Why Does a 7-Year-Old Pneumatic Fender's Reaction Force Jump 55%? A Real Engineering Case from an Exposed Berth
An exposed berth at a Southeast Asian container terminal recorded abnormal reaction force data during a routine berthing operation in its seventh year of service. When a 45,000 DWT container vessel contacted the fender at a berthing velocity of 0.15 m/s, the peak hull surface pressure reached 28 tf/m², exceeding the berth structure's allowable design value (18 tf/m²) by 55%. Visible cracks appeared on the concrete deck, and berthing operations were restricted to smaller vessel types. The berth was equipped with Φ2500×5500 mm pneumatic rubber fenders that performed normally during initial service, but reaction forces began rising annually from the fifth year onward. Multiple adjustments to berthing angle and speed by the maintenance team failed to resolve the issue. This case reveals a critical failure mode in long-term pneumatic fender service — rubber hardening causing continuous reaction force increase — a problem often overlooked during the selection phase.
Problem Diagnosis and Technical Analysis
On-site inspection data from the failed fenders revealed typical rubber aging and hardening characteristics:
- Surface hardness increased from an initial 62 Shore A to 78 Shore A (measured within 50 mm depth)
- Surface cracks distributed circumferentially, approximately 3–8 mm deep, non-penetrating
- Measured reaction force exceeded the ISO 17357-1:2014 standard curve value by approximately 18–22%
- Hull surface pressure reached 28 tf/m² at 60% deflection, versus 15–18 tf/m² under standard conditions
Root Cause: Structural Evolution of the Crosslink Network
The rubber body of a pneumatic fender undergoes conversion of polysulfide bonds to disulfide and monosulfide bonds during long-term service. Polysulfide bonds have longer chain lengths, providing rubber with flexibility and high elongation at break. Over time, these bonds shorten under the combined action of heat, oxygen, UV radiation, and dynamic stress, ultimately transforming into a more rigid short-chain crosslink structure. This chemical process directly causes increased rubber hardness and reduced elastic recovery capacity.
Accelerating Factors
- UV exposure: The exposed berth has no shading, and the fender surface receives direct UV radiation, accelerating surface oxidation
- Temperature cycling: The 50–100 mm depth range experiences the greatest temperature fluctuation
- Ozone attack: Ozone in the coastal environment reacts with rubber molecular chains
Solution and Technical Justification
To address the reaction force increase caused by rubber hardening, Wuxi ChuncoTech Rubber proposes a combined solution of "graded inflation pressure adjustment + surface protection upgrade".
Material and Structural Optimization
NR/EPDM blend compound: Adding no more than 30 phr of EPDM to NR significantly improves property retention. External protective layer: A weather-resistant EPDM cover layer, 8–12 mm thick, is added to block direct UV action.
Graded Inflation Pressure Adjustment Strategy
| Service Year | Measured Hardness | Recommended Pressure |
|---|---|---|
| 0–3 years | 62–66 | 50 kPa |
| 3–5 years | 66–72 | 45 kPa |
| 5–8 years | 72–78 | 40 kPa |
| 8+ years | >78 | Replacement |
Implementation and Verification
Implementation was carried out in three phases: Baseline inspection, Pressure adjustment and protection upgrade, and Performance verification. Follow-up inspection after 12 months showed that surface hardness increase was controlled within +2 Shore A.
Conclusion and Technical Recommendations
For fender selection analysis, aging assessment services, or inflation pressure optimization specific to your berth parameters, contact the Wuxi ChuncoTech Rubber technical team.
Website: https://www.chuncotechrubber.com/