View Latest Blog Entries
Close
Categories
Testing & Assessment Certification Standard & Regulation Aging Wires & Systems Maintenance & Sustainment Management Conference & Report Protection & Prevention Research Miscellaneous Arcing
Popular Tags
Visual Inspection High Voltage AS50881 MIL-HDBK MIL-HDBK-525 FAR AS4373 Maintenance Electromagnetic Interference (EMI) FAR 25.1707 Wire System Arcing Damage
All Tags in Alphabetical Order
2021 25.1701 25.1703 abrasion AC 33.4-3 AC 43 Accelerated Aging accessibility ADMT Aging Systems AIR6808 AIR7502 Aircraft Power System aircraft safety Aircraft Service Life Extension Program (SLEP) altitude arc damage Arc Damage Modeling Tool Arc Fault (AF) Arc Fault Circuit Breaker (AFCB) Arc Track Resistance Arcing Arcing Damage AS22759 AS22759/87 AS23053 AS29606 AS4373 AS4373 Method 704 AS50881 AS5692 AS6019 AS6324 AS81824 AS83519 AS85049 AS85485 AS85485 Wire Standard ASTM B355 ASTM B470 ASTM D150 ASTM D2671 ASTM D8355 ASTM D876 ASTM F2639 ASTM F2696 ASTM F2799 ASTM F3230 ASTM F3309 ATSRAC Attenuation Automated Wire Testing System (AWTS) Automotive Avionics backshell batteries bend radius Bent Pin Analysis Best of Lectromec Best Practice bonding Cable Cable Bend cable testing Carbon Nanotube (CNT) Certification cfr 25.1717 Chafing Chemical Testing Circuit Breaker circuit design Circuit Protection cleaning clearance Coaxial cable cold bend collision comparative analysis Compliance Component Selection Condition Based Maintenance Conductor Conductor Testing conductors conduit Connector connector installation Connector rating connector selection connector testing connectors contacts Corona Corrosion Corrosion Preventing Compound (CPC) corrosion prevention Cracking creepage D-sub data analysis data cables degradat Degradation Delamination Derating design safety development diagnostic Dielectric breakdown dielectric constant Dimensional Life disinfectant Distributed Power System DO-160 dry arc dynamic cut through E-CFR electric aircraft Electrical Aircraft Electrical Component Electrical Power Electrical Testing Electrified Vehicles Electromagnetic Interference (EMI) Electromagnetic Vulnerability (EMV) Electrostatic Discharge EMC EMF EN2235 EN3197 EN3475 EN6059 End of Service Life End of Year Energy Storage engines Environmental Environmental Cycling environmental stress ethernet eVTOL EWIS certification EWIS Component EWIS Design EWIS Failure EWIS sustainment EWIS Thermal Management EZAP FAA FAA AC 25.27 FAA AC 25.981-1C FAA Meeting failure conditions Failure Database Failure Modes and Effects Analysis (FMEA) FAQs FAR FAR 25.1703 FAR 25.1707 FAR 25.1709 Fault fault tree Fixturing Flammability fleet reliability Flex Testing fluid exposure Fluid Immersion Forced Hydrolysis fuel system fuel tank ignition Functional Hazard Assessment functional testing Fundamental Articles Fuse Future Tech galvanic corrosion Glycol Gold Gold plating Green Taxiing Grounding hand sanitizer handbook Harness Design harness protection hazard Hazard Analysis health monitoring heat shrink heat shrink tubing high current high Frequency high speed data cable High Voltage High Voltage Degradation HIRF History Hot Stamping Humidity Variation HV connector HV system ICAs IEC 60851 IEC60172 IEEE immersion insertion loss Inspection installation installation safety Instructions for Continued Airworthiness insulating material insulating tape Insulation insulation breakdown insulation resistance insulation testing interchangeability IPC-D-620 ISO 17025 Certified Lab ISO 9000 J1673 Kapton Laser Marking life limit life limited parts Life prediction life projection Lightning lightning protection liquid nitrogen lithium battery lunar Magnet wire maintainability Maintenance Maintenance costs Mandrel mean free path measurement mechanical stress Mechanical Testing MECSIP MIL-C-38999 MIL-C-85485 MIL-DTL-17 MIL-DTL-23053E MIL-DTL-3885G MIL-DTL-38999 MIL-E-25499 MIL-HDBK MIL-HDBK-1646 MIL-HDBK-217 MIL-HDBK-454 MIL-HDBK-516 MIL-HDBK-522 MIL-HDBK-525 MIL-HDBK-683 MIL-STD-1353 MIL-STD-1560 MIL-STD-1798 MIL-STD-464 MIL-T-7928 MIL-T-7928/5 MIL-T-81490 MIL-W-22759/87 MIL-W-5088 MIL–STD–5088 Military 5088 modeling moon MS3320 NASA NEMA27500 Nickel nickel plating No Fault Found OEM off gassing Outgassing Over current Overheating of Wire Harness Parallel Arcing part selection Partial Discharge partial discharge at altitude Performance physical hazard assessment Physical Testing polyamide polyimdie Polyimide-PTFE Power over Ethernet power system Power systems predictive maintenance Presentation Preventative Maintenance Program Probability of Failure Product Quality PTFE pull through Radiation Red Plague Corrosion Reduction of Hazardous Substances (RoHS) regulations relays Reliability Research Resistance Revision C Rewiring Project Risk Assessment S&T Meeting SAE SAE Committee Sanitizing Fluids Secondary Harness Protection separation separation distance Separation Requirements Series Arcing Service Life Extension Severe Wind and Moisture-Prone (SWAMP) Severity of Failure shelf life Shield Shielding Shrinkage signal signal cable Silver silver plated wire silver-plating skin depth skin effect Small aircraft smoke Solid State Circuit Breaker Space Certified Wires Splice standards Storage stored energy superconductor supportability Sustainment System Voltage Temperature Rating Temperature Variation Test methods Test Pricing Testing testing standard Thermal Circuit Breaker Thermal Endurance Thermal Index Thermal Runaway Thermal Shock Thermal Testing tin Tin plated conductors tin plating tin solder tin whiskering tin whiskers top 5 Transient Troubleshooting TWA800 UAVs UL94 USAF validation verification video Visual Inspection voltage voltage differential Voltage Tolerance volume resistivity vw-1 wet arc white paper whitelisting Winding wire Wire Ampacity Wire Bend Wire Certification Wire Comparison wire damage wire failure wire performance wire properties Wire System wire testing Wire Verification wiring components work unit code
Key Takeaways
  • The goal of the forced hydrolysis test is to represent decades of wet/humid environmental exposure on an aircraft.
  • Forced hydrolysis testing is typically limited to wires/cables where polyimide is part of the insulation system.
  • Pass/fail criteria of the test effectively depend on a dielectric voltage withstand post-test used to identify any breaches in insulation.

