Petroleum Development Oman L.L.C.Unrestricted November 2004 Document ID: SP-1190 Filing Key: Design for Sour Service Specification Keywords: H2S, Sour Gas, Design, Specification, Layout, Classification This document is the property of Petroleum Development Oman, LLC. Neither the whole nor any part of this document may be disclosed to others or reproduced, stored in a retrieval system, or transmitted in any form by any means (electronic, mechanical, reprographic recording or otherwise) without prior written consent of the owner. Revalidated and updated references. Definitions clarified.C.Authorised for Issue: Signed: …………………………… Anton Sluijterman. Sluijterman UEP Scope/Remarks PDO-ERD-08-04 rewritten to new format.0 2.C. Version No. Sluijterman UEP/1 A. 1. . UEP CFDH – Process Engineering The following is a brief summary of the most recent revisions to this document.0 Date September 2000 November 2004 Author A. 6 CLASSIFICATION PROCEDURE...........4 5.......................3 5...........................................2 3............................................................................................................................................................0 PYROPHORIC MATERIALS....14 APPENDIX A: GLOSSARY OF TERMS...........10 H2S DETECTION.......................................Content 1................................................................................................................................................5 DESIGN PHILOSOPHY FOR SOUR SERVICE..............................6 DESIGN REQUIREMENTS TO PREVENT H2S RELEASE.................................1 1..............................................4 BACKGROUND......................3 2...................................9 DESIGN TO MINIMISE EFFECT OF H2S RELEASE......................4 4.............................................................................................................................................15 ........3 4...4 PURPOSE AND SCOPE..........................................................................2 4...........................................................................2 1.......2 5..................................................................................................................5 INTRODUCTION..............................................5 SOUR SERVICE FACILITY CLASSIFICATION.................................................. DEFINITIONS & ABBREVIATIONS..........................................5 EXPOSURE EFFECTS AND CHARACTERISTICS...................................................0 5..6 GENERAL............................................0 1......................................................................................................................................................................1 4....................................7 PIPING.......................................5 5............................................................................................................................................................7 SAMPLING SYSTEM...........................................3 4...........................................................13 7............................13 6.....................................................................................0 3.................4 COMPLIANCE WITH THIS SPECIFICATION.....................................................................................................................................................10 WELL ORIENTATION...........................................................0 2.....................1 5......................................................................................1 2...............................7 VENTS AND DRAINS......................8 INSTRUMENTS.......................................................7 ROTATING EQUIPMENT..10 LAYOUT..............................13 DISPOSAL OF SOUR GAS...........................................1 3..........0 RELATED BUSINESS CONTROL DOCUMENTS.....0 4............................................................................................................................................................4 GENERAL GUIDELINES................................6 FACILITY CLASSIFICATION......................2 3..............................................................................................................................11 CONTROL ROOMS................................................................................ Design for Sour Service Specification 1.2 Purpose and scope This document specifies the design requirements for facilities designated as Sour Service. transportation and treatment of these hydrocarbons require special care in the design of the equipment and the facilities. maintenance and surveillance shall be such as to prevent a potentially hazardous situation from developing.3 Compliance with this specification The user shall obtain written approval from the Corporate Function Discipline Head (CFDH) Process Engineering for any deviation from this specification. the practices should assure the early detection and rectification of the potentially hazardous situation.0 Introduction 1. The Shell HSE manual on H 2S in Operations (EP 95-0317) provides a good overview of the sour service hazards considerations.0 In a significant number of cases. 