Petroleum liquids - Automatic pipeline sampling (ISO 3171:1988)

Recommends procedures for crude oil and liquid petroleum products being conveyed by pipeline. Does not apply to liquefied petroleum gases and liquefied natural gases. The principal purpose ist to give guidelines for specifying, testing, operating, maintaining and monitoring crude oil samples.

Produits pétroliers liquides - Echantillonnage automatique en oléoduc (ISO 3171:1988)

Naftne tekočine – Avtomatično vzorčenje iz cevovoda (ISO 3171:1988)

General Information

Status
Published
Publication Date
31-Oct-1999
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
01-Nov-1999
Due Date
01-Nov-1999
Completion Date
01-Nov-1999

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2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Produits pétroliers liquides - Echantillonnage automatique en oléoduc (ISO 3171:1988)Petroleum liquids - Automatic pipeline sampling (ISO 3171:1988)75.080Naftni proizvodi na splošnoPetroleum products in generalICS:Ta slovenski standard je istoveten z:EN ISO 3171:1999SIST EN ISO 3171:1999en01-november-1999SIST EN ISO 3171:1999SLOVENSKI

STANDARD
SIST EN ISO 3171:1999
SIST EN ISO 3171:1999
SIST EN ISO 3171:1999

ISO INTERNATIONAL STANDARD 3171 Second edition 1988-12-01 INTERNATIONAL ORGANIZATION FOR STANDARDIZATION ORGANISATION INTERNATIONALE DE NORMALISATION MEXfiYHAPOP,HAR OPI-AHM3A~Wl IlO CTAHflAPTM3A~MM Petroleum liquids - Automatic Pipeline sampling Produits p6 troliers liquides - &han tillonnage au toma tiq& en olboduc Reference number ISO, 3171 : 1988 (E) SIST EN ISO 3171:1999

ISO 3171 : 1988 (El Foreword ISO (the International Organization for Standardization) is a worldwide federation of national Standards bodies (ISO member bedies). The work of preparing International Standards is normally carried out through ISO technical committees. Esch member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, govern- mental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. Draft International Standards adopted by the technical committees are circulated to the member bodies for approval before their acceptance as International Standards by . the ISO Council. They are approved in accordance with ISO procedures requiring at least 75 % approval by the member bodies voting. International Standard ISO 3171 was prepared by Technical Committee ISO/TC 28, Petroleum produc ts and lubrican ts. This second edition cancels and replaces the first edition (ISO 3171 : 1975) of which it constitutes a technical revision. Users should note that all International Standards undergo revision from time to time and that any reference made herein to any other International Standard implies its latest edition, unless otherwise stated. @ International Organkation for Standardkation, 1988 0 Printed in Switzerland ii SIST EN ISO 3171:1999

ISO 3171 :1988 (EI Contents Page 0 1 2 3 4 5 6 7 8 9 IO 11 12 13 14 15 16 17 Introduction .......................................................... 1 Scope and field of application . . ........................................ 1 References ........................................................... 2 Definitions ........................................................... 2 Principles.. ........................................................ 4 Selection of sampling Point (inotuding stream conditioning) ............... 6 Profile testing. ....................................................... 7 Sampling probe design. .... . ............................................ 9 Sampler design and installatiom ....................................... 9 Control equipment .......... . ........................................ 10 Flowmeasurement .................................................. 11 Sample receivers and Containers. ...................................... 12 Samplehandling .................................................... 13 Safety precautions .................................................. 15 Operating procedures ................................................ 15 Proving the sampling System. ......................................... 17 Estimation of Overall sampling System uncertainty ........................ 20 Bibliography ........................................................ 23 Annexes A Estimating water-in-oil dispersion ....................................... 32 B Example of water concentration profiletests at a crude oil terminal .......... 51 C Guide for initial screening of potential sampling locations .................. 54 SIST EN ISO 3171:1999

