Non-welded socket connection: Innovations in internal coating repair techniques (rapid socket crimping method ZAP-LOK)

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Welding is currently the most common method for connecting oil and gas pipelines. Due to the high temperatures associated with welding, it is difficult to maintain the integrity of the coating at the joints of the pipelines, which makes these areas vulnerable to corrosion. Currently, leaks at the joints of coated pipelines in the oil and gas fields operated by Sinopec’s Northwest Oilfield Branch account for 10% of all leaks. Therefore, the need for new technologies for connecting pipes with internal coatings is becoming increasingly urgent. The rapid socket press-fitting method is known abroad as ZAP-LOK; it involves first expanding one end of the steel pipe and then shaping the other end. During connection, the smaller end of one steel pipe is pressed into the larger end of another pipe, allowing for a rapid socket connection through elastic interference fit, with sealant being filled into the gap at the ends of the inner and outer pipes. The quick socket compression splicing technology has notable advantages: it features a simple structure, is easy and fast to install, has a wide range of applications, has been in use for a long time, and its technology is mature and stable. Compared to traditional welding techniques, the rapid socket press-fit technology can increase welding efficiency by 30%, reduce interface corrosion by 50%, lower pipeline construction costs by 15%, and ensure 100% integrity of the pipeline’s internal coating. The Anti-Corrosion Research Institute of the Petroleum Engineering Technology Research Institute at Sinopec’s Northwest Oilfield Branch conducted a study to evaluate the feasibility of non-welding connection techniques for steel pipelines, and used experiments to assess the viability of the rapid socket press-fit method. The evaluation results show that the joints made using Hi-Lock connectors in the experiments exhibited good coating integrity, mechanical properties, sealing performance, and corrosion resistance, meeting the relevant standards and design requirements. Specifically: (1) The coating on the joints had good integrity; its appearance, thickness, and absence of defects were all within acceptable limits, while its adhesion, resistance to bending and impact, and hardness met the requirements specified in SY/T0547-2010. (II) The overall stress and strain distribution in the pipe segment is uniform, and the structure is symmetric; the mechanical properties of the pipe at the joint at the end of the Hi-Lock pipe segment have not degraded due to the applied forces. (III) Good corrosion resistance: The inner surface coating at the joints of Hi-Lock pipe sections showed no signs of corrosion after being tested for 1 month under conditions of a temperature of 70°C, total pressure of 4 MPa, CO2 partial pressure of 0.48 MPa, H2S partial pressure of 0.263 MPa, and an oxygen concentration of 0.5 mg/L; moreover, its adhesion strength and original performance remained unchanged. Current field application tests are being conducted to comprehensively evaluate the feasibility and adaptability of the rapid socket compression splicing technology by comparing conditions before and after operation. In recent years, countries such as the United States and Canada have regarded this pipe joining technology as an important method for the high-quality and efficient installation of pipelines. To date, over 60% of the oil field transportation pipelines in Canada have been laid using rapid socket splicing technology. Currently, in China, several pipelines in the Liaohe Oilfield and Dagang Oilfield utilize this joining technology; to date, these pipelines continue to operate normally. Compared to traditional pipe welding methods, the rapid push-fit joining technology offers unparalleled advantages in terms of cost control, installation efficiency, and anti-corrosion performance. Its application will undoubtedly help Sinopec’s Northwest Oilfield overcome the bottleneck in anti-corrosion treatment for internally coated pipes, surmount challenges related to pipeline anti-corrosion technologies, and truly achieve “zero leaks and zero pollution,” thereby paving the way for high-quality and efficient sustainable development.