1. The scope includes: Characteristics and hazards of H2S Facilities classification Design requirements to prevent H2S release Design to minimise H2S release Pyrophoric materials The classification requirements of this specification shall be applied retroactively. The specification does not cover the requirements for material selection or materials testing techniques. Should such a situation nevertheless occur. The production. 1. The operation.1 Background Version 2. produced hydrocarbons contain hydrogen sulphide in sufficient concentration to pose a potential hazard to personnel and equipment. November 2004 1190 4 SP- . Dizziness. (3) Minimising exposure of operational and maintenance personnel to H 2S risk. The process consists of four basic steps: (1) Identification. (2) Assessment. Prolonged exposure (20 to 30 minutes) may cause irreversible pulmonary oedema. The HEMP approach. process selection should seek to minimise H 2S levels. personal protective equipment and escape. by designing for unattended plant operation and minimum maintenance requirements. In relation to H2S. breathing will stop if not treated quickly. loss of sense of reasoning and balance. and tools to assist its implementation. This includes consideration of training. (5) Ensuring that adequate personnel protection is provided. accumulation of fluid in the lungs. (4) Ensuring that detailed design minimises the risk of H2S release. H2S is highly soluble in both water and oil which enables it to be carried in solution for considerable distances from a place of origin to escape in unexpected areas. (2) Ensuring that risks associated with H2S are quantified and recorded. (4) Recovery. Victims need prompt artificial ventilation and/or cardiopulmonary resuscitation techniques. Possible eye irritation. gas detection.e. and avoid generation of process streams with very high levels of H2S. The process of facility classification is discussed further in section 3. the principal aspects to be considered are : (1) Minimising process stream H 2S levels.1 Exposure effects and characteristics Version 2. The sense of smell will be lost rapidly and it will irritate the eyes and throat. The key effects are summarised below: Concentration in air 1 ppm 10 ppm 200 ppm 500 ppm Effect Odour or rotten eggs can be clearly detected Unpleasant odour.g. At concept and front end design stages.0 General guidelines 2. This is the long term exposure limit. Unconsciousness after short exposure. e. November 2004 1190 5 SP- . (3) Control. 2.0 The exposure effects and characteristics of hydrogen sulphide are described in the HSE Manual EP-95-0317.2 Design philosophy for Sour Service The Hazard and Effects Management Process (HEMP) should be applied to the consideration of H2S throughout the design process and facility life. are described fully in EP 95-0300.Design for Sour Service Specification 2. i. access control. November 2004 1190 6 SP- . resulting from reducing the process liquid to atmospheric pressure.000. resulting from reducing the process fluid to atmospheric pressure C = process stream pressure (kPa (g) ). For liquid or mixed phase release. 3. These points shall be agreed with Operations and included in the Area HSE Case and the Plant Design Manual (ERD-00-12). 3. Report TR/001/94 “H2S Risk Assessment Methodology and Classification of PDO Production Facilities”.3 Classification procedure During the design phase. with a wind velocity of 1 m/s. an empirical relationship between process stream pressure and H 2S concentration has been established which enables the determination of whether a 200 ppm H 2S concentration exists at 2m distance without individual gas dispersion calculations. This methodology has been adopted by this specification and shall be applied during the design and operational phase. PR-1078. For gas release only. Sept 1994). depending on the concentration of H2S in the gas phase. the Project Engineer shall be responsible for reviewing the impact of the modification on H 2S classification and initiating any required change. as follows: P * C > 1.000 where: P = concentration of H2S in the gas phase. individual dispersion calculations shall be performed.0 3. If concentrations greater than 500 ppm are predicted then points where the product of pressure and concentration are expected to be highest shall be identified.1 General A risk assessment methodology has been developed for use in determining the H 2S Classification of all PDO Production facilities (ref.2 Facility classification The production facilities shall be assigned to one of three categories. resulting from reducing