ISO 3171 :1988 (EI Tables 1 Recommended Sampler characteristics for crude oil and refined products . . . . 11 2 Typical operating Parameters for intermittent fixed-grab-volume Samplers . . . 16 3 Typical Sampler maintenance and Performance report for an intermittent grabsampler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 4 Sampling test ratings for injected water concentrations of 1 % and above . . . 20 5 Symbols ........................................................... 34 6 Suggested resistance coefficients ..................................... 36 7 Valuesofpforbends ................................................ 37 8 Expected concentration ratio. ......................................... 37 9 Acceptability of Profile ............................................... 38 10a Water concentration Profile test ata crude oil terminal (set 1) ............. 52 10b Water concentration Profile test at a crude oil terminal (set 2) ............. 53 11 Suggested minimum flow rates versus mixing elements ................... 54 Figures 6 7 8 9 IO 11 12 Initial or periodic Validation of a sampling System ......................... 24 Graphical representation of concentration profiles in a horizontal pipe ....... 25 Location of sampling Point ........................................... 25 Multipoint probe for Profile sampling ................................... 26 Arrangement of multipoint probe in horizontal Pipeline for 300 mm diameter pipelinesorlarger ................................................... 27 Typical timing diagram for Sampler System testing ........................ 28 Bargraph presentation of automatic Profile test at three locations .......... 29 Results from Profile tests (typical profiles) ............................... 30 Typical sampling Systems ............................................ 31 Energy rate and drop size ............................................. 45 Settlingrate ........................................................ 47 Turbulente (diffusivity) .............................................. 49 13a Water concentration Profile test at a crude oil terminal (example 1) . . . . . . . . 52 13b Water concentration Profile test at a crude oil terminal (example 2) . . . . . . . . 53 SIST EN ISO 3171:1999

INTERNATIONAL STANDARD ISO 3171 : 1988 (EI Petroleum liquids - Automatic Pipeline sampling 0 Introduction The purpose of collecting a Sample of the material flowing through a Pipeline is to determine the mean composition and quality of the bulk quantity. Samples of the bulk quantity in the line may be analysed to determine composition, water and sedi- ment content, or any other important attributes such as den- sity, viscosity or, with special precautions, vapour pressure. Manual methods of Pipeline sampling are adequate for homogeneous liquids whose composition and quality do not significantly vary with time. If this is not the case, automatic sampling is the recommended procedure since the continuous or repetitive extraction of small samples from a Pipeline ensures that any changes in the bulk contents are reflected in the col- lected Sample. In Order that the Sample shall be as represen- tative as possible it is essential to ensure that the recommenda- tions of this International Standard with respect to the required homogeneity of the liquid at the sampling location and to the required frequency of extraction of the small samples are met. Consideration should be given to having standby samples pro- vided by manual methods that may be referred to if the automatic Sampler fails to perform satisfactorily; however, manual sampling will be subject to uncertainty if Pipeline con- ditions are varying. (See ISO 3170.) The equipment and techniques described have generally been used for sampling stabilized crude Oil, but may also be applied to unstabilized crude oil and refined products provided con- sideration is given to the relevant safety precautions and the diff iculties of Sample handling. Representative sampling of crude oil for density and water and Sediment content is a critical process. Extensive studies have shown that, in crude oil transfers, four distinct Steps are re- quired for determining representative values : a) adequate stream conditioning of the Pipeline contents; b) reliable and effective sampling, ensuring proportionality between sampling ratio and flow rate in the line; c) adequate conservation and transporting of the Sample; d) adequate conditioning and dividing into Parts for ac- curate laboratory analysis. This International Standard refers to existing methods of sampling and the type of equipment presently in use. lt is, however, not intended that it should exclude new equipment not yet developed for commercial use, provided that such equipment enables samples to be obtained that are represen- tative, and is in accordance with the general requirements and procedures of this International Standard. The annexes to this International Standard contain calculation procedures about Pipeline mixing theory and Profile testing and also give basic guidelines for Sampler location. lt is realized that in many countries some or all of the items covered by this International Standard are subject to man- datory regulations imposed by the laws of those countries; such regulations must be rigorously observed. In cases of con- flict between such mandatory regulations and this International Standard, the former should prevail. 1 Scope and field of application 1.1 This International Standard recommends procedures to be used for obtaining, by automatic means, representative samples of crude oil and liquid Petroleum products being con- veyed by Pipeline. NOTE - Although throughout this International Standard the term crude oil is used, this should be taken to include other Petroleum liquids where the technique and equipment are also applicable. 1.2 This International Standard does not apply to the sampling of liquefied Petroleum gases and liquefied natura1 gases. 1.3 The principal purpose of this International Standard is to give guidelines for specifying, testing, operating, maintaining and monitoring crude oil Samplers. 1.4 The sampling procedures for crude oil are intended to provide representative samples for the determination of a) the oil composition and quality; b) the total water content; c) other contaminants that are not considered to be part of the crude oil transferred. 1 SIST EN ISO 3171:1999

