Oil and Gas Pipeline Welding: Current Practices and Emerging Technologies

Abstract: Oil and natural gas are fundamental to ensuring national energy security. Pipeline construction, safe operation, and efficient utilization are at the core of developing oil and gas storage and transportation systems. Welding technology plays a crucial role in ensuring the safety, engineering quality, and construction cost-effectiveness of pipeline systems, making it a central focus in pipeline engineering and oil and gas transportation research. This paper reviews the characteristics, current development status, and key equipment of pipeline welding technologies both in China and abroad. It also analyzes welding strategies for challenging construction sections and explores future trends in welding processes, equipment, and related standards.

Introduction

To date, the total length of oil and gas pipes in operation worldwide has exceeded 2,019,000 kilometers. Although the COVID-19 pandemic temporarily impacted pipeline construction, China has experienced a swift recovery, and pipeline development has regained its rapid momentum. In contrast, overall oil and gas consumption has declined in many other countries and regions, resulting in a slowdown in pipeline construction. Globally, regions such as North America, Europe, and Russia remain major hubs of pipeline infrastructure, with advanced technological development and large-scale construction leading the industry. Pipeline transportation has become the dominant method for delivering oil and gas. However, given the complexity of pipeline construction and operating environments, ensuring pipeline safety and extending service life is of critical importance. The advancement of welding technology directly impacts a pipeline’s ability to perform reliably throughout its service life. As pipeline systems evolve toward larger diameters, higher pressures, and greater deformation tolerances, the demands for material selection, design, and construction are increasingly stringent. In response, pipeline welding technology has progressed accordingly, with significant advancements in welding materials, methods, automation, and equipment.

1. Progress in the Development of Oil and Gas Pipeline Welding Technology at Home and Abroad

Foreign pipeline welding technology developed earlier than in China, gradually evolving from manual welding to automatic welding. Early manual welding techniques mainly included cellulose electrode downhill welding and low-hydrogen electrode downhill welding. Automatic welding technology dates back to the 1970s. For example, the former Soviet Union developed a highly adaptable flash welding machine, while CRC-Evans in the United States introduced an automatic welding system consisting of several specialized machines. Their independently developed equipment—such as the PFM beveling machine, IWM internal welding machine, P260 single-torch external welding machine, and P625 double-torch external welding machine—has been widely adopted in numerous countries. Similarly, France’s Serimax has developed the PFM beveling machine, the MAXILUC copper-lined butt welding machine, and the Sal-urax series of external welding machines. Their welding process typically involves copper-lined butt welding, root welding with external welding machines, followed by fill and cap passes also performed using external welding equipment.

In China, pipeline welding technology has undergone several major phases. During the 1970s, the industry primarily relied on the traditional manual uphill welding process using low-hydrogen electrodes. In the 1980s, cellulose and low-hydrogen electrode downhill welding techniques became increasingly popular. By the 1990s, self-shielded flux-cored wire semi-automatic welding technology was introduced, paving the way for the development of today’s all-position automatic welding technologies. Driven by the comprehensive advancement of China’s economy and technological capabilities, fully automatic welding technology has entered a rapid development phase. Notably, the Tunisian natural gas project undertaken by China National Petroleum Corporation in 1995 and the Kuskan oil pipeline project in 1996 were the first domestic instances to apply semi-automatic welding technology. Since the beginning of the 21st century, automatic welding technology in China has developed rapidly and continues to advance.

1.1 Common Pipeline Welding Methods and Their Characteristics

(1) Manual Welding

Traditional manual pipeline welding depends heavily on human operation and has several limitations. Common manual welding methods include arc welding, cellulose electrode downhill welding, and low-hydrogen electrode downhill welding. For example, arc welding involves manually controlling the electrode and arc to perform the weld, but it is relatively inefficient. Cellulose electrode downhill welding uses special electrodes with strong penetration, making it well suited for thin-walled, large-diameter pipes and mixed root welds. Low-hydrogen electrode welding provides good toughness and performs better in environments that require high impact resistance or in cold climates. However, manual welding as a whole suffers from low productivity and heavy reliance on the operator’s skill, making it challenging to meet the increasing demands for high engineering quality. To overcome these challenges, developing more efficient automated welding technologies is essential. This transition will promote the advancement of pipeline welding toward higher levels of automation and intelligence.

(2) Semi-Automatic Welding

Semi-automatic welding combines the advantages of manual control with mechanical automation, improving welding efficiency by manually operating the welding torch while mechanically feeding the wire. Key semi-automatic methods include self-shielded flux-cored wire welding and CO₂ gas-shielded welding. In self-shielded flux-cored wire welding, gases released from the flux core protect the arc. It is cost-effective, highly adaptable, and widely used in pipeline projects. CO₂ gas-shielded welding provides better weld quality and groove compatibility by using external gas to protect the weld pool. Another semi-automatic method is tungsten inert gas (TIG) welding, which uses an arc between a tungsten electrode and the weld pool. However, its use is limited, typically applied to root passes and welds in tight or hard-to-reach areas. Although semi-automatic welding offers improvements over manual welding, it still requires significant manual involvement and skilled operators. Additionally, its equipment costs are higher than those for manual welding, while its level of automation remains lower than that of fully automatic welding. In some cases, semi-automatic welding can also be less efficient. Overall, it serves as a transitional technology—improving efficiency through partial automation while retaining manual flexibility—but its level of automation and stability still need further improvement.

Automatic welding encompasses both semi-automatic and fully automatic technologies. Fully automatic welding employs mechanical systems to complete the entire welding process with minimal human intervention. Several semi-automatic methods, such as solid wire shielded welding, can also be adapted for fully automated systems. The main fully automatic welding methods include solid wire gas-shielded welding, self-shielded flux-cored wire welding, combined automatic welding processes, submerged arc welding, and dual-torch joint welding. Compared to semi-automatic methods, fully automatic welding significantly enhances welding quality and efficiency through mechanized operation. It is particularly well-suited for challenging environments, such as mountainous regions with complex terrain. However, traditional automatic welding equipment can struggle under such conditions. To address this, engineers have developed flexible, specialized automatic welding systems that greatly improve construction efficiency in challenging environments. As automatic welding technology continues to advance, it provides high-quality solutions for complex terrains such as mountainous regions and drives the progress of industrialized pipeline construction. It is not only widely used in conventional applications but also plays a crucial role in specialized environments with challenging working conditions.