Girth weld cracking is one of the main failure modes in oil and gas pipelines; girth weld cracking inspection has great economic and social significance for the intrinsic safety of pipelines. This paper introduces the typical girth weld defects of oil and gas pipelines and the common nondestructive testing methods, and systematically generalizes the progress in the studies on technical principles, signal analysis, defect sizing method and inspection reliability, etc., of magnetic flux leakage (MFL) inspection, liquid ultrasonic inspection, electromagnetic acoustic transducer (EMAT) inspection and remote field eddy current (RFDC) inspection for oil and gas pipeline girth weld defects. Additionally, it introduces the new technologies for composite ultrasonic, laser ultrasonic, and magnetostriction inspection, and provides reference for development and application of oil and gas pipeline girth weld defect in-line inspection technology.

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Literature Review: Theory and Application of In-Line Inspection Technologies for Oil and Gas Pipeline Girth Weld Defection

As pressure pipelines are usually mounted overhead or buried underground, the in-pipe inspection equipment that can run through inside pipelines is strongly demanded. Currently, the application of robotic systems for pressure pipelines in-pipe inspection is considered as one of the most attractive solutions available. Therefore, a new robot-based system for pressure pipelines in-pipe inspection was developed. A new defect detection method for pressure pipes was presented based on ultrasonic phased array technique. The developed system mainly included three parts: a tracked mobile robot for providing the driving force of the system movement, a camera used to photograph the inner surface videos or photos inside pipelines and an ultrasonic phased array module for defects detection. The structure characteristics of water/steel interface was investigated, as well as the focusing performance of convex phased array. The detection parameters such as elements size and dynamic apertures were studied and optimized with CIVA simulations. The in-pipe inspection experiments in pressure pipelines with an outer diameter of 219 mm were also carried out. The results show that the robot-based system could successfully go through inside the pressure pipelines and the ultrasonic phased array technique could implement inner surface scanning and defect detecting, which indicates that the new defect detection method can improve the pressure pipelines inspection effect.

A New Robot-Based System for In-Pipe Ultrasonic Inspection of Pressure Pipelines

Globally, more and more attention has been paid to the integrity of Girth Welds (GW) of oil and gas pipelines due to their failures with high consequences. A primary concern is that defects originate during field construction but over time may be subject to external loads due to earth movement. GW defects in newly built pipelines are also assumed to exist but would be much smaller in size, and more difficult to detect, which motivated the investigation into minimum defect detection capabilities of the inspection technologies. This study presents the evaluation results of UltraScan™ Circumferential Crack-Like Detection (USCCD) technology for oil pipeline GW inspection, based upon the pull test and in field data from Inline Inspection (ILI) of pipeline by PetroChina Pipeline Company (PPC) using GE PII (General Electric Company, Pipeline Integrity Inspection) 32” UltraScan™ CCD Tool. The performance of USCCD is given according to the ILI data, pull test results and dig NDE (Non-Destructive Examination). It can be concluded that crack-like defects with clear edges can be detected during ultrasonic propagation; however, the irregular shape of weld makes the inspection more difficult. It is still a challenge to identify the type of defects, and depth sizing can only be classified not quantified, which would require more excavations. However, this technology is feasible for the alternative technology of GW defect inspection.

Application of USCCD on Girth Weld Defect Detection of Oil Pipelines

Compressive sensing (CS) has emerged as a promising technique for collecting and reconstructing digital signals. In this article, we design a CS method for magnetic flux leakage (MFL) detectors based on the problem’s physics. A method is presented to reconstruct $x$ and $y$ components of magnetic $\overrightarrow {B}$ field using a few samples. First, the problem is formulated into an optimization framework where the goal is to minimize Euclidean distance between real and reconstructed signals while preserving the CS acquisition criteria. The resulting optimizations are then simplified and solved through the established majorization minimization (MM) method. Meanwhile, a Gaussian sampling strategy is adopted where samples with more information have a higher chance of being selected. Validation of the proposed method is accomplished through the performance comparison among the proposed method and several established high-performance CS techniques on gathered experimental data. The extensive validation of the signals gathered from 17 artificial defects on the 12-m pipe reveals that the signals can be compressed and recovered with exceptional fidelity when the problem’s physical structure is known.

