Fracture Behavior in West Jefferson Test Under Low-Temperature Condition for X65 Steel Pipe With High Charpy Energy: Current Activities in HLP Committee, Japan, Report 1

This paper describes the results of pressure vessel fracture test which called West Jefferson and/or partial gas burst testing using Grade API X65 linepipe steel with high Charpy energy that exhibits inverse facture in the Drop Weight Tear Test (DWTT). A series of pressure vessel fracture tests which is as part of an ongoing effort by the High-strength Line Pipe committee (HLP) of the Iron and Steel Institute of Japan (ISIJ) was carried out at low temperature in order to investigate brittle-to-ductile transition behavior and to compare to DWTT fracture behavior. Two different materials on Fracture Appearance Transition Temperature (FATT) property were used in these tests. One is −60 degree C and the other is −25 to −30 degree C which is defined as 85 % shear area fraction (SA) in the standard pressed notch DWTT (PN-DWTT). The dimensions of the test pipes were 24inches (609.6 mm) in outside diameter (OD), 19.1 mm in wall thickness (WT). In each test, the test pipe is cooled by using liquid nitrogen in the cooling baths. Two cooling baths are set up separately on the two sides of the test vessel, making it possible to obtain fracture behaviors under two different test temperatures in one burst test. The test vessel was also instrumented with pressure transducers, thermocouples and timing wires to obtain the pressure at the fracture onset, temperature and crack propagation velocity, respectively. Some informative observations to discuss appropriate evaluation method for material resistance to brittle facture propagation for high toughness linepipe materials are obtained in the test. When the pipe burst test temperatures are higher than the PN-DWTT transition temperature, ductile cracks were initiated from the initial notch and propagated with short distance in ductile manner. When the pipe burst test temperatures were lower than the PN-DWTT transition temperature, brittle cracks were initiated from the initial notch and propagated through cooling bath. However, the initiated ductile crack at lower than the transition temperature was not changed to brittle manner. This means inverse facture occurred in the PN-DWTT is a particular problem caused by the API DWTT testing method. Furthermore, results for the pipes tested indicated that inverse facture occurred in PN-DWTT at the temperature above the 85 % FATT may not affect the arrestability against the brittle fracture propagation and it is closely related with the location of brittle fracture initiation origin in the fracture appearance of PN-DWTT.

Development of an Effective ASME IX Welding Procedure Qualification Program for Pipeline Facility and Fabrication Welding

For cross country pipeline welding in Canada, welding procedures shall be qualified in accordance with the requirements of CSA Z662 Oil and Gas Pipeline Systems. For pipeline facility and fabrication welding on systems designed in accordance with CSA Z662 or ASME B31.4, welding procedures qualified in accordance with the requirements of ASME Boiler & Pressure Vessel Code Section IX are permitted and generally preferred. Welding procedures qualified in accordance with ASME IX provide advantages for pipeline facility and fabrication applications as a result of the flexibility achieved through the larger essential variable ranges. The resulting welding procedures have broader coverage on material thickness, diameter, joint configuration and welding positions. Similarly, ASME IX is more flexible on welder performance qualification requirements and accordingly a welder will have wider range of performance qualifications. When applied correctly, the use of ASME IX welding procedures often means significantly fewer welding procedures and welder performance qualifications are required for a given scope of work. Even though ASME IX qualified welding procedures have been widely used in pipeline facility and fabrication welding, it is not well understood on how to qualify the welding procedures in accordance with ASME IX and meet the additional requirements of the governing code or standard such as CSA Z662 in Canada. One significant consideration is that ASME IX refers to the construction code for the applicability of notch toughness requirements for welding procedure qualification, yet CSA Z662 and ASME B31.4 are both silent on notch toughness requirements for welding procedure qualification. This paper explains one preferred method to establish and develop an effective ASME IX welding procedure qualification program for pipeline facility and fabrication welding while ensuring suitability for use and appropriate notch toughness requirements. The paper discusses topics such as base material selection, welding process, welding consumable consideration and weld test acceptance criteria.

