The term “wet bottom” is used in two common standards for corrosion testing - ASTM G85 and SAE J2334. ASTM G85 calls for a few cm of water retained in the bottom of the chamber; SAE J2334 calls for either a reservoir of immersively-heated water or standing water at the bottom of the chamber with compressed air bubbled through it.
The purpose of the wet bottom in both standards is twofold, both stemming from the lack of relative humidity (RH) control in most corrosion testers:
- prolong the time it takes for specimens to dry off when specimen drying is desired, and
- to increase the humidity to promote continuous specimen wetness during certain phases of a test cycle.
The Q-FOG CRH tester’s precise control of relative humidity makes the wet bottom condition completely unnecessary. Controlling RH is a more precise way to accomplish the goals outlined above.
- In the case of SAE J2334, the conditions specified are a chamber temperature of 50 °C and 100% RH. The Q-FOG CRH can meet this easily without the use of a wet bottom condition.
- ASTM G85 Annex 2 and Annex 3 include the wet bottom condition as a means to produce a gradual increase of humidity from 65 to 95 % (Annex 2) and to avoid dry conditions inside the test chamber (Annex 3). In both cases, a wet bottom isn’t necessary in the Q-FOG CRH. The tester can precisely control the relative humidity during transitions from one RH level to another, and can operate high RH conditions in steps that require specimens to remain wet. In fact, even the Q-FOG CCT can meet this requirement using the HUMID function.
The problem using the wet bottom for corrosion test methods is its lack of repeatability or reproducibility. If you are concerned about running a repeatable and reproducible test that requires a wet bottom condition, we recommend the Q-FOG CRH with its standard RH control system, in place of the inferior wet bottom technique, for precise, repeatable wet/dry transitions.