The maintenance cycle and key contents of the cryogenic trunnion ball valve need to be formulated in combination with its working environment (such as cryogenic media, high pressure conditions) and frequency of use to ensure sealing performance, operational flexibility and equipment safety. The following are specific maintenance cycles and key contents:
I. Classification of maintenance cycles
1. Daily inspection (daily/per shift)
Applicable scenarios: continuously operating cryogenic pipeline systems (such as LNG transportation, air separation equipment).
Purpose: timely detection of sudden problems such as leaks, abnormal sounds or operation jams.
2. Monthly maintenance (every 1 month)
Applicable scenarios: valves with high frequency of use or key process nodes.
Purpose: Check the status of seals, lubrication conditions and the risk of loose fasteners.
3. Quarterly/half-year maintenance (every 3-6 months)
Applicable scenarios: valves with medium frequency of use or harsh low-temperature environments.
Purpose: deep cleaning, lubrication renewal and functional testing.
4. Annual overhaul (every 1 year)
Applicable scenarios: all cryogenic trunnion ball valves, especially valves that have been in operation for a long time without disassembly.
Purpose: Comprehensive disassembly inspection, replacement of wearing parts, pressure testing and performance calibration.
2. Key points of maintenance in each cycle
1. Key points of daily inspection
Leakage inspection:
Use a combustible gas detector (such as LNG leakage detection) or soapy water to apply flanges, valve stem stuffing boxes and other sealing points to confirm that there is no bubble leakage.
Observe whether there is "frosting" on the valve surface (it may be caused by internal leakage and cause low-temperature medium to overflow).
Operation status monitoring:
Check whether the valve switch position is consistent with the process requirements (such as fully open/fully closed) to avoid erosion and wear of the sealing surface due to half-open state.
Listen for abnormal friction sound or vibration inside the valve to determine whether the ball and valve seat are blocked.
Environmental inspection:
Confirm that the insulation layer is intact, without damage or condensation accumulation (to prevent ice from affecting operation).
Check whether the bracket and bolts have signs of low-temperature brittle fracture (such as cracks and deformation).
2. Monthly maintenance focus
Lubrication system inspection:
Add low-temperature grease (such as silicone-based grease, temperature-resistant - 60℃~200℃) to the active parts such as the valve stem stuffing box and trunnion bearing to prevent the hardening of the grease from causing the valve stem to stick.
Record the lubrication time and amount, and establish a lubrication account.
Fastener review:
Symmetrically check the torque of the flange bolts and bracket connection bolts, and use a torque wrench to tighten according to the design requirements (to prevent the bolts from shrinking and loosening at low temperatures).
Check whether the anti-loosening device (such as locking nut, spring gasket) is intact.
Function test:
Manually operate the valve switch once to confirm that the opening and closing torque is normal, without jamming or abnormal resistance.
Perform remote switch test on the electric/pneumatic actuator to check whether the signal feedback is accurate.
3. Quarterly/semi-annual maintenance focus
Deep cleaning:
Disassemble the flanges at both ends of the valve (if allowed), use dry nitrogen to purge the valve cavity, and remove impurities, rust residue and low-temperature medium condensate.
Check the sealing surface (ball, valve seat) for scratches, wear or corrosion. Minor damage can be polished with fine sandpaper (800 mesh or above), and serious damage requires replacement of parts.
Sealing performance test:
Perform a low-pressure gas sealing test (such as 0.6MPa nitrogen), maintain pressure for 30 minutes, and detect whether the leakage volume meets the standard (such as API 598 requirements).
For double block and bleed (DBB) structure valves, test whether the pressure relief function of the middle cavity is normal.
Anti-static device inspection:
Measure the conductive resistance between the valve stem and the valve body (should be ≤10Ω), confirm that the anti-static spring or conductive component is reliably connected, and prevent static electricity accumulation from causing safety accidents.
