Why Did the Gas Collector Pipe of the Hydrogen Production Unit Crack Suddenly?
Release date:
Nov 30,2023
A company adopts Technip reformers to produce hydrogen and syngas in its hydrogen production process. The upper gas collector pipe of the reformer serves as the feed system, with a medium mixture of steam and natural gas flowing inside. An endothermic reaction takes place inside the reformer tubes under the action of catalysts to generate hydrogen and other gases. The upper gas collector pipe is made of TP347H steel, with a design operating temperature of 635°C and a design operating pressure of 4.3 MPa.
A company adopts Technip reformers to produce hydrogen and syngas in its hydrogen production process. The upper gas collector pipe of the reformer serves as the feed system, with a medium mixture of steam and natural gas flowing inside. An endothermic reaction takes place inside the reformer tubes under the action of catalysts to generate hydrogen and other gases. The upper gas collector pipe is made of TP347H steel, with a design operating temperature of 635°C and a design operating pressure of 4.3 MPa.
Penetrant testing was carried out on the cracked gas collector pipe and its adjacent areas in accordance with NB/T 47013.5—2015 Non-destructive Testing of Pressure Equipment – Part 5: Penetrant Testing. The test results revealed only one crack on the pipe wall of the gas collector pipe, located in the base metal near the welded joint. Macroscopic observation of the cracked gas collector pipe showed that the crack was circumferential without branches, with a length of approximately 120 mm, as shown in Figure 2. The maximum opening width appeared at the middle section of the crack, indicating that the crack initiation zone was in the middle of the crack.
Metallographic specimens were taken from the cracked section of the gas collector pipe perpendicular to the weld, covering the base metal, heat-affected zone and weld seam on the observation surface. After grinding and polishing, the specimens were etched with aqua regia prior to microscopic observation, as illustrated in Figure 3. The microstructure of the gas collector pipe weld consisted of austenite plus delta ferrite, presenting a normal structure. The microstructure of the heat-affected zone was composed of austenite, delta ferrite and precipitated phases; the granular precipitated phases were distributed along the austenite grain boundaries. The base metal featured a microstructure of austenite with granular precipitated phases distributed at austenite grain boundaries, and sensitization occurred in the structure.
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