The development of high-frequency straight seam
welded pipe has evolved from traditional roller forming to row roller forming, and now to the current application of flexible forming (FFX), straight edge forming, and equal rigidity (URD) racks. The forming technology has been continuously improved, and intelligent forming has been achieved to a certain extent. The welding and heat treatment power supply has evolved from electronic tube type to full solid state, greatly improving heating efficiency as well as digital and intelligent control levels. Through in-depth research and continuous enhancement of the high-frequency welding process, welding and quality control technologies focusing on weld zone reinforcement have been developed, greatly reducing the likelihood of gray spots and bringing welding seam performance close to that of the parent material. By implementing a consistent management model, quality control of high-frequency welded pipes has been extended to the design and production stages of raw materials, thereby improving product performance and quality, which have been widely applied in submarine pipelines and high-grade oil well pipes.
The equipment level of HFW welded pipes in China has been greatly improved, with some large and medium-diameter production lines reaching international advanced standards. Through continuous improvement of welding and heat treatment processes, weld zone enhancement technology has been initially mastered, significantly improving welding quality, with the performance of some welding seams approaching that of the parent material. P110 casing has been developed, and X65-grade HFW pipes have been used in submarine pipelines. Significant progress has been made in the high-frequency pipe equipment made in China, including the main machine in Shijiazhuang, the high and medium-frequency power supply in Baoding, and main auxiliary machines such as loopers and flying saws in Shenyang. The development of information systems for high-frequency welded pipe production lines has progressed rapidly, with some enterprises successfully implementing and running ERP and MES systems. China has nearly 50 high-level large and medium-diameter HFW welded pipe units, with an annual production capacity exceeding 5 million tons. The market is highly saturated, yet several units are still under construction. Moving forward, the growth model should shift towards focusing on technological updates and process improvements, developing new products, conserving energy, reducing consumption (e.g., promoting solid-state power supplies and contact welding processes), and enhancing the level of informatization.
Due to continuous improvements in the quality of hot-rolled coils and significant advancements in pipe-making equipment and technology, the quality of spiral welded pipes has rapidly improved. Spiral pipes have performed well in oil and gas trunk lines in China and Canada, with no major quality or safety issues. Their favorable performance-price ratio has gained acceptance among an increasing number of users, leading to the continuous expansion of spiral pipes' application in the oil and gas pipeline market. Major pipeline owners in the United States, India, and Europe, who previously did not use spiral welded pipes in oil and gas pipelines, have now adopted them in large quantities. A prime example is the three recently built X80 natural gas long-distance pipelines worldwide. The application ratio of X80 spiral welded pipes exceeds 70%, with some using a design factor of 0.8, enhancing the application level of spiral welded pipes.
In recent years, the demand for high-quality spiral welded pipes has driven the rapid development of pre-finishing unit construction. A decade ago, there were only four or five spiral coal pipe pre-finishing units worldwide. Now, there are over 20, with India building more than 10 new pre-finished coal units, Turkey one, China three, and the United States four new pipe-making units. India and South Korea have built spiral welded pipes and supporting coating two-in-one production lines in the United States. In 2009, three pre-finished spiral welded pipe production lines were completed and began production, with an annual design capacity of 300,000 tons. European Steel Pipe Borg Steel Pipe Company built a new pre-finished production line for spiral Huang pipes in Florida, with an annual output of 200,000 tons. India's spiral pipe finishing equipment is relatively simple. Most use a trolley type with rotating rollers, some use a spiral roller with a bottom, and only a few utilize the German upper transmission type, but the results are very good.
The application of low-stress forming, residual stress control, pipe end expansion, non-destructive testing technologies, and high-toughness welding wire flux has greatly improved the quality of China’s spiral welded pipes. The successful first pressure test of the western section of the West-East Gas Transmission Line 2 has had a significant global impact. China’s spiral welded pipes not only support domestic pipeline construction but are also exported in large quantities. However, China’s spiral welded pipes are mainly produced using the one-step method, and pre-finishing welding technology is much less prevalent than in India. China’s pre-finishing welding process is still in the development stage, with the quality and efficiency of fine welding relatively low, lagging far behind India. The equipment level of China’s spiral welded pipe pre-welding units is lower than India’s, but the equipment level of fine welding units is higher. We should focus on improving the quality of the pre-welding process and enhancing fine welding capabilities. Some international oil companies only consider pre-finishing units during pipe factory inspections and disregard one-step units. The impact of adopting the two-step method on major pipeline bidding is already evident. If we do not catch up quickly, we will face technical barriers when entering the international market.
