Boilers are essential components of numerous industries, including marine operations, where they play a crucial role in generating steam for propulsion, power generation, and other onboard processes. Safety valves are critical elements of boiler systems, designed to protect against potentially hazardous conditions by relieving excess pressure. However, for safety valves to effectively perform their function, regular operational testing is essential. This article aims to emphasize the importance of testing safety valves, provide insights into their operation, maintenance, and testing procedures, and offer links to existing Class rules and regulations pertaining to safety valve live tests on marine boilers.

Safety valves act as the last line of defense against catastrophic boiler failures caused by excessive pressure. Their primary purpose is to ensure the pressure within the boiler remains within safe limits by discharging excess steam when the predetermined set pressure is exceeded. However, if safety valves are not periodically tested, their reliability may diminish over time, leading to potential risks such as boiler explosions or damage. Thus, regular testing of safety valves is critical to ensure the continued safety and proper functioning of the entire boiler system.

Safety valves are mechanical devices that rely on pressure to operate effectively. When the pressure inside the boiler reaches the predetermined setpoint, the safety valve opens to release excess steam and reduce pressure. This action helps prevent the pressure from surpassing the boiler’s maximum allowable working pressure (MAWP) and protects against potential over-pressurization hazards.

For boilers, the safety devices are to be tested and the safety valves are to be operated using the relieving devices. For exhaust gas heated economizers/boilers, the safety valves are to be tested at sea by the Chief Engineer and details recorded in the Log Book.

All safety valves are to be set under steam to a pressure not greater than the approved pressure of the boiler. As a working tolerance the setting is acceptable provided the valves lift at not more than 103 per cent of the approved design pressure. During a test of 15 minutes with the stop valves closed and under full firing conditions the accumulation of pressure is not to exceed 10 per cent of the design pressure. During this test no more feed water is to be supplied than is necessary to maintain a safe working water level.

To maintain the reliability and effectiveness of safety valves, regular maintenance is essential. Here are some key maintenance practices:

1. 1. Visual Inspection: Conduct routine visual inspections to identify any signs of damage, corrosion, or leaks. Ensure the valve is clean and free from debris that may obstruct its operation.

   2. Lubrication: Apply the recommended lubricants to moving parts to ensure smooth valve operation. However, it is crucial to use lubricants compatible with the valve’s construction materials.

   3. Testing: Regularly test safety valves to verify their performance and ensure they are operating within acceptable tolerances. This helps identify any issues with the valve’s lifting pressure, seat tightness, or disc movement.

The workshop bench testing procedure for safety valves, is done usually during dry dock inside yard workshop and,  typically involves the following steps:

1. 1. Preparation: Prior to testing, isolate the boiler from the system by shutting off the boiler and relevant valves. Follow proper lockout/tagout procedures to ensure the safety of personnel. Cool down and drain boiler pressure.

   2. Bench Testing: Remove the safety valve from the boiler and place it on a test bench. Connect it to an appropriate testing apparatus capable of accurately measuring pressure and flow rates.

   3. Set Pressure Verification: Verify the valve’s set pressure by gradually increasing the pressure until the valve starts to lift. Compare the observed set pressure with the manufacturer’s specified value.

   4. Seat Tightness Testing: After verifying the set pressure, gradually reduce the pressure until the valve reseats. This tests the tightness of the valve’s seating surfaces and ensures proper closure after relieving excess pressure.

   5. Overpressure Testing: Conduct an overpressure test to ensure the valve can handle pressures above the setpoint without any leakage or damage. This test provides an additional safety margin and evaluates the valve’s overall strength.

   6. Documentation: Record the test results, including the set pressure, lift pressure, reseat pressure, and any deviations or observations. Maintain a comprehensive maintenance log for each safety valve.

An in situ test of boiler safety valves, also known as a live test, involves testing the valves while the boiler is in operation. This procedure allows for the assessment of the safety valves’ performance under actual operating conditions. Here is a step-by-step description of the in situ test procedure for boiler safety valves:

Preparation:

• • • Review the boiler system’s operating manual and safety valve manufacturer’s instructions to understand the specific requirements and procedures for testing the safety valves.
    • Ensure all necessary safety precautions are taken, such as wearing appropriate personal protective equipment (PPE) and following lockout/tagout procedures to isolate the boiler and associated equipment.
    • Verify that all required testing instruments and equipment, such as pressure gauges and flow measurement devices, are available and calibrated.

