Objective The plugging resulting from scale precipitation and perforation due to corrosion easily occurs in breathing tube in sulfide-containing natural gas station, which has big potential risks for the security and environmental protection.

Methods The scales obtained from five natural gas stations, such as TB101-X1 well station, were analyzed by SEM, EDS and XRD, the plugging main reasons were discussed according to the flash steam operating conditions of the breathing tube.

Results High hydrogen sulfide accumulates in breath tube when the flow of flash steam is low velocity under the normal temperature and slight positive pressure. Accordingly, elemental sulfide is precipitated from high hydrogen sulfide. It is found that liquid water form from flash steam due to condense with the decrease temperature of flash steam with the extension of breath tube, more liquid water is carried by flash steam into breathing tube when the produced water tank keeps high level water. The corrosion of carbon steel tube occurs under the combination of hydrogen sulfide and sulfate and chloride ions to form corrosion scale, such as iron sulfide and ferrous sulfate and iron oxide. When the produced water is discharged from storage tank, negative pressure forms in the tank and oxygen is inhaled into the tank through breathing tube. Therefore, oxygen corrosion and elemental sulfide precipitation occurs through the reaction of oxygen and hydrogen sulfide. Corrosion scales and elemental sulfide are precipitated at the internal tube wall when the flash steam keeps low velocity. At earlier and medium stages, the scales are uneasily found. However, the scales will distinctly plug the breathing tube at the later stage, as resulted in the increase of pressure in the tank due to the accumulation of flash steam.

Conclusions The technical countermeasures, such as replenishing breathing tube using natural gas when tank is under negative pressure, optimizing the material of breathing tube, adding gas-liquid separation assembly between tank and the inlet of breathing tube, can prevent and reduce the blockage of the breathing tube in essence, and have strong guiding significance for maintaining the unobstructed breathing tube and ensuring the safe production and operation of the gas field water tank.