Abstract: Landfill leachate may cause pipe corrosion and scaling during its collection and transportation due to its complex and harmful components. High-density polyethylene (HDPE) has been widely used as pipe materials in landfill design. In this study, HDPE samples were placed in young leachate (1# leachate) and old leachate (2# leachate) to study their scaling potentials and characteristics. Through periodical monitoring the water quality parameters of the leachates, including Ca²⁺, Mg²⁺, Cl^-, ORP and pH, and analysis of weight changes of the samples and SEM morphology, the possible causes of pipe scaling was inferred. The results show that: (1) With the implementation of experiment, the concentration of calcium and magnesium ions in the leachate decrease significantly, among which Ca²⁺ varies significantly. The concentration of Ca²⁺ in the 1# leachate decreases by 85% while that in the 2# leachate decreases by about 75% after 50 days of the experiment. (2) The immersion of HDPE pipe material affect the leachate quality. In the initial stage of the experiment, it has an impact on Ca²⁺, Cl^- and ORP, while it causes an increase of pH at the middle and late stages. (3) The scale on the HDPE samples placed into the 1# leachate and 2# leachate is 1.10 and 0.682 mg/cm², respectively, indicating that the scaling occurs more serious in the 1# leachate. (4) The concentrations of Ca²⁺ and Mg²⁺ are negatively correlated with the scaling (P < 0.05), and the Ca²⁺ is identified as the key influencing factor (P < 0.01). Temperature, pH and ORP are positively correlated with the scaling, whilst Cl^- is negatively correlated. (5) In the early stage of the experiment, the scale formation was identified as chemical crystallization and precipitation, whilst the scales were gradually transformed into amorphous sediments in the later stage. In conclusion, the scaling is more serious when placing the pipe samples into the 1# leachate. Ca²⁺ and Mg²⁺ are identified as the dominant influencing factors. Monitoring and controlling their concentrations is critical to mitigate pipe scaling during the leachate collection and transportation.