| Oil & Gas Journal, 92:49, 12/5/1994 |
Patrick Dalton, Arkady Sobolevsky
Gulf Interstate Engineering
Houston
J.T. Powers
Belmont Engineering Services
Houston
Alexander Aynbinder
Ventech Engineering Inc.
Houston
Yuriy Tabakman
Consultant
Houston
Results of final pressure testing of any newly Pt built oil or natural-gas pipeline determine the new system's maximum allowable operating pressure (MAOP).
This is equally true for projects in the former Soviet Union (FSU) where many new pipelines and several projects for rehabilitating existing pipelines are being planned.
This final article in a series of three on design codes in the FSU and U.S. compares the pressure testing requirements of each set of codes.
The first article (OGJ, Mar. 7, p. 67) provided a general introduction to both code systems. It also examined in detail their stress analysis provisions.
The second (OGJ, July 11, p. 52) compared the U.S. and FSU technical requirements for line pipe in pressure piping service.
The FSU, with one of the largest petroleum and natural-gas pipeline systems in the world, is transforming itself from a state-planned economy into a market economy. This process requires large-scale investment and the organization of joint ventures.
The process includes numerous pipeline projects involving joint ventures between western oil and gas companies and FSU partners. Western companies participating in energy joint ventures need to become familiar with official FSU federal oil and gas industry codes, standards, recommended practices, and other regulations.
This article is primarily to familiarize Western engineers with the practices of their FSU partners.
It introduces the general, mandatory standard used by the FSU oil and gas industry for pressure testing and acquaints Western engineers with current FSU pressure-testing practices. It shows the relationship between this code and the other FSU oil and gas industry codes, standards, and regulations.
When applicable, this article directly compares FSU pressure-test procedures and requirements applicable to steel pipelines under provisions of the FSU code, ASME B31.4, and ASME B31.8.
The article's goals are to emphasize the principal differences in the pipeline pressure-test philosophies and methods and, in examples, describe specific details of the technical aspects of pressure-testing procedures such as, for example, the selection of the test media, test pressures, and test durations required by these codes for commissioning transmission pipelines.
For oil and oil-product pipelines that will be tested hydraulically, comparing the hydrostatic test pressure requirements of the FSU codes and ASME B31.4 is complicated.1 The FSU codes require a certain pressure at the lowest point of the test section; ASME B31.4 requires a minimum pressure at any point.
For planar pipeline sections, when the pressure at the highest point is equal to the pressure at the lowest point, the test pressure stated in the FSU code (the pipe mill-test pressure) and the test pressure required by ASME B31.4 (125% of the internal design pressure) are approximately equal.
For gas pipelines, a comparison of strength test procedures used by the FSU code and ASME B31.84 can be made concerning the test pressures and media.
For hydraulically tested gas lines, the FSU code has a specific test pressure only for the highest point of the test section and a limitation on the pressure at the low point.
For location Classes 3 and 4 in ASME B31.8, there are rules concerning hydraulic testing, with a stated value for the minimum pressure at the highest point.
Comparing these pressures at the highest points, the FSU code value is approximately 27% lower than the value in ASME B31.8.
When gas lines will be pneumatically tested, the test pressures according to both code systems are approximately equal.
The test pressures on the properties of compressor and pump stations as well as the facilities of these stations are approximately 20% more when performed in accordance with the FSU, codes.
The strength-test durations for hydraulic tests according to the FSU codes are approximately 6 times that of ASME B31.4 and 12 times that of ASME B31.8. The strength-test durations for pneumatic tests in accordance with the FSU codes are 6 times that required by ASME B31.8.
The leak-test pressures for hydrotesting oil and oil product lines in accordance with the FSU codes are 10% less than those required by ASME B31.4. The leak-test durations for hydraulic tests are at least 3 times more in the FSU codes than in ASME B31.4.
Leak-test duration requirements are not found in ASME B31.8.
An accompanying box provides FSU terms and their definitions.
