Wall-Wash Test Precautions and some Causes of Failure
Always use disposable plastic gloves when wall washing – the human hand contains more salt than normal requirements and is a common cause of chloride contamination.
Wear clean clothes and do not allow working gloves in the tank, avoid all contact of clothing with the tank, wear protective disposable shoe covers.
Use a clean bucket on a clean line for transferring test equipment into the tank.
Wash the funnel and sample bottles with certified methanol prior to collecting the sample.
Always test the distilled water and certified methanol prior to use for testing and always run a standard against the test sample.
The glue used for the seals on some types of sample bottles have been known to cause sample contamination.
When using acids for washing wear the proper protective equipment.
Take your time, sampling in a hurry or rushing through the test procedures cause failure.
If the sample passes all tests, be suspicious, and test again.
Never test a wet tank, the tank wall must be dry.
Allowing a tank to “rest” after prolonged washing (especially hot washing) can often turn a failed tank into a passed tank.
Keep a record of your wallwash results, especially if testing multiple tanks. Consulting this record over days of tank cleaning may provide a useful indication of which washing procedure is working best.