First, Standard Positioning and Scope of Application for Seamless Steel Pipes for Petroleum Cracking
GB/T 9948-2025 is a dedicated standard for seamless steel pipes used in petroleum cracking units. It integrates four standards, including the original GB/T 9948-2013 and GB/T 6479-2013, and is applicable to furnace tubes, heat exchangers, pipelines, and pressure vessels in petroleum refineries. This standard focuses on addressing the material performance requirements under high temperature (≤650℃), high pressure (≥10 MPa), and corrosive media (such as H₂S, CO₂) environments, covering the entire process of steel pipe requirements from catalytic cracking units to delayed coking units.

Second, Material System and Performance Requirements for Seamless Steel Pipes for Petroleum Cracking
(1) Material Classification of Seamless Steel Pipes
Carbon structural steel: 20G, 20MnG, 25MnG, suitable for low temperature and low pressure conditions. Alloy structural steels: 15MoG, 12CrMoG, 12Cr2MoG, 12Cr1MoVG, etc., with the addition of elements such as Mo, Cr, and V to improve high-temperature strength and creep resistance.
Stainless heat-resistant steels: 1Cr18Ni9, 1Cr18Ni11Nb, used in highly corrosive environments.
(2) Key performance indicators of seamless steel pipes:
Tensile strength: ≥410 MPa (carbon steel) to ≥560 MPa (alloy steel).
Yield strength: ≥245 MPa (carbon steel) to ≥415 MPa (high alloy steel).
Creep strength: ≥100 MPa after 100,000 hours at 600℃.
Oxidation resistance: Oxidation rate ≤0.1 g/(m²·h) at 650℃.
Microstructure stability: Grain size ≤6 is required to avoid microstructure coarsening after long-term use at high temperatures. 

Third, Manufacturing Process and Quality Control of Seamless Steel Pipes for Petroleum Cracking
(1) Manufacturing Process of Seamless Steel Pipes
Hot-rolled steel pipes: outer diameter 22~530 mm, wall thickness 20~70 mm, suitable for large-diameter, thick-walled steel pipes.
Cold-drawn steel pipes: outer diameter 10~108 mm, wall thickness 2.0~13.0 mm, surface finish up to Ra3.2 μm.
(2) Heat Treatment of Seamless Steel Pipes
Carbon steel: normalizing (900~930℃) + tempering (670~720℃).
Alloy steel: quenching (930~960℃) + tempering (680~720℃).
Stainless steel: solution treatment (≥1040℃) followed by rapid cooling. (3) Inspection and Testing of Seamless Steel Pipes
Pipe-by-pipe inspection: Hydrostatic test (pressure ≥ 20 MPa), flaring test (flaring rate ≥ 15%), flattening test (no cracks after flattening).
Non-destructive testing: Ultrasonic testing (compliant with GB/T 5777-2019), eddy current testing (compliant with GB/T 7735-2016).
Additional tests: Intergranular corrosion test (according to GB/T 4334-2020 Method E), high-temperature creep strength test (600℃/100 MPa/100,000 hours).

Fourth, Specification Range and Dimensional Tolerances of Seamless Steel Pipes for Petroleum Cracking
(1) Specification Range of Seamless Steel Pipes
Outer diameter: 10~760 mm (covering from small-diameter steel pipes in catalytic cracking units to large-diameter pipes in delayed coking units).
Wall thickness: 1.5~120 mm (meeting different pressure rating requirements). 
(2) Dimensional Tolerances of Seamless Steel Pipes
Hot-rolled steel pipe: Outer diameter ±1.0%, wall thickness ±10% (minimum ±0.5 mm).
Cold-drawn steel pipe: Outer diameter ±0.3 mm (D≤50 mm) or ±0.8% (D>50 mm), wall thickness ±10%.

Fifth, Application Scenarios and Typical Cases of Seamless Steel Pipes for Petroleum Cracking
(1) Catalytic Cracking Unit
Reactor temperature control system: Uses 12Cr1MoVG steel pipe, capable of withstanding 620℃ high temperature and 15 MPa pressure.
Regenerator flue gas pipeline: Uses 1Cr5Mo steel pipe, with excellent resistance to H₂S corrosion.
(2) Delayed Coking Unit
Heat exchanger tube bundle: Uses 35CrMo steel pipe, combining high-temperature strength and resistance to thermal fatigue.
(3) Chemical Equipment
High-pressure reactor: Uses 12Cr2MoWVTiB steel pipe, meeting the extreme conditions of 650℃/25 MPa.