Sealing Verification of Cast Steel Manual Stop Valve J41H-16C After Overhaul

In thermal power plants, stop valves are key equipment to ensure the safe operation of pipeline systems. Cast steel manual stop valve J41H-16C is often used for the control of main steam, water supply and oil systems due to its high temperature and corrosion resistance. However, valves may leak due to wear of the sealing surface, impurity deposition or mechanical fatigue during long-term operation. After overhaul, how to scientifically verify its sealing is the core link to ensure system stability and safety. Below we will analyze the sealing verification method of stop valve J41H-16C DN100 after overhaul based on actual operating experience, and share some practical tips with you.

I. Sealing verification after overhaul: Why is it so critical?

The sealing performance of the stop valve directly affects the safety and economy of the fluid system. Taking the stop valve J41H-16C DN100 as an example, its sealing surface is usually composed of a combination of metal and non-metallic materials, and may undergo slight changes during the overhaul due to disassembly, cleaning or replacement of seals. If it fails to pass strict verification, it may cause the following problems:

• Media leakage: Steam or oil leakage not only wastes resources, but also may cause safety hazards.
• Pressure fluctuation: Poor sealing can lead to unstable system pressure and affect the operating efficiency of the turbine or pump.
• Corrosion intensification: If the medium contains corrosive components, such as oxygen in the feed water, leakage may accelerate the corrosion of the pipeline or equipment.

Therefore, the sealing verification after maintenance is not only a necessary step in the acceptance process, but also the “last line of defense” to prevent failures.

II. Detailed explanation of verification steps: comprehensive inspection from static to dynamic

Step 1: Appearance and sealing surface inspection

Before the formal test, the J41H-16C stop valve needs to be carefully inspected for appearance.

Sealing surface status: Use a magnifying glass or surface roughness meter to check the contact surface between the valve disc and the valve seat to ensure that there are no scratches, cracks or deposits. If pits or wear are found, the seal needs to be repaired or replaced.

Stuffing box seal: The valve stem stuffing box of the J41H-16C manual stop valve is a common leakage point. Check whether the packing is aged and whether the gland is evenly tightened. If necessary, replace the graphite or flexible graphite packing.

Flange connection: Confirm that the flange gasket is not deformed or aged, and the bolt tightening torque meets the standard.

Step 2: Water pressure strength test

This is a basic test to verify the integrity of the valve housing of the stop valve J41H-16C. Close the stop valve, inject clean water or antifreeze into the valve cavity, and increase the pressure to 1.5 times the rated pressure. Maintain the pressure for 30 minutes and observe whether there is leakage in the valve body, flange and connection.

Note: The test medium should avoid containing corrosive components; if the ambient temperature is below 5°C, antifreeze measures should be taken.

Step 3: Sealing surface leakage test

For the one-way sealing characteristics of the J41H-16C stop valve, pressure should be applied from the inlet side and the outlet side should be open.

Test process:

Close the stop valve and fill the test medium (such as air or nitrogen) into the inlet side, and the pressure is set to 1.1 times the rated pressure.

Maintain the pressure for 10 minutes and observe whether there are bubbles or liquid leakage on the outlet side.

If the medium is gas, apply soapy water to the sealing surface and check whether there is continuous bubble generation.

Qualification standard: According to ISO 5208 standard, Class A seal requires no visible leakage, and Class D allows trace leakage.

Step 4: Dynamic sealing test

Verify the sealing stability of the stop valve during the opening and closing process by simulating actual working conditions.

Operation method:

Under the test medium, repeatedly open and close the valve 5-10 times to observe whether the sealing surface is stuck or leaking.

Use a pressure sensor to record the pressure fluctuations during the opening and closing process to ensure that there is no abnormal pressure drop. This dynamic test can detect instantaneous leakage problems caused by sealing surface adhesion or packing wear.

Step 5: Quantify the leakage by pressure drop method

For scenarios with high precision requirements, the pressure drop method can be used to further quantify the leakage rate.

Implementation steps:

Close the stop valve, fill the valve cavity with nitrogen to 1.1 times the rated pressure, and turn off the gas source.

Record the pressure drop value within 10 minutes of pressure maintenance.

If the pressure drop does not exceed 0.5%, it is considered qualified.

Applicability: This method is suitable for large-diameter or high-pressure stop valves and can accurately reflect the long-term stability of sealing performance.

III. Common problems and countermeasures

1. Analysis of the root causes of sealing surface leakage

Impurity intrusion: If the valve cavity is not thoroughly cleaned during maintenance, metal debris or welding slag may be embedded in the sealing surface, causing leakage.

• Solution: Use ultrasonic cleaning or high-pressure flushing to ensure that there is no foreign matter on the sealing surface.
• Deformation of the sealing surface: Frequent operation or thermal stress may cause the valve seat to deform and reduce the fit.
• Solution: Use laser cladding or surfacing repair technology to restore the geometric accuracy of the sealing surface.

2. Tips for troubleshooting stuffing box leakage

The packing gland is too tight or too loose: Too tight will accelerate the wear of the packing, and too loose will cause leakage.

• Adjustment suggestions: According to the principle of “tighten first and then loosen”, tighten the gland bolts in batches to ensure that the packing is evenly compressed.
• Mismatched packing material: Ordinary graphite packing may fail under high temperature or corrosive media.
• Optimization plan: Use flexible graphite or PTFE composite packing to improve temperature resistance and corrosion resistance.

After a power plant repaired the J41H-16C stop valve, it was found that there was a slight leakage when opening and closing. The technicians checked the sealing surface and found that there was a 0.1mm depression in the valve seat, which was manually ground and polished to Ra≤0.8μm. Then the test showed that the pressure only dropped by 0.2% within 10 minutes of pressure maintenance, verifying that the repaired valve was leak-free. After the rectification, the stop valve ran continuously for 12 months without leakage, and the system pressure stability increased by 15%.

The sealing verification of the cast steel manual stop valve J41H-16C seems to be a technical operation, but it actually contains rich experience accumulation. From static testing to dynamic simulation, from macroscopic inspection to microscopic repair, every link may affect the final result. Through scientific methods and rigorous attitudes, not only can the long-term reliability of the valve be ensured, but also the efficient operation of the thermal power plant can be guaranteed.

When looking for high-quality, reliable stop valves, YOYIK is undoubtedly a choice worth considering. The company specializes in providing a variety of power equipment including steam turbine accessories, and has won wide acclaim for its high-quality products and services. For more information or inquiries, please contact the customer service below:
E-mail: sales@yoyik.com
Tel: +86-838-2226655
Whatsapp: +86-13618105229
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