ULTRASONIC IN-LINE INSPECTION : HIGH RESOLUTION CRACK DETECTION FOR PIPELINES USING A NEW GENERATION OF TOOLS
More than three million kilometers of high pressure liquid and gas pipelines are installed all over the world. Generally steel pipelines provide the safest means to transport large quantities of oil, oil related products and natural gas. However, just like any other technical component, they can deteriorate. As a result flaws can appear and grow until the pipeline fails. The appearance of cracks, especially Stress Corrosion Cracking is of increasing concern. These flaws must be identified, before they endanger the integrity of the line. This paper will introduce a new generation of high resolution inspection tools applying ultrasonic technology to detect, size and locate cracks and crack-like defects in the body and welds of transmission pipelines. These devices are pumped through the section of pipe to be inspected together with the medium being transported therein. They enable an inspection of the entire circumference and length of the pipe of up to several hundred kilometers in a single run. The paper will describe the non-destructive testing principles applied and introduce the major components of the inspection system, including the tool and defect specifications. The paper will also explain the data analysis process, including examples of data recorded by the tools. Introduction: It is generally accepted that high pressure pipelines provide the safest means to transport large quantities of oil and natural gas. It must be understood, however, that pipelines are exposed to a variety of environmental influences and loading conditions. As a result flaws can appear and grow. One challenging category of flaws are cracks and crack like anomalies such as stress corrosion cracking or fatigue. In order to ensure the integrity of a line cracks must be detected, sized and assessed, before they reach a critical dimension which can eventually lead to a failure of the pipeline. Specialized inspection tools, usually referred to as in-line inspection tools or intelligent pigs, have first been introduced nearly 40 years ago to detect and locate pipeline anomalies such as dents and metal loss. From technical generation to generation these inspection tools have become more refined and sophisticated, incorporating better and better defect specifications. Present day tools have reached a level of sensitivity and accuracy that allows the inspection data obtained to be utilized for advanced fitness-for-purpose calculations and integrity assessments. Detailed information on the history, physical principles used, technologies, tools and vendors is available in the literature [1-4]. Ultrasonic In-Line Inspection Tools: Ultrasonic tools for the in-line inspection have first appeared in the early 1980`s. The mission of these tools was the detection and sizing of metal loss. Crack inspection tools first appeared in the middle 1990 ́s . The major advantage of ultrasonic tools is their ability, unlike the competing magnetic flux leakage tools, to provide quantitative measurements of the pipe wall inspected. Experience has also proven that only the use of ultrasound provides a reliable means to detect cracks and crack like anomalies in pipelines [5]. This paper will focus on a new generation of ultrasonic crack detection tools. Ultrasonic inspection tools are in general fitted with a sufficient number of ultrasonic transducers to ensure full circumferential coverage of the pipe. They work in a pulse-echo mode with a rather high repetition frequency. Straight incidence of the ultrasonic pulses is used to measure the wall thickness and 45o incidence is used for the detection of cracks. While the wall thickness measurement is more or less established, in-line crack detection of pipelines has only been available for some years now. In terms of data processing, ultrasonic tools represent one of the most challenging tasks in ultrasonic non-destructive testing. Several hundred sensors have to be controlled, their echoes have to be recorded, on-line data processing has to be able to reduce the amount of data recorded and ensure that all relevant data are stored. The inspection speed of the tool depends on the medium and may vary within a certain range. The inspection process has to be fully automatic and cannot be supervised during a run. The data are stored on solid state memories that are the safest and most reliable means of storing data in such a hostile environment. The distance is measured using several odometer wheels. Hardware Introducing The Tools: Some design elements have been proven successful in the past and have been maintained in the new generation. Others have been completely modified. Figure 1 shows a photo of the newly developed tools in a 24" configuration. Figure 1 High Resolution Ultrasonic In-Line Inspection Tool for 24" pipelines. The tool is made up of two pressure vessels housing batteries, electronics, recording devices and a trailing sensor carrier housing the ultrasonic transducers. The tool is made up of a number of pressure vessels and a trailing sensor carrier. The