the process fluid or process gas to atmospheric pressure: 0 to 49 ppm Sweet facility 50 to 499 ppm Low Risk Sour facility 500+ ppm requires further assessment Facilities shall be classified as High Risk Sour if both: the concentration of H2S in the gas phase. Sampling facilities shall be included in the detailed design to enable monitoring of the identified points during the operational phase of the facility.Design for Sour Service Specification Version 2. The re-assessment requirements during the operational phase are covered by the “Hydrogen Sulphide Management” procedure. the process engineer shall quantify H2S concentrations and identify the points on the facility where highest concentrations are anticipated to occur.0 Sour service facility classification 3. Where modifications are made to the facility during the operational phase. exceeds 500 ppm and an 1 inch diameter release can cause a 200 ppm or higher H 2S in air concentration at a 2m distance from the point of release. to reduce the number of potential leak sources. All design considerations should consider the potential for the increase of H 2S concentration in process streams over the life of the plant and the probability that the classification may change from Low Risk to High Risk Sour over the production life cycle. Samples should be taken from the areas of process plant expected to contain the highest concentrations of H 2S. as per section 3.Design for Sour Service Specification 4. which are for hydrotesting shall have their outlets blocked-off by blind flanges. to minimise the probability of H2S release. November 2004 1190 7 SP- . 4. which shall be in accordance with specification SP-1126. Flanges on piping in Sour Service should be minimised wherever practical. Where this is not possible. venting may be allowed but shall be designed such that personnel cannot be exposed to H2S concentrations above 10 ppm.1 Piping To minimise corrosion. Where this cannot be achieved the sample return line shall be flared or vented. Double block and bleed isolation shall be provided for High Risk Sour facilities. piping should be designed and installed in such a way that dead ends and areas of intermittent flow are eliminated. Closed system bomb sampling systems shall be used in High Risk Sour service. 4.0 Version 2. The use of bomb sampling in Low Risk Sour service should also be considered where there is a high Gas Oil Ratio.2 Sampling system The location of sampling points necessary for future monitoring of facility classification. Sample return lines should be routed back into a lower pressure process stream. All liquid in sour service shall be piped into a closed drains system. 4. to ensure compatibility with local sample handling facilities. Screwed fittings shall not be used in Sour Service.0 Design requirements to prevent H2S release The following guidelines shall be followed where a facility is classified as High Risk Sour or Low Risk Sour. Vents and drains. Material selection for sour service is addressed separately in ERD-08-02. low and atmospheric pressure levels. Details of sample points shall be determined in consultation and agreement with Production Chemistry Department. Special attention should be paid to the vents from Glycol Regenerator vapour outlets. Where posible these sample points have to be combined with sample points for other purposes. Typically 3 sample points would be expected to cover high. which may contain very high levels of H2S. shall be determined in consultation with Operations during design.3 Vents and drains Depressurising of equipment and process lines in Sour Service should be to a flare system. A PDO rotating equipment specialist shall be consulted for all rotating equipment specifications.4. Shaft seals The following mechanical seal types shall be considered: (a) Dry gas seals (most preferred) for design pressure below 120 bar (b) Conventional oil film seals for design pressure above 120 bar (c) Mechanical seals (restricted by speed/pressure) used typically in refrigeration systems and small machines. Blanket gas shall be used for distance piece venting.40. nitrogen). (b) Duplex filters shall be installed on the fuel gas inlet to ensure removal of ferrous sulphide (fine black dust). Vent gas shall be discharged to AP flare. Such oil shall be reclaimed (vacuum degassing or air stripping) before re-circulating or be discarded.29. A combined lubricating and seal oil system may be used unless the process gas contain levels of H2S greater than 6 mole %. The compressor vendor shall provide (as part of the documentation package) process engineering flow schemes of lubricating and seal oil systems. If the H2S concentration is greater than 6%. seal gas and flare and drain connections which clearly shows how the above sour service requirements have been incorporated into the design. November 2004 1190 8 SP- . which cannot be adequately removed by a sour seal oil reclaimer.1 CENTRIFUGAL COMPRESSORS The design shall be in accordance with DEP 31. (d) Turbine enclosures shall be ventilated to ensure a safe working atmosphere.32-Gen. (e) Stack height shall be determined based on dispersion of exhaust gas to ensure that ground level concentrations of SO2 do not exceed 5 ppm. then separate lubrication and seal oil systems shall be provided.g. If an AP flare system does not exist.40.30-Gen and DEP 31. then local venting may be allowed. 