Guidance for safe bitumen tank management - Refined Bitumen ...

Guidance for safe bitumentank managementMineral Products Associationmpa asphaltMineral Products Association

2 - guidance for safe bitumen tank managementMPA Asphalt is part of the Mineral Products Association (MPA) - the tradeassociation for the aggregates, asphalt, cement, concrete, dimension stone, lime,mortar, and silica sand industries and is the sectoral voice for mineral products.Its membership also includes companies manufacturing road construction andquarrying plant and equipment and UK producers of petroleum bitumen.The Refined Bitumen Association is the consolidated voice of the UK bitumensupply industry. Its membership comprises the UK’s major bitumen producers who,between them, supply nearly all of the country’s bitumen.The RBA promotes the most effective use of bituminous materials within theconstruction industry, provides technical support and funds research intobituminous products. It is also involved in the development of industry policy onquality assurance and best practices relating to safety, storage and handling ofbitumen.Whilst every care is taken to ensure the accuracy of the general information and advice offered herein or given by staff of the Mineral ProductsAssociation and the Refined Bitumen Association, no liability or responsibility of any kind can be accepted by the Mineral Products Association, theRefined Bitumen Association or their staff.

4 - guidance for safe bitumen tank managementGuidance for safe bitumen tank managementINTRODUCTIONThere are around 325 asphalt manufacturing plants throughout theUK involving approximately 1300 bitumen storage tanks. Spillagesfrom these bitumen storage tanks as a result of overfilling have a highpotential for serious injury as bitumen is stored at high temperaturesand has a large thermal capacity.Statistics compiled for the 6 years, from 1998 to 2003 for reportedbitumen spillages at UK delivery sites, show that on average across theindustry there were 60 spillages, with 78, 79 & 82 for the years 2001,2002 & 2003 respectively. There has been an improvement from a highof 82 spills in 2003, but the number of spills still averages 27 per year forthe 3 years 2010 to 2012.This document explains the fundamental principles that need to beadopted at all asphalt plants, for the safe operation of bitumen storagetanks, to reduce the risk of occurrence of a potentially serious incident.THE ORIGIN OF SPILLSSpills have occurred from the bitumen tanks on many sites due tooverfilling as a result of the incorrect determination of the availableullage space due to a number of factors:1. Lack of Knowledge of Tank Dimensions & Capacity2. Use of Incorrect Conversion Factors3. Unsuitable or Wrongly Applied Tank MeasurementInstrumentation4. Incorrect Interpretation/Presentation of Tank ContentsMeasurement Information5. Poor Communication between the Delivery Tanker Driverand Asphalt Plant Operating Personnel1. TANK DIMENSIONS & CAPACITYA. Storage Tank Capacity and the Determination of UllageThe correct determination of the ullage space in a given bitumenstorage tank is crucial to preventing spills and to ensure this, it isimportant to establish what is the actual working storage capability ofa given tank.There is a lack of uniformity across the asphalt industry, with bothtank manufacturers and site operating companies, when stating thestorage capacity of site bitumen tanks, in terms of the terminologyused and the units of measurement. Also, in some cases there is alack of awareness by site operating personnel regarding the storagecapability of their bitumen tanks and frequently there are no details ordrawings readily available for reference regarding important tank sizingdimensions, including their height, diameter, positions of off take andoverfill pipes, etc.It is vital that this information is available to enable the accuratecalculation of tank capacities, obtained either from tank manufacturers’drawings or by on site tank survey measurements and for the industry toadopt common terminology for defining tank capacity.B. Definition of Tank CapacityUsing the following terms and definitions we can calculate the tankstorage capacity for any given tank (as long as the correct tank data isavailable):Nominal Tank Capacityl Internal volume in m 3 from the tank bottom to the tank top.Unavailable Tank Capacityl Internal volume in m 3 from the normal tank draw off pipework tothe bottom of the tank + Inside volume in m 3 from the overfill/vent pipe to the tank top.Available Tank Capacityl Internal volume in m 3 from the normal tank draw off pipeworkto the overfill/vent pipe.Safe Working Tank Capacityl 90% of the available tank capacity in m 3 .Conversion from volume to massl Multiply volumes in m 3 by 0.92 tonnes/m 3 to express thecapacity in tonnes.By way of an example in the use of these terms and to show howconfusion can arise, consider a new tank recently installed on acustomer site to hold 100 tonnes of bitumen.Nominal tank capacity 105.8m 3 97.3 tonnesUnavailable tank capacity 5.3m 3 + 1.0m 3 = 6.3m 3 5.8 tonnesAvailable tank capacity 99.5m 3 91.5 tonnesSafe working tank capacity 89.6m 3 82.4 tonnes

