Australian New Zealand Standard AS / NZS Pipelines – Gas and Liquid Petroleum – Field Pressure Testing – Western Australia. AS – , Field Pressure Testing, Revision committed formed, Expected AS – , Safety Management Studies, With. AS/NZS Accessed by CITIC PACIFIC MINING PTY LTD on 03 Dec AS/NZS Australian/New Zealand Standard?.
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End-points of this order can be expected in the field pressure test. The Standard recognizes that a number of different types of test section require a leak test and provides that the method of leak detection be appropriate to the section under test. Column 6 represents the additional volume of water added to compress the residual air. The relationship between pressure and temperature can be determined by the use of a test section embodying typical variables set aside for this purpose and monitored over an extended stabilizing period.
AS Pipelines-Gas and liquid petroleum – Field pressure testing_图文_百度文库
The volume added to the section for each increment of pressure is a function of the stiffness of the section and is made up of the volume added to expand the internal diameter of the steel pipes and the volume added to compress the water in the test section.
The instrument measures precisely both pressure and pressure change. The leak sensitivity will be improved by a hold period of 2 or 3 days, and the Standard recognizes this as an acceptable basis for testing sections with a volume larger than 25 ML.
The basis of the engineering approach to equipment requirements is to assess firstly what is to be done with the readings obtained and then the standard of equipment needed to provide the right number of significant figures. Table A1 shows the relationship between elapsed time and the amount of air that will have been dissolved as a percentage of the amount that can be dissolved.
Chart recorders do not provide adequate sensitivity. B1 1 Where a restrained pipeline contains a significant amount of pipe of a differing thickness, or for a telescoped pipeline, Equation B1 becomes—? This decay is well above the allowable unaccountable pressure change of The test program should also detail the division of the pipeline into test sections, and the physical and environmental characteristics of each section.
The slower strain rate cancels approximately one third of the von Mises effect. If the curvature has not been eliminated or the end-point pressure is less than kPa, the volume of residual air shall be determined and shall comply with the limit in the Test Program. The leak test sensitivity can be improved by extending the test period. The values in Column 4 are derived from those in Column 3 by the subtraction of each reading in Column 3 from the highest reading in Column 4.
SCOPE OF ACCREDITATION
During the hold period, visible parts of the test section shall be inspected for leaks. Falling pressure readings are reliable and convenient, and the calculations are simplified if readings are taken in pressure decrements of kPa each.
This Section defines the minimum requirements for accuracy, sensitivity and repeatability of test equipment and the practices to be observed to ensure that readings of test instruments reflect test section parameters and avoid spurious influences. If there are no observed leaks and the leak test is to be carried out at the same pressure, the test is simply continued with the strength-test hold period counting as part of the leak test period.
This philosophy was generated largely by efforts to secure maximum capacity from existing lines by retesting or applying original high level testing in order to increase operating stresses. For information about these services, users should contact their respective national Standards organization.
Simple methods for measurements and calculations for field use are included in Appendix F, for which it might reasonably be deduced that air above kPa is more of a danger than a limitation on leak detection. Hydrostatic testing of a pipeline is usually carried out by testing a number of isolated test sections. The pipeline industry has, however, traditionally carried out leak tests at a higher pressure for a number of reasons, including the following: The amount of exposed pipe in the test section.
For a typical deadweight tester, or equivalent high performance pressure instrument, this would be expected to be 1 kPa. An ice-point verification is sufficient.
It is necessary to be able to detect leaks of L, 40 L or 20 L per 24 h against the background uncertainty of measurement of pressure and pipe wall temperature. In Table F1 it is assumed that corresponding pressure and volume readings will be taken at the falling pressures shown in Columns 1 and 2.
However, the von Mises effect on the onset of yield is modified in the field by the effects of the different straining rates see Paragraph E6. This level of strain corresponds to about 0. Higher pressures can be used and would be applicable where combined strength and leak tests are carried out at the same pressure. In both cases, the result is pressure strength for each test section of the pipeline. It is thought that a slightly less accurate result which always overestimates the product loss is preferable to one which may underestimate the loss.
The reliability of laboratory tensile tests for assessing premature end-points is further reduced because they are often performed on flattened strap test pieces removed from pipe by oxy-cutting. It may also be used for testing other pipelines including pipelines designed to, or operated to, AS Although the actual time has not been well defined, 2 h is considered sufficient.
A specific end-point that reflects the stress-strain behaviour of the pipe in a test section can be derived by converting the typical stress-strain curve of the pipe into a pressure-added volume curve of the test section taking the progressive compression of the test liquid into account and applying statistical methods to the distribution of pipe strengths and pipeline elevations.
For test pressures above kPa, a residual air volume less than 0. Assessment of thermal stability is recommended at leak test pressure, to avoid potential disturbances to thermal stability during addition or removal of any test liquid necessary to reach leak test pressure, and may be carried out during the leak test period.
The potential gas leakage rate from a hole of diameter 0. Other methods discussed in A A4. High performance pressure calibrators may provide equivalent performance.
The effect of dissolution of air remaining in the test section is described in, and may be estimated in accordance with Paragraph A4. The value of relevant and significant external loads. During the elastic phase of pressurization and during any pressure change, the same quantity of water is added 2885.55 subtracted to produce a given change of pressure.
This Standard was prepared to provide a basis on which approving authorities could assess tests or testing programs. At the end of the strength test hold period, any observed leaks are noted or repaired and the section is leak-tested. The effect of this aspect of the Standard will again be to encourage the setting of the mill test pressures at a level more appropriate to the field test pressure rather than the traditional test pressures used for pipe to API 5L.
It should be recognized that changes in pressure result in changes in temperature due to the effects of adiabatic compression or decompression. Yielding will not occur at a pressure below a previous test pressure.
A revised end-point may be defined equivalent to the yield stress of the pipe material 0. Standardized spreadsheet routines could be supplied to testers undertaking such work, requiring insertion of density and pipe details to derive the variables. These entries are for information only. Before commissioning or recommissioning of aas pipeline, field pressure tests are specified in AS