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OISD-STANDARD - 112 First Edition Amended edition, October, 2002 FOR RESTRICTED CIRCULATION ONLY

SAFE HANDLING OF AIR-HYDROCARBON MIXTURES AND PYROPHORIC SUBSTANCES

Prepared by:

Committee on Process Design and Operating Philosophies

OIL INDUSTRY SAFETY DIRECTORATE 7th Floor, New Delhi House

27-Barakhamba Road New Delhi - 110001.

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NOTES

OIL INDUSTRY SAFETY DIRECTORATE publications are prepared for use in the Oil and gas industry under Ministry of Petroleum and Natural Gas. These are the property of Ministry of Petroleum and Natural Gas and shall not be reproduced or copied and loaned or exhibited to others without written consent from OISD.

Though every effort has been made to assure the accuracy and reliability of data contained in these documents, OISD hereby expressly disclaims any liability or responsibility for loss or damage resulting from their use. These documents are intended only to supplement and not to replace the prevailing statutory requirements.

Note 1 in superscript indicates the changes / modifications / additions as approved in 17th Safety Council Meeting held in July, 1999

Note 2 in superscript indicates the changes / modifications / additions as approved in 20th Safety Council Meeting held in October, 2002.

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FOREWORD The Oil Industry in India is 100 years old. As such variety of practices have been in vogue because of collaboration / association with different foreign companies and governments. Standardisation in design philosophies and operating and maintenance practices at a national level was hardly in existence. This, coupled with feed back from some serious accidents that occurred in the recent past in India and abroad, emphasized the need for the industry to review the existing state of art in designing, operating and maintaining oil and gas installations. With this in view, the Ministry of Petroleum & Natural Gas, in 1986, constituted a Safety Council assisted by Oil Industry Safety Directorate (OISD), staffed from within the industry, in formulating and implementing a series of self regulatory measures aimed at removing obsolescence, standardising and upgrading the existing standards to ensure safer operations. Accordingly, OISD constituted a number of Functional Committees of experts nominated from the industry to draw up standards and guidelines on various subjects. The present document on Safe Handling of Air-Hydrocarbon Mixtures and Pyrophoric Substances was prepared, by the Functional Committee on Process Design and Operating Philosophies, based on the accumulated knowledge and experience of Industry members and the various national and international codes and practices. It is hoped that provisions of this standard if implemented objectively, may go a long way to improve the safety and reduce accidents in Oil and Gas Industry. Suggestions are invited from the users for further improvement after it is put into practice. Suggestions for amendments to this standard should be addressed to,

The : Co-ordinator,

Committee on “Process Design and Operating Philosophies”, Oil Industry Safety Directorate,

7th Floor, New Delhi House 27-Barakhamba Road New Delhi - 110001.

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COMMITTEE ON

PROCESS DESIGN AND OPERATING PHILOSOPIES List of Members

-------------------------------------------------------------------------------------------------------------------------- S. No. Name Designation & Organisation Position in Committee -------------------------------------------------------------------------------------------------------------------------- S/Shri 1. W. D. Lande Dy. Gen. Mgr., HPCL Member, Leader 2 V.S. Save Ch. Manager, HPCL Member 3. G. Raghunathan, Ch. Manager, HPCL Member 4. S.V. Puthli Sr. Manager, HPCL Member 5. N. Lal Dy. Gen. Mgr., ONGC Member 6. N.N. Gogoi Dy. Gen. Mgr., OIL Member 7. M.A. Sreekumar Sr. .Manager CRL Member 8. .A. Varadarajan Sr. Manager, MRL Member 9. .B.K. Trehan Addl. Director, OISD Member Coordinator. -------------------------------------------------------------------------------------------------------------------------- In addition to the above several experts from industry contributed in the preparation, review and finalisation of the document.

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SAFE HANDLING OF AIR-HYDROCARBON

MIXTURES AND PYROPHORIC SUBSTANCES

CONTENTS

Section Description 1.0 Introduction 2.0 Scope 3.0 Elements of Fire 4.0 Prevention of Explosive Gas Mixture 4.1 Sources of Entry of Oxygen 4.2 Elimination of Oxygen 4.2.1 During Unit Start-up 4.2.2 Inert Gas 4.2.3 Vacuum Systems 4.2.4 LPG tank lorries and wagons 4.2.5 Flare header 4.2.6 Filing of new /repaired LPG Cylinders 4.3 Elimination of Hydrocarbons 4.3.1 During unit shut-dowm 4.3.2 Furnace lighting 4.3.3 Leaks and spills 4.3.4 Blowdown system 4.3.5 Air blowing of hydrocarbon lines 4.4 Precautions in Processes using Air 5.0 Pyrophoric Substances 5.1 Sources of hazards 5.2 Precautions and safety measures 6.0 References

