Seamless steel pipes for petrochemical and chemical plants

In modern chemical and petroleum industries, seamless steel pipes serve as a crucial basic material, undertaking the important task of transporting high-temperature, high-pressure, and corrosive media. Their performance directly impacts the safe operation and production efficiency of plants. This article will comprehensively analyze the technical key points of seamless steel pipes used in petrochemical and chemical plants, covering material characteristics, application scenarios, standards and specifications, and future development trends.

Material Characteristics and Core Advantages: Due to their seamless, integrated structure, seamless steel pipes significantly outperform welded steel pipes in terms of pressure resistance and sealing performance. Taking seamless steel pipes used in petroleum cracking units as an example, these pipes need to withstand temperatures above 450℃ and hydrogen sulfide corrosion, typically using chromium-molybdenum alloy steel (such as 15CrMoG) or austenitic stainless steel (such as 0Cr18Ni9). These pipes must be certified according to GB 5310 "Seamless Steel Tubes for High-Pressure Boilers," with a tensile strength of at least 415 MPa and a yield strength of not less than 205 MPa. In hydrocracking units, the pipes must also possess resistance to hydrogen embrittlement, usually achieved by adding trace elements such as vanadium and niobium to improve grain boundary stability.

Typical Application Scenarios and Technical Parameters:

1. Oil Refining Units: Atmospheric and vacuum distillation units utilize large-diameter seamless steel pipes (Φ219mm~Φ813mm) for pipelines, with working pressures up to 4MPa. The regeneration cyclone separator in catalytic cracking units requires 310S heat-resistant stainless steel pipes to withstand the scouring of 900℃ flue gas.

2. Ethylene Cracking: Data shows that the furnace tubes in the convection section of the cracking furnace mostly use HP40Nb centrifugal cast tubes with a chromium-nickel content of 25Cr-35Ni, maintaining a creep rupture strength above 30MPa at 1000℃.

3. Coal Gasification Furnaces: Shell coal gasification units require slag discharge pipelines with both wear resistance and corrosion resistance, typically employing bimetallic composite pipes with an inner layer of high-chromium cast iron (HRC≥58) and an outer layer of carbon steel pressure-bearing material.

It is worth noting that different media have different material requirements. When transporting media containing chloride ions, super austenitic stainless steel (e.g., 254SMO) with a PREN (pitting equivalent) value greater than 40 is required; while liquefied natural gas (LNG) cryogenic pipelines require steel containing 9% nickel to maintain good toughness at -196℃.

Comparison of domestic and international standards: my country's petrochemical pipelines mainly follow standards such as GB/T 8163 (fluid transportation) and GB 9948 (petroleum cracking), which are based on ASTM A335 (American standard) and EN 10216 (European standard). Taking P91 steel pipe as an example, GB 5310 and ASME SA335 have significantly different requirements for impact energy: the Chinese standard requires a transverse impact energy ≥40J (20℃), while the American standard requires a longitudinal impact energy ≥54J. A Zhihu column specifically emphasizes that in overseas EPC general contracting projects, attention must be paid to the additional requirements for hydrogen sulfide environments in the NACE MR0175 standard, including hardness control (HRC≤22) and sulfur content (≤0.01%).

Key Quality Control Nodes:

1. Manufacturing Process: The final rolling temperature of hot-rolled pipes must be higher than Ar3 by 50℃ to avoid banding; cold-drawn pipes require intermediate annealing to eliminate work hardening.

2. Testing Technology: In addition to conventional ultrasonic testing, large-diameter thick-walled pipes also require TOFD (Time-of-Flight Diffraction) technology to detect delamination defects; high-temperature steel pipes should undergo intergranular corrosion testing (e.g., GB/T 4334 E method).

3. On-site Installation: The hydrostatic test pressure should be 1.5 times the design pressure, and the holding time should be no less than 10 minutes. A petrochemical project case shows that excessively high chloride ion content (>25ppm) in the test water can lead to stress corrosion cracking in austenitic steel pipes.

Technological Innovation and Development Trends:

1. Material Upgrades: The China Petrochemical Engineering Research Institute is promoting TP347HFG fine-grained stainless steel, which has a 20% higher creep strength than traditional TP347 and is suitable for ultra-supercritical conditions up to 700℃.

2. Composite Technology: Titanium/steel composite pipes manufactured using explosive fusion and hot rolling processes reduce costs by 60% compared to pure titanium pipes and have been successfully applied in acetic acid plants.

3. Intelligent Monitoring: An online corrosion monitoring system based on fiber optic sensors can provide early warnings of pipe wall thickness changes with an accuracy of 0.1mm. After its application in an oil refinery, this system extended the maintenance cycle from 3 years to 5 years.