5 - guidance for safe bitumen tank managementAs can be seen from the above, the tank is only capable of safely storing82.4 tonnes of bitumen that can be used for asphalt production andnot 100 tonnes as implied. The use of a more rigorous statement of thecapacity required would have prevented such a misunderstanding.See the diagrams in Appendix 1 for representation of the above terminologyfor vertical and horizontal tanks.C. The Determination of UllageFollowing on from the definitions previously discussed, decidingwhether there is sufficient space in a particular storage tank to safelyreceive a planned delivery of bitumen of known weight (expressed intonnes) without overfilling involves:l Determination of the unused part of the safe working capacityin volumetric terms expressed in cubic metres.l Conversion of this volume into the mass (or weight) of bitumenthat can be safely stored, using the worst case density figure of0.920 tonnes/m 3 .Implicit in these calculations is the assumption that the tank shapes(either horizontal cylinders, vertical cylinders or rectangular cuboids)are uniform and remain so when the tanks are filled/emptied and thatthe tank dimensions provided by the manufacturer are accurate.2. CONVERSION FACTORSThere is an obvious difficulty in expressing the capacity of a giventank in weight, as the weight of a particular grade of bitumen that canbe stored in a given volume depends on the density of the bitumen,which varies according to the storage temperature. Significantly, thereare considerable differences, between both tank manufactures andoperating sites, in the density values used for a given grade of bitumenbeing stored, often far too high, that could never be applicable for therange of temperatures at which it is normally stored.Conversion from volumetric to mass units, should use the worstcase density for the bitumen being stored, to avoid overfilling, i.e.the density of the bitumen at its highest recommended storagetemperature (the lowest value of density likely to be encountered),when a given mass of bitumen occupies its largest volume.It turns out that the worst case density value for all grades of bitumentypically stored is around 920kg/m 3 (or 0.920 tonnes/m 3 ), which is the valuethat should be used when converting from volume to mass.3. TANK CONTENTS MEASUREMENTINSTRUMENTATIONIn practice, measurement of the liquid level or ullage distance and theconversion of either of these into an expression of the tank contentsare usually accomplished by some form of tank contents measurementinstrumentation. The readings from these, according to their range ofmeasurement and the units used, are interpreted by the operator, todecide whether there is sufficient room in a given tank to safely receivea tanker delivery of bitumen.To warn of abnormal conditions, which if left unheeded could leadto difficulties including the possibility of an overspill, various alarmsare provided, either derived from the measurement equipment, or byindependent means.A. Measurement Derived AlarmsMeasurement signals from the contents measuring instrumentationare often used to generate various alarms, usually to warn ofabnormal operating conditions, typically high level (HLA), or highhigh level (HHLA) alarms, to prevent a potential overspill conditionand less commonly low level (LLA) alarms to prevent a possible tankoverheating condition.A measurement derived alarm must be fitted to all bitumen tanks.In the event of a malfunction of the contents measuringinstrumentation, or as a result of incorrect setting up, these types ofalarms could fail to provide any overspill safeguard.On some of the tanks fitted with mechanical buoyancy level indicators,both of the Cat & Mouse and rotary types, high level and sometimeslow level alarms are generated using micro or proximity type switchesoperated by a pointer mechanism.B. Independent High High Level Alarm DevicesIn an attempt to avoid overspills, sites have equipped their tanks withhigh level alarm generating devices, that act independently from thecontents measuring instrumentation, to provide an independent highhigh level alarm (HHLA).These alarms are derived from fixed position switches or probes withinthe tank, which operate when the bitumen makes contact with them.These must be used in addition to the measurement derived high levelalarms.Independent high level switch devices must be fitted to all bitumen storagetanks, to provide a safeguard from spills in the event of a fault or problemwith the contents measuring instrumentation, or because of some errorin the translation of level measurement into volumetric contents, dueto possible tank dimensional or deformation abnormalities and/or thebuild up of product on the side walls of the tank.