The SNIP design-code system has several documents for transmission pipeline design and construction, including installation and pressure testing. (SNIP is the English pronunciation of the Russian acronym for Construction Standards and Regulations.)
Operation and maintenance of these pipelines are not jurisdictionally covered by the SNIPS. As in the U.S. system, the FSU codes refer to several other codes including SNIPS, GOSTs (State Standards/Specifications), ONTPs (State Standards Governing Technological [Process] Designs), and VSNs (Interministerial Construction Codes).
The principal stipulations for pressure testing transmission pipelines to FSU standards were originally defined in SNIP III-42-80, the FSU standard that governed the construction and commissioning of transmission pipelines in the FSU.3
Published in 1981, this document contained the requirements and methods for pressure testing pipelines during and after construction, including the selection of the test media, test pressures, and test durations.
These test parameters depended on the pipeline's category and designation, which are found in SNIP 2.05.06-85 4 which has been briefly introduced in the first of this series of articles (OGJ, Mar. 7, p. 67).
In January 1983, the U.S.S.R. State Construction Committee (Gosstroi) issued an addendum to SNIP III-42-80 requiring cyclic strength and leak pressure testing of pipelines.
The requirements were for a minimum three cycles in which the pressure was at least that necessary to produce a hoop stress in the pipe metal of 75 to 90% of the specified minimum yield strength (SMYS).
In February 1989, Gosstroi approved and published VSN 011-88, which was prepared by the Ministry of Construction for the Oil & Gas Industries.5 Superseding SNIP 111-42-80's pressure-testing requirements, this document withdraws the cyclic testing requirements and establishes new rules and procedures for pressure testing.
VSN 011-88 states that it is in effect until the next issuance of the SNIP pertaining to work execution and acceptance. Since 1989, SNIP III-42-80 has not been revised or reissued. There is also no evidence of a new work execution and acceptance code being developed.
Consequently, VSN 011-88 is the current code in effect for pressure testing FSU transmission pipelines.
The following general notes should be considered before further technical evaluation and discussion of Western and FSU codes.
SNIP III-42-80 is a federal regulatory document prescribing mandatory requirements, and VSN 011-88 is a mandatory industry code.
It covers only steel pipelines 1,420 mm (56 in.) OD or smaller and all product pipelines designed according to SNIP 2.05.06-85 and VSN 51-3-85/51-2.38-85.'
The FSU code's requirement that the test pressure equal the mill-test pressure precludes an occasion when the MAOP is determined from the final strength test, as can be the case in ASME B31.8.
An accompanying box compares the pressure test philosophies and methods.
The FSU code and ASME B31.4 both have situations for which two-step pressure testing is required. And there are instances under both U.S. codes when a single-step test is acceptable.
Another box summarizes the required test media.
Because this article's purpose is to familiarize the Western engineer with the practices of FSU testing procedures, only the method described in VSN 011-88 is discussed. Western guidelines are provided in ASME B31.4 and B31.8.
Table I lists the VSN test parameters, test pressures, and test durations.
According to VSN 011-88, several pipeline sections require multiple strength testing.
These sections must be tested individually before their integration into the pipeline and as a unit after completion of pipeline construction.
The first strength tests for these sections are at a higher pressure than the final test when they are part of the pipeline system.
The VSN lists the sections requiring this testing regimen, the testing stages, and the pressures required for these preliminary tests.
This section is tested as a separate section at a pressure equal to 125% of the operating pressure if the test is performed pneumatically or 150% of the operating pressure if the test is performed hydrostatically for 6 hr.
The first step is not required when the under-water crossing section is installed as part of a sequential line-laying (column-like) installation method. In this sequence, the joints are welded just before the crossing segment is pulled into the predredged trench.
ASME B31.4 and B31.8 do not require the preliminary testing step that VSN 0111-88 requires.
These U.S. codes contain only general statements regarding pressure testing pipeline crossings (for example, paragraph 841.323). The crossings can be tested in each case in the same manner and to the same pressure as the pipeline on each side of the crossing.
Copyright 1994 Oil & Gas Journal. All Rights Reserved.