ISO 3171 : 1988 (EI If the sampling procedures for a), separate samples may be required. b) and c) are in conflict, NOTE - The results of the laboratory analysis may be used for calculating adjustments to the declared quantity of crude oil trans- ferred. The procedure for carrying out the adjustments does not form part of this International Standard. 1.5 Sample handling is included, covering all aspects follow- ing collection to the transfer of the Sample to laboratory apparatus. 1.6 This International Standard describes the practices and procedures believed at the present time to be the most likely to lead to representative sampling and hence to accurate water determination. However, the accuracy of the water determina- tion on Pipeline samples obtained using automatic Samplers will depend upon the arrangement and characteristics of all the various elements making up the sampling System, and on the accuracy of the subsequent analytical procedures. A theoretical technique for evaluating the combined accuracy of the automatic sampling System and the analytical test is given in clause 16. A practical test procedure for field use is described in clause 15. Normally, the acceptable accuracy limits for a particular automatic sampling System will be specified in agreement between the interested Parties. Table 4 of clause 15 classifies the Performance of automatic sampling Systems by ratings based on the accuracy of practical test results. These ratings may be used as a guide to possible Performance and as a basis for individual agreement. 2 References ISO 3165, Sampling of Chemical products for industrial use Safety in sampling. ISO 3170, Petroleum products - Liquid hydrocarbons Manual sampling. NOTE - See also clause 17, Bibliography. 3 Definitions For the purpose definitions apply of this International Standard, the following - - 3.1 acceptable (accuracy) limits: The limits within which the determined concentration of water in a Sample is accept- able relative to the true value or other specified value, at the 95 % probability level. 3.2 automatic Sampler: A System capable of extracting a representative Sample from the liquid flowing in a Pipe. The System consists of a sampling probe and/or a separating device, an associated controller and a Sample receiver. 3.2.1 intermittent Sampler: A System for extracting liquid from a flowing stream, a Sample receiver to contain the Sample grabs taken from the stream, and a means for controlling the amount of Sample taken by varying the sampling frequency or grab volume in relation to flow rate. 3.2.2 continuous Sampler: A System for extracting liquid from a flowing stream which has a separating device which continuously withdraws liquid from the main Pipeline in relation to flow rate, an intermediate Sample receiver, and a means for controlling secondary withdrawal to a final Sample receiver. 3.3 calculated Sample volume: The theoretical Sample volume obtained by multiplying the Sample grab volume by the number of actually collected grabs. 3.4 competent person: A person who by reason of his or her training, experience, and theoretical and practical knowledge is able to detect any defects or weaknesses in the plant or equipment and to make an authoritative judgement as to its suitability for further use. NOTE - This person should have sufficient authority to ensure that the necessary action is taken following his or her recommendation. 3.5 controller: A device which governs the Operation of the automatic Sampler in Order to provide a representative Sample. 3.6 fixed-rate Sample; time-proportional Sample : A Sample taken from a Pipeline during the whole period of transfer of a batch, composed of equal increments at uniform time intervals. 3.7 flow-proportional Sample: A Sample taken from a Pipeline during the whole period of transfer of a batch, at a rate which is proportional to the rate of flow of the liquid through the Pipeline at any instant. 3.8 grab: The Portion of liquid extracted from the pipe by a Single actuation of the separating device. The sum of all the portions results in a Sample. 3.9 homogeneous mixture: A liquid is homogeneous if the composition is the same at all Points. For the purposes of this International Standard a liquid is homogeneous if the Variation in composition does not exceed the limits provided in 4.4. 3.10 integrity of the Sample: The condition of being com- plete and unaltered, i.e. the Sample being preserved with the same composition as when it was taken from the bulk of the liquid. 3.11 isokinetic sampling: Sampling in such a manner that the linear velocity of the liquid through the opening of the sampling probe is equal to the linear velocity of the liquid in the Pipeline at the sampling location and is in the same direction as that of the bulk of the liquid in the Pipeline approaching the sampling probe. 2 SIST EN ISO 3171:1999