4.29.Design for Sour Service Specification 4. These filters shall have water-flushing connections to avoid auto-ignition of pyrophoric iron when they are opened. Distance piece venting and draining shall be in accordance with DEP 31.0 Rotating equipment This section provides a checklist for rotating equipment in Sour Service. If an AP flare system does not exist.4. Seal vent A seal leak detection system shall be installed.31-Gen. 4. then local venting may be allowed. If sour gas is used then: (a) Turbine engine materials and pipework shall be compatible with the sour fuel.29.60. Lubricating and seal oil system for above 120 bar system. Seal oil collected in the contaminated seal oil trap shall not be recycled. Seal vent gas shall be directed to AP flare. Reciprocating compressors seal leak detection system shall be installed. (c) Fuel supply shall be superheated to vendor specification.4 Version 2.2 Gas turbines and gas engines Sour gas should not be used as fuel gas wherever possible. Dry gas seals shall be provided with a sweet buffer gas (e. November 2004 1190 9 SP- .29.Design for Sour Service Specification 4.3 Version 2. This device may be a seal pot with a level switch or pressure transmitter with switch.0 Centrifugal and positive displacement pumps If High Risk Sour gas can be released in the event of a seal leakage.30-Gen. vented to an AP flare.02.5 Instruments Sour gas shall not be used as instrument gas. Pneumatic instruments in Sour Service shall use instrument air or sweet gas. The double seal requirement for the centrifugal pump shall be governed by DEP 31. If Low Risk Sour gas can be released in the event of a seal leakage. consideration should be given to installation of a seal leakage detection device. 4. a seal leakage detection device should be installed.4. where possible.1 Plant layout and spacing For plant layout and spacing refer to PDO SP-1127. Location. These shall be located as far apart as possible. 5.3 Emergency escape exits Emergency escape exits in Low Risk Sour and High Risk Sour facilities shall be provided such that escape is possible upwind of (or at worse.Design for Sour Service Specification 5. Gas containing H2S may be heavier or lighter than air. transportation routes. Clear entrance and exit routes should be maintained and confined areas within the facilities should be avoided. High Risk and Low Risk Sour wellheads located in predominantly ‘sweet’ fields shall be fenced.0 Design to minimise effect of H2S release The following guidelines shall be followed to minimise the effect of an H2S release. escape gates shall be provided on opposite sides of the facility. Locations where operators make routine inspections for H 2S release should be easily accessible when wearing a compressed air breathing apparatus. The H2S concentration at the station fence during normal operation shall not exceed 10 ppm. be located upwind of prevailing winds to minimise exposure risk to personnel approaching them. Dispersion calculations shall be performed for all normal or operational vents.1 Well orientation Well site access roads should. Areas of restricted ventilation (both high and low). and so can accumulate in low or high places. The seals of rotating and reciprocating equipment which are a potential cause of High Risk Sour releases shall be given special consideration in plant layout and spacing to avoid trapping high concentrations of H2S and to take fullest advantage of the natural atmospheric dispersal effects. terrain. 5. therefore.2 Fences Fences referred to in this document are all to stop personnel accidentally entering H 2S areas. 5. consideration should be given to taking advantage of the prevailing wind direction. should be avoided. 5. In addition to this specification the following design criteria shall be followed.2. perpendicular to) the prevailing wind direction. Pipelines and flowlines in sour service do not need to be fenced. spacing. so as to allow sour gas releases to disperse. and height of flares or vent stacks should be determined based on acceptable gas dispersion calculations. Elevated platforms shall use stairs only so that there is no hindrance when carrying breather sets or rescuing H2S affected personnel. Equipment handling sour fluid shall not be placed inside a totally enclosed area. climatic conditions. 