front of the tool is covered by a protecting bumper unit, covering the transmitter housing shown here. The individual pressure vessels are connected through universal joints which allow the tool to negotiate bends. The first body contains batteries ensuring a safe supply of power to the tool for up to several days. The electronic and recording unit of the tool is housed in the second vessel and incorporates enough channels to cover pipeline diameters from 20" to 42" for crack detection application. The sensor carrier is made of polyurethane and houses the ultrasonic transducers. To adapt the tool to a different pipe diameter the polyurethane cups are exchanged, which can be done quickly. Tools sizes to cover pipeline diameters below 20" are also available, the current smallest diameter for crack detection being 10". In general there are two different sensor carrier designs for ultrasound tools. One for wall thickness or corrosion measurement and one for crack detection. The crack detection version, shown here, contains sensors orientated at a predetermined angle to the pipe wall which ensures that ultrasonic shear waves will travel under a 45o-angle within the metal. Figure 2 shows the arrangement of the ultrasonic sensors for crack detection. In order to avoid any blind zones in the vicinity of the longitudinal weld half the sensors are mounted in a clock wise orientation and the other half in an anti clockwise orientation. All sensors are mounted on metal plates. The polyurethane sled will ensure a constant stand-off. Figure 2 The assembly for the crack detection sensors The design will also have to ascertain that wax cannot clog the exposed parts of the sensor carrier. In the crack detection mode for this given diameter there will be 360 inclined sensors corresponding to a sensor pitch of 10 mm for either direction (clockwise and counter clockwise), together with 24 sensors for wall thickness measurement. These latter sensors are needed for the detection of girth welds, allowing a precise location of the defects. The sensor spacing is designed such that every part of the pipeline is covered by several sensors. Figure 3 shows the configuration of the ultrasonic sensors on the body of the sensor carrier for a crack detection sensor carrier.
Health Monitoring of New and Aging Pipelines- Development and Application of Instrumented Pigs
More than 3 million kilometers of high pressure liquid and gas pipelines are installed all over the world.Usually steel is the safest means to transport large quantities of oil and oil related products and natural gas however, just like any other technical component, pipelines also deteriorate with time, result of which, flaws appear and they grows until the pipeline fails. That is why Pipeline operators worldwide maintain the good health of buried cross-country pipelines with a combination of good quality external coating and cathodic protection. Beside this various other techniques like cleaning and debris removal by scrapper pigging at intervals depending upon the life of pipeline and the products being transported through the same are used. Use of corrosion inhibitors and internal coating is also done to protect the internal surface from corrosion. It is of greatest importance to ensure the safety, efficiency,environmental integrity and regulatory compliance of the worldwide pipeline infrastructure. Achieving this objective entails the need for effective inspection technologies, incorporating the accuracy and reliability required for optimized maintenance strategies. Intelligent pigs are used for inline inspection of buried pipelines to monitor their thorough health,assess the risks associated with their operation,pilferage checking and cracks etc. These IPIGS are capable of detecting metal loss upto 5-10 percent of wall thickness on inner as well as external surfaces of pipeline. IPIGS based on ultrasonic and eddy current sensors are capable of detecting cracks also.[10] On the basis of the wall thickness loss and the intensity of defects, pipeline risk assessment is done and preventive and corrective measures are planned. This paper presents the technical details of instrumented pig with its advantages and disadvantages over conventional methods of pipeline protection and inspection. It also elaborates the concept of multiple technology intelligent pig and scope for future research on intelligent pigging. (abstract)
Microstructure of the solder-casting zone in bridges of dental gold alloys.
The composition and structure were studied in the cast and in the solder of bridges which had failed clinically. Both materials were gold alloys but with different contents of Pt, Ag and Zn. The metallographic investigation revealed defects mostly in the solder, situated in the subsurface layer. SEM studied of the fracture surface revealed large porosites and a structure of dense parallel lines--striations--, indicating that the material had failed from fatigue. The materials in the fractured bridges were identified by micro-probe measurements. It was stated that cast material and solder material used together, were of different composition.