Isolation and Preparation for Testing:

• • • Shut down any auxiliary equipment connected to the boiler and close relevant isolation valves.
    • Verify that the main steam valve and any other upstream valves are closed.
    • Confirm that the pressure within the boiler has dropped to a safe level before proceeding with the test.

Test Setup:

• • • Identify the safety valve to be tested and visually inspect it for any signs of damage, corrosion, or leakage. Ensure it is clean and free from debris.
    • Attach or open pressure gauges to appropriate ports or connections to monitor the boiler pressure.
    • In some situations, mainly ashore, install flow measurement devices, such as an orifice plate or flowmeter, to measure the steam flow rate discharged by the safety valve during the test.
    • Ensure all connections and fittings are properly tightened and secured.

Testing:

• • • Gradually increase the boiler pressure.
    • Monitor the pressure from inside boiler using the installed pressure gauges.
    • Observe the safety valve for signs of lifting, such as the discharge of steam and the movement of the valve’s disc.
    • Measure and record the lift pressure, which is the pressure at which the safety valve starts to open and discharge steam.
    • If required, continuously monitor and record the steam flow rate through the safety valve using the installed flow measurement devices.
    • Stop the boiler and allow the pressure to drop.
    • Once the valve has lifted and discharged steam, observe the valve’s reseating and make note of the reseat pressure, which is the pressure at which the valve closes after relieving excess pressure.

Evaluation and Analysis:

• • • Compare the measured lift pressure and reseat pressure with the manufacturer’s specified values or any applicable regulatory requirements.
    • Assess the steam flow rate and ensure it is within the acceptable range for the specific safety valve and boiler system.
    • Evaluate the overall performance of the safety valve based on its response time, seat tightness, and ability to relieve excess pressure effectively.

Documentation and Maintenance:

• • • Record all relevant test data, including the lift pressure, reseat pressure, steam flow rate, and any observations or deviations from expected performance.
    • Update the maintenance log or equipment records with the test results and note any necessary actions, such as adjustments, repairs, or replacement of the safety valve.
    • Follow any specific maintenance and reinstallation procedures recommended by the safety valve manufacturer or regulatory guidelines.

It is important to note that the specific procedure for conducting an in situ test of boiler safety valves may vary depending on the boiler system, safety valve type, and applicable regulations. Therefore, it is crucial to consult the boiler manufacturer’s instructions, regulatory guidelines, and industry best practices when performing these tests to ensure accurate and reliable results while prioritizing safety.

In the maritime industry, the operational testing of safety valves on marine boilers is governed by various regulatory bodies and classification societies. These organizations establish rules and guidelines to ensure the safe operation of vessels. Some relevant regulatory bodies and their associated regulations include:

1. 1. International Maritime Organization (IMO): The IMO sets global standards for safety and environmental performance, including boiler safety. The “International Convention for the Safety of Life at Sea” (SOLAS) contains regulations related to boiler safety on ships.

   2. Classification Societies: Classification societies such as the American Bureau of Shipping (ABS), Lloyd’s Register (LR), and DNV GL provide rules and guidelines for the construction, maintenance, and testing of marine boilers. These rules often include specific requirements for safety valve testing and maintenance.

To access the latest Class rules and regulations pertaining to safety valve live tests on marine boilers, please visit the respective websites of the classification societies mentioned above. They provide comprehensive information on safety standards and procedures.

In conclusion, the operational testing of safety valves is of paramount importance for ensuring the safe and reliable operation of boilers, particularly in marine applications. By conducting regular tests, adhering to maintenance practices, and following established regulations, vessel engineers can minimize the risk of boiler failures, protect onboard personnel, and safeguard marine environments. Prioritizing the testing and maintenance of safety valves contributes significantly to the overall safety culture and the longevity of boiler systems.

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