6 - guidance for safe bitumen tank managementFurther, where the contents measurement is based on the use ofhydrostatic instruments, then the fitting of independent high levelswitches must be an essential priority, as it is not possible with thistechnology to provide with absolute certainty measurement derivedalarms that directly relate to the level of bitumen stored.C. Setting Up of Tank Contents InstrumentationTaking into account the earlier parts of the report relating to availabletank capacity and safe working tank capacity, the minimum tankcontents instrumentation to prevent overspills must include a contentsmeasuring instrument, a measurement derived high level alarm (HLA)and an independent fixed position point contact high high level alarm(HHLA) switch. These must be arranged such that:l The tank contents instrumentation must be installed with ameasurement span set to cover the height range correspondingto the available tank capacity.l A measurement derived high level alarm (HLA) must be provided,set at the height corresponding to the safe working capacity,that is 90% of the available tank capacity, with instructions to thedriver to stop loading, should it be initiated.l An independent fixed position point contact high high levelalarm (HHLA) switch must be installed, set at the height in thetank corresponding to 92.5% of the available tank capacity,providing the protection to prevent the tank overfilling, withinstructions to the delivery driver to shutdown immediately,should it be initiated.4. INTERPRETATION/PRESENTATIONOF TANK CONTENTS MEASUREMENTINFORMATIONSafe bitumen storage tank management requires the clear presentationof the information to both plant operating personnel for all aspectsof the operation and to the delivery tanker driver during the delivery/offloading process.A. Delivery Tanker Driver Minimum InformationRequirementslllLarge individual amber indicator lamps, one per tank to provideHLA warning which is activated off the level measuring systemand positioned to be easily visible by the driver from the normalloading point(s), linked to a common audible alarm klaxon, with akey operated audible mute push button switch.Large individual red indicator lamps, one per tank to provideHHLA warning which is activated off the independent alarmand positioned above the HLA amber indicator lamps, linked toa common red flashing beacon with an integral audible siren,with a key operated audible mute push button switch, to enableoperating personnel to silence the audible alarm.Large sign or signs easily visible to the driver explaining themeaning of these alarms and the action to be taken in the eventof them being initiated.It is recommended that the following should also be installed:lAll instruments and alarms must be part of an annualmaintenance programme. This must include calibration ofinstruments and alarms by competent and qualified personnel. Itis recommended that calibration is carried out by the instrument/alarm supplier.lFor tanks greater than 31m 3 safe working capacity large individualgreen indicator lamps, one per tank to provide confirmationthat there is safe working capacity to accommodate a 31m 3 load(approximately 28.5 tonnes) of bitumen, positioned below theHLA amber indicator lamps.See the diagrams in Appendix 2 for examples of measurement and alarmset ups using non contact radar, contact radar (TDR) and hydrostaticpressure measurement systems.l Large sign or signs easily visible to the driver explaining themeaning of these indications.B. Site Operational Personnel Information RequirementsIt is difficult to be too prescriptive with this, as it depends on theparticular arrangement and layout of each site and the way in whichthe operation of the asphalt plant and its associated bitumen tanksis managed. However, the relevant site personnel need to be awareof the operational status of the bitumen tanks at all times, particularlyduring the potentially hazardous bitumen tanker delivery process andinformation regarding this must, therefore, be presented in the place orplaces where this can be achieved.

7 - guidance for safe bitumen tank managementAs a starting point, it is considered that tank contents measurementinformation, along with the alarm presentation equipment described,must be presented in the vicinity of the tanks. The minimuminformation to be provided should be as follows:l Large sign on each tank stating the Safe Working Capacity inTonnes, based on a density conversion factor of 0.920 tonnes/m 3 .l Large individual digital type display contents gauge, one pertank showing the amount of bitumen being stored within theavailable part of the tank expressed in Approximate Tonnes, toone decimal place, based on a density conversion factor of 0.920tonnes/m 3 .It is recommended that the following also be supplied:l Large individual digital type display gauge, one per tank,mounted alongside the contents gauge showing the amountof Safe Ullage Space in the tank available for the next load,expressed in Approximate Tonnes, to one decimal place, based ona density conversion factor of 0.920 tonnes/m 3 .Note: With modern microprocessor based digital signalconditioning/display instrumentation, this is capable of beingprovided at modest cost and could avoid errors in safe ullagedetermination. Also, this measurement readout would be of useto the delivery tanker driver, who would be able to more closelymonitor the progress of the offloading operation.l Tank temperature display (°C) derived from a dedicatedtemperature transmitter positioned at the same level as thedraw off pipework, to be as far as possible above the tankheating system.5. COMMUNICATION BETWEEN THEDELIVERY TANKER DRIVER AND ASPHALTPLANT OPERATING PERSONNELIt is important that communication between drivers and plantpersonnel is clear to ensure correct selection of tank for the dischargingof bitumen. The driver must present the delivery documentation toplant personnel who must confirm grade and quantity is correct.The plant personnel must confirm the appropriate storage tank andreceiving flange for the delivery. All flanges must have independentpadlock and keys that will be issued and controlled by plant personnel.It is recommended that a Bitumen Discharge Permit is used to supportthis process. Under no circumstances should the keys and padlocks becommon for different flanges/tanks.SUMMARYThe safe management of bitumen storage tanks and the avoidance ofoverfilling involve a combination of:lllThe correct calculation of ullage using information from thetank contents instrumentation, to determine whether or notthere is sufficient room in a given tank to allow a new load to bedelivered, without overfilling.Accurate and reliable contents measurement, withunambiguous presentation of the salient information.The provision of suitable safeguards to warn of an impendingoverfill condition, should something go wrong.C. Centralised Presentation of Measurement & AlarmInformationIn most instances it is considered that all of the measurementand alarm information presented in the vicinity of the tanks, asjust described, should also be communicated to the asphaltplant control room. This may be a separate “mixer cabin” typecontrol room near to the asphalt plant, or within a control roomshared with the weighbridge as on some sites, where there islikely to be an operator in attendance, who can monitor thebitumen tanker delivery off loading process.On new plants it is envisaged that the alarm and measurementinformation communicated from the bitumen tanksideinstrumentation will be interfaced into the asphalt coatingplant’s computer based control and data acquisition system, forVDU display using the standard measurement and alarm datapresentation packages available within the system.See Appendix 3 that shows a schematic drawing of a possible modelfor the display of tankside information.lParticipation and commitment from both the tanker driver andsite operations personnel during the delivery/offloading process.