Pipeline Diagnostics With Ultrasonic Meters

Canada and the United States have vast energy resources, supported by thousands of kilometers (miles) of pipeline infrastructure built and maintained each year. Whether the pipeline runs through remote territory or passing through local city centers, keeping commodities flowing safely is a critical part of day-to-day operation for any pipeline. Real-time leak detection systems have become a critical system that companies require in order to provide safe operations, protection of the environment and compliance with regulations. The function of a leak detection system is the ability to identify and confirm a leak event in a timely and precise manner. Flow measurement devices are a critical input into many leak detection systems and in order to ensure flow measurement accuracy, custody transfer grade liquid ultrasonic meters (as defined in API MPMS chapter 5.8) can be utilized to provide superior accuracy, performance and diagnostics. This paper presents a sample of real-time data collected from a field install base of over 245 custody transfer grade liquid ultrasonic meters currently being utilized in pipeline leak detection applications. The data helps to identify upstream instrumentation anomalies and illustrate the abilities of the utilization of diagnostics within the liquid ultrasonic meters to further improve current leak detection real time transient models (RTTM) and pipeline operational procedures. The paper discusses considerations addressed while evaluating data and understanding the importance of accuracy within the metering equipment utilized. It also elaborates on significant benefits associated with the utilization of the ultrasonic meter’s capabilities and the importance of diagnosing other pipeline issues and uncertainties outside of measurement errors.

Implementation of CSA Z662-15 Annex K Option 2 on a 610mm Liquid Pipeline

For more than two decades, CSA Z662 Annex K has provided a method for developing alternative acceptance criteria for weld flaws in mechanized welded pipelines. Increasingly, over the years, fracture mechanics practitioners have found the method overly conservative and restrictive with respect to brittle fracture criteria when compared to other accepted fracture mechanics-based engineering critical assessment ECA codes and methods. These limitations rendered the CSA Annex K method difficult to implement on pipelines constructed with materials not possessing optimal toughness and in cases requiring consideration of fracture toughness at temperatures lower than the typical minimum design metal temperature (MDMT) of −5°C. This paper presents experiences implementing CSA Z662-15 Annex K Option 2 methodology on a 610 mm diameter liquids pipeline and compares and contrasts the utility and benefits of the code revision. This pipeline required consideration for installation during winter months, necessitating installation temperatures as low as −30°C. In addition to evaluation of actual ECA results, analytical evaluations of the Option 2 methodology were also conducted considering parameters outside those used on the project. The new Annex K Option 2 method was found to be of considerable benefit in preparation of a practical ECA. Since fracture toughness testing was conducted at the anticipated lowest installation temperature, the flaw criteria were, as expected, principally controlled by elastic/plastic crack growth consideration. The failure assessment diagram implemented into the CSA Z662-15 Annex K Option 2 provided tolerance for both longer and deeper flaws than that afforded by Option 1 (which resorts to the former 2011 Annex K method). Furthermore, the reduced restriction to the surface interaction ligament (p distance) offers additional advantages including increased flexibility in weld profile design and weld pass sequencing. Fracture toughness (CTOD) testing of TMP pipeline steels used in the project at −30°C often produced transitional fracture toughness results. It was found that the particular project materials were quite sensitive to the level of test specimen pre-compression (an acceptable plastic straining method to reduce residual stress gradients) applied to the CTOD specimens to enhance fatigue crack-front straightness. It was found that optimizing the level of pre-compression (to achieve acceptable pre-crack straightness while minimizing plastic pre-strain) achieved a balance between fully satisfying testing requirements, providing a conservative assessment of CTOD, and facilitating a functional Annex K ECA.

Oil Pipeline Standoff Leak Detection: A Novel Approach for Airborne Remote Detection of Small Leaks

