Aux 1 Unit 6 Q5

A fusible plug installed on the compressor discharge of a compressed air system serves as a critical safety device, designed to protect against the catastrophic consequences of excessive temperature rise in the discharge line.

1. Fusible Plugs Explained – saVRee

Purpose

Its main purpose is to prevent fire or explosion hazards that can arise from overheating of the compressed air.

How it works:

• Melting Point: The fusible plug is made of a metal alloy with a specific melting point, typically lower than the melting point of the surrounding materials in the compressor and piping.   1. Overview on Fusible Plug – Safety Bag safetybagresources.com
• Location: It is strategically positioned in the discharge line close to the compressor outlet, where it’s directly exposed to the compressed air.
• Temperature Sensing: The plug constantly monitors the temperature of the discharged air.
• Overheating: If the air temperature exceeds the plug’s melting point due to a malfunction in the compressor’s cooling system, interstage coolers, or aftercoolers, the fusible alloy within the plug melts.
• Pressure Release: The melting of the plug creates an opening in the discharge line, allowing the hot compressed air to escape rapidly.
• Preventing Fire/Explosion: This rapid venting prevents further temperature rise and potential ignition of lubricating oil or other flammable materials within the compressor or piping, thus averting a fire or explosion.

Scenarios Triggering Fusible Plug Operation

• Cooling System Failure: If the compressor’s cooling system malfunctions (e.g., due to a pump failure, blockage in the cooling water circuit, or insufficient coolant), the compressed air temperature can rise rapidly.
• Intercooler/Aftercooler Failure: If the intercoolers or aftercoolers between compressor stages fail to cool the air adequately, the temperature in the discharge line can increase, potentially triggering the fusible plug.
• Compressor Overload: Running the compressor beyond its design limits or with excessive load can also lead to overheating and activation of the fusible plug.

Important Considerations:

• Set Temperature: The melting point of the fusible plug is carefully selected based on the compressor’s design and operating parameters to ensure it activates only in critical situations where other safety measures might be insufficient.
• One-Time Use: Once the fusible plug melts, it needs to be replaced before the compressor can be operated again.
• Preventive Maintenance: Regular inspection and timely replacement of the fusible plug are essential to ensure its effectiveness as a safety device.

In Summary:

The fusible plug on the compressor discharge acts as a last line of defense against overheating and potential fire or explosion hazards in compressed air systems. Its operation, triggered by excessive temperature, helps safeguard the compressor, surrounding equipment, and personnel on board the vessel.

A fusible plug on an air receiver serves as a crucial safety device, designed to prevent catastrophic overpressure scenarios in compressed air systems, particularly those found on marine vessels.

Primary Purpose:

• Overpressure Protection: The fusible plug’s main function is to act as a secondary safety measure against excessive pressure buildup within the air receiver. In the event that the primary pressure relief valve malfunctions or fails to operate, the fusible plug acts as a last line of defense.

How it Works:

1. Material Composition: It’s typically made of a metal alloy with a specific, relatively low melting point (usually lower than the melting point of the receiver itself).
2. Installation: The fusible plug is strategically located on the air receiver, often on the top or in a position where it will be exposed to the highest temperatures within the receiver.
3. Temperature Trigger: If the temperature within the receiver rises abnormally high, often due to a fire in the vicinity or a severe compressor malfunction, the fusible plug’s core melts.   1. Fusible Plugs – Bonut Engineering Ltd bonut.co.uk
4. Pressure Release: The melting of the core creates an opening in the plug, allowing the high-pressure air inside the receiver to escape rapidly and in a controlled manner.   1. Fusible plug – Wikipedia en.wikipedia.org
5. Preventing Catastrophe: This rapid venting of air prevents the receiver from rupturing or exploding due to excessive pressure, thus averting a potentially disastrous situation.

