Pipeline Fracture Research Articles

Methods of determining the stress-strain state and fracture toughness of gas- and oil-line pipe (survey)

We have surveyed the existing methods of determining the stress-strain state and fracture toughness of gas and oil lines. The discussion illustrated the promise of methods of evaluating the stress-strain state that are based on allowance for the strain-hardening of the material of the pipe or plastic indicators attached to its surface and deformed along with it. The first method, being destructive, can be used to evaluate the effect of different shaping methods on the strength of the pipe material, to analyze accidental pipeline fractures, and to generate a data bank on the stress-strain state of sections of a pipeline that have lost their longitudinal stability and are scheduled for replacement. Information obtained from the first method can also be used to establish correlations between the geometric parameters of such sections (deflection, curvature) and their stress-strain state. This will make it possible, with the use of reliable statistical methods, to predict the stress level on curved sections of pipelines without having to cut out samples for testing and analysis.

Analysis of pipeline fracture by fast crack propagation

An analysis is presented of the influence of wave processes in gases and in a pipeline wall on extended fracture by fast crack propagation. The influence of design and technological parameters of the pipeline and of the pipe metal fracture toughness on the extent of fracture is shown.

Material fracture toughness determination for polyethylene pipe materials using small scale test results

The Small-Scale Steady State (S4) test has been recently developed in order to assess the fracture behaviour of polyethylene (PE) gas distribution pipe material during rapid axial crack propagation. Based on an investigation of the S4 test, a simulation model of S4 test has been developed. This paper describes the use of the results obtained from the S4 test and program modified from PFRAC (Pipeline Fracture Analysis Code) to evaluate the fracture toughness of the material,G, which could not be directly obtained from the test, and to predict critical pressure,p c , for rapid crack propagation (RCP) in a full scale PE pipe. The algorithms for contact conditions are developed to consider the opening pipe wall impact against a series containment rings and the capabilities of PFRAC are also extended. WhenG d is evaluated, investigations are made on the effect of temperature, wall thickness and crack velocity. In addition, procedures to evaluate the critical pressure for the S4 test pipe are also discussed.

The development and validation of a dynamic fracture propagation model for gas transmission pipelines

A fracture control methodology that will prevent the possibility of long-running crack propagation, based on the crack-tip opening angle (CTOA) is outlined here. Two aspects are considered: (1) the calculation of the maximum CTOA for a given geometry and loading and (2) the determination of the critical material property for fracture, (CTOA) c. The vehicle for CTOA calculations was a fluid/structure/fracture interaction inelastic dynamic computational model for fast long-running fracture in pipelines. Validation of the approach used in this analysis was provided through quantitative comparisons with measured full-scale burst test data. A convenient two-specimen dropweight tear test was used to determine the (CTOA) c for line pipe steels. The linking of the latter with the quantification of a maximum CTOA for steady-state ductile fracture, using the numerical model, provides the basis for an approach that evaluates the conditions needed to ensure crack arrest.

Development of converter to change gas-liquid two-phase slug flow to bubbly flow in a vertical tube.

The mechanical and/or the thermal fatigue fracture of pipelines due to the pulsating characteristics of slug flow will be prevented, if slug flow is changed to bubbly flow. Ten kinds of flow pattern converters are developed and tested in a vertical tube of 30.3 mm I.D. The converter composed of five stages of porous plates is useful. The sintered porous plates of spherical particles made of acrylonitrile-butadiene-styrene resin and bronze are selected from 76 kinds of porous plates.

Fracture Propagation in Underwater Gas Pipelines

Two full-scale ductile fracture propagation experiments on segments of line pipe pressurized with nitrogen gas have been conducted underwater at a depth of 40 ft (12 m) to evaluate the ductile fracture phenomenon in underwater pipelines. The pipes were 22-in. (559-mm) diameter and 42-in. (1067-mm) diameter. Fracture velocities were measured and arrest conditions were observed. The overpressure in the water surrounding the pipe resulting from the release of the compressed nitrogen gas contained in the pipe was measured in both experiments. The overpressure in the water reduces the stress in the pipe wall and thus slows down the fracture. In addition, the water surrounding the pipe appears to be more effective than soil backfill in producing a slower fracture velocity. Both of these effects suggest a greater tendency toward arrest for a pipeline underwater than would be the case for the same pipeline buried in soil onshore. Further verification of this effect is planned and a modified version of the existing model for predicting ductile fracture in buried pipelines will be developed for underwater pipelines.