8 - guidance for safe bitumen tank managementAPPENDIX 1CAPACITY OF VERTICAL CYLINDRICAL BITUMEN STORAGE TANKSNominal capacityUnavailable capacityOverflowSafe WorkingLevel SWLDraw offAvailable tank capacitySafe working capacityOverflowSafe WorkingLevel SWLDraw off= Heating elements = 90% of

9 - guidance for safe bitumen tank managementAPPENDIX 1CAPACITY OF cuboid type BITUMEN STORAGE TANKSNominal capacityUnavailable capacityDraw offOverflowDraw offOverflowSafe WorkingLevel SWLAvailable tank capacitySafe working capacityDraw offOverflowDraw offOverflowSafe WorkingLevel SWL= Heating elements = 90% of

10 - guidance for safe bitumen tank managementAPPENDIX 1CAPACITY OF horizontal CYLINDRICAL BITUMEN STORAGE TANKSNominal capacityUnavailable capacityOverflowSafe WorkingLevel SWLDraw offAvailable tank capacitySafe working capacityOverflowSafe WorkingLevel SWLDraw off= Heating elements = 90% of

11 - guidance for safe bitumen tank managementAPPENDIX 2schematic installation diagram of non-contact radar and independent HIGH high level alarm switchNon contactradar deviceIndependent highlevel switch probe100%IndependentHHLASafe workingHLA92.5%90%DesirablemeasuringrangeLow levelLLA5%0%Draw off pipeOverfill/vent pipeHeater bank

12 - guidance for safe bitumen tank managementAPPENDIX 2schematic installation diagram of TDR contact radar & independent HIGH high level alarm switchTDR contactradar deviceIndependent highlevel switch probeUpperblanking zone100%IndependentHHLASafe workingHLA92.5%90%DesirablemeasuringrangeSS WireLow levelLLA5%Lower blanking zoneWeightDraw off pipe0%Overfill/vent pipeHeater bank

13 - guidance for safe bitumen tank managementAPPENDIX 2schematic installation diagram of hydrostatic contents gauge and independent HIGH high level alarm switchIndependent highlevel switch probe100%IndependentHHLASafe workingHLA92.5%90%DesirablemeasuringrangeDraw offpipeLow levelLLA5%Signal elevation(zero suppression)0%Overfill/vent pipeHeater bankHydrostaticpressure TX

14 - guidance for safe bitumen tank managementAPPENDIX 3POSSIBLE MODEL FOR THE DISPLAY OF TANKSIDE INFORMATIONTTXI/O processinginstrumentsLTX HHLSTank 1 Tank 2 Tank 3 High highlevel alarm(HHLA)Safeworkingcapacity80 TonnesFlashingbeaconInstrument panelAvailable tank contentsAudible sirenwith keyoperated mute45.0TonnesAvailable safe ullage35.0Tank temperature150Tonnes°CHigh levelalarm (HLA)Low levelFlashingbeaconLarge indicator lampsHigh high levelalarm (HHLA)High levelalarm (HLA)Ullage availablefor full load ofbitumenAudible klaxonwith keyoperated muteInformation tomixer cabin controlroom and/orremote monitoringsystem

15 - guidance for safe bitumen tank managementOther information1. Guide to Safe Delivery of Bitumen (UK Edition)Refined Bitumen Associationwww.bitumenuk.com2. Model Code of Safe Practice in the PetroleumIndustry Part 11: Bitumen Safety CodeEnergy Institutewww.enegyinst.org

16 - safe bitumen tank managementMPA Asphalt is part of the Mineral ProductsAssociation, the trade association for the aggregates,asphalt, cement, concrete, dimension stone, lime,mortar and silica sand industries.© MPA Asphalt August 2013MPA AsphaltGillingham House, 38-44 Gillingham StreetLondon SW1V 1HUTel +44 (0)20 7963 8000 Fax +44 (0)20 7963 8001mpaasphalt@mineralproducts.orgwww.mineralproducts.orgRefined Bitumen Association LtdHammerain House, Hookstone AvenueHarrogate, North Yorkshire HG2 8ERTel +44 (0) 1423 876 361 Fax +44 (0) 1423 873 999www.bitumenuk.com