table 4.1 Characteristics of MDPE used in rotationally moulded oil storage tanks Table 6.1 Oil storage tank overfill protection devices Table 7.1 Pollution from oil storage tanks - causes and preventative measures Table 8.1 Outdoor, indoor and roof installations Table 8.2 Tank system support construction and treatment Table 8.3 Temperature requirements for oil storage Table A2.1 Filling pipes and connection sizes for petroleum oils classes A2, C, D, E, F, G and H: source BS 799 Part Table A2.2 Oil tank drain valves: minimum clearway openings: source BS 799 Part CIRIA C535

15 1 Introduction 1.1 BACKGROUND The use of proprietary prefabricated oil storage tank systems for above ground oil storage is now becoming increasingly widespread for domestic, agricultural, commercial and industrial applications. The term proprietary tank systems was introduced in CIRIA Report 163 Construction of bunds for oil storage tanks as a generic term to describe the vast range of prefabricated oil storage tank systems that incorporate an additional containment facility manufactured as an integral part of the primary containment tank. In recent years there has been a great deal of confusion, among buyers and regulators alike, about these products and whether they meet the environmental agencies guidelines. Because of the wide range of designs, innovations and specifications available it is difficult to determine which systems are designed to provide adequate environmental protection against oil pollution. It must be recognised that proprietary tank systems are different from tanks with conventional in-situ bunds constructed from reinforced masonry or concrete. However, it is possible that well designed and manufactured products can achieve the same level of environmental protection as conventionally bunded tanks, provided that they are correctly sited, maintained and operated in accordance with the manufacturer s instructions, and with regard to current good practice for pollution prevention. The relevant legislation for oil tank design and installation varies throughout the UK. A summary is given in Section The situation in England is currently being rationalised through the production of the Control of Pollution (Oil Storage) Regulations (England) 2001 by the Department of the Environment Food and Rural Affairs (DEFRA). These regulations will to come into force in March 2002 and cover all commercial and industrial sites and require that all above ground oil storage facilities are bunded, with the exception of: the storage of waste oil (covered by the Waste Management Licensing Regulation 1994) oil stored in containers contained within a building or wholly underground containers of a capacity of 200 litres or less oil stored on premises used mainly or wholly as private dwelling if the container is 3500 litres or less (oil storage will be covered under revisions of the Building Regulations), for refining oil, or for the onward distribution of oil to other places oil stored on any farm if the oil is for use in connection with agriculture within the meaning of the Agriculture Act It is likely that similar regulations will be implemented in Scotland and Wales in due course. CIRIA C535 15

16 1.2 SCOPE This report provides detailed guidance on good practice in the design, construction and use of above ground proprietary prefabricated bunded oil storage tank systems in the United Kingdom for domestic, agricultural, commercial and industrial applications. It also assesses the level of environmental protection offered by these systems against common causes of oil pollution incidents and the preventative measures that can be taken to avoid them. The study is restricted to above ground proprietary prefabricated bunded oil storage tank systems constructed of steel or plastic with capacities up to litres and mobile oil storage bowsers. The report provides independent guidance for users and regulators on the level of environmental protection offered by proprietary prefabricated tank systems. It is designed to complement The control of Pollution (Oil Storage) (England) Regulations 2001; environmental agencies Pollution Prevention Guidelines document PPG2 (1998); The Control of Pollution (Silage, Slurry And Agricultural Fuel Oil) Regulations 1991 and as amended 1997; and the relevant British Standards and the Building Regulations. 1.3 STRUCTURE OF THE REPORT The report is divided into 11 chapters, and includes a list of definitions to clarify commonly used terms (Chapter 2). A review of current design and manufacturing techniques for prefabricated bunded steel oil storage tank systems is given in Chapter 3. Those that are reviewed include: conventional open bunded steel tank systems, enclosed bunded steel tank systems, self bunded steel tank systems, gravity draw-off bunded steel tank systems, multicompartment bunded steel tank systems, refurbished steel tank systems and steel tanks systems for specialist applications. Chapter 4 covers the design and construction of integrally bunded plastic oil storage tank systems. Chapter 5 covers mobile bowsers. The main features of each type of oil storage facility are reviewed. These include: application, fabrication, construction of bunds, structural support of primary tank within the bund, fill pipes and connections, draw-off pipes and connections, vent pipes drains and inspection hatches. Where relevant, reference is made to appropriate manufacturing standards. Chapter 6 reviews the different types of oil storage tank ancillary equipment available for protection against overfilling and spillage. These include: simple non-mechanical contents indicators direct reading float gauges remote reading contents gauges electronic contents gauges distant reading, remote reading and radio transmission tank management system other protective devices. Typical causes of oil storage tank related pollution and preventative measures that can be taken to avoid them are covered in Chapter 7. This examines bund design, the factors responsible for general leakage, overfilling, jetting, impact damage, vandalism, fire, rainwater accumulation and disposal. 16 CIRIA C535