5.2. and the proximity of populated or public areas. As a minimum.2 Layout In selecting a facility site.2. November 2004 1190 10 SP- . All working locations should be equipped with at least two escape routes in separate directions.0 Version 2. personal H 2S detection or personnel protective equipment. Assembly points shall be located such that the local H2S concentration during the worse credible accidental hydrocarbon release does not exceed 10 ppm.5 F 1003A: Low Risk Sour Service Facility Sign F 1003B: High Risk Sour Service Facility Sign WS 004: H2S Hazard Warning Sign Windsocks Each Sour Service designated facility shall have sufficient windsocks located so that they may easily be observed from any position within the station. 5.3 H2S Detection The primary objective of fixed H 2S detection is to provide a warning to prevent entry of personnel into a known hazardous area.0 Warning signs Each facility designated as being in Sour Service shall have a warning sign (in both English and Arabic language) indicating whether it is classified as High Risk Sour or Low Risk Sour in accordance with ERD-89-01.2. shall be incorporated in the design of all High Risk and Low Risk Sour facilities.1 for further guidance on the selection and design of H2S detection systems. Where the possibility exists for an H 2S concentration greater than 10 ppm at an assembly point. Where this would result in an assembly point location at an excessive distance from the facility (which might create additional problems of access and communication). Maps showing “worst case” H 2S concentrations contours shall be included in the Facility HSE Case and be displayed in the facility Control Room. 5. a relaxation to a local concentration no greater than 50 ppm at the assembly point may be allowed provided that Operations agreement is obtained. Refer to HSE Manual EP-95-0317 Section 4. A Fixed Detection system should be provided around all process plant facilities classified as High Risk Sour.6 Assembly points The preparation of a comprehensive Evacuation Plan. Consideration should be given to installation on Low Risk facilities as part of the overall facility safeguarding philosophy.2. Dispersion calculations shall be performed for all Sour Service facilities to verify that assembly points are suitably located. including consideration of requirements for assembly points. A fixed system does not in itself provide personnel protection and shall not be considered a substitute for entry precautions. The following signs (as detailed in ERD-89-01) are applicable: 5. The maps should include 50 ppm and 10 ppm contours.2. November 2004 1190 11 SP- . local Emergency Procedures shall highlight that Personal H 2S Gas Detectors may continue to alarm at the assembly point.4 Version 2.Design for Sour Service Specification 5. For control rooms and other buildings with central air conditioning systems. For buildings where the air conditioning system does not duct air throughout the building (such as standard gathering station control rooms). (4) Remote monitoring centre. only the audible alarm in the control room should silence. Consideration may be given to a shutdown action on H2S detection for High Risk Sour facilities. due to the risk of spurious shutdown.3 Alarms Fixed H2S detectors shall alarm audibly and visually at the: (1) Station control room panel. This alarm shall be distinguishable from the station fire alarm. to close on detection of H2S. Sensors are installed to detect H 2S dispersed into the plant area from any source. The alarm accept button shall be on the station control room panel. and thus also cover less likely sources of release.20 ppm. and should not normally be connected to the plant shutdown. one inside the main entrance and others in the principal rooms (e.3. is not readily available. fixed H 2S detectors shall be installed. (3) H2S detector location. one fixed H 2S detector shall be installed in the air conditioning inlet. and shall alarm at 10 ppm. For High Risk Sour facilities. These detectors should be designated for H2S alarm only.3.1 Version 2. Portable H2S detectors both electronic and manual devices (with small hand pump) are used for H2S detection. The alarm shall also be audible throughout the facility under all normal operating conditions. 5.3. November 2004 1190 12 SP- . A sensor is installed to detect leakage from a single source where the H 2S concentration in the fluid is relatively high and /or there is a relatively high probability of a leak. located adjacent to or in High Risk Sour or Low Risk Sour designated facilities. 