The Full Scale Burst Test of Large Diameter, High Pressure Gas Pipelines

Five major steel companies in Japan organized a committee in 1978 for investigation of shear fracture of pipelines, whose pipes are large diameter and high pressure resistant API 5LX X70 grade made by UOE Process. The main task of this committee was planning and execution of full scale burst tests for finding appropriate evaluation methods of characteristics for arresting the propagation of shear cracks. Since 1978 five full scale burst tests have been completed and the test results were described together with analysis. This paper is a kind of interim report, but the committee mentioned to a few outstanding conclusions relating to the effects of separation against fracture and critical energy values for arresting the crack propagation.

Study on the Propagating Shear Fracture of Line Pipes by the Partial-gas Burst Test

In order to evaluate the crack arrestability of line pipes to the propagating shear fracture, the partial-gas burst test was carried out on many line pipes of varied notch ductility, sizes and test conditions. A method to estimate the fracture energy of test pipes was established and the required notch ductility for line pipes against the propagating shear fracture of actual pipelines was introduced.

部分ガスバースト試験によるラインパイプの高速延性破壊の研究

In order to evaluate the crack arrestability of line pipes to the propagating shear fracture, the partial-gas burst test was carried out on many line pipes of varied notch ductility, sizes and test conditions. A method to estimate the fracture energy of test pipes was established and the required notch ductility for line pipes against the propagating shear fracture of actual pipelines was introduced.

Fracture Control Testing and Acceptance Criteria for Line Pipe

Summary A model specification for imposing mill test and acceptance criteria for fracture control is discussed. The specification applies to line pipe with wall thickness up to 1.5 in. (38 mm) intended for use in cross-country pipelines at temperatures between 32 and 250 deg. F (0 and 121 deg. C). Methods for establishing minimum acceptance levels (MAL) for Charpy V-notch specimens and drop-weight tear test specimens are described.Fracture controls are established to ensure crack arrest; methods for establishing acceptance criteria are based on equations modified from relationships found in Ref. 1.API grades B through X-70 are covered. Fracture control criteria are established separately for four service classes. Introduction Fracture control for pipelines has been of major interest to the industry for more than 25 years. This interest was prompted by the occurrence of pipeline fractures in which uncontrolled crack propagation, in lengths up to 3,000 ft (914 m), was observed.Initially, interest centered on the development of methods to prevent brittle fractures. More recently, interest has shifted to the prevention of uncontrolled ductile fractures. In both cases, the objective of studies funded by the industry and pipe vendors was to find out why such fractures occurred and to develop design and metallurgical methods of prevention.Study and development have been worldwide. While the causes of uncontrolled fractures now are understood reasonably well, controversies still exist about the best methods to be adopted for cost-effective fracture control. Nevertheless, results are sufficiently detailed to allow us to begin developing engineering standards and specifications to impose fracture controls on pipelines. These standards and specifications must take into account relevant design and metallurgical factors. A model specification was developed incorporating these factors; the specification is provided in the Appendices. Background Relevant literature is extensive and is not subjected to review in this paper. It is sufficient for the purpose of this paper to state that an extensive literature review effort was made and that, where possible, a conservative approach was used in those areas still subject to controversy. Key literature is cited in Refs. 1 through 3.The principles behind pipeline fracture control are straightforward - one must either incorporate crack stoppers in the pipelines or have line pipe toughness adequate to stop a fast-running crack. For a long pipeline, crack stoppers are impractical and, further, complicate construction. The preferred method is to specify adequate toughness; in most cases this can be accomplished by design and metallurgical controls at little or no extra cost.Both brittle and ductile fractures must be provided for. Brittle fracture can be eliminated by requiring a low brittle/ductile transition temperature. This sometimes is done by specifying Charpy impact energies, but a more reliable method is the use of a drop-weight tear test. The latter method is used in the proposed model specification.Much of the more recent industry work addresses the problem of specifying ductile fracture arrest in line pipe using Charpy impact toughness. JPT P. 527＾