The annual production capacity of spiral submerged arc welded pipes for oil and gas transportation in China has reached four million tons. Going forward, we should prioritize transforming pre-finishing welding processes over constructing new units. The level of informatization in China’s spiral welded pipe units lags far behind Europe’s. We should focus on informatization construction and transform existing production lines. Recently, PetroChina launched an informatization construction project for spiral coal pipe units.
Straight seam submerged arc welded pipes remain the primary pipe type used in oil and gas pipelines, particularly in crossing pipes, submarine pipelines, and thick-walled pipelines. The development of high-strain pipes and X90 to X120 ultra-high-strength steel pipes primarily adopts straight seam submerged arc welding technology. JCOE technology is undoubtedly one of the most significant developments in straight seam submerged arc welded pipe technology over the past decade. Its emergence has significantly reduced the investment needed for straight seam submerged arc welded pipe production lines, enabling small and medium-sized pipe manufacturers to enter the field of straight seam submerged arc pipe manufacturing. Due to the low investment in JCOE units, flexible production processes, and product quality comparable to UOE, it has developed rapidly worldwide, especially in China, India, and Russia. Currently, the number of JCOE units worldwide has exceeded 50, significantly surpassing the number of UOE units globally. JCOE has become one of the mainstream processes for producing straight seam submerged arc welded pipes. From a forming principle perspective, JCOE is better suited for forming smaller-diameter, thicker-walled submarine steel pipes, as well as producing thick-walled elbow mother pipes. For example, the thick-walled X80 elbow mother pipes for the West-East Gas Transmission Line 2 are all produced using the JCOE process.
In 2005, Welspun Company of India successfully produced the deepest ITP pipeline in the Gulf of Mexico using the JCOE process, setting a record with a 2,400-meter deep seam pipeline, dispelling doubts about the reliability of JCOE steel pipes, and enabling JCOE steel pipes to successfully enter the seabed pipeline market. OMK Vyksa Steel Pipe Company of Russia passed the audit by DNV and the Nord Stream Pipeline Owner and secured 25% of the order for the Nord Stream Pipeline, the Baltic Sea Seabed Natural Gas Pipeline (500,000 tons in total for Phase 2). Its TESA 1,420 mm JCOE large-diameter straight seam submerged arc welded pipe production line is producing steel pipes for the Nord Stream Pipeline, the largest seabed pipeline.
A Factory in China has successfully developed a CNC JCO forming machine, with forming quality comparable to that of advanced foreign equipment. It is widely used by Chinese straight seam submerged arc welded pipe manufacturers and is also exported in large quantities to India, Mexico, and other countries, significantly contributing to the further promotion of JCOE process technology. The equipment level of the main engine in China’s LSAW pipe units is higher than that of India and is comparable to the world’s top level. In terms of informatization and automation, China is on par with India but still lags significantly behind the advanced production lines in Europe and Japan. China lags behind Europe and India in the development and performance of X65 and X70 sour service pipelines but leads in X80 performance.
The annual production capacity of China’s LSAW pipes has exceeded 3 million tons, far surpassing Chinese market demand. However, many companies are still eager to enter the market, and some production lines are under construction. It is estimated that by 2011, China’s LSAW pipe production capacity will reach 4 million tons per year, while national demand for large-diameter conveying steel pipes is only 3 million tons per year, with spiral welded pipes still widely used. Competition in the foreign market is also very fierce, making it inappropriate to build new production lines. It is necessary to effectively change the development model, implement informatization and automation transformations of existing production lines, improve quality assurance capabilities, vigorously develop new products—such as offshore oil pipes and heavy thick-walled structural steel pipes—and open up new markets.
4. Conclusion
Over the past decade, welded pipe technology has made significant strides, and the production capacity and quality of welded pipes have greatly improved. However, market competition has become more intense, and the demands for improving steel pipe performance and reducing costs have increased. China’s welded pipe enterprises should accelerate equipment transformation and upgrades to meet the requirements for high performance, high steel grade, large wall thickness, and high dimensional accuracy in pipelines. They should thoroughly update non-destructive testing equipment to ensure reliable operation. Through informatization transformation, they should achieve a leap from basic automation to full-line automation and informatization, elevating their operations to the level of advanced pipe factories in Europe and Japan. This will enable users to trust Chinese products more than Indian products, helping China establish a strong foothold in the competitive market and become a true global steel pipe power.
