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EPDM (Ethylene Propylene Diene Monomer) and NBR (Nitrile Butadiene Rubber) are widely used in marine seals, but their suitability varies by marine scenario. Below is a structured breakdown of their differences and selection rules:

1. Core Performance Differences for Marine Use

▶ Seawater & Salt Corrosion Resistance

EPDM Seals: Excellent performance—resists hydrolysis and salt spray, passing ISO 9227 1000+ hours salt spray testing without cracking or swelling. It’s ideal for parts in direct seawater contact, such as hull deck seals, hatch gaskets, and underwater valve seals.

NBR Seals: Poor performance—swells and hardens easily in seawater (volume change ≥30% after 14 days of immersion), which leads to seal failure. It’s not suitable for areas exposed to seawater.

▶ Oil & Fuel Resistance

EPDM Seals: Weak performance—swells significantly in mineral oil, diesel, or lubricants (volume change ≥50% via ASTM D471). Avoid using it in marine fuel tanks, engine oil lines, or gearbox seals.

NBR Seals: Excellent performance—resists mineral oil, diesel, and marine lubricants (volume change ≤15% via ASTM D471). It’s perfect for fuel system seals like fuel tank gaskets, engine oil seals, and hydraulic line seals.

▶ Temperature Adaptability

EPDM Seals: Wide temperature range (-40℃ to 120℃, up to 150℃ for high-grade products), capable of handling extreme marine temperatures—from cold polar seas to hot engine rooms.

NBR Seals: Narrow temperature range (-30℃ to 100℃, max 120℃ for premium grades)—becomes brittle at low temperatures (risk of cracking in cold oceans) and softens in high-heat engine areas.

▶ UV & Weather Resistance

EPDM Seals: Strong resistance—withstands UV radiation, ozone, and rain, showing no aging or cracking after 5 years of outdoor marine use. Suitable for exposed parts like deck seals or superstructure gaskets.

NBR Seals: Weak resistance—ages quickly under UV and ozone (becomes brittle in 1-2 years of outdoor use). Only use it in indoor marine spaces, such as engine room interior seals.

▶ Compression Set (Seal Longevity)

EPDM Seals: Good elasticity retention (≤30% after 70℃×22h testing), ensuring long-term sealing for low-maintenance parts like hull bulkhead seals.

NBR Seals: Excellent elasticity retention (≤20% after 70℃×22h testing), more suitable for high-pressure seals (e.g., fuel pump gaskets) that need frequent compression.

2. Marine Application Selection Guide

Choose EPDM Seals When: The seal is exposed to seawater, UV, or wide temperature fluctuations. Typical applications include hull underwater seals, hatch covers, deck drain gaskets, and freshwater system seals (e.g., water tanks).

Choose NBR Seals When: The seal contacts oil/fuel and is in a protected space (no seawater or UV exposure). Typical applications include marine engine oil seals, fuel tank gaskets, hydraulic cylinder seals, and gearbox gaskets.

3. Critical Marine Safety Reminder

Never replace EPDM with NBR in seawater-exposed areas (e.g., using NBR for hull seals)—this can cause water intrusion, hull damage, or even marine accidents. For rare marine parts that need both seawater and oil resistance, consider hybrid materials (e.g., EPDM-NBR blends) or fluororubber (FKM), though these options are more costly.