Specific performance characteristics of IP68 seals in different water depth environments

The performance of IP68 seals is not linearly consistent across different water depths; rather, it is influenced by hydrostatic pressure, material properties, structural design, and time. While the IP68 standard allows manufacturers to customize test conditions (such as “1.5 meters/30 minutes” or “10 meters/7 days”), in practical applications, the hydrostatic pressure increases by approximately 0.1 MPa (1 bar) for every 10 meters of water depth, posing a progressively greater challenge to the sealing system.

The following is a detailed explanation of the performance, failure risks, and engineering solutions for IP68 seals in typical water depth ranges:

1. 1. Core Principles of the Relationship between IP68 Sealing Performance and Water Depth

Hydrostatic pressure formula:
P = ρgh
where :

PP: Hydrostatic pressure (Pa)

ρρ: Density of water (seawater ≈ 1025 kg/m³)

gg: Gravitational acceleration (9.8 m/s²)

hh: Water depth (m)

⚠️ Key point: IP68 certification does not mean unlimited applicability! It must be based on the specific parameters declared by the manufacturer.

1. 1. Performance and Risks in Different Water Depth Ranges
   2. Shallow water area (0–10 meters)

Typical applications: swimming pool cleaning robots, aquaculture sensors, and urban flood monitoring equipment.

Performance:

The standard IP68 module (EPDM + 304 stainless steel) can operate stably;

Soaked for 72 hours without water entering;

The main risks come from biological attachment (algae clogging drainage holes) or mechanical impact.

Recommended solution:

Single O-ring + cap structure;

Smooth surface treatment for stain resistance.

1. 2. Medium water depth (10–50 meters)

Typical scenarios: Port inspection ROV, offshore wind power foundation monitoring, and reservoir dam inspection.

Performance:

Ordinary EPDM experiences increased compression set and decreased resilience after prolonged immersion.

Without a backup ring, the O-ring may be squeezed into the gap (extrusion) at 0.3MPa.

Chloride ions in seawater accelerate metal corrosion.

Failure Case:
A wind power project used an IP68-1.5m module for a water depth of 15m. Three months later, water entered the junction box due to seal extrusion.

Recommended solution:

Double O-rings + PTFE retaining rings;

The frame has been upgraded to 316L stainless steel;

Material hardness ≥70 Shore A.

1. 3. Deep water area (50–300 meters)

Typical scenarios: Deep-sea exploration ROV, submarine fiber optic cable repair, and oil and gas platform inspection.

Performance:

EPDM has an increased elastic modulus and becomes brittle at low temperatures (usually <5°C in the deep sea).

High pressure causes grease to leak out, and dry friction exacerbates wear.

Helium permeability increased significantly (helium leak detection verification required).

Technical requirements:

Sealing material: Fluororubber (FKM) or perfluoroether rubber (FFKM);

Structure: Metal-to-metal main seal + elastic auxiliary seal;

Shell: Titanium alloy or high-strength aluminum alloy (pressure resistant and non-deformable).

Industry standard:
Requires API 17F or DNV-RP-F119 deep-sea equipment certification.

1. 4. Extremely deep water (>300 meters)

Note: This depth typically exceeds the standard IP68 range and enters the realm of pressure vessel level seals.

Solution:

An oil-filled and pressure-balanced system is used to eliminate the internal and external pressure difference.

The electronic compartment is fully encapsulated (without any penetrating components);

The IP rating concept gives way to absolute pressure tolerance (such as “withstands 60 MPa”).

III. Time Factor: Short-Term vs. Long-Term Immersion

📊 Data Reference:
A certain EPDM seal at 0.3MPa (30m):

72 hours: Leakage rate <1×10⁻⁴ mL/s;

30 days: Compression set reaches 35%, micro-permeability begins.

1. 1. Manufacturer Labelling Standards and User Instructions

According to IEC 60529, IP68 must specify the conditions, for example:

✅ Compliance label: IP68 (5 m, 7 days)

❌ Non-compliant labeling: Only writing “IP68”

User self-inspection checklist:

Does the manufacturer provide third-party test reports (such as TÜV, UL)?

Is the test medium fresh water or seawater? (Seawater is more corrosive)

Does it include temperature cycling (e.g., -10°C → +40°C)?

Should we verify the dynamic operating conditions (vibration + pressure)?

1. 1. TST SEAL Selection Recommendation: Match the sealing rating according to water depth.

IP68 sealing modules is highly dependent on specific water depth, time, and media:

Shallow water: General-purpose IP68 modules are reliable;

For medium to deep water applications: the pressure-time curve must be verified to avoid situations where the nominal IP68 rating is insufficient in practice.

Deep water: The IP68 concept is weakened, and the focus shifts to pressure-resistant design.

TST SEAL’s ultimate principle:
“Don’t just look at the IP68 label, look at the test data behind it” – especially in high-risk fields such as marine, energy, and military industries.

For advice and solutions on selecting sealing modules, please feel free to contact me via email .