Breaking down the importance of perfecting dry times and how to create an optimal drying environment for Liquid Penetrant Inspections  

By Cheri Stockhausen, Product Applications Manager 

Importance of Correctly Drying Parts 

Proper drying of parts allows the uniform application of dry powder developer and nonaqueous developer for the best inspection results. Slightly damp parts or pooled water areas will inhibit the developer application and possibly cause areas of incomplete developer coverage. Water-soluble and water-suspensible developers also require the correct drying of the test parts after applying the developer to prevent streaking and running of the developer coating. 

Note: Flowchart shows parts being dried before dry powder and nonaqueous developer, but dried after water-soluble and water suspendable developer.

Optimal Drying Conditions 

For best results, parts should be dried in a forced air circulating oven before application of dry powder and nonaqueous developer and after application of water soluble or water suspendible developer.

Developer Options

ZP-4D Dry powder developer (Form a) for Type 1 fluorescent penetrant testing QPL SAE AMS 2644  Pratt & Whitney approved	ZP-9F Solvent-based developer (Form d, Form e) for Type 1 fluorescent and Type 2 visible penetrant testing  QPL SAE AMS 2644  Pratt & Whitney approved	ZP-14A  Water-soluble developer (Form b) for Type 1 fluorescent penetrant testing  QPL SAE AMS 2644 approved	ZP-5B  Water suspendable developer (Form c) for Type 1 fluorescent and Type 2 visible penetrant testing  QPL SAE AMS 2644 approved

5 Tips for Drying Liquid Penetrant Test Parts 

1. An oven temperature range of 140 – 145 ⁰F (60 – 63 ⁰C) is suggested. The maximum oven temperature is 160 ⁰F (71 ⁰C) for fluorescent penetrant inspection systems. 
2. If permitted by governing specifications, low-pressure air blow-off (5 psi or less) may be used to remove excess water from parts before placing parts in the oven.  
3. Place parts in the oven for optimum airflow. Do not crowd parts. 
4. Do not place parts with pooled water in the oven. 
5. Remove parts from the oven as soon as they are dry.  

Learn about the available properties of developers and the relationship between dwell time and inspection quality here. 

Published November 24, 2020