Behaviour of Crude Oil Under Fresh-Water Ice

Abstract Experiments were carried out in a cold room at −15 °C to investigate the behaviour of Norman Wells crude oil under fresh water ice. The crude, when injected in water under the ice, separates into droplets and rises to the ice-water interface, where the oil droplets coalesce to form a slick. The spreading of oil under ice is complicated by the coalescence of oil drops at the ice-water interface, and the spreading process is found to be different from that of oil on water or on ice. If sufficient turbulence exists in the water, both oil-in-water and water-in-oil emulsions are formed. An oil lens sandwiched between the ice acts as an insulating layer and thus increases the temperatures drop cross the ice. Introduction The discovery of oil in commercial quantities in Northern Canada could lead to the construction of oil pipelines to the southern markets. Such pipelines would cross many rivers and streams that are subjected to ice conditions of varying seasonal length. It is conceivable that oil spills under ice-covered rivers may result from such pipeline crossings, The spills can be large, such as those caused by a major pipeline fracture, or they can be small, such as those developing through holes of a few centimeters diameter in the pipe. In addition, accidents involving oil tankers, storage tanks and tank trucks may also result in oil spills in ice-covered rivers. Although results on oil pollution research are published in an increasing number, available information on the behaviour of oil spilled under ice is limited. The only systematic study reported in the literature is by Wolf and Hoult(1). They investigated the effects of crude and diesel oils on the porous substructure of Arctic sea ice and found that the oil, when injected under the ice, was pocketed below the ice surface. They also reported that as freezing continued, more ice formed beneath the oil and that the oil acted as an insulating layer impeding the flow of heat- However, in order to assess the effect of an oil spill under ice-covered rivers and to help in developing clean-up techniques for such an oil spill, more must be understood about the behaviour of oil under ice, The present work investigates the behaviour of crude oil under fresh-water ice, Parts of the work were presented at the 1975 Conference on Prevention and Control of Oil Pollution(2). Experimental A circular aluminum basin, 150 cm in diameter and 70 cm deep was installed in a cold room where the temperature was maintained at −15 ±2 °C. Heating tapes were glued to the outside of the tank and covered with 10 cm of polystyrene insulation. The heating tapes were connected to variacs set at very low power to cancel out the bottom and side heat losses. This arrangement resulted in one-dimensional freezing in the basin, A stirrer was mounted on the side of the basin and a circular boom installed to prevent the oil from rising up the tank walls.

Fracture propagation control in gas pipelines: A survey of relevant studies

This paper reviews the problem of crack propagation in gas pressurised pipelines. After summarising the fracture control philosophy for pipelines, the main terminology and basic concepts are defined. A review of the brittle fracture problem summarises Battelle and British Gas studies relating fracture appearance and crack behaviour, and the background to the adoption of the DWTT fracture appearance criterion in specifications is detailed. The application of the strain energy theory to full-scale test results is discussed. A balance between strain energy stored in the pipe wall and fracture energy explains why brittle fractures arrest if the stress is below a critical level. The problem of ductile fracture propagation is reviewed and the results of full-size tests carried out by British Gas to provide toughness levels for fracture arrest are presented. The nature of ductile fracture propagation is discussed with reference to analogies with fracture initiation. Steady state, constant velocity, fractures imply specific shapes of the G (energy available)-velocity characteristic curves. In particular, a falling G with increasing fracture velocity is necessary. Some published theories to account for this effect are summarised and it is concluded that considerations of inertia in the fractured pipe wall provide the required relationship. Laboratory toughness tests for assessing brittle and ductile fracture resistance in relation to pipeline fracture behaviour are discussed. The relevance of fracture mechanics tests, particularly R curve analysis, is highlighted. The paper concludes with a list of areas of work which warrant further study.

Fracture of pressurized cylindrical shells

Pipeline fracture is analyzed via Lagrangean mechanics. The bursting pipeline is a system with two degrees of freedom. The two equations of motion for the crack are derived and solved for a simplified case. The fluid mechanics of a pressurized pipe during fracture is discussed and the different behavior of liquids and gases is indicated.

Fluid Interaction with Fracture Propagation in Pipelines

An analysis of catastrophic pipeline fracture is given. The fluid mechanics and fracture mechanics of the system are mutually interdependent, but they are treated separately and then compared graphically by parameters essential to both processes. The pressure drop behind the crack opening is determined for both processes. The pressure drop behind the crack opening is determined for both liquids and gases, and from this information the energies of the crack system are determined. The relationship between the crack opening angle and length of pressurized crack system is plotted on the same chart as the opening angle and crack length relationship required for catastrophic failure. The intersection of these two relationships determines the failure point.

Fracture of steel pipelines

This paper reviews the measures taken in Canada to prevent failure in oil and gas pipelines, the former relying on prevention of initiation by a ‘leak-before-break’ approach, the latter by measures aimed at preventing fracture propagation. The effect of stable slow crack growth is discussed.