ISO3171:1988 (EI 3.12 mixer: A device which provides a homogeneous mix- ture of the liquid within a Pipeline or Container in Order to obtain a representative Sample. 3.12.1 powered mixer: A mixing device which depends on an external Source of power for the energy required to mix the liquid. 3.12.2 static mixer: A mixing device having no moving Parts and located within a pipe or tube. lt depends on the kinetic energy of the moving liquid for the energy required to mix the liquid. 3.12.3 variable-geometry static mixer: A mixing device with Parts inside the pipe or tube which tan be adjusted to modify its characteristics at different flow rates. 3.13 Pipeline: Any section of pipe used for the transfer of liquid. An unobstructed pipe does not have any internal fittings such as a static mixer or orifice plate. 3.14 Profile testing: A technique for simultaneous sampling at several Points across the diameter of a Pipe. Terms used in connection with Profile testing are as follows: 3.14.1 Overall mean : The average of either the Point averages or the Profile averages. (Note that the result is the Same.1 3.14.2 Point: A Single sampling orifice in the Profile. 3.14.3 Point average: The average of the water concentra- tion at the same Point in all profiles (neglect Points with less than 1 % watet=). 3.14.4 Profile: A set of samples taken simultaneously at several Points across a diameter of the Pipe. NOTE - The term is also used to denote the series of sampling Points themselves and the set of results obtained by analysis of the samples taken at these Points. 3.14.5 Profile average: The average of the water concentra- tion at each Point in the same Profile (neglect the Profile if it has less than 1 % water). 3.15 representative Sample: A Sample having its physical or Chemical characteristics identical to the average charac- teristics of the total volume being sampled. NOTE - Since errors cannot be quantified exactly, compliance with this ideal tan only be expressed as an uncertainty that tan be obtained either from practical tests or by theoretical calculation. 3.16 Sample: The Portion of liquid extracted from the Pipeline that is subsequently transferred to the laboratory for analysis. 3.17 Sample conditioning : Homogenization necessary to stablize the Sample during Sample handling in preparation for analysis. 3.18 Sample Container: A vessel used for the storage, transportation and preconditioning of the total quantity, or a Proportion of the total quantity, of the Sample for analytical work or for division into identical small sub-samples to be analysed. 3.19 Sample handling : The conditioning, transferring, dividing and transporting of the Sample. lt includes transferring the Sample from the receiver to the Container and from the con- tainer to the laboratory apparatus in which it is analysed. 3.20 Sample loop: A by-pass to the main Pipeline being sampled through which a representative Portion of the total flow is circulated. 3.21 Sample receiver; receptacle: A vessel connected to the automatic Sampler in which the Sample is collected during the samplisitg Operation. A receiver may be permanently at- tached to .the Sampler or it may be portable. In either case, it should be designed to maintain the integrity of the Sample. NOTE - In certain circumstances, it is possible to collect the total Sample in more than one Sample receiver. In such circumstances, the Sample integrjty has to be maintained for each individual Sample volume. 3.22 Sampler Performance factor (PF) : The ratio between the accumultited Sample volume and the calculated Sample volume (see14.6). 3.23 sampling frequency: The number of grabs taken in unit time. 3.24 sampling interval: The grabs. time between successive 3.25 sampling location: The Cross-section of the pipe where the sampling probe is, or is proposed to be, located. 3.26 sampling into the Pipeline: probe: The Sampler element that extends 3.27 sampling ratio : represented by one grab. The quantity of Pipeline contents NOTE - lt tan beJexpressed as either the volume, in cubic metres grab, or the equiva4ent length of Pipeline, in metres per grab. Per 3.28 separating; device: A device that separates a small volume of liquid from the batch of liquid that the small volume represents. 3.29 stream conditioning : The distribution and dispersion of the Pipeline contents, upstream of the sampling location. 3 SIST EN ISO 3171:1999