17 Guidance on tank selection, siting, installation, inspection and maintenance of proprietary prefabricated oil storage tank systems is covered in Chapter 8. Chapters 9 and 10 provide a series of good practice recommendations for proprietary bunded oil storage tank systems and mobile bowsers. Specific guidance is given in the following areas: system design and construction pipework and connections overfill protection security tank markings tank system testing siting, installation and commissioning dispensing fuel and tank refilling inspection and maintenance user information tank disposal. The recommendations are designed to minimise the risk of oil pollution and to be implemented easily. The report concludes by identifying long term recommendations that the oil storage industry needs to pursue in order to sustain a reduction in oil pollution incidents. These are provided in Chapter 11. CIRIA C535 17

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19 2 Definitions 2.1 PROPRIETARY TANK SYSTEMS AND PREFABRICATED BUNDS The term proprietary tank system was introduced in CIRIA Report 163 Construction of bunds for oil storage tanks (CIRIA 1997) as a generic term to describe the large range of prefabricated oil storage tank units that incorporate an additional containment facility manufactured as an integral part of the primary containment tank. In recent years there has been confusion among buyers, users and regulators alike about these products and whether they offer the same degree of environmental protection as a conventional, in-situ constructed, bund installation. There are many designs, innovations and specifications of proprietary tank systems available that offer a wide range of features. Since the systems are prefabricated, it is difficult to determine which products provide an acceptable level of protection against loss of oil (for whatever reason) for an acceptable cost and those systems that do not. It must be recognised that proprietary tank systems are different from tanks with in-situ bunds constructed from reinforced masonry or concrete. However it is possible that well designed and manufactured products can achieve or exceed the level of environmental protection provided by conventional bunds, provided they are correctly manufactured, sited, installed and operated in accordance with manufacturers instructions and with regard to current good practice for pollution prevention. They may achieve this in different ways. A prefabricated bund is an additional containment system in which a primary tank and its associated pipework are contained (apart from draw-off pipes to fixed equipment and extended fill and vent pipes installed in accordance with BS 5410 parts 1, 2 and 3). Its purpose is not only to contain any oil that might spill or leak from the tank but also from the associated pipework. It is designed to hold the contents of the tank plus a defined margin (at least 10 per cent of the maximum contents of the primary tank) in the event of the tank leaking and to contain any leaks. Note: some uncertainty has been expressed as to whether a prefabricated tank system with double skinned construction satisfies the above criteria for secondary containment. For it to be considered satisfactory, the secondary containment must be able to contain at least 110 per cent of the primary tank brim-full contents and losses from associated pipework and valves in the event of a leak or overspill in the primary tank system, and be vented to the atmosphere (see Section 3.3: Self-bunded tanks for specification of satisfactory tank). 2.2 PRIMARY CONTAINMENT The primary container of a tank system is defined, in CIRIA Report 163 Construction of bunds for oil storage tanks, as the container within which the material (oil) is stored eg tank, drum together with any outer container that: a b c d provides structural support to the inner container, or is connected to it structurally, or relies on the same structural supports, or is situated very close to it. CIRIA C535 19