SAFE HANDLING OF AIR-HYDROCARBON MIXTURES AND PYROPHORIC SUBSTANCES

1.0 INTRODUCTION Most of the refined petroleum products are used as sources of heat energy by combustion with air in engines or heaters. The same type of combustion can occur on a larger scale in petroleum refining or handling units with disastrous effects, if air mixes with petroleum fractions in the wrong place and in right proportions. Process units which use air for regeneration or reaction, provide many opportunities for forming flammable combinations of air and hydrocarbon mixtures. hence, the handling of air and hydrocarbons should be done in a safe manner to prevent the formation of flammable mixtures which can cause a disaster. Also there are some substances which catch fire spontaneously when exposed to air under atmospheric conditions. These are basically compounds of iron sulphides and are known as Pyrophoric substances. The Pyrophoric character depends upon the chemical reactivity of the substance and the physical condition of the surface. It can also be affected by the presence of foreign materials which may catalyse the thermal characteristics of the substance. 2.0 SCOPE The purpose of this document is to provide relevant technical standards for reducing fire hazards of air hydrocarbon mixtures and pyrophoric substances. The document also illustrates the nature and origin of air hydrocarbon mixtures and pyrophoric substances. The document is applicable to petroleum production, refining and marketing installations. 3.0 ELEMENTS OF FIRE All fires have three constituents viz. combustible substances like hydrocarbon etc., air or oxygen which should be present in he right proportions and a source of ignition. If any one of the three constituents is removed, fire can not occur. Therefore. it is important to prevent the combination of these constituents by eliminating any one of them at all times But, hydrocarbon at temperature above it’s auto-ignition point or pyrophoric substances will ignite by itself without any source of ignition. The auto-ignition point is the lowest

temperature at which the material will ignite by itself in contact with oxygen / air without any source of ignition. Hence, the contact of oxygen / air to these materials available at and above their auto-ignition temperatures should be eliminated. The hydrocarbon and air present in the right proportions means that the concentration of hydrocarbon in air is between the explosive limits. There are two explosive limits to hydrocarbons, the Lower Explosive Limit (LEL) i.e. the lowest concentration of the hydrocarbon present in air hydrocarbon mixture below which the mixture will not ignite and the Higher Explosive Limit (HEL) i.e. the highest concentration of the hydrocarbon present in the air-hydrocarbon mixture above which the mixture will not ignite. The explosive limits and auto-ignition temperatures of some commonly handled flammable liquids, gases and solids are listed in Table I. These flammability limits are valid only under atmospheric conditions. The range of explosive limit is wider at higher pressure and temperature or oxygen is substituted for air. 4.0 PREVENTION OF EXPLOSIVE GAS MIXTURES. 4.1 SOURCES OF ENTRY OF OXYGEN Elimination or air/oxygen from any system in the plants is an essential requirement to prevent a fire hazard. oxygen can be present in the system containing hydrocarbons or enter through any of the sources given below: i) Atmospheric air leakage through open or defective valves and flanges in vacuum systems ii) Atmospheric air entering open lines and vessels. iii) Atmospheric air associated with process or wash water. iv) Atmospheric air entering open equipment when internal pressure or level is lowered. v) Compressed air used in line blowing. vi) Compressed air used for agitation.

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vii) Oxygen or air in solution in feedstock. viii) Oxygen or air used in oxidation processes. ix) Oxygen contamination of nitrogen or other compressed gases used for purging or processing. 4.2 ELIMINATION OF OXYGEN 4.2.1 During Unit Start Up

To ensure safe start up of a unit it is most important to remove the air from the system by purging or evacuation, before hydrocarbons are introduced. All the air shall be purged with inert gas, steam, water, etc. and the system should be proved free of oxygen (i.e. less than 0.5% vol. ) by use of analysers. Systems once purged shall be kept under positive pressure with the purging medium or fuel gas as required by the service of the equipment, after it is proved to have no leak.

