Repair Sleeves Research Articles

Operation Recommendations for Tension Joints and Clamps on a 63 kV Overhead Transmission Line Conductor Based on Experimental Tests

This study provides the operation recommendations for the tension fittings used on a 63 kV overhead transmission line conductor based on experimental tests. In this way, the tension fittings, including the dead-end clamp, the mid-span joint, and the repair sleeve, are assembled on the lynx conductor under different faulty and healthy assembly conditions in the laboratory. The lynx conductor is one of the widely used conductors in the 63 kV overhead power lines. The electric current injection test, along with thermal imaging and also tensile test, are conducted on the studied samples. The results show that the surface temperature of the lynx conductor is higher than the surface temperatures of the dead-end clamp and mid-span joint under normal and overload current conditions. Also, the crimping pressure of the aluminum and steel pipes less than the standard value, the crimping length of the steel cores of conductor less than the standard value, and the crimping length of the aluminum pipes more than the standard value can lead to a developmental defect which should be repaired or replaced at the first opportunity of the transmission line service outage. The repair sleeve is under more thermal stress than the dead-end clamp and mid-span joint, even in the standard assembly condition. A slight temperature difference of a repair sleeve compared with the same type fitting may be a severe operating condition. Also, the use of two consecutive repair sleeves to cover the conductor cut strands is not recommended. Furthermore, the loose connection of bolts at the junction of the jumper terminal to the dead-end clamp causes a very high temperature which should be repaired immediately. If the temperature difference between two defective and healthy dead-end clamp or mid-span joint is more than 13 °C, a critical defect is diagnosed; however, the temperature difference between two repair sleeve more than 7 °C indicates a critical operation condition for defective one.

Research on the influence of the repair sleeves on the strength and the stress-strain state of the pipeline section

Na Ukrainie do transportu ropy i gazu wykorzystuje się tysiące kilometrów rurociągów stalowych. Są one stale narażone na działanie środowiska, zewnętrznych krótko- i długoterminowych obciążeń przesyłanych produktów. Wszystko to powoduje uszkodzenia materiału rurociągów, co skutkuje m.in. ubytkiem metalu na powierzchni, pojawieniem się wgnieceń, rys czy zagłębień. Wady te mogą znacznie skrócić żywotność uszkodzonych odcinków, a w niektórych przypadkach prowadzić do wypadków wiążących się z utratą przesyłanego produktu i szkodami w środowisku. Aby temu zapobiec, w praktyce rozpowszechniły się różne metody naprawy rurociągów w miejscach uszkodzeń, w tym stosowanie specjalnych rękawów naprawczych na rurociągach. Te ostatnie są wykonane zarówno ze stali, jak i z materiałów polimerowych, mają różnorodną konstrukcję i złożoność. Naukowcy i inżynierowie koncentrują się na rozwoju złączy rurowych. Jednocześnie, jak wykazał przegląd osiągnięć naukowych w tej dziedzinie, wymagają one dodatkowej uwagi w zakresie badania stanu naprężenia–odkształcenia uszkodzonych odcinków rurociągów w miejscach montażu rękawów naprawczych. Artykuł poświęcony jest temu problemowi. W szczególności przeprowadzono badania eksperymentalne wytrzymałości rurociągu w dwóch przypadkach: 1) bez istniejących wad; 2) z wadą i rękawem naprawczym. Ponadto, korzystając z podobnych danych początkowych, wykonano obliczenia przy użyciu trójwymiarowego modelowania ciała stałego oraz metody elementów skończonych. W rezultacie ustalono wyraźną korelację między wynikami doświadczeń polowych a modelowaniem matematycznym. Może to wskazywać na możliwość wykorzystania tego ostatniego do celów praktycznych jako prostszej metody realizacji. Ustalono, że montaż rękawa zmniejsza poziom naprężeń normalnych w sąsiedztwie wady o co najmniej 16%, a poziom naprężeń lokalnych przed frontem wady – do 86%. Jednocześnie montaż rękawa naprawczego może zwiększyć naprężenia obok wady nawet o 50%. Należy to uwzględnić podczas wykonywania prac naprawczych.