Key Points:

• Secondary Safety: The fusible plug is not the primary pressure relief device. It acts as a backup in case the primary safety relief valve fails to operate.
• Temperature-Activated: It’s triggered by high temperature, which is often a consequence of overpressure or fire.   1. Fusible Plugs Explained – saVRee savree.com
• Sacrificial Device: Once the fusible plug melts, it’s rendered useless and needs to be replaced.
• Regular Inspection: Regular inspections are critical to ensure the fusible plug is in good condition and has not corroded or become damaged.

Benefits:

• Prevents Catastrophic Failure: It helps avoid a potentially disastrous explosion of the air receiver, safeguarding personnel, equipment, and the vessel itself.
• Simple and Reliable: It’s a simple, passive device with no moving parts, making it highly reliable.
• Cost-Effective: It’s a relatively inexpensive safety feature that provides critical protection.

In Summary:

The fusible plug on an air receiver is an essential safety component that provides a last line of defense against overpressure caused by overheating or other malfunctions. It acts as a sacrificial device, melting and venting pressure to prevent a potential explosion, thereby significantly enhancing the safety of compressed air systems on marine vessels.

In water-cooled air compressors, a bursting disc serves as a crucial safety device specifically designed to protect the intercooler or aftercooler from damage caused by overpressure.

1. BURSTING DISC ON MAIN AIR COMPRESSOR… FOURTH ENGINEER SHOULD KNOW..

Purpose:

• Protect the Intercooler/Aftercooler: The primary function of a bursting disc on a water-cooled air compressor is to safeguard the intercooler or aftercooler from excessive pressure buildup. This prevents potential catastrophic failure of these heat exchangers, which could lead to water leaks, air contamination, and even explosive ruptures.   1. BURSTING DISC ON MAIN AIR COMPRESSOR… FOURTH ENGINEER SHOULD KNOW.. www.youtube.com

How it Works:

1. Location: The bursting disc is installed on the water side (coolant side) of the intercooler or aftercooler, typically on the end covers or headers.
2. Pressure Differential: It’s designed to rupture at a pressure slightly higher than the normal operating pressure of the cooling water circuit but significantly lower than the pressure of the compressed air in the air side of the heat exchanger.
3. Air Leakage into Water Side: If a tube within the intercooler/aftercooler develops a leak or rupture, high-pressure air can escape into the water side.
4. Pressure Buildup: This air leakage causes a rapid pressure increase in the water jacket or shell of the heat exchanger.
5. Bursting Disc Rupture: As the pressure rises beyond the bursting disc’s design limit, it ruptures, creating an opening for the pressurized water and air to escape.
6. Damage Prevention: The rupture of the bursting disc relieves the pressure, preventing the intercooler/aftercooler from being damaged or exploding due to the excessive internal pressure.

Advantages:

• Fast Response: Bursting discs react almost instantaneously to overpressure, providing rapid protection for the intercooler/aftercooler.
• Reliable: They are simple, non-mechanical devices with no moving parts, ensuring high reliability.   1. Where and how are rupture discs used? – OsecoElfab blog post www.osecoelfab.com
• Accurate Burst Pressure: They are manufactured with precise burst pressure ratings, ensuring predictable performance in overpressure situations.

Importance:

• Safety: Preventing intercooler/aftercooler failure helps avoid potential safety hazards like water leaks, air contamination, and explosions, protecting personnel and the vessel.
• Equipment Protection: It safeguards the intercooler/aftercooler, a critical and often expensive component of the compressed air system, from damage, reducing maintenance and repair costs.
• Operational Continuity: By preventing intercooler/aftercooler failure, the bursting disc helps ensure the continuous operation of the compressed air system, which is crucial for various shipboard functions like engine starting and pneumatic controls.

In summary, the bursting disc on a water-cooled air compressor is a vital safety feature that protects the intercooler or aftercooler from overpressure damage. It acts as a last line of defense, ensuring the integrity of the heat exchanger and the overall safety and reliability of the compressed air system.