ISO 3171 : 1988 (El 3.30 time-proportional Sample : See 3.6. 3.31 water. 3.31.1 dissolved water: The water contained forming a Solution at the prevailing temperature. within the oil 3.31.2 suspended water: The water within the oil that is finely dispersed as small droplets. NOTE - lt may, over a period of time, either collect as free water or become dissolved water, depending on the conditions of temperature and pressure prevailing. 3.31.3 free water: The water that exists as a from the Oil, and typically lies beneath the Oil. separate layer 3.31 .4 total water: The sum of all the dissolved, and free water in a cargo or parcel of Oil. suspended 3.32 worst-case conditions : The operating conditions for the Sampler that present the most uneven and unstable con- centration Profile at the sampling location. NOTE - This will usually be at minimum flow rate, minimum oil den- sity and minimum oil viscosity but may also be influenced by other factors such as emulsifiers and surfactants. 4 Principles 4.1 Purpose This clause defines the principles which it is essential to observe during sampling operations in Order that the represen- tativity of the Sample taken corresponds to the specifications of this International Standard, and meets the acceptability criteria given in 4.4. 4.2 Principles to be observed In Order to determine the oil composition, quality and total water content of a batch of crude Oil, samples that are representative of the batch are taken and analysed. The batch may be either a discrete Pipeline transfer over a given period of time, or the whole or part of the cargo of a tanker, either loading or unloading. Representativity depends on four conditions, all of which should be observed, since failure to comply with any one of them could affect the quality of the final result. 4.2.1 The first condition is that the samples that are taken from the Pipeline should have the same composition as the average composition of the crude oil over the whole cross- section of the Pipeline at the location and time of sampling. lt is not easy to comply with this condition, because of the possi- bility of a variable concentration gradient existing across the section. This condition requires that at the sampling location: a) the distribution or concentration of the water in the crude oil should be uniform across the section of the Pipeline within the acceptance limits given in 4.4; b) the diameter of the entry port of the sampling probe should be large in relation to the maximum water droplet size. The port opening should not be smaller than 6 mm (sec 7.3). 4.2.2 The second condition is that representativity should persist throughout the period of transfer of the batch, the com- Position of which may Change between the Start and finish of sampling. The rate of sampling, whether it is continuous or in- termittent, should be in proportion to the flow rate in the Pipe. When an intermittent Sampler is used the sampling frequency and grab size should both be sufficient to guarantee acceptable representativity. Furthermore, the representativity of the Sample should be maintained in the automatic Sampler from the sampling probe up to the final receiver. Samples should be taken with an ap- pliance that camplies with the recommendations in clauses 7, 8, 9 and 10. 4.2.3 The third condition is that the Sample should be main- tained in the same condition as at the Point of extraction, without loss from it of liquid, solids or gases and without contamination. Storage and transfer of samples should comply with the recom- mendations in clause 11. 4.2.4 The fourth condition concerns division of a Sample into a number of sub-samples in such a way as to ensure that each of them has exactly the same composition as the original Sample. The procedure for dividing each Sample into sub-samples, and for transferring them to laboratory appliances, is given in clause 12. NOTE - lt should be emphasized that this fourth condition concerns a critical activity and any error introduced is capable of destroying the representativity achieved by the first three. 4.3 Sampling tolerantes and Validation In Order to ensure that each Sample sent to the laboratory for analysis is representative of the whole batch, the composition of the Sample should not differ from the composition of the batch by more than the tolerantes given in table 4 and as applied in 15.5. In Order to ensure that any departure from the conditions given above (see 4.2) does not result in a Sample representativity which exceeds the tolerantes given in table 4, each step of the sampling Operation should be validated as shown in figure 1. 4 SIST EN ISO 3171:1999