A temperature-dependent global failure criterion for a composite/metal joint

Abstract The use of composites to repair localized corrosion damage in metallic pipelines has significantly increased in the past years. Repair techniques using polymer-based composites are interesting, since they do not require draining the line and stop operation. However, pipelines conveying liquids may work at elevated temperatures, what can be a limitation for the use of polymeric materials. The adhesion between pipe and composite is the key to the effectiveness of the repair (sleeves or patches), mainly in the case of through-thickness defects. This paper is a preliminary attempt to propose and analyse a global failure criterion for a particular class of adhesively bonded composite-metal joints. Single-lap joints (SLJ) were fabricated with metal and composite adherends bonded with an epoxy resin reinforced with Aramid fibres. The surface treatment adopted in this study was the same used in the field for repairs. The performance of these joints in pure bending and in shear was studied at four test temperatures: 25 °C, 50 °C, 70 °C and 90 °C. The mechanical behaviour is rate and temperature dependent. A global energy criterion for the joint fracture is proposed. It is verified experimentally that, for a given temperature, the critical energy is the same in both kinds of tests and that this energy decreases almost linearly with temperature.

Benefits of low-yield weld filler metals for safe welding on live gas transmission pipelines

Making connections in gas pipelines that may not be taken out of service requires special techniques. Hot tapping is often applied. Split tees are welded to pipelines that are and remain completely operational. The split tees are placed on the pipeline and then welded together using longitudinal welds to make one tee piece. After inspection, circumferential welds are made to create the connection between the tee piece and the pipeline. This same welding technique is also used to repair damage to pipelines. This can be in the form of a buttering up (surfacing) repair as part of a pipeline rehabilitation program or installing full-encirclement repair sleeves. Installing repair sleeves can also be a follow-up to an in-line inspection that has established that there is damage to the pipeline or to an activity that has been reported as doing damage as a result of external interference (e.g., excavation, trenchless techniques for installation of cables or other pipelines, plowing). N.V. Nederlandse Gasunie has had research conducted since 1978 by, among others, Netherlands Organization for Applied Scientific Research (TNO) in order to obtain a sound basis for a reliable and safe way to weld on live gas pipelines. This article covers over 20 years of operational experience with welding on live gas transmission pipelines. The article addresses regulations, critical aspects of welding on operational gas pipelines, and the control of these critical aspects. The metallurgical background issues are also discussed.

Optimization of Pipe Repair Sleeve Design

For the repair of pipeline defects, repair sleeves are the most widely used method in petrochemical industry. The objective of this work was to optimize the thickness of nonpressure containing repair sleeve, by refining the existing design practice. Laboratory studies involving instrumentation of small-scaled repair sleeve system coupled with finite element analysis were carried out to refine the design procedure and optimize the thickness of the sleeve. Using a unified approach for finite element modeling, including failure pressure estimation and simulation of sleeve installation pressure, 24 cases ranging from 6 to 60 in. nominal diameter were investigated. In this paper, the details of the optimization approach used in this investigation are presented.

Analysis of Boundary Conditions for the Simulation of Welding at the Repair of Gas Pipelines with Steel Sleeve

Theoretical part of the manuscript deals with basic information about repair of gas pipeline with steel repair sleeves and simulation programme SYSWELD. Experimental part includes analysis of boundary conditions in two-pass fillet welding joint. Results of the analysis will be used for simulation in simulation programme SYSWELD.

Weld failures in sleeve reinforcements of pipelines

Based on fractographic, metallurgical, mechanical and fracture mechanics analyses, the causes of three failures in welded full encirclement sleeve repairs in a 24 in gas pipeline were evaluated. These failures were related to poor manufacturing procedures. The material used to build the sleeves was old and had poor transverse strength. High heat input cellulosic electrodes were used to weld the field joints, which lead to hydrogen embrittlement in the HAZ, also helped by relatively high circumferential stresses and defects of lack of fusion. A series of changes were introduced, including improvements in the in-plant fabrication and the in-field installation of the repair sleeves. A low hydrogen weld procedure with controlled penetration, NDE specifications and epoxy fillers were introduced to minimize the risk of sleeve failures and plastic collapse of the pipe.

Local collapse of gas pipelines under sleeve repairs

Local collapse of the pipe wall under full encirclement sleeve reinforcements is associated with breaks and blow outs that cause large gas losses and abrupt depressurisation in gas pipelines. Although these defects do not represent an imminent risk of failure, they should be eliminated because they impede the normal passage of the “instrumented pig” for internal inspection. Four failed repairs were experimentally evaluated, and the effects of different geometric factors were numerically assessed via non-linear numerical modelling of fluid flow and pipe response. All possible causes of the appearance of these defects and measures to minimise their occurrence were evaluated. The position of the repaired portion with respect to the blow out, local geometry of the repair and previous defects, and the amount of gas caught in the interstice between the pipe and the reinforcement, have an important part in the event. The measures for the prevention of this problem involve the use of fillers and improved construction of repair sleeves.