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TABLE 1

AUTO-IGNITION TEMPERATURES AND EXPLOSIVE LIMITS

--------------------------------------------------------------------------------------------------------------------------------------- Material Explosive limits Auto-ignition % volume in air Temperature ------------------------------------ ------------------------------- Lower Higher Deg.C --------------------------------------------------------------------------------------------------------------------------------------- Carbon Monoxide 15.7 70.9 610 Hydrogen 9.5 65.2 530 Acytelene 2.4 52.3 335 Hydrogen Sulfide 4.3 45.5 260 Methane 6.3 11.9 645 Ethylene 4.0 28.6 540 Propylene 4.2 9.5 530 Cyclopropane 2.4 10.4 497 Propane 2.4 9.5 Natural Gas 9.8 24.8 450 Butadiene 1-3 2.0 11.5 n-Butylene 1.8 12.0 i-B utane 1.8 8.4 n-Butane 1.9 11.5 490 Methyl Ethyl ketone 1.81 11.5 404 Methyl n-butyl ketone 1.22 8.0 n-Pentane 1.3 4.9 309 Benzol 1.4 8.0 580 Cyclohexane 1.31 8.35 n-Hexane 1.3 8.6 487 Toluene 1.0 7.3 810 Styrene 1.1 6.1 490 n-Heptane 1.0 6.0 233 o- Xylene 1.0 5.3 496 n-Octane 0.84 3.2 232 n-Nonane 0.74 2.9 --- n-Decane 0.6 5.4 463 Petroleum ether 1.4 5.9 246 Stoddard’s solvent 1.1 6.0 232-260 Gasoline (Typical) 1.3 6.0 350 Kerosene (Typical) 1.16 6.0 325 Lubricating oil, spindle (Typ) -- --- 248 Lubricating oil, cylinder )Typ.) -- --- 417 Asphalt (Typical) -- --- 280 Reduced Crude (Typical) --- -- 300 ---------------------------------------------------------------------------------------------------------------------------------- (Reference: Most of the data has been taken from Petroleum Refinery Engineering by W.L. Nelson and Lange’s Handbook on Chemistry)

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4.2.2 Inert Gas: It is not uncommon that inert gases, used for purging operations, contain more than maximum allowable oxygen content (i.e 0.5% vol). Hence, periodical analysis of the inert gas shall be done to ensure that the system being purged with the inert gas, is operating within the tolerable limit of oxygen content. 4.2.3 Vacuum Systems: Systems working under vacuum conditions can pull in air through leaky flanges, pump glands/seals, left open vents and drains, etc. Vacuum system shall be tested and checked thoroughly, for leaks and tightness, before start-up and periodically during operation. Also a sample point of the exhaust gases from the ejector system shall be analysed periodically for oxygen content. 4.2.4 LPG Tank Lorries and Wagons: At times tank lorries/wagons, used for transporting LPG are taken out of service temporarily, for maintenance or on alternate service. Before taking them back on LPG service, it shall be ensured that the containers are purged so as to lower the oxygen content below 0.5% volume. At all LPG tank lorry/wagon loading locations the oxygen content in tank lorries and wagons shall be checked before loading, especially after maintenance work has been carried out on the TL/TW or when the pressure gauge on TL/TW reads less than 1_atm_abs. If oxygen content is greater than 0.5% (vol.), then the tank lorry or wagon shall be evacuated and purged with inert gas and vented out to atmosphere at a safe location until the oxygen content is 0.5% (vol.) or less. Water should be used for displacing air from the tank lorries/wagons which should be provided with a bottom drain to facilitate complete removal of water which would otherwise cause corrosion and product contamination. 4.2.5 Flare Headers : The flare header shall always be maintained at minimum positive pressure to prevent entry of air into flare system. Gases entering the flare header, shall not contain oxygen (e.g. off gases ex Merox oxidiser) are routed to flare, an on line continuous and reliable Oxygen

