Over Washing Of Components
AC7114/1 Non-destructive Testing Facility Penetrant Survey Revision H Discussion
NADCAP audit checklist AC7114/1 section 6.9.6 requires that over washing / removal is controlled when using water to remove penetrant or a combination of air & water, and when using air to aid post wash drying and removal of Dry developer powder.
The NADCAP auditor will observe all the removal processes, and require that there is a minimum distance of 12 inches (30cm) where possible.
NDT operators can often receive NCR's for the above on a regular basis, NDT inspectors will know through experience that it is not easy to;
- Wash off components at a distance more than 12 inches (30 cm)
- Post wash air dry at a distance more than 12 inches (30 cm)
- Remove excess dry developer at a distance more than 12 inches (30 cm)
The Responsible Level 3 should reference in the Penetrant procedure / Work Instruction the following, the most important part of this information is in capital letters.
Water wash for Water Washable and Post Emulsifiable Methods
For manual operation the water spray gun shall be adjusted to give a course spray of low velocity.
The spray gun nozzle shall be held at least 300mm away from the component WHERE COMPONENT GEOMETRY PERMITS, paying particular attention to areas of entrapment such as undercuts, blind holes, and oil ways.
Post Wash Air Dry
Air blast pressure shall not exceed 25psi or the pressure stated in the relevant process control chart at a distance not less than 300mm from the part to nozzle tip WHERE COMPONENT GEOMETRY PERMITS.
Excess Developer Removal
If permitted excess powder shall be removed by clean dry air blow off 5 psi maximum at a distance not less than 300mm WHERE COMPONENT GEOMETRY PERMITS and at the maximum pressure as stated in the relevant process control chart.