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The overhead system of the coking unit’s splitter tower is subject to low-temperature corrosion caused by H2S, HCl, NH3, and H2O; it represents a key area for corrosion in the unit. As such, the oil and gas lines in this tower are the focus of regular corrosion monitoring. It is necessary to use methods such as periodic thickness testing to assess the degree of corrosion in these lines, in order to prevent corrosion-related leaks and to verify the effectiveness of the anti-corrosion measures in place. During the fixed-point thickness measurement inspection of the unit, it was found that starting from the first elbow at the top outlet of the fractionation tower (C202), the thickness loss in the oil and gas line at the top of the tower was greater than 50%. As shown in Figure 1 (hereinafter referred to as: oil and gas line elbow), based on relevant specifications and strength checks, it was determined that it could no longer be used safely; therefore, the elbow was replaced, and the other parts of the pipeline are in normal condition. The overhead oil and gas line originates from the top of the fractionation tower (C202) and extends to the inlet of the air cooler (A201). The pipe specifications are φ377×9.5 mm; the material used is 20. The fluids flowing through this line include overhead oil and gas, water vapor, coke powder, etc. The design temperature is 250°C, the operating temperature is 135°C, the design pressure is 1.0 MPa, and the operating pressure is 0.14 MPa. Since its commissioning in 2011, some sections of this pipeline were replaced during the last maintenance session (once a year) due to corrosion-induced thinning. Figure 1 Schematic diagram of oil and gas pipeline