While natural gas pipelines already benefit from airborne, remote detection of leaks [1, 2], oil pipeline leak detection has been for a long time reliant on SCADA systems limited in their capability to detect very small leaks, and/or visual inspection of the right of way (line flyers, pipeline employees or members of the public). This paper presents a novel and complementary way of detecting small leaks (i.e. sensitivity of 0.1 L/minute, 1 barrel/day) of oil (crude or refined products) using an optical detection system mounted on an airborne platform (UAV, plane or helicopter). The scope of this paper is based on the requirements provided by TransCanada, namely sensitivity (herein referred as LOD — Limit of Detection) and accuracy (herein referred as spatial resolution) as similar to their description in API 1130, while the topic of reliability is addressed in our noted concerns on the false alarms that may be generated in Infrared-DiAL based systems due to soil reflectivity. Robustness, as described in API 1130, was out of scope. Keeping in mind the requirement of airborne operation, three different approaches for the detection of leaks along long pipeline ROWs were studied. Infrared Differential Absorption lidar (IR-DiAL), UltraViolet Raman lidar (UV-Raman lidar) and UltraViolet Laser-Induced Fluorescence lidar (UV-LIF lidar) have been tested in realistic conditions. In the first round of tests, laboratory spectral measurements of vapors in a closed cell were performed. In the second round of tests, the breadboards were placed in a mobile laboratory and the light beams aimed at a large open at 40 to 50 meters and reflected off a sand target. Finally, the mobile laboratory with the breadboards was installed at ∼40 meters from a leak simulator. The leak simulator was made by using a large sand container in which petroleum products were leaked. Intermediate scale leak simulator tests showed that it is clearly a challenge to correlate a measured concentration to an actual leak size. Tests have also shown that there is a strong concentration gradient in the air above a leak. This indicates that a better overall detection performance should be obtained with a measurement using the air next to the ground, and that it is feasible to detect a leak of less than 1 barrel/day. UV-Raman tests performed in the outdoors suggested a Limit Of Detection (LOD) of the system below 1 500 ppm-m when detecting all hydrocarbons. Because of the hardware that would be needed to lower this detection limit, results suggest abandoning the Raman technique for remote leak detection from an airborne platform. IR-DiAL showed the best sensitivity for the detection of hydrocarbons (< 1 ppm-m of LOD). However the effective LOD will be reduced because of the soil spectral reflectance variations that may lead to a high false alarm rate for concentrations of hydrocarbons lower than 235 ppm-m. The UV-absorption approach was also briefly tested, suggesting a LOD for benzene of between 1.5 and 2.5 ppm-m. The UV absorption of benzene is not affected by ground spectral reflectance variations. This is an approach that will be investigated further.

A New Approach to Pipeline Leak Detection Using Electromagnetic Sensing

Many different approaches have been adopted for identifying leaks in pipelines. Leak detection systems, however, generally suffer from a number of difficulties and limitations. For existing and new pipelines, these inevitably force significant trade-offs to be made between detection accuracy, operational range, responsiveness, deployment cost, system reliability, and overall effectiveness. Existing leak detection systems frequently rely on the measurement of secondary effects such as temperature changes, acoustic signatures or flow differences to infer the existence of a leak. This paper presents an alternative approach to leak detection employing electromagnetic measurements of the material in the vicinity of the pipeline that can potentially overcome some of the difficulties encountered with existing approaches. This sensing technique makes direct measurements of the material near the pipeline resulting in reliable detection and minimal risk of false alarms. The technology has been used successfully in other industries to make critical measurements of materials under challenging circumstances. A number of prototype sensors were constructed using this technology and they were tested by an independent research laboratory. The test results show that sensors based on this technique exhibit a strong capability to detect oil, and to distinguish oil from water (a key challenge with in-situ sensors).

Geotechnical Instrumentation: Monitoring Longitudinal Stress of a High Pressure Pipeline During Longwall Mining Operations — A Case Study in West Virginia

Longwall mining operations could compromise the integrity of high pressure pipelines by way of surface subsidence and soil strains. Prior to implementing field programs for monitoring subsidence, a preliminary mitigation/stress analysis study should be designed to determine the possible effects of the longwall mining operations on the pipeline(s). If the stress analysis indicates possible high stresses beyond the allowable limits of a pipeline, then a mitigation plan should be developed and implemented. Regardless of the anticipated stress level in a pipeline, a strain monitoring program is usually recommended. The purpose of this paper is to discuss the design of a pipeline strain monitoring program, which includes the installation of strain gages at critical locations along two adjacent pipelines. The study area includes a 12 inch diameter steel pipeline (for natural gas transport) and a 12 inch HDPE pipeline for water transport. The study area is located in a mountainous region of West Virginia. Prior to the field program, a laboratory pilot study was performed with strain gages on a test section of HDPE pipe to determine the best mounting procedures. The field implementation program included the installation of strain gages on the gas and water pipelines. Multiplexers, data loggers, a solar array and a satellite modem for 24/7 data transfer were installed, and monitored throughout the study. During the field implementation program several meteorological and geologic events occurred which caused some design changes in the field program.

