In the MDEA unit of the LNG liquefaction plant, leaks due to sand holes occurred in various sections of the fluid flow pipelines ranging from the absorption tower to the flash tank, and from the flash tank to the regeneration tower

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1. Process of the leakage unit: The natural gas introduced by the raw gas pressurization unit has a pressure of 4.5 MPa (gauge pressure); its CO2 content is ≤3.0% (mol), while methane accounts for 82.681% (mol). It enters the absorption tower from the bottom and moves upward through the tower； The MDEA solution is poured in from the upper part of the absorption tower, where it comes into full contact with natural gas. The CO2 in the natural gas is absorbed and enters the liquid phase. After absorbing CO2, the MDEA solution in the absorption tower has a temperature of 30–45°C; the liquid level in the tower is regulated by the control valve LV-2101. The mixture is then depressurized to 0.5 MPa (gauge pressure) and sent to the flash tank. The rich liquid obtained there is heated to 90–100°C using a heat exchanger with the lean liquid, after which it is sent to the upper part of the regeneration tower, where it is regenerated through stripping until the leanness of the liquid meets the required standards. The operating temperature at the lower part of the regeneration tower is 115°C to 125°C, to ensure thorough regeneration of the MDEA solvent. The MDEA solution exiting the regeneration tower (the lean solution) is cooled to around 40°C through a heat exchanger between lean and rich solutions as well as a lean solution cooler, and then pressurized to 5.3 MPa by a lean solution pump before being fed into the absorption tower. 2. Main components of the medium in the leaking pipeline: water, MDEA (N-methyldiethanolamine), CO2, trace amounts of methanol, a small amount of methane, trace amounts of H2S, etc. 3. Main materials used for the leaking pipeline and fittings: equal-diameter tees – CF 415 (carbon steel); filters (carbon steel); return pipelines (seamless steel pipes – carbon steel); flange accessories (seamless steel pipes – carbon steel); flange reducers (steel grade 20); welded connections at flange reducers (steel grade 20). I’m seeking advice from experts – has anyone encountered such issues? What could be the cause of repeated leaks due to sand holes in carbon steel materials?