20 The above definition means that, according to CIRIA Report 163, most proprietary tank systems detailed in this report could be regarded as high specification primary containers because they have an outer container that may be one or all of a to d above. This is the fundamental difference between traditional tank systems that require in-situ bunds designed and constructed in accordance with CIRIA Report 163, and the proprietary tank systems covered in this report. The proprietary tank systems covered by this report must have an additional containment for the contents of the primary tank and associated pipework and ancillary equipment and, for the purposes of this report, the term bund is used to describe this additional containment capability. A conventional in-situ constructed bund is used to describe secondary containment as defined in CIRIA Report 163. To summarise: For proprietary tank systems the prefabricated bund provides additional, local, containment for the primary tank and associated pipe work in one manufactured item. For conventional tanks, an in-situ constructed bund provides secondary containment (this may be local or remote), which is separately constructed on site. 2.3 SECONDARY CONTAINMENT CIRIA Report 163 defines secondary containment as a containment system that is capable of preventing the escape of material (oil) to the aquatic environment in the event of failure of the primary storage or container. It should be noted that a doubleskinned primary container will not, in itself, provide secondary containment. 2.4 INTEGRALLY BUNDED TANK A tank where the bund forms an integral part of the tank. As detailed above, the proprietary tank systems detailed in this report could be regarded as high specification primary containers under the definitions provided in CIRIA Report 163, because their additional secondary containment for the primary tank and associated pipework is an integral part of the tanks system. This is the fundamental difference between properly designed and constructed conventional tank systems using in-situ bunds and proprietary tank systems that may not require in-situ bunds. For the purposes of this report the term bund is used to describe the secondary containment associated with a prefabricated tank system. In CIRIA Report 163 the secondary containment systems described are conventional in-situ constructed bunds. These proprietary tank systems are classified as follows: A: Open bunded: A tank, located within an open bund (ie the top of the bund is not enclosed and may allow the ingress of rainwater or debris) where the bund forms an integral part of the tank (see Figure 3.1). B: Partially enclosed bunded: A tank, located within a bund that has an enclosure to prevent the ingress of rainwater and debris into the bund. The top of the tank is not enclosed within the bund and the bund forms an integral part of the tank (see Figure 3.6). C: Totally enclosed bunded: A tank located within a bund that has a lid to prevent the ingress of rainwater and debris to the bund. The bund forms an integral part of the tank (see Figure 3.4). 20 CIRIA C535

21 D: Compartment-bunded: A tank system comprising a primary tank and bund compartment where four sides of the primary tank are of twin-skinned construction (ie the bottom, sides and one end) and additional capacity for the bund (ie to ensure that the bund has a capacity of at least 110per cent of the primary tank) is provided at one end of the tank system (see Figure 3.7). E: Gravity-fed bunded: A tank system designed for use with gravity draw-off applications where other forms of tank systems are not suitable. The primary tank is elevated on a support frame to provide sufficient head for the application (see Figure 3.8). F: Multi-compartment bunded: A tank designed with several compartments for storing fuel oil that may be of different grades. If the compartments are hydraulically linked, the volume of the overfill compartment should be designed to hold at least 110 per cent of the total volume of the tank. Separate fill, vent and draw-off pipes should be provided for each compartment. (Refer to guidance on bunds in CIRIA Report 163 for further guidance on the sizing of bunds containing multiple tanks) (see Figure 3.10). 2.5 MOBILE BUNDED BOWSERS A mobile oil storage tank with integral bund that cannot move under its own power, which is specifically designed to contain oil during transport and is fitted with oil dispensing facilities. 2.6 EQUIPMENT CABINET An equipment cabinet is a cabinet containing pumps and fill, or draw-off, pipe work (or both), which includes a drip tray that can contain the contents of the pump and pipe work plus 10 per cent. This may be separate from the bund and should be enclosed and secured when not in use. 2.7 PETROLEUM FUEL OIL CLASSES A, C, D, E, F, G, AND H Class A2: Road diesel (ultra low sulphur diesel) suitable for diesel engine use. Class C1: Paraffin a light distillate grade of fuel oil used with unflued domestic appliances. Class C2: Kerosene a light distillate grade used in domestic applications eg central heating hot water boilers. Used also in other industrial processes eg furnaces, requiring a low sulphur content distillate oil fuel. Class D: Gas oil (red diesel) suitable for diesel engine use in agricultural and off highway applications in engines that can perform on a fuel of specified ignition quality. Also widely used in commercial space heating installations, food processing and agricultural drying processes, small furnaces and other industrial processes requiring a distillate fuel. Class E: Light fuel oil used for industrial boilers for central heating and hot water production. Used also in some drying processes. Some diesel engines can use this with appropriate configuration and fuel conditioning. Class F: Medium fuel oil used for general industrial purposes including the firing of furnaces, boilers and air heaters where suitable storage, handling and burner preheating arrangements for a heavier residual oil are available. Some diesel engines can use this with appropriate configuration and fuel conditioning. CIRIA C535 21

