Long-term Maintenance Specifications of Coalescing Filters for Gas Pipeline Liquid & Impurity Removal

Long-term Maintenance Specifications of Coalescing Filters for Gas Pipeline 

Liquid & Impurity Removal

1. Working Condition Characteristics & Core Factors Affecting Long-Term Service Life

1.1 Medium Pollution Characteristics of Gas Pipeline Dehydration & Purification

This specification applies to natural gas, LNG vaporization pipeline, city gate station, pressure regulating station and industrial fuel gas pipeline coalescing separators, where high-performance Coalescer & Separator Cartridge acts as the core purification component to remove mixed pollutants in fuel gas. The medium contains three types of pollutants: solid impurities (pipeline rust, mineral sand, welding slag, scaling particles), free liquid (condensed water, light hydrocarbon condensate, compressor lubricating oil mist), and tiny emulsified liquid droplets below 5μm. The medium has alternating gas-liquid impact, temperature fluctuation and trace corrosive components such as CO₂ and H₂S, which easily cause multiple attenuation failures of conventional filter cartridges:

Solid particles block fiber pores, leading to rapid differential pressure rise and shortened service cycle;

High gas flow shear force breaks coalesced large liquid droplets into micro-emulsions, reducing outlet gas dryness index;

Alternating erosion of liquid hydrocarbon and water damages the hydrophilic-lipophilic balance of filter media, permanently losing coalescing separation performance;

Condensate corrosion causes skeleton pitting and sealing ring swelling leakage, forming gas bypass pollution.

Only anti-corrosion multi-layer composite Coalescer & Separator Cartridgecan withstand long-term gas-liquid alternating impact and corrosive medium to maintain stable separation efficiency for pipeline fuel gas treatment.

1.2 Core Preconditions for Long-Term Stable Operation of Filter Cartridges

To maintain stable separation efficiency and extend service cycle of each Coalescer & Separator Cartridge, the whole operation and maintenance process must control four core links: matched inlet pre-separation protection, standardized daily parameter monitoring, regular timed liquid discharge and impurity removal, and safe standardized disassembly, cleaning and replacement. This document formulates full-process operation norms covering daily patrol, periodic maintenance, fault disposal, disassembly and replacement, and prohibited operation limits, guiding staff to properly inspect and replace the aging Coalescer & Separator Cartridge on schedule, for reference by station operation and maintenance personnel.

2. Pre-Operation Matching Protection Measures (Fundamental to Extend Filter Cartridge Service Life)

2.1 Front-End Two-Stage Pre-Filtration Configuration Standard

All coalescing separators for gas pipelines must be equipped with graded pre-interception devices to reduce the solid pollution load of coalescing filter cartridges by 60%–80%:

Primary coarse separation: Labyrinth cyclone pre-separator at the inlet, intercept solid particles above 30μm and large free liquid droplets, regularly discharge sediment and accumulated liquid at the bottom ash bucket every shift;

Secondary pre-filter: 20μm metal mesh filter installed between cyclone and coalescing tank, intercept medium-sized rust and scaling particles, replace the metal screen every 30–45 days according to pressure difference growth rate.

If the front pre-separation device is missing or damaged, the service life of coalescing filter cartridges will be reduced by more than 50%.

2.2 System Flow Velocity Matching Restriction

Excessive gas surface flow velocity will shorten the residence time of liquid droplets in the filter media, resulting in incomplete coalescence and accelerated abrasion of fiber layers. Graded flow velocity limits under different liquid content conditions:

Low liquid clean gas (liquid content ≤50ppm): Allowable surface flow velocity ≤0.35 m/min;

Medium condensate gas (liquid content 50–200ppm): Allowable surface flow velocity ≤0.28 m/min;

High liquid incoming gas (liquid content 200–500ppm): Allowable surface flow velocity ≤0.20 m/min.

When the pipeline instantaneous peak flow exceeds the design value by more than 15%, open the bypass regulating valve to split flow and avoid long-term overload operation of filter cartridges.

3. Daily Patrol & Real-Time Monitoring Operation Specifications (Shift Standard Work)

3.1 Mandatory Patrol Inspection Items Per Shift

Differential pressure recording (core judgment index): Record the inlet and outlet differential pressure value of the coalescing tank every 4 hours, compare with the initial differential pressure of new filter cartridges (standard initial ΔP＜0.03MPa). When the differential pressure growth per shift exceeds 0.008MPa, mark early warning and increase drainage and pre-filter inspection frequency;

Liquid level inspection of the bottom liquid bin: Check the liquid level gauge display, confirm the automatic drainage valve operates normally, manually assist drainage when the liquid level exceeds 2/3 of the liquid bin volume, strictly prohibit long-term high liquid level operation;

Leakage inspection: Check flange sealing surface, liquid discharge pipeline, differential pressure sampling pipeline for gas leakage, listen for abnormal airflow noise inside the tank body;

Medium parameter check: Record pipeline inlet gas temperature, operating pressure and instantaneous flow, prohibit long-term overpressure (exceeding 1.1 times design pressure) and ultra-low temperature operation;

Outlet gas sampling spot check: Take gas sample at the outlet sampling port every shift to test residual liquid content, if the liquid content continuously exceeds 30ppm, judge that the filter cartridge coalescing performance is attenuated.

3.2 Standard Timed Drainage Operation Procedure

Operation pre-check: Confirm the downstream pipeline can bear instantaneous flow fluctuation, arrange special personnel to monitor the outlet pressure gauge;

Step 1: Slowly open the front valve of the drainage pipeline, slightly open the drain valve to discharge mixed liquid of water and hydrocarbon, keep the opening small to avoid gas mass escape;

Step 2: Observe the drainage outlet state, close the drain valve immediately after the liquid turns into continuous gas flow, close the front valve of the drainage pipeline;

Post-operation record: Record drainage time, liquid discharge volume and liquid composition characteristics in the equipment operation log;

Drainage cycle reference: Clean urban pipeline gas every 24 hours; oil field incoming gas with high condensate content every 8–12 hours.

