Vladimir Denisov

    An analysis of constructing and operating oil and gas pipelines show that when assessing quality of pipes a special attention should be paid to the ability of welded seams to resist corrosion. The universally recognized standards of the American petroleum institute (API) for making pipes give preference to neither line nor spiral way, which they are welded in. The choice totally depends on consumers’ requirements. The experience of operating spiral-welded pipes shows that they are sufficiently reliable in the very different conditions: in densely populated Europe (Germany, U.K, Holland, Italy, Norway and others), in swampy territories and permafrost areas of North and South America (U.S., Canada, Argentina, Peru), in deserts of Asia and Africa (Kuwait, Algeria, Nigeria and others). Spiral-welded pipes are laid at the bottom of rivers, lakes and seas. Diameters of these pipelines are different, from 529 mm to 1.220 mm, and the operating pressure reaches 100 atm. The protracted operation of pipelines did not reveal any shortcomings, which would be typical of spiral-welded pipes only.

R E F E R E N C E The Pipe Metallurgical Company (TMK) was founded in April 2001. It incorporates three Russian enterprises, the Volzhsky pipe plant, Seversky pipe plant and Sinarsky pipe mill, as well as Romania’s Artrom pipe plant. Their total capacity to make pipes of different types amounts to 3.1 million tons a year. The company’s share of Russia’s domestic pipe market exceeds 40 %. TMK accounts for more than 30 % of the Russian pipe export. The industrial MDM Group is a strategic investor of TMK-incorporated enterprises

Nevertheless, Russian gas and oil specialists prefer line-welded pipes being firmly prejudiced against the spiral-welded ones. And there is a reason for this. At the beginning of the 1960s the Zhdanovsky metallurgical mill became the first one in the USSR to start making spiral-welded pipes for gas pipelines. The new technology required careful preparation of all production process stages. The quality of coiled steel was still low, pipe molding and welding processes were not adjusted, non-destructive testing of seams was not done. But the mill’s management was pushing for a quick start- up of pipes’ serial production. What is more, those pipes were immediately being put to use. The first gas pipeline built with spiral-welded pipes did not withstand internal pressure. It was an avalanche-like fracture, the extent of the breach amounted to about 2.500 m. Experts blamed the accident on a bad choice of the seam type.
However, specialists know well that avalanche-like fractures happened at gas pipelines constructed with line-welded pipes as well. For example, in North America such fractures extended to 10.000 m and 12.500 m. And the reason turned out to be not the geometric pattern of the seam but the use of low-tenacity steel for making pipes. It was the metal brittleness in conjunction with the strong pressure of compressed gas inside pipelines, which caused such extensive fractures..
Still, Russian specialists did not give up on the idea of setting up a production of spiral-welded pipes. As time went by, the Volzhsky pipe plant (VTZ) was built, which started using the spiral-welding technology. From the very beginning this plant was recognized as the country’s leader in the pipe-making industry. With the start of market reforms VTZ experienced a number of failures but later its managers were quite enterprising and successful. They did restructuring, which allowed VTZ to get rid of inefficient capacities and debt obligations, to introduce new technologies. As a result, operating characteristics of pipes were significantly improved and large orders arrived. Today, VTZ is among leaders in the pipe-making industry and still remains Russia’s only enterprise capable of making pipes with 1. 420 mm in diameter.
The Volzhsky pipe plant gets coiled steel from the Novolipetsky integrated iron-and-steel mill (NLMK), where experts did an extensive research on technological processes. By all its properties this steel turned out fit for making large-sized pipes. NLMK’s specialists worked out optimal rates of steel continuous casting, adjusted the mode of heating and rolling slabs, reeling and cooling steel coils. The strip’s crescent shape was reduced to minimum, there was no problem with its dimensional accuracy by length and width either.
The pipe plant personnel designed systems for automatic control of all main processes to mold strip and pipes, installed equipment for ultrasonic and X-ray television control of welded seam, mastered the process of heat treatment of pipes through cross-section. Later, a three-ply insulation of pipe external surface was introduced. There is an all-around system of step-by-step checking of pipes’ quality, which meets international requirements. VTZ’s specialists were the first ones in the world to master the system of assessing pipes’ quality by non-destructive methods through cross-section after all technological operations are already completed.

