IEC 68-2-66 Test Method Cx: Steady-State Damp Heat (Unpressurized Saturated Vapor)
Apr 18, 2025
Foreword
The purpose of this test method is to provide a standardized procedure for evaluating the resistance of small electrotechnical products (primarily non-hermetic components) by high and low temperature and humid environmental test chamber.
Scope
This test method applies to accelerated damp heat testing of small electrotechnical products.
Limitations
This method is not suitable to verify external effects for specimens, such as corrosion or deformation.
Test Procedure
1. Pre-Test Inspection
Specimens shall undergo visual, dimensional, and functional inspections as specified in the relevant standards.
2. Specimen Placement
Specimens shall be placed in the test chamber under laboratory conditions of temperature, relative humidity, and atmospheric pressure.
3.Bias Voltage Application (if applicable)
If bias voltage is required by the relevant standard, it shall be applied only after the specimen has reached thermal and humidity equilibrium.
4. Temperature and Humidity Ramp-Up
The temperature shall be raised to the specified value. During this period, air in the chamber shall be displaced by steam.
Temperature and relative humidity must not exceed specified limits.
No condensation shall form on the specimen.
Stabilization of temperature and humidity shall be achieved within 1.5 hours. If the test duration exceeds 48 hours and stabilization cannot be completed within 1.5 hours, it shall be achieved within 3.0 hours.
5. Test Execution
Maintain temperature, humidity, and pressure at specified levels as per the relevant standard.
The test duration begins once steady-state conditions are reached.
6. Post-Test Recovery
After the specified test duration, chamber conditions shall be restored to standard atmospheric conditions (1–4 hours).
Temperature and humidity must not exceed specified limits during recovery (natural cooling is permitted).
Specimens shall be allowed to fully stabilize before further handling.
7. In-Test Measurements (if required)
Electrical or mechanical inspections during the test shall be performed without altering test conditions.
No specimen shall be removed from the chamber before recovery.
8. Post-Test Inspection
After recovery (2–24 hours under standard conditions), specimens shall undergo visual, dimensional, and functional inspections per the relevant standard.
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Test Conditions
Unless otherwise specified, test conditions consist of temperature and duration combinations as listed in Table 1.
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Test Setup
1. Chamber Requirements
A temperature sensor shall monitor chamber temperature.
Chamber air shall be purged with water vapor before testing.
Condensate must not drip onto specimens.
2. Chamber Materials
Chamber walls shall not degrade vapor quality or induce specimen corrosion.
3. Temperature Uniformity
Total tolerance (spatial variation, fluctuation, and measurement error): ±2°C.
To maintain relative humidity tolerance (±5%), temperature differences between any two points in the chamber shall be minimized (≤1.5°C), even during ramp-up/down.
4. Specimen Placement
Specimens must not obstruct vapor flow.
Direct radiant heat exposure is prohibited.
If fixtures are used, their thermal conductivity and heat capacity shall be minimized to avoid affecting test conditions.
Fixture materials must not cause contamination or corrosion.
3. Water Quality
Use distilled or deionized water with:
Resistivity ≥0.5 MΩ·cm at 23°C.
pH 6.0–7.2 at 23°C.
Chamber humidifiers shall be cleaned by scrubbing before water introduction.
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Additional Information
Table 2 provides saturated steam temperatures corresponding to dry temperatures (100–123°C).
Schematic diagrams of single-container and double-container test equipment are shown in Figures 1 and 2.
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Table 1: Test Severity
| Temp. (°C) | RH (%) | Duration (h, -0/+2) |
temperature
relative humidity
Time (hours, -0/+2)
±2℃
±5%
Ⅰ
Ⅱ
Ⅲ
110
85
96
192
408
120
85
48
96
192
130
85
24
48
96
Note: Vapor pressure at 110°C, 120°C, and 130°C shall be 0.12 MPa, 0.17 MPa, and 0.22 MPa, respectively.
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Table 2: Saturated Steam Temperature vs. Relative Humidity
(Dry temperature range: 100–123°C)
Saturation Temp(℃)
Relative
Humidity(%RH)
100%
95%
90%
85%
80%
75%
70%
65%
60%
55%
50%
Dry Temp (℃)
100
100.0
98.6
97.1
95.5
93.9
92.1
90.3
88.4
86.3
84.1
81.7
101
101.0
99.6
98.1
96.5
94.8
93.1
91.2
89.3
87.2
85.0
82.6
102
102.0
100.6
99.0
97.5
95.8
94.0
92.2
90.2
88.1
85.9
83.5
103
103.0
101.5
100.0
98.4
96.8
95.0
93.1
92.1
89.0
86.8
84.3
104
104.0
102.5
101.0
99.4
97.7
95.9
94.1
92.1
90.0
87.7
85.2
105
105.0
103.5
102.0
100.4
98.7
96.9
95.0
93.0
90.9
88.6
86.1
106
106.0
104.5
103.0
101.3
99.6
97.8
96.0
93.9
91.8
89.5
87.0
107
107.0
105.5
103.9
102.3
100.6
98.8
96.9
94.9
92.7
90.4
87.9
108
108.0
106.5
104.9
103.3
101.6
99.8
97.8
95.8
93.6
91.3
88.8
109
109.0
107.5
105.9
104.3
102.5
100.7
98.8
96.7
94.5
92.2
89.7
110
110.0
108.5
106.9
105.2
103.5
101.7
99.7
97.7
95.5
93.1
90.6
(Additional columns for %RH and saturated temp. would follow as per original table.)
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Key Terms Clarified:
"Unpressurized saturated vapor": High-humidity environment without external pressure application.
"Steady-state": Constant conditions maintained throughout the test.
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