Safety prohibition: Do not stand directly facing the drainage outlet during operation to prevent liquid splashing and gas impact injury.

4. Periodic Medium Maintenance & Filter Cartridge Auxiliary Cleaning Specifications

4.1 Permitted Light Anti-Blockage Back-Blowing Operation Conditions

Back-blowing cleaning is only applicable to filter cartridges with differential pressure rising moderately and no obvious coalescing failure (outlet liquid content qualified), and shall not exceed 2 times in the whole service cycle.

Back-blowing medium: Dry oil-free compressed air, air source dew point ≤-20℃, residual oil ≤0.01ppm;

Control parameters: Back-blowing pressure ≤0.3MPa, single back-blowing duration 0.15–0.20s, intermittent back-blowing 5–8 times each time;

Operation flow: Switch the separator to bypass operation → close inlet and outlet main valves → open tank exhaust valve to reduce pressure to normal pressure → connect back-blowing pipeline for reverse blowing → close exhaust valve, close back-blowing pipeline → slowly fill the tank with gas to rated working pressure, resume production;

Post-cleaning inspection: Record the reduced value of differential pressure, if the differential pressure rebounds to the early warning threshold within 3 working days after back-blowing, arrange batch replacement of filter cartridges.

4.2 Strictly Prohibited Cleaning Behaviors (Permanently Damage Coalescing Function)

Forbid washing filter cartridges with clean water, neutral detergent and organic solvent: Liquid hydrocarbon mixed with solid impurities will form irreversible hard blocks inside the fiber layer, and the surface hydrophilic-lipophilic balance film will be dissolved and damaged, completely losing the ability to capture tiny liquid droplets;

Forbid high-pressure air gun external strong blowing after disassembly: Excessive airflow shear force scratches the thin coalescing fiber layer, causing fiber delamination and liquid droplet re-entrainment;

Forbid mechanical beating, wire brush scrubbing filter cartridge pleats: Destroy the gradient composite structure of filter media, reduce unit area dirt holding capacity by more than 40%

5. Filter Cartridge Replacement Judgment Threshold & Standard Safe Disassembly & Installation Operation

5.1 Four Mandatory Replacement Judgment Standards

Batch replacement of filter cartridges shall be carried out when any of the following indicators reaches the limit value:

The inlet and outlet differential pressure reaches 0.15MPa (2 times the initial differential pressure), and the differential pressure cannot drop to the normal range after back-blowing cleaning;

Two consecutive shift outlet gas sampling tests show residual liquid content exceeding 30ppm, and the liquid discharge system operates normally without blockage;

After disassembly inspection, the filter media has pleat collapse, fiber shedding, surface large-area hard mud scaling and delamination of composite layers;

The cumulative continuous operation time reaches the upper limit of the design cycle: clean urban gas 12 months, oil field high-liquid incoming gas 6 months.

5.2 Pre-Replacement Safety Preparation Procedures (Explosion-Proof Mandatory Norms)

Switch the separator to the production bypass pipeline to ensure uninterrupted downstream gas supply;

Close the inlet and outlet cut-off valves of the coalescing tank, lock the valve position and hang a warning sign;

Open the top exhaust valve and bottom drain valve in sequence, fully discharge the mixed liquid and residual gas inside the tank;

After the pressure gauge shows zero pressure, introduce fresh air into the tank for forced ventilation for no less than 30 minutes, detect the combustible gas concentration inside the tank, and start disassembly operation only after it meets the safety access standard;

Prepare matched new filter cartridges, complete spare sealing rings, cleaning tools and waste filter cartridge collection containers, and confirm that the filter cartridge model, skeleton material and media grade are consistent with the original configuration.

6. Common Long-Term Attenuation Fault Analysis & Rectification Measures

Fault 1: New filter cartridges have qualified separation effect at the initial stage, differential pressure rises sharply within 1–2 weeks

Root causes: Front-end pre-filter is missing or blocked, solid impurities quickly block filter media pores; long-term pipeline flow exceeds the allowable surface flow velocity limit, accelerating dirt accumulation.

Rectification measures: Clean or replace the front pre-filter metal screen; increase the number of filter cartridges to reduce unit area flow velocity, and adjust the bypass split flow valve to control peak flow.

Fault 2: The outlet gas residual liquid content exceeds the standard, and the differential pressure is still in the normal range

Root causes: Excessive gas flow shear force breaks coalesced large liquid droplets; tank top exhaust valve jams, accumulated gas wraps part of the filter cartridge to fail to participate in separation; filter media hydrophilic-lipophilic balance fails after long-term liquid hydrocarbon erosion.

Rectification measures: Reduce pipeline operating flow; disassemble and overhaul the automatic exhaust valve; arrange batch replacement of filter cartridges with failed coalescing performance.

7. Daily Operation & Maintenance Record Management Specifications

Special operation log configuration: Record shift patrol differential pressure, liquid discharge volume, outlet gas sampling data, back-blowing cleaning time, pre-filter cleaning and filter cartridge replacement information, with the signature of the operator on duty;

Data archiving cycle: All maintenance records shall be filed and stored for no less than 24 months, which can be used as the basis for analyzing the change rule of gas incoming pollution load and optimizing the filter cartridge replacement cycle;

Abnormal traceability management: Once the separation index exceeds the standard or the differential pressure rises abnormally, mark the abnormal time, phenomenon and disposal measures in the log, and track the operation state for 3 consecutive shifts to confirm the elimination of hidden dangers.