«This is the only correct approach», well-known Russian expert on making pipes, doctor of economics Nikolai Bogatov believes. «Making large-sized pipes should not copy foreign technological schemes, but it has to become a new step in developing metallurgical and pipe production», he says.
A series of complex tests for a more comprehensive study of operating characteristics of Russia’s pipe products was carried out near the city of Nizhny Novgorod. Tests were conducted simultaneously by single methodological principles on both spiral-welded and line-welded pipes. Comparative results showed that a line-welded pipe withstood 1.627 cycles of loading before it was destructed. In its turn a spiral-welded pipe endured 4.407 cycles or 2.7 times more. Besides, during tests there were static loadings of pipes after 450 mm-long nicks were cut on them. A line-welded pipe was destructed with the collapsing pressure amounting to 60 bars (the designed collapsing pressure equaled 60.4 bars). But a spiral-welded pipe was not destructed even when the pressure reached 100 bars, although the designed collapsing pressure for it was 63 bars. The second loading of this pipe with the pressure of up to 100 bars did not destroy it either. Then, the artificial nick was deepened, researchers expected that the destruction would occur with the pressure reaching 44 bars. But the pipe sustained and was destructed only under the pressure of 77 bars. As a whole, results of comparative tests showed that the static crack resistance of a spiral-welded pipe is 1.7 times higher than that of a line-welded pipe.
The quality of the Volzhsky pipe plant’s spiral-welded pipes is also proved by the experience of their operation. Two sections of the Lazarevo-Nizhny Novgorod oil pipeline were examined. One of them consisted of 203.3 m-long spiral-welded pipes and the second one had 225.7 km-long line-welded pipes. Both of them were located in the same environment. During the checking of spiral-welded pipes’ inner surface 603 cases of metal peeling were found. There were 2.691 cases discovered on line-welded pipes.
The author of this article does not intend to contrast one type of pipe products with another or publicize one technology to the detriment of another. Nevertheless, it is necessary to help get rid of bias since it still influences the large companies’ marketing policy and their commercial decisions.
The bad experience with the Zhdanovsky plant’s products should have been left in the past as some kind of a historic and technological exceptional case. But for a long time one thing prevented putting a full stop: despite the high quality of spiral-welded pipes, which was proved by tests and operation, there was a ban on their use at key sections of oil and gas pipelines. In particular, this ban was explained by the lack of data on a spiral seam’s behavior at bended sections of a trunk pipeline, in zones of flexural strains.

R E F E R E N C E The Caspian Pipeline Consortium (CPC) was formed in 1992 by the governments of the Russian Federation, Republic of Kazakhstan and Sultanate of Oman for building a 1.580 km-long pipeline to transport crude from Tengiz and other fields of Kazakhstan and Russia to the terminal on the Black Sea coast near the city of Novorossiysk. The oil pipeline goes across both countries. Its construction was started in May 1999. On March 26, 2001 pumping oil from the Tengiz field to the CPC pipeline system began. In the autumn of 2001 the consortium got down to testing operation of the Tengiz-Novorossiysk pipeline. After the system’s first stage designed capacity is reached, the pipeline will carry 28.2 million tons of oil a year. In the future the annual throughput capacity of oil pipeline system will increase up to 67 million tons. Shares of the governments, which founded CPC, are: Russia has a 24 % stake, Kazakhstan owns a 19 % stake and Oman’ share equals 7 %. The rest is distributed among private oil companies.

Today the Volzhsky pipe plant is incorporated in the Pipe Metallurgical Company. It keeps increasing the production of spiral-welded pipes of different diameters. In 2001 VTZ produced 164.8 thou. tn. of them and in the first quarter of 2002 the volume totaled 55 thou. tn.
Exactly this enterprise won a tender on supplying pipes to the Caspian pipeline consortium (CPC). In 1999– 2000 more than 135 thou. tn. of spiral-welded pipes were shipped for building an oil pipeline from the Caspian coast to terminals on the Black Sea. In 2001 fulfilling the order of Gazprom VTZ started supplying pipes of 1.420 mm in diameter with wall thickness of 15.7 mm for the Yamal-Europe gas pipeline construction. Also, pipes of 720 mm in diameter ordered by the Transneft company for the Baltic pipeline system as well as pipes with diameter of 1.020 mm to 1.220 mm were shipped for the Ukrainian bypass oil pipeline.
In the opinion of Edward Shaposhnikov, the chief specialist of the Welding-and-Mounting Trust, who participated in building the Caspian and Baltic pipeline systems, spiral-welded pipes proved their good construction adaptability, the geometrical parameters are acceptable not only at their faces but also along the whole pipe body and this allowed to do a high-quality welding.
Expanding shipments of pipes made to important orders has become for the Volzhsky pipe plant quite a weighty argument proving the high quality of its products. Careful research and tests of spiral-welded pipes carried out by Russian and foreign experts showed the reliability of spiral- welded joints in zones of flexural strains as well. There are official normative documents on cold bending of VTZ-made spiral-welded pipes, which were approved by Russia’s State technical supervision agency. This considerably increases the possibility of utilizing such pipes and simplifies the procedure of supplying them as a complete set: when laying pipelines in rugged terrain the use of cold-bended curves is a necessary operation, which builders often have to do along the routes. And the last news: controlling agencies have lifted restrictions on using spiral-welded pipes in other major sections of pipeline constructions as well.
So, achievements, failures and new successes in making spiral-welded pipes in Russia prove once again a well-known observation that progress rarely moves straight forward. Usually the development goes in a spiral.