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2 1 Background Leak Tests Measurement Uncertainty Hydrocarbon Test Fluids Project Aim Project Scope and Methodology Theoretical Analyses and Computer Modelling Field Testing and Comparison with Theoretical Modelling Hydrocarbon Test Fluid Data Final Report Literature Survey Research Program and Schedule... 7 Appendix 1 initial literature review of 8

3 Following discussions with the Proponent and other stakeholders in the project, this report sets out the general scope of work to be undertaken by the researchers during the course of the project. Each pipeline is required to be demonstrated as leak free by satisfying the requirements for a leak test, before it is placed into service. Leak testing is also carried out on some in-service pipelines to demonstrate their ongoing integrity. A leak in a closed pipeline can be suggested by a change in the measured pressure over time. For small diameter and short length pipelines, the change in pressure with loss of test fluid is large, and usually the pipeline can be declared leak free (or otherwise) by simple observation of the pressure data during the test period. For large diameter and long pipeline test sections, the Standard provides a table of allowable but unaccountable leakage rates. This is the equivalent fluid loss calculated from the residual change in pressure between the start and the end of the test period, after accounting for all measurable causes of pressure change (most importantly temperature change, but including measurable fluid loss from leakage at connections, test hoses etc.). It is recognised in AS that the identification of leaks with certainty against the uncertainty of the measurement methods and instrumentation presents difficulties. Usually the largest contributor to pressure change during a leak test is the change in temperature. It is recommended in AS that the bulk temperature of the fluid be measured throughout the test at a number of discrete locations, and the data averaged. The assumption is that the pipe wall temperature at a location represents the bulk temperature of the fluid at that point. This averaging of infrequent measurements, the uncertainty associated with the above assumption, along with uncertainties associated with the actual pressure and temperature measurements, introduces an error into the calculated pressure loss due to changes in the system. This in turn affects the quality of the assessment of whether a test section contains a leak. Other factors that contribute to the measurement uncertainty include instrument errors, instrument placement, mixing and stratification within the test fluid, and temperature change resulting from the Joule-Thompson effect during pressurisation. The uncertainty associated with this prediction places an upper limit on the maximum volume of a test section because the uncertainty approaches the pressure change equivalent to the nominated leak test acceptance criterion. When this occurs, either the test section length must be reduced, or the duration of the leak test increased. 3 of 8

4 These considerations suggest that it would be useful to analyse and quantify the various measurement uncertainties. AS is used for hydrostatic testing of liquid hydrocarbon pipelines. The consequences of a small leak from a liquid hydrocarbon pipeline are likely to be much more significant than a similarly sized leak from a gas pipeline, because environmental and safety considerations. A second activity associated with this research is to source and tabulate (or preferably to correlate into a polynomial equation) the compressibility data for typical liquid hydrocarbons usually used for in-service re-testing of liquid petroleum pipelines. This data is required because a number of liquid hydrocarbon pipeline systems require re-testing at regular intervals to demonstrate their integrity, and in the absence of reliable compressibility data for the test fluid, an erroneous assessment on the leak tightness of the pipeline may be made. AS provides a validated correlation for determining the contribution of water compressibility to the accountable component pressure loss. However, the Standard does not have a validated method for liquid hydrocarbon fluids, despite the significantly higher compressibility of hydrocarbon fluids. It is likely that the environmental impact from a leaking pipeline that is sentenced as leak tight because of an incorrect assessment of the fluid compressibility will be very significant. This part of the project will research available data sets for compressibility of the candidate hydrocarbon fluids used in testing, against the variables of pressure and temperature, and will reduce the data to a correlation equation for the candidate fluids that will in the future be included in the Standard. The candidate fluids are: Aviation Turbine fuel (used for in-service testing of aircraft refuelling systems) Automotive Diesel fuel Hydrocarbon fluid compressibility varies with the composition of the hydrocarbon fluid and the test temperature. The research will develop an appreciation of the uncertainty in the correlation proposed for fluid compressibility and will recommend a method by which this can be incorporated into the Standard. The purpose of this project is to develop an appreciation of each measurement uncertainty and to establish a methodology where these components can be combined to enable better design of each test section for hydrostatic leak test. This understanding will enable the Standard to be revised to incorporate a method of designing the test section to achieve a demonstrable uncertainty. The benefit of this is expected to permit a more flexible leak testing methodology which simplifies the requirements for sections 4 of 8

