Corrosion of tubewell pipes may cause excessive discharge of sand with water. This occurs due to the degradation and weakening of the pipes, leading to the breakdown of the protective layer and the exposure of the underlying metal to the surrounding environment.

Below are the details explaining why excessive discharge of sand with water occurs as a result of tubewell pipe corrosion:

1. Corrosion process:
- Corrosion is a natural electrochemical process that occurs when metals are exposed to an environment that promotes their oxidation.
- In the case of tubewell pipes, the most common form of corrosion is galvanic corrosion, which happens when dissimilar metals come into contact in the presence of an electrolyte such as water.
- The presence of impurities in the water, such as dissolved oxygen, salts, and minerals, accelerates the corrosion process.

2. Pipe degradation:
- As corrosion progresses, the protective layer on the surface of the pipe deteriorates, making the metal more susceptible to further degradation.
- The corrosion reactions cause the metal to weaken, leading to the formation of pits, cracks, and other irregularities on the pipe's surface.
- These imperfections act as initiation points for the accumulation of sand particles, which can erode the pipes further.

3. Sand discharge:
- As the pipes corrode and weaken, the water flowing through them exerts pressure on the surrounding soil or sand.
- The weakened pipes are more prone to deformation and collapse, creating gaps and openings through which sand can enter.
- The sand particles suspended in the water are then discharged along with the water, leading to excessive sand discharge.

4. Consequences of sand discharge:
- The excessive discharge of sand with water can cause several problems. It can clog filters, screens, and other components of the tubewell system, reducing its efficiency.
- The sand can also cause abrasion and wear on the pump impellers, leading to increased maintenance and repair costs.
- Additionally, the presence of sand in the water supply can damage household appliances, irrigation systems, and other equipment that rely on clean water.

In summary, the corrosion of tubewell pipes leads to the excessive discharge of sand with water due to the degradation and weakening of the pipes. This can cause various operational and maintenance issues, impacting the performance and reliability of the tubewell system.