When internal or external leakage occurs in forged steel ball valves, standardized diagnostic and handling measures should be taken based on the type, location and working conditions of the leakage.

I. Internal Leakage Treatment

Internal leakage refers to the situation where the medium still leaks from the upstream sealing surface to the downstream when the valve is fully closed.

1. Fault diagnosis and confirmation

Online verification: After closing the valve, open the downstream discharge valve or blowdown valve and observe whether there is a continuous flow of medium.

DBB valve verification: For the double-ball DBB structure, open the middle cavity discharge port and verify the integrity of the upstream and downstream seals respectively.

Eliminate false internal leakage: Confirm whether the valve is truly in the fully closed position, and rule out "not fully closed" caused by limit offset or insufficient torque setting of the electric head.

2. Treatment of internal leakage in floating ball valves

To check for dirt clogging: Try slightly opening the valve by 10% to 20% and then closing it again to use the medium to flush the sealing surface. Repeat 1-2 times. If the internal leakage is eliminated, it is a temporary particle entrapment.

Grease injection auxiliary sealing: If the valve seat is equipped with a grease injection port, inject special emergency sealing grease for valves to temporarily restore the seal and arrange for gas supply to stop and the valve seat to be replaced.

Disassembly and maintenance: If the above measures are ineffective, stop the operation, empty it, and then disassemble the valve to check for damage, scratches or cold flow deformation on the sealing surfaces of the ball and the valve seat. For minor cases, grinding and repair are required; for severe cases, the valve seat and ball need to be replaced.

3. Treatment of internal leakage in fixed ball valves

Online troubleshooting: Open the middle cavity discharge port and determine whether the internal leakage comes from the upstream valve seat or the downstream valve seat. Internal leakage in the upstream valve seat can usually be repaired by online grease injection, while internal leakage in the downstream valve seat needs to be drained and treated later.

Grease injection intervention: Inject sealing grease into the grease injection port of the upstream or downstream valve seat to restore the sealing specific pressure. It is suitable for temporary emergency use of soft-sealed valve seats.

Disassembly and maintenance: When grease injection is ineffective, stop the operation and disassemble. Check whether the valve seat spring has failed, whether the piston effect valve seat is stuck, and whether the sealing surface is eroded. Replace the failed valve seat assembly. Grind or replace the sealing surface of the ball as needed.

4. Verification after maintenance

The bidirectional high-pressure gas seal test is carried out in accordance with API 598. Zero bubbles are the qualified standard.

Ii. Handling of External Leaks

External leakage refers to the escape of the medium from the sealing interface between the valve body and the external environment. The main leakage points are the valve stem packing area, the valvebody connection area, and the grease injection port/discharge port.

The packing of the valve stem is leaking

Symptom: The medium seeps out or spurts out between the valve stem and the stuffing box.

Processing steps

1. Try to tighten the gland: Use a wrench to symmetrically and evenly tighten the packing gland nuts by 1/4 turn each time, and observe whether the leakage decreases. Do not apply pressure on one side to avoid the valve stem getting stuck.

2. Automatic compensation for live load disc spring: If a live load disc spring stuffing box has been configured, confirm whether the disc spring has failed. When the disc spring breaks or the compression amount is exhausted, the disc spring assembly needs to be replaced.

3. Online pressurized grease injection: If the stuffing box is equipped with a grease injection port, inject special sealing grease for valves as a temporary leak sealing measure.

4. Disassembly and replacement of packing: If the above measures are ineffective, remove the gland under safe emptying and pressure relief conditions, take out the old packing, and replace it with PTFE/ graphite braided packing of the same specification. Press it in circle by circle according to the specifications, and lock the gland symmetrically and evenly. Operation under pressure is strictly prohibited.

2. Leakage at the connection of the valve body

Common leakage points of forged steel ball valves: flange gasket between the valve body and the valve cover, sealing surface connection between the valve body and the end.

Processing steps

1. Tighten the bolts: Tighten the flange bolts at the leakage point symmetrically and evenly, and observe the leakage changes.

2. Replace gaskets: If tightening is ineffective, stop the operation to vent and relieve pressure. Disassemble the connection points and replace the graphite wound gasket or PTFE gasket. Before installation, clean the sealing surface, pre-tighten the bolts symmetrically and evenly, and lock them in two steps according to the torque value.

3. Sealing surface damage repair: If there are pits or scratches on the sealing surface, the minor ones will be ground and repaired, while the severe ones will be surfacing and reprocessed.

3. Leakage at the grease injection port/discharge port

Grease injection port: Check if the check valve is faulty and replace the grease injection port.

Discharge port: Check whether the discharge valve itself has failed to seal properly or whether the connecting threads are loose. Tighten or replace the discharge valve.

4. Leakage from the valve body itself

Forged steel valve bodies, due to forging defects or cracks, cause the medium to seep out from the valve body, which is a serious accident hazard.

Treatment method:

Immediately isolate and drain. The valve must not be used any longer.

· Determination of scrapping: In principle, forged steel valve bodies with penetrating cracks or organizational defects should be scrapped directly. Welding repair is not recommended as the heat-affected area may cause changes in the mechanical properties of the material and there is a risk of rupture under high-pressure conditions.

Iii. Acceptance of the processed standards

Test method for acceptance criteria of leakage types

Internal leakage zero bubble API 598, bidirectional 1.1 times design pressure gas seal

For the shell with no visible leakage, conduct a water pressure strength test at 1.5 times the design pressure, and visually inspect the valve stem packing area

Low dissipation (optional) ≤50 ppmv ISO 15848-1, helium leak detection

Iv. Record and Traceability

The time of leakage occurrence, location, diagnosis process, handling measures and post-repair test data should be entered into the valve maintenance file and incorporated into the full life cycle management. For valves with repeated leakage, it is necessary to trace whether the design selection, materials or operating conditions exceed the original design boundaries.