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Salt fog

Verifies the battery pack or system survives prolonged salt-laden atmosphere exposure — addressing coastal-environment corrosion of housings, connectors, and grounding paths.
Clause (method) 8.2.9
Clause (pass criteria) 5.2.9
Object pack / system
Status vs. 2020 revised
Observation period Not specified separately — see note below

Note: Clause 8.2.9 does not state a separate post-test observation period. The "test" is the 6-cycle exposure itself. Apply pass criteria after the final cycle completes; verify with the testing agency whether a stand period is to be inserted before insulation re-measurement.

Pass criteria

After the salt fog test, the battery pack or system shall show no leakage, no housing crack, no fire, and no explosion. The insulation resistance after testing shall not be less than 100 Ω/V (DC), or 500 Ω/V if an AC circuit is present.

Source: GB 38031-2025, clause 5.2.9 (PDF p. 12).

Pre-conditions

  • Exemption: Test objects completely placed in the passenger compartment, luggage compartment, or a closed cargo compartment are exempt from the salt fog test. (8.2.9.1)
  • Pre-treatment: Standard, per clause 7.2.
  • SOC: Highest working SOC per clause 6.1.10.
  • Installation state: Per manufacturer specification. (8.2.9.4)
  • Insulation baseline: Measure before the test per Appendix B (clause 6.1.5).

Test parameters

Parameter Value Source
Method base GB/T 28046.4-2011 §5.5.2 + GB/T 2423.17-2024 8.2.9.2
Salt NaCl, chemically pure or analytically pure 8.2.9.3
Diluent Distilled or deionized water 8.2.9.3
Concentration (50 ± 5) g/L mass concentration 8.2.9.3
pH 6.5–7.2, measured at 35 °C 8.2.9.3
Spray temperature 35 °C 8.2.9.4
Cycle period 24 h (8 h spray + 16 h dwell) 8.2.9.4
Spray duration per cycle 8 h at 35 °C 8.2.9.4
Dwell duration per cycle 16 h 8.2.9.4
Low-voltage power-on monitoring During hours 4 and 5 of each cycle 8.2.9.4
Number of cycles 6 8.2.9.5
Cycle profile Per Figure 12 8.2.9.4

Procedure

  1. Confirm the test object is not exempt under 8.2.9.1 (i.e., not fully enclosed in passenger/luggage/closed cargo compartment).
  2. Confirm pre-treatment per 7.2 and measure baseline insulation per Appendix B. (6.1.5)
  3. Adjust SOC to highest working value. (6.1.10)
  4. Prepare salt solution: NaCl + distilled/deionized water at (50 ± 5) g/L; verify pH 6.5–7.2 at 35 °C. (8.2.9.3)
  5. Place the test object in the salt fog chamber in the manufacturer-specified installation state. (8.2.9.4)
  6. For each 24-hour cycle: a. Spray the test object with the solution at 35 °C for 8 hours (cycle hours 0–8). (8.2.9.4) b. During cycle hours 4 and 5, perform low-voltage power-on monitoring. (8.2.9.4) c. Dwell for 16 hours with no spray (cycle hours 8–24).
  7. Repeat for 6 cycles total (144 hours). (8.2.9.5)
  8. After the 6th cycle, re-measure insulation per Appendix B; inspect for leakage, housing cracks; confirm no fire/explosion.

After-test observation

Clause 8.2.9 does not state a separate post-test observation period — the 6-cycle exposure constitutes the test. Pass criteria apply after the final cycle completes.

Engineering note (non-normative): The cheatsheet flags this row as "not specified separately ⚠". The wording in 8.2.9.5 ends with "A total of 6 cycles should be conducted" with no follow-on stand period — unlike 8.2.5/8.2.8/8.2.10 which all explicitly add "observe for 2 hours". Treat this as a deliberate omission. If your test agency wants a stand period, document the addition.

What changed from GB 38031-2020

  • Listed in the preface change list as both requirements (5.2.9) and method (8.2.9) revised.

Migration impact: Already-type-approved vehicle models must comply from 2027-08-01. New type approvals from 2026-07-01. See Re-certification timeline.

Engineering notes (non-normative)

The notes below are practical interpretation, not part of the standard.

Engineering note (non-normative): The exemption for fully enclosed packs (passenger/luggage/closed cargo compartment) is meaningful for many EV configurations — under-floor packs in passenger sedans typically qualify. The exemption hinges on "completely placed in" — partial enclosure (e.g., pack with one face exposed to the wheel well) does not qualify; verify this in the documented installation state before claiming exemption.

Engineering note (non-normative): Low-voltage power-on monitoring during cycle hours 4–5 (mid-spray) is a functional check during peak ingress conditions. Define what is monitored (BMS heartbeat, contactor state, low-voltage rail) before the campaign starts; the standard does not enumerate the monitored signals, but the absence of a heartbeat during this window is a clear non-conformance even before post-test insulation is measured.

Engineering note (non-normative): The 6-cycle / 144-hour total puts this test in chamber for nearly a week. Sequence it late in the campaign — corrosion damage is largely cosmetic on the housing but can permanently degrade exposed connector contacts, which means reuse of the article for subsequent tests is risky.