Forced Hydrolysis

Fluid immersion of electrical components is often done to determine material compatibility. However, there are fluid immersion tests that are more about material degradation and accelerated aging than compatibility; this is where forced hydrolysis testing comes in. While it is not part of every wire/cable qualification testing, it is applicable to some constructions, and how/why that is the case is important when building qualification plans and selecting parts for use.

Objectives and History

Forced hydrolysis testing exposes a wire or cable to a long-term submerged water application at near-boiling temperatures. The original idea behind this was part of the degradation analysis around polyimide wire. It is known that direct exposure to humidity, heat, and mechanical stress will rapidly degrade polyimide films (if not for additional precautions or advanced techniques for material protection). To verify the long-term endurance of polyimide wire, the idea of forced hydrolysis was developed.

Understanding the rationale for forced hydrolysis testing starts by understanding how polyimide insulation is used and how it degrades. The film that was used in wires constructed the 70s, 80s, and early 90s was known as H-film. It had great mechanical properties, great flame resistance, and great radiation resistance, but when exposed to heat, humidity, and mechanical stress, the insulation degraded rapidly usually leading to rapid wire degradation observed with radial insulation cracks. After this was identified, companies developed techniques to extend the life of polyimide film for wiring applications.

Other wire insulation types, such as ETFE and PTFE, are unlikely to show degradation under these test conditions, and as a result, wires with those material types are not typically tested to forced hydrolysis. In fact, forced hydrolysis testing for aerospace wiring is only included as part of qualification testing if the insulation construction includes a polyimide film, such as the AS22759/80 – /92 or AS22759/180 – 192.

Test Performance and Applicability

In this test, several lengths of the wire are cut, typically about 18-24 in. These samples are then wrapped around a mandrel, for the 20-gauge wire size, the mandrel diameter is about 0.5 in. While not specifically called out in most forced hydrolysis test methods, the mandrel diameter and sample size should scale based on the wire or cable diameter being evaluated. The sample is then submerged in a saline solution at 70°C for thousands of hours. The ends of the sample are positioned above the water line to avoid fluid ingress between the wire conductor and the insulation.

Forced Hydrolysis
Specimens are submerged in the water solution (highlighted in blue) throughout testing with their end fixed in a position above the water level.

While no testing is performed on the samples during the long fluid immersion, a simple modification would be the periodic performance of dielectric voltage withstand tests where a voltage is applied to the conductor and a ground return is placed into the fluid bath. This would verify the insulation integrity and determine if any samples have insulation breaches thereby reducing the test duration based on sample performance.

Effectively, the test’s pass/fail criteria is entirely based on the post-test dielectric withstand assessment. The sample is considered to have passed the forced hydrolysis test if it is found without an insulation breach at the end of the exposure duration.

As stated earlier, this test technique is primarily designed for polyimide-insulated wires. However, the same technique may be used for other component tests where long-term fluid exposure is required. For example, if a component is to be submerged in a fuel application for years or decades, the forced hydrolysis test can be adjusted to use kerosene in place of a saline solution. This is very similar to the fluid immersion test albeit with a much tighter bend on the wire cable under evaluation (Fluid immersion testing usually calls for the bend radius to be at least 14x the specified maