How Does A Single Steel Plate Become A High-pressure Pipe?

In the Fourth West-to-East Gas Pipeline and deep-sea oil and gas development and other major projects, high-pressure pipes are "industrial blood vessels" for transporting energy, and their pressure-bearing capacity can reach more than 25MPa, which can withstand the test of extreme environment. Little known is that these "steel tough guys" all come from a flat steel plate. The transformation from thin plate to high-pressure pipe needs to go through dozens of precise processes, and each step embodies the wisdom of industrial manufacturing.

Not all steel plates can be used as raw materials for high-pressure pipes, and their material selection has strict standards. Taking X80 steel grade steel plate commonly used in long-distance pipelines as an example, it is required that not only the yield strength is above 551MPa, but also excellent low-temperature toughness, and the impact energy of weld should exceed 100J at -20℃. Baoji Petroleum Steel Pipe will also add 0.015% Nb and 0.003% B in the second project of Sichuan-East Gas Transmission to enhance the stability of the material.

After material selection, the steel plate needs to pass "physical examination" such as ultrasonic inspection and magnetic particle inspection to eliminate internal cracks, inclusions and other defects. The State Administration of Market Supervision requires that the steel plate for high-pressure pipe must be traced back to the whole process of heat number, material and other information to ensure that the source can be traced.

Forming is a key step in transforming steel plate into tube. At present, the mainstream JCOE process can be called "precision shaper". In this process, the edge of the steel plate is pre-bent (J process), then the steel plate is formed into a C-shape by gradual bending (C process), then it is closed into an open O-shaped tube blank (O process), and finally the size is calibrated by a diameter expander (E process) to ensure that the roundness error of the tube body is controlled within 0.5%.

The 1422 mm diameter high-pressure pipe used in the fourth line of West-to-East gas transmission needs to adjust the bending parameters by computer simulation to avoid cracking of the steel plate due to uneven stress. After adopting this process, the peak circumferential residual stress of Baoji petroleum steel pipe is reduced by 38% compared with the traditional process, which fully meets the international standard DNV-ST-F101.

Weld is the lifeline of high-pressure pipe, and double-sided submerged arc welding technology is the core to ensure its strength. When welding, the arc burns under the flux layer, which not only isolates air pollution, but also forms a dense weld. Welding parameters should be accurately controlled, such as preheating temperature of internal welding should be stabilized at 120-140℃ and current fluctuation should not exceed 50 a..

In order to cope with the risks of hydrogen embrittlement, Huayou steel pipe innovatively adopts laser-arc hybrid welding technology in the manufacture of hydrogen energy transmission pipe, which makes the grain size of weld reach ASTM 9 or above, and the hydrogen permeability is only 43% of that of traditional technology. After welding, the weld should be checked by X-ray inspection and ultrasonic inspection to ensure that there are no minor defects.

High-pressure pipes must pass the "limit test" before leaving the factory. Hydrostatic test is the basic link, and it is necessary to raise the pressure in the pipe to 1.5 times of the design pressure and keep the pressure for 10 minutes. For example, the pipe used in Deep Sea No.1 Project needs to bear the test pressure of 37.5MPa. For pipes used in corrosive environment, it is necessary to carry out hydrogen induced cracking (HIC) test to ensure that they will not leak in the medium containing CO and HS for 30 years.

92% of the head enterprises have deployed MES system to archive flaw detection data and water pressure results in real time. The national spot check shows that only the products that pass the GB/T 9711 standard full wall thickness impact test can get the "admission ticket" to enter major projects.

steel pipe

According to different application scenarios, the finished pipe needs to be customized. Deep-sea pipe is made of low Mn and high Cr material and treated with slow cooling, so that the weld hardness is controlled at HV10≤280;; The pipes used in the South-to-North Water Transfer Project will be sprayed with solvent-free epoxy coating of more than 500μm on the inner wall, and the corrosion resistance will be verified by cathodic stripping test.

The transformation from a steel plate to a high-pressure pipe is not only a morphological change, but also a comprehensive embodiment of industrial precision and standards. These high-pressure pipes carrying technological breakthroughs are supporting the high-quality development of China's energy transmission and infrastructure projects and becoming an important cornerstone for the construction of an industrial power.