5 containing a small volume, and permits larger test sections when more complex measurement and data analysis methods are used. The outcome of this research will be used to develop AS to better address: Test section design Discrimination between accountable and unaccountable pressure loss in a test section where water is the test fluid Discrimination between accountable and unaccountable pressure loss in a test section where a hydrocarbon is the test fluid Documentation of measurement processes and analysis to design the temperature measurement requirements to achieve the level of discrimination between accountable and unaccountable pressure loss in any test section volume. The project will commence with work to develop sufficient background information to enable the researcher to properly define the project. This will include: Review of the work undertaken in CRC project Review of FORTRAN code developed under CRC project to model (under highly simplified conditions) the temperature variation with location and time of the water, pipewall and soil, during filling and stabilization. Upgrade of this code for purposes of the present project. Review of AS , in particular the concepts of the leak testing criteria Review the requirements of TdTUV which is the basis of the Standard s use of the permitted unaccountable loss. Review and appreciation of the instrumentation used in hyrodrostatic testing and if possible, witness a test. Develop a scope and schedule for each component of the work This phase of the project will comprise the following components: Identification and categorization of the parameters/sources of uncertainty in leak tests. Attending uncertainty training workshops offered by the National Measurement Institute. Upgrade of the FORTRAN code to include the effects of adiabatic compression and air dissolution. CFD (Computational Fluid Dynamics) analysis of the effect of a number of variables (eg non-uniform pipeline elevation) on temperature stabilization and influence on the temperature difference between pipe wall and bulk fluid. This will include conjugate heat transfer analysis. 5 of 8

6 Determining the effect of location of pipeline temperature measurement predicted bulk fluid temperature (eg sensor on outside coating, on pipe wall or in bulk fluid). Incorporation of pipeline elevation uncertainty analysis in FORTRAN code. Development of a tool (eg in Excel) to quantify the overall uncertainty in leak tests. Development of equation for overall measurement uncertainty in terms of components. The aims of this phase of the project will be to: Obtain and review a number of Leak Test pressure data sets previously measured in fullscale pipeline tests, including data about the location and influence of environmental variables on pipeline leak test stabilization (eg elevation, fill, buried/exposed, location data for pipelines). Endeavour to obtain new field test data, through liaison with industrial partners, with increased detail in temperature data for validation purposes (eg both bulk fluid and wall temperatures to be determined and logged continuously at specific locations with respect to time). Carry out modelling to determine fit of theoretical approach with field test results and develop possible case study for inclusion in industry guidance/standard. The proposed research will: Obtain and tabulate property data of candidate hydrocarbon fuels. Develop a correlation of data in appropriate equation form. Develop an analysis of the effect of hydrocarbon properties on the implementation and interpretation of leak tests and make recommendations as to the incorporation of this in the standard. 6 of 8

7 The project scope will include a survey of relevant literature. At the time of writing this interim report, literature survey is continuing. An outline of the relevant literature identified thus far appears in Appendix 1. The major milestones and delivery dates are listed below: 7 of 8

8 Retigen, P P L, Measurement Science for Engineers, Kogan Page Science, 2004 Wheeler, A J and Ganji, A R, Introduction to Engineering Experimentation, Prentice Hall, 1996 Yaws, C L, Chemical Properties Handbook: Physical, Thermodynamic, Environmental, Transport, Safety, and Health related properties of Organic and Inorganic Chemicals, McGraw-Hill, Kent, J A, ed, Kent and Riegel s Handbook of Industrial Chemistry and Biotechnology, Vol 2, 11 th Edition, 2007 Standards Australia, AS AS , Pipelines - Gas and Liquid Petroleum, 2007 Vereinigung der Technischen Überwachungs-Vereine e.v.,vdtuv-merkblatt, Wasserdruckprüfung von erdverlegten Rohrleitungen nach dem Druck-Temperatur-Meverfahren (D-T-Verfahren): Hydrostatic Pressure Testing of Buried Pipelines - Pressure-Temperature Measurement Procedure (P-T procedure), Essen, Germany, 1968 Pawlak, Rex L., Temperature induced pressure measurement uncertainty, Instrumentation in the Aerospace Industry : Proceedings of the International Symposium, 1993, p Pawlak, Rex L., Reducing temperature induced measurement uncertainty in pressure data, v 41, 1995, p Clark, D.L., Temperature compensation for a piezoresistive pressure transducers at cryogenic temperatures,, v 37, n pt B, 1991, p Hurll, John, Understanding measurement uncertainty: An introduction,, v 41, n 2, March, 2008, p Dahlgren, Matt, Measurement uncertainty of free-stream air velocity measurement in subsonic wind tunnels,, v 467,, 2006, p Kinney, Jonathan, et al, Impact of measurement uncertainty on ultrasonic meter speed of sound calculations,,, 2001, p Van Reet, J. D., Skogman, K. D., Effect of measurement uncertainty on real time pipeline modelling applications,, v 6, 1987, p Oracheski, J.D., Rausch, Neil, Tank volume measurement systems: Volume measurement uncertainty analysis,, v 3,, 2004, p of 8