ISO3171 :1988 (EI 4.4 General principles for sampling Hydraulic laws governing the behaviour of heterogeneous liquids which will mix or will not mix in the pipe show that for stream conditioning a sufficiently high energy dissipation rate should be provided to keep drops of water and heavier solid particles suspended in the crude Oil. Such an energy dissipation rate may be provided either from the velocity in an unobstructed Pipe, or from a mixing device immediately upstream of the sampling location. In considering the distribution of water over the Cross-section, the acceptable limits of the values found in the Profile test (clause 6) should be relative to the mean concentration of water in that plane and should be within + 0,05 g/lOO g for samples having a water content up to 1 g/lOO g and should be + 5 % of the mean concentration (relative) for samples having a water content greater than 1 g/lOO g [but see also case 2 (4.4.2)1. NOTE - Although the concentrations they also apply to volume units. a bove are quoted in mass units, As there is a range of concentrations at different Points in the Cross-section, sampling at a predetermined Point is unaccept- able, and it will be necessary to install a mixing device (see 5.3). NOTE - If there is any free water, or an emulsion having a high con- centration of water, at the bottom of the Pipe, representative sampling is not possible. 4.5 Dispersed Phase - variations with time lt is unlikely that the concentration of a dispersed Phase com- ponent in the bulk liquid will be constant with time. For example in the discharge of crude oil from a marine tanker, in addition to more gradual changes in the base water content, there may also be periods when peaks of relatively high concen- trations of water travel down the Pipeline. Experimental obser- vations indicate that these “transients” may contain over 50 % water and may be shorter than a minute in duration. Depending on the unloading procedures, the significance of the water discharged in the form of transients may vary relative to the base level carried with the bulk of the discharged cargo. In a horizontal Pipe, three cases may be used to describe the ways in which the concentration of the different phases may vary over the Cross-section of the pipe depending on hydraulic conditions (flow rate, product density and viscosity, dispersed Phase composition, interfacial tension modifiers, etc. ). lt is apparent that the representativity of samples taken in such applications will be dependent upon the ability of the automatic Sampler System to reflect, both accurately and proportionally, the integrated water content of these peaks in the total col- lected Sample volume. 4.4.1 Case 1 (see figure 2, Profile type 1) In this case, the concentration is the Same, within the accept- able limits as defined above, across the entire Cross-section of the Pipeline for all concentrations of water. The existing con- ditions are acceptable for sampling, since water is evenly distributed over the pipe Cross-section. A representative Sample consequently exists at the inlet of the sampling probe, which tan be placed at any Point on the diameter although it is essential that care should be taken not to place the sampling probe too near the wall in Order to minimize wall effects. 4.4.2 Case 2 (see figure 2, Profile type 2) With intermittent-type Samplers, accuracy will depend on the type of equipment and its frequency of Operation in relation to the frequency and duration of the transients. With continuous- type Samplers, accuracy will depend on the external collection and mixing arrangements and on the rate of secondary sam- pling if applied. For both types of Sampler, the Overall duration of the oil transfer, the duration of any water transients and the sampling frequency have statistical significance in the deter- mination of sampling accuracy. Theoretical analysis of the effect of dispersed Phase transients on the Performance of the different types of Samplers leads to the following general conclusions : a) in short-term transfers in which there is a possibility of frequent, short-duration transients, the accuracy of the continuous type of automatic Sampler is least affected by the transients; b) in short-term transfers in which there may be relatively few long-duration transients, the accuracy of the intermittent-type Sampler approaches that of the con- tinuous type of automatic Sampler; Sampling at this location will only be acceptable if the water concentration found at the sampling Point under worst-case conditions is equal to the mean concentration within the acceptable limits as defined above. c) for long-term transfers, the mean error introduced by transients of any duration, using either type of Sampler, is within the limits of acceptability defined in this International Standard. 4.4.3 Case 3 (see figure 2, Profile types 3a and 3b) In this case, the concentration across the Cross-section of the pipe is non-linear, indicating the presence of Segregation (type 3a). Some erratic profiles may also be encountered (type 3b). 4.6 Low water content Attention is drawn to the fact that, if the concentration of water is about 0,l % (mlm), i.e. near the level at which water is soluble in crude Oil, the concentration profiles will show a good uniformity of water distribution under all hydraulic con- di

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