Structure-Aware Compressive Sensing for Magnetic Flux Leakage Detectors: Theory and Experimental Validation

The target of inline crack inspection is normally related to the detection of axial cracks (weld cracks, SCC etc.) as axial cracks are usually expected under typical loading conditions in pressurized pipe. Ultrasonic crack inspection tools for this type of cracks have been available for over 20 years and have become a standard application in the ILI business. However, under certain conditions circumferential cracking may occur and the inspection technique needs to be modified accordingly. Especially under offshore conditions with limited pipeline accessibility not only the early detection of crack-like defects is required but also a precise depth sizing is important in order to minimize the risk of crack-related pipeline failure. In order to ensure a high probability of detection together with state-of-the-art depth sizing, a 10″ inline inspection tool was developed for the detection of circumferentially orientated weld cracks. The tool combines the advantages of the pulse-echo technique on the detection side with the excellent capabilities of the TOFD (time-of-flight-diffraction) technique for accurate sizing. Both techniques are implemented into a tethered tool where the pulse-echo unit serves for fast screening while the relatively slow TOFD-unit is used for sizing of any detected crack-like features.In order to qualify the new tool for a special offshore application (inspection of circumferential cracking at welded anode pads) extensive testing was performed using a 10″ test pipeline prepared by Statoil. The test line contained 64 artificial weld defects for reference purposes as well as an unknown number of fatigue cracks in the weld area which were generated by fatigue testing of the corresponding pipes. The tests were full blind tests with no advance knowledge on locations and sizes of the cracks. The sizes of the fatigue cracks (length, depth) were determined by destructive examinations carried out after inline testing. The subsequent comparison of the destructive results with the non-destructive results showed that the specification of the tool with regard to detection and sizing was fully met. In the paper, the inspection concept and the setup of the new tool are described, and the results of the qualification tests are presented.Copyright © 2014 by ASME

Qualification of a combined ultrasonic inspection tool for detection and sizing of circumferential weld cracks in offshore pipelines

Typically inline inspection is carried out for the detection and sizing of geometry defects, corrosion / wall thickness loss and cracking defects. Regarding cracking, most of the time axial cracking (SCC, seam weld cracks....) is observed due to the typical loading condition in pressurized pipes. Since 1994 ultrasonic crack inspection tools are available for the reliable detection of such cracks using conventional ultrasonic shear wave technique. This technique is well suited for detection but has limited depth sizing capabilities as the reflection amplitudes are affected by several other factors apart from depth. Under special conditions (bending forces, poor welding) cracking can also appear in circumferential direction. For this type of cracks, basically the same type of tool can be used with a modified sensor carrier providing similar detection and sizing performance as for axial cracking. In offshore applications, however, accurate sizing in particular of crack depth is an important requirement as offshore verification and repair work is usually very cost-intensive. In order to provide a high POD together with good sizing performance a tethered 10" tool was developed for inspection of circumferential cracks at anode pads welded on the pipes. It contains a pulse - echo (PE) unit for reliable detection and a TOFD (time-of-flight-diffraction) unit for accurate sizing of circumferential cracks. The PE technique is used for fast screening during the forward inspection. The TOFD measurement which is basically stationary is performed on the backward inspection by stopping at every location where a crack indication was detected by the PE inspection. Extensive testing of the new tool was performed at a 10" test pipeline with circumferential cracking at original anode pads. Blind testing took place with 64 artificial weld defects and an unknown number of fatigue cracks at the anode pads which were generated by full scale fatigue testing of the corresponding pipes. After testing the sizes of the fatigue cracks (length, depth) were determined by destructive examination. The comparison of the results from ILI inspection and destructive testing showed that the ILI tethered tool fully met the specification with regard to detection and sizing. After the successful validation the tool was used for a tethered inspection of a 10" offshore pipeline (length 8 km). In the paper the inspection concept and the setup of the new tool will be described. Results from the qualification tests as well as from the first inspection run performed with the new tool will be presented.

Herbert Willems

Papers

Qualification of a combined ultrasonic inspection tool for detection and sizing of circumferential weld cracks in offshore pipelines

Combined ultrasonic tethered tool for inspection of weld cracks in offshore pipelines: tool qualification and first results from offshore inspection