22 2.8 HEAD 2.9 VALVES Class G and H: Heavy fuel oils used for firing large industrial furnace and boilers where the necessary storage and heating arrangements are installed. Some diesel engines can use this with appropriate configuration and fuel conditioning. Should be stored and handled with plant equipped with appropriate heating facilities. That pressure, exerted by a liquid (in this case oil) on the bottom, sides and top of the tank system. A variety of valves may be associated with oil storage tank systems. These include: Check/non-return valve: a valve designed to prevent spillage of oil by acting against the head placed upon the valve by the product at the bottom of the tank (see Section 6.7.1). Fire valve: an automatically operated, quick closing valve held open by any one of the methods described in BS799 Part (see Section 6.7.2). OFTEC have developed a standard (OFS E103) for the construction of fire valves. Overfill cut-out valve: a valve designed to stop further refilling of the primary tank in a tank system when it is full. Also known as an anti-spillage valve. See Section OFTEC have developed a standard (OFS E105) for the construction of overfill cut out valves. Drain valve: a valve designed to allow the removal of sludge or water (see Section 3.1.9). Recommendation is that this is via an internal suction pipe fitted through the tank top, sludge and water are pumped out. Ball valve: a valve comprising a spherical acting unit as detailed in Section Gate valve: a valve where the acting unit is a gate that may be used to vary the flow of a liquid (see Section 6.7.1). Draw-off valve: a valve used to regulate the flow of oil from a storage tank system. Isolation valve: a valve used to prevent the flow of oil from the primary tank, or tanks, in an oil storage tank system TANK SYSTEM CAPACITIES In describing oil storage tank systems, several terms are used to describe the capacity (ie the amount that can be contained within a vessel). These include: Overfill capacity: The capacity provided within a bund to ensure containment of oil (or other fluids) in the event of an overfill, in addition to the capacity provided within the bund to contain the brimful capacity of the primary tank. Bund capacity: The volume of fluid that may be contained within the bund of a storage tank system (the bund capacity should be at least 110 per cent of the brimful capacity of the primary tank). Brimfull capacity: The maximum volume of fluid held by a primary tank without overflowing. Nominal capacity: The maximum volume of fluid that may be stored in the tank as identified by the tank manufacturer (this should be no greater than 97 per cent of the brimfull capacity). 22 CIRIA C535

23 2.11 PUDDLE FLANGE A flange welded into the wall of the bund to secure a low-level gravity draw-off TWIN-SKINNED CONSTRUCTION Twin-skinned construction utilises two closely spaced layers of material (eg steel, glass reinforced plastic) to form the walls of a tank system. In the construction of twin skinned metal tank systems, a common approach is to plug weld a secondary skin to the inner skin of the tank at specified points. The interstitial space between the inner skin and the outer skin is generally less than 5 mm. See Figure 2.1 for detail. See Section 3.3 for further information on the use of this form of construction in the bunding of above ground proprietary prefabricated oil storage tank systems. Outer steel skin Inner steel skin 25mm dia (variable) Weld Welds < 5mm Figure 2.1 Detail of a common form of twin-skinned construction for steel tanks 2.13 TANK SYSTEM FOUNDATION/BASE An appropriately designed and constructed impermeable platform upon which a tank system is mounted (see Section 8.3.2). CIRIA C535 23