2) H2S Area Monitoring. which duct the chilled air throughout the building. gas tight dampers should be installed on the inlet to the air conditioning unit. 5.g.Design for Sour Service Specification 5. the control room and the rest room). if telemetry is installed. (2) Main entrance to the station. as part of an overall Safeguarding Philosophy. or to direct it to a safe location.0 Fixed detectors in open air There are two approaches that can be applied to fixed H2S detection in open areas: 1) H2S Leak Detection. At other locations both audio and visual alarms shall remain on till H 2S level comes down below the acceptance level. the visual indication should remain on. This system may be applied in areas where the installation of individual detectors for each potential source cannot be justified. On acceptance of alarm at control room.2 Fixed detectors in enclosed areas Buildings and enclosures where personnel can enter during normal operations (except well cellars). The air conditioning unit shall be shutdown on H 2S detection. This may be applied on equipment for which an alternative design measure to minimise the probability and/or quantity of a release. All fixed detectors shall have a range of 0 . shall contain fixed H2S detectors set to activate alarms at 10 ppm. 5 Disposal of sour gas Sour gas that is to be disposed of in normal operation shall be flared.Design for Sour Service Specification 5. breathing apparatus sets and portable H 2S detector. The elevation of the flare stack and the fencing at the base shall fulfil the following criteria: (1) 50 ppm or less H2S at the stack base. spare O2 bottle. (2) By level instrument vents (not the liquid drains). While specifying the filter specification the particle size to be removed should be specified depending on the service requirement. If a filter or cyclone separator is used to remove ironsulphides. water-flushing connection shall be provided to avoid auto ignition while removing the pyrophoric debris. (2) 10 ppm or less H2S at the fence. These shall be of at least 30 minutes duration.0 Control rooms Control rooms shall be designed in accordance with PDO-ERD-30-04. Various engineering options may be considered to tackle the iron-sulphide problem. frequent pigging to keep the pipe line clean of ironoxide. HSE manual EP 95-0317 shall be consulted to determine the procedure for handling pyrophoric iron sulphide. 6. for example.10-Gen. shall be supplied as part of the control room project. The above resuscitator. etc. (3) By drain vessels on small facilities such as remote manifolds which do not have a flare system. 5. Attempts shall be made in design to minimise sour gas release to environment.4 Version 2.10. e. November 2004 1190 13 SP- . (4) By sour oil tank breather. Iron oxide present on the internal surfaces will react with the H 2S and form pyrophoric iron sulphide.: (1) By pump seal pots which vent above the sun roof. Dispersion calculations shall be done to determine the stack height and fence location assuming that flare is not ignited for H 2S and is ignited for SO 2. (3) 5 ppm or less SO2 at the fence.0 Pyrophoric materials Pyrophoric iron sulphide can be formed on the internal surfaces of carbon steel equipment containing H2S. For Sour Service designated facilities the additional requirements are :(1) An oxygen resuscitator and spare O2 bottle shall be retained in each control room.1 ppm) as long as the partial pressure of H 2S exceeds the partial pressure of oxygen in the environment..g. Flare systems shall be designed in accordance with DEP 80.45. Any one of these options may be incorporated into the design. use of coated pipe to avoid iron-sulphide formation. (2) At least three wall mounted self-contained breathing apparatus sets for emergency use shall be installed in each control room. use of filters or cyclone separators at the station inlet to remove iron-sulphide fines. small volumes of sour gas may be allowed to be vented locally to atmosphere. Pyrophoric iron sulphide can form even at very low H 2S concentration (< 0. If no other solution is available. Overview EP 95-0300 HSE Manual.02. Pressure Relief and Flare System DEP 80. Centrifugal Compressors DEP 31.32-Gen.01.0 Related Business Control Documents PDO Business Control Documents Number Preparation Plant Design Manual ERD-00-12 Materials Selection for Sour Service ERD-08-02 Signs and Signboards ERD-89-01 Hydrogen Sulphide Management PR-1078 Isolation of Process Equipment Specification SP-1125 Drain Systems Specification SP-1126 Plant Equipment Layout Specification SP-1127 Identification of On-Plot Pipework Specification SP-1166 Shell Standards and Manual Centrifugal Pumps Number DEP 31.60.38.40.10.Basis of Design DEP 31.0 Version 2. Piping General Requirements DEP 31.29.30-Gen.01. Design of Pipeline Pig Trap Systems DEP 31.11-Gen. HSE Manual.10-Gen.31-Gen.30-Gen. Hydrogen Sulphide (H2S) in Operations EP 95-0317 November 2004 1190 14 SP- .29.45. Rotary Type Compressors DEP 31. Reciprocating Compressors DEP 31.38.29.29.10-Gen.Design for Sour Service Specification 7. Piping Classes .40.13-Gen.40.10. Safety and Environment Petroleum Development Oman LLC.0 Appendix A: Glossary of Terms. Parts per million Sulphur Dioxide 15 SP- . Definitions & Abbreviations AP CFDH DEP ERD HEMP H2S HSE PDO Ppm SO2 November 2004 1190 Atmospheric Pressure Corporate Function Discipline Head Design and Engineering Practice Engineering Reference Document Hazard and Effect Management Process Hydrogen Sulphide Health.Design for Sour Service Specification Version 2.