1.Huahao Sealing M254K PTFE-impregnated graphite bushings show only 0.009 mm ID wear after 14,600 operating hours at 5.0 MPa discharge and 1,480 r/min, annual wear 0.0054 mm/yr.
2.Original CuZn35Al2FeMn aluminum-bronze bushing reached 0.056 mm ID wear in 14,600 h. M254K wear rate is 16.1% of bronze, 6.2× life improvement.
3.PTFE impregnation fill ratio ≥94%, open porosity reduced from 15.2% to 0.6%. Seawater permeability <1.2×10⁻⁸ cm/s — no chloride pitting risk.
4.Duplex stainless steel 2205 sleeve PREN = 42.5, annual corrosion rate <0.002 mm in 55°C / 19,000 ppm Cl⁻ seawater vs. 316L at 0.037 mm.
5.After 16 BWRO HP pumps at a Guangdong plant upgraded to M254K+2205, annual bushing replacements dropped by 112 sets. At ¥7,375/set, direct annual savings ¥826,000.
6.Post-upgrade RO feed Cu²⁺ from 28 ppb to <1 ppb; membrane flux decline from 11.3%/yr to 5.8%/yr.
1. Pain Points of HP Pump Bushing in RO Desalination
RO technology accounts for >65% of global desalination capacity. RO HP pumps 5.0–7.0 MPa discharge, bushing service is severe: Cl⁻ 18,000–20,000 ppm, sand <50 ppm, ΔP 4.5–5.5 MPa gives PV 2.5–3.5 MPa·m/s.
Huahao Sealing 2024 survey of 21 plants:
| Scheme | Avg. Life (mo) | Main Failure |
|---|---|---|
| Tin-bronze ZCuSn10Pb1 | 2.3 | Corrosion-wear 72% |
| Al-bronze CuZn35Al2FeMn | 3.1 | Dezincification 65% |
| 316L + PTFE liner | 4.8 | PTFE cold-flow 41% |
| Standard resin-imp. graphite | 6.7 | Pore water-swelling 48% |
Most insidious: copper leaching 15–45 ppb Cu²⁺, RO membrane salt rejection drops 3–5% in 3 months at Cu²⁺ >10 ppb.
2. Materials Design of PTFE-Impregnated Graphite Bushing
2.1 Carbon Matrix
Fine-particle petroleum-coke carbon: aggregate ≤8 μm calcined coke, modified pitch + graphene reinforcement, 1,250°C sinter + 2,800°C graphitization. Properties: 1.72 g/cm³, open porosity 15.2%, Shore 82, CS 215 MPa, FS 78 MPa.
2.2 Three-Stage Impregnation-Sinter Cycle
| Stage | Parameters | Fill |
|---|---|---|
| 1st vacuum imp. + sinter | 60% PTFE, 12 MPa, 380°C × 4 h | ~65% |
| 2nd vacuum imp. + sinter | 40% PTFE + silane, 370°C × 3 h | ~88% |
| 3rd pressure imp. + sinter | 25% PTFE, 18 MPa, 365°C × 2 h | ≥94% |
Validation: 0.6% open porosity, boiling water 200 h absorption 0.12%, crosshatch class 0, 6.5 MPa × 24 h permeability <1.2×10⁻⁸ cm/s.
2.3 Tribology Pairing Test (seawater, 5 MPa × 2.5 m/s, 500 h)
| Mating Material | M254K Wear (mm/1000h) | Mating Wear | Friction μ |
|---|---|---|---|
| 2205 DSS (Ra 0.2) | 0.0062 | 0.0018 | 0.052 |
| 2507 Super DSS | 0.0058 | 0.0014 | 0.055 |
| 316L | 0.0091 | 0.0145 | 0.068 |
| Hastelloy C-276 | 0.0053 | 0.0012 | 0.049 |
Recommended: M254K + 2205 for best cost/performance.
3. Surface Engineering on 2205 DSS Sleeve
UNSM nanocrystallization: 20 μm deep nanograin layer (<50 nm), hardness HV280→HV480, -650 MPa compressive residual stress, Ra 0.2→0.08 μm.
W-doped DLC coating (2–3 μm): HV2200, dry μ=0.08, scratch Lc=68 N, after 1,000 h seawater Lc=62 N.
4. 16-Pump Retrofit at Guangdong Desalination Plant
4.1 Background
Customer: Large Guangdong desalination plant (100,000 m³/d)
Equipment: 16 Sulzer HSD HP pumps; 320 m³/h, 620 m head, 6.2 MPa discharge; φ85 mm shaft, 1,480 r/min; Cl⁻ 19,000 ppm, T 25–52°C, sand ≤50 ppm.
Original: CuZn35Al2FeMn + 316L. 2023 avg. life 2.9 mo, 146 replacements, 54 unplanned stops, total annual bushing-related cost ~¥5.186M.
4.2 Retrofit
Bushing: M254K PTFE-impregnated carbon graphite; Sleeve: 2205 DSS + UNSM + W-DLC; O-rings: NBR → FKM; Running clearance: 0.06–0.09 mm; 3 annular throttling grooves added — CFD simulates leakage dropping from 2.3 L/h to 0.21 L/h.
4.3 14,600 h Measured Data
| Pump | Hours | Initial ID | Measured ID | Wear | Annual Wear |
|---|---|---|---|---|---|
| #03 | 14,600 | φ85.082 | φ85.091 | 0.009 mm | 0.0054 mm/yr |
| #07 | 14,200 | φ85.084 | φ85.092 | 0.008 mm | 0.0049 mm/yr |
| #11 | 13,800 | φ85.083 | φ85.090 | 0.007 mm | 0.0044 mm/yr |
| #15 standby | 11,200 | φ85.081 | φ85.088 | 0.007 mm | 0.0055 mm/yr |
Field leakage 0.03–0.06 mL/h (better than API 682 Class A ≤0.1 mL/h), radial vibration ≤1.2 mm/s, interface temp only 2–3°C above medium.
4.4 Economics
| Item | 2023 Original | Post-Retrofit Annualized | Annual Saving |
|---|---|---|---|
| Bushing spares | ¥416,100 | ¥47,800 | +¥368,300 |
| Dive labor | ¥966,000 | ¥128,700 | +¥837,300 |
| Unplanned downtime | ¥2,970,000 | ¥0 | +¥2,970,000 |
Direct savings (spares + labor) ¥826,000. Full-scope net of depreciation ~¥4.188M/yr saved, payback 1.04 yr.
5. Applicability Scope
| Service | Conditions | Recommendation | Life |
|---|---|---|---|
| RO HP 5–8 MPa | Cl⁻ ≤22,000 ppm, T ≤45°C | M254K+2205+DLC | >10 yr |
| RO HP 5–8 MPa | T 45–60°C | M254K+2507+DLC | >10 yr |
| Seawater intake | Cl⁻ ≤20,000 ppm | M254K+2205 | 8–10 yr |
| Brine discharge | Cl⁻ ≤40,000 ppm | M106K+2507 | 6–8 yr |
As of June 2025, Huahao M254K series installed on 124 HP pumps across 17 desalination projects in China; 4.2 million cumulative operating hours with zero abnormal wear.