Effects of Segregation on the Mechanical Performance of X70 Line Pipe

Elemental segregation during continuous casting of steel is an inherent part of the solidification process. After rolling, the segregation is evident through banding of the microstructure, particularly at the centerline where the enrichment of such elements as carbon, manganese, molybdenum and chromium, may locally increase the hardenability of the steel and result in the formation of harder microstructural features. While operational steps may be taken to minimize segregation during casting, complete elimination of segregation is almost impossible. Various slab rating systems have been defined over the years which are employed as a means to measure slab quality taking into account such factors as internal cracks and segregation. While these slab rating systems were intended to aid mill operators in assessing slab quality, in recent years slab ratings have been prescribed as a means of assessing pipe quality. In this study the properties of pipe produced from a slab with Mannesmann rating of 2 are compared to those of pipe produced from a slab with a rating of 3. The work has been supplemented by microprobe analyses to measure the degree of segregation. Increased levels of Mn and Si were found at the centerline of pipe processed from the Mannesmann 3 slab. In the final pipe, these centerline bands were 10 to 20 μm in thickness and exhibited increased hardness (HV 50g) in the Mannesmann 3 pipe as compared to the Mannesmann 2 pipe. Despite evidence of increased segregation, the mechanical properties (YS, UTS, Charpy, DWTT) of both pipes comfortably met X70 property requirements.

The Influence of the Bourdon Effect on Pipe Elbow

Pipe elbows are frequently used in a pipeline system to change the directions. Thermal expansion and internal pressure results in bending moments on the bends causing ovalization of the initial circular cross-section. The ability of the bend to ovalize will result in an increase in the bend flexibility when compared to straight pipes [1]. In case of bends subjected to internal pressure, the pipe will start to straighten out due to the difference between the intrados and extrados surface areas. The internal pressure causes unbalanced thrust forces tending to open up the elbow depending on its stiffness and surrounding constraints. These forces tending to cause ovalization of the cross section and causing the tendency of pipe bends to open up are termed the “Bourdon effect”. If these unbalanced thrust forces are not taken into consideration, unanticipated deformations and high stress levels could occur at the elbow location that may not be accounted for in traditional stress analysis [2]. A better understanding of the influence of the Bourdon effect on the elbow design parameters is required. Past studies have investigated the behaviour of pipe elbows under closing bending moment and proposed factors that account for the increased flexibility and high stress levels resulted from ovalization. These factors are used in the current design codes [3],[4] &[5] and known as the flexibility factor and stress intensification factor. In this investigation, pipe elbows with different nominal pipe size and various bend radiuses to internal pipe radius ratios (R/r) are studied to get a better understanding of the Bourdon effect and its influence on the pipe stresses and deformations. Differential equilibrium equations are solved to derive a mathematical model to evaluate the unbalanced thrust forces resulted from the Bourdon effect on a pipe elbow. The forces evaluated from the derived model are compared to finite element model results and showed excellent agreement. A comparison between the CSA-Z662 code and the FEA results is conducted to investigate the applicability of the stress intensification factors used in the current design code for different loading cases. The study showed that the external bending moment direction acting on the pipe has a significant effect on the distribution of stresses on the pipe elbow and significantly depending on the level of applied internal pressure.

The Specifications Dilemma Posed by Ultra High Toughness Line Pipe Steels

Pipelines transporting compressible hydrocarbons like methane or high-vapor-pressure liquids under supercritical conditions are uniquely susceptible to long-propagating failures in the event that initiation triggers this process. The unplanned release of hydrocarbons from such pipelines poses the risk for significant pollution and/or the horrific potential of explosion and a very large fire, depending on the transported product. Accordingly, the manufacturing procedure specification (MPS) developed to ensure the design requirements are met by the steel and pipe-making process is a critical element of the fracture control plan, whose broad purpose is to protect the environment and ensure public safety, and preserve the operator’s investment in the asset. This paper considers steel specification to avoid long-propagating shear failures in advanced-design larger-diameter higher-pressure pipelines made of thinner-wall higher-grade steels. Assuming that the arrest requirements can be reliably predicted it remains to specify the steel design, and ensure fracture control can be affected through the MPS and manufacturing procedure qualification testing (MPQT). While standards exist for use in MPQTs to establish that the MPS requirements have been met, very often CVN specimens remain unbroken, while DWTT specimens exhibit features that are inconsistent with the historic response and assumptions that underlie many standards. In addition, sub-width specimens are often used, whereas there is no standardized means to scale those results consistent with the full-width response required by some standards. Finally, empirical models such as the Battelle two curve model (BTCM) widely used to predict required arrest resistance have their roots in sub-width specimens, yet their outcome is widely expressed in a full-size context. This paper reviews results for sub-width specimens developed for steels in the era that the BTCM was calibrated to establish scaling rules to facilitate prediction in a full-size setting. Thereafter, issues associated with the use of sub-width specimens are reviewed and criteria are developed to scale results from such testing for use in the MPS, and MPQT, which is presented as a function of toughness. Finally, issues associated with the acceptance of data from unbroken CVN specimens are reviewed, as are known issues in the interpretation of DWTT fracture surfaces.