Analyser, provided with an alarm and interlock to automatically shut off the source of oxygen to the particular process unit. 4.2.6 Filing of New/Repaired LPG Cylinders: The cylinders should be evacuated to an absolute pressure of 0.2 kg/cm Sq. before filing with LPG. Alternatively nitrogen or inert gas should be used to purge oxygen from cylinders before filling with LPG. 4.3 ELIMINATION OF HYDROCARBONS 4.3.1 During Unit Shut Down: During shut down it shall be ensured that hydrocarbons are thoroughly purged off with steam or inert gas such that the hydrocarbon content in the equipment is below the lowest LEL of the hydrocarbons handled and system is positively isolated by blinds to prevent re-entry of any hydrocarbons. 4.3.2 Furnace Lighting: Before lighting up the burners, the furnace shall be purged with steam to remove any hydrocarbon vapours and gases until the hydrocarbon content in the furnace is below the lowest LEL of the hydrocarbons handled. 4.3.3 Leaks and Spills: In case of light hydrocarbons, leakage from drains and vents shall be arrested immediately to prevent vapour cloud formation. Drains and vents of equipment on light hydrocarbon service shall be provided with double block valves and capping/end blinded may be ensured. One valve with capping/end blinding shall be provided only on those, which are operated during turn around. Note 2 4.3.4 Blowdown System: The drains of closed equipment (viz.: pumps, heat exchangers, etc.) handling light distillates in the range of C5 TO 140 Deg. C shall be routed through a closed blowdown system to prevent formation of explosive mixtures. Also an alternative open drain should be provided with double valve and cap to facilitate the checking of the depressurised nature if the equipment, this shall be operated after the equipment has been isolated (by valves) and depressurised to the closed blowdown.,

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4.3.5 Air Blowing of Hydrocarbon Lines: Air blowing of lines involves, contact of air with hydrocarbons in a closed system High pressure which increased the temperature, the flammability range and lowers the auto-ignition temperature, may be developed in this operation. Hence the air blowing of system containing hydrocarbon may result in an internal combustion leading to an occurrence of explosion. To prevent such possibilities, the air blowing of hydrocarbon lines shall be done subject to following conditions: I Pipelines on lube oil service - if oil

temperature is below 93 Deg. C and flash point is above 121 Deg. C.

ii. Pipelines on reduced crude and heavy

oil service - if oil temperature does not exceed 93 Deg. C

iii Pipelines on asphalt service - if asphalt temperature does not exceed 204 Deg. C Air blowing of pipelines leading into closed vessels and tanks shall not be done. Such lines shall be disconnected from vessels before air blowing. 4.4 PRECAUTIONS IN PROCESSES

USING AIR. In processes, like regenerative type Catalytic Cracking, Reforming, Bitumen Blowing and other processes requiring air, the addition of air should be carefully controlled such that the off gases form the process does not contain oxygen more than 0.5% volume. Adequate safeguards should be provided to ensure that there are no undesirable run away reactions, explosions and other unsafe conditions. The details of these safeguards are not included in this document since each process has specific requirement and has to be reviewed while integrating with the rest of the plant. In treating plant where hydrocarbons like LPG, gasoline, and kerosene are treated catalytically in presence of air it is usually possible to operate with only that amount of air which will remain dissolved in the liquid. Protective measures in such operations shall include a careful tie-in between hydrocarbon feed and oxygen supply rate to prevent the formation of explosive mixutre. Also the physical

arrangement of vessel and piping should be designed to eliminate pockets where vapour can collect. 5.0 PYROPHORIC SUBSTANCES 5.1 SOURCES AND HAZARDS In Oil and Gas industry the major source of pyrophoric substance is the iron sulphide Pyrophoric iron sulphide is a corrosion product that may form on the walls of vessels, tanks, towers, pipes, flare headers, etc. which contain or handle hydrocarbon containing sulphur compounds (viz. hydrogen sulphide, mercaptan, etc.) and aromatic tar. It also gets deposited in the sludge or tank bottom wastes. When pyrophoric substances come in contact with air they react with the oxygen generating heat. If the heat is not dissipated, the temperature would rise high enough to ignite a flammable mixture. In tanks and vessels having vents open to atmosphere, iron sulphide formed is normally converted to iron oxide scale, generating little heat which gets dissipated immediately and hence does not pose any potential hazard. But in gas blanketed tanks or equipment where little or no air is present, large quantities of the iron sulphides may form. If such equipment are purged with air in preparation for entry or work, the air/vapour mixture in the equipment would reach its flammability range at some stage of purging. At the same time, the pyrophoric iron sulphide would be exposed to the air and react with the oxygen generating sufficient heat to become a source of ignition. 5.2 PRECAUTIONS AND SAFETY MEASURES Following precautions shall be taken in carrying out work on equipment which are likely to have pyrophoric deposits: I Process lines and other in-line

equipment like vessel, columns, pumps, pump strainers, etc shall be purged with inert gas or steam and the inner surface kept wet by use of water sprays (by fog nozzles) or saturate steam before and while opening out for repair, replacement or overhauling. Before opening up for air entry / man entry, chemical solution washing should be used to diffuse pyrophoric iron, if any. Note 1

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NOTES