Given below are two statements, one is labelled as Assertion (A) and other as Reason (R). Choose the correct answer from the options given below.
Assertion (A): Fire tube boilers do not operate at high pressures while water tube boilers operate at high pressures.
Reason (R): Due to high temperature of flue gases, fire tubes may fail due to creep.

Explanation:

Fire Tube Boilers:

• Fire tube boilers are a type of boiler where hot gases from combustion pass through one or more tubes running through a sealed container of water. The heat from the gases is transferred to the water, which then generates steam. The design of fire tube boilers is simple and suitable for low and medium-pressure applications. However, they are not designed to operate at high pressures because of the structural limitations of the fire tubes themselves.

Why Fire Tube Boilers Cannot Operate at High Pressures:

1. Material Limitations: The fire tubes in fire tube boilers are subject to high temperatures due to the flue gases passing through them. At high pressures, these materials can experience creep – a time-dependent deformation of materials under stress at elevated temperatures. This makes them prone to failure.

2. Structural Design: The cylindrical shape of the fire tubes limits their ability to withstand high internal pressures. At higher pressures, the thin walls of the fire tubes are more likely to rupture, compromising the safety and integrity of the boiler.

3. Efficiency and Safety: Fire tube boilers are inherently less efficient at high pressures because the surface area available for heat exchange is limited. Additionally, operating at high pressures increases the risk of catastrophic failure, making them unsuitable for such applications.

Water Tube Boilers:

• Water tube boilers, on the other hand, are designed to handle high pressures. In these boilers, water circulates inside the tubes, and hot gases flow over the outside of the tubes. This design allows for better heat transfer and the capability to operate at higher pressures and temperatures.

Why Water Tube Boilers Can Operate at High Pressures:

1. Structural Advantages: The tubes in water tube boilers are smaller in diameter and have thicker walls compared to fire tubes. This allows them to withstand the high internal pressures typically found in power plants and industrial applications.

2. Efficient Heat Transfer: The arrangement of tubes in water tube boilers provides a larger surface area for heat transfer, enabling them to generate steam efficiently even at high pressures.

3. Safety: In case of a tube failure, the water tube boiler design ensures that only a small amount of water is lost, reducing the risk of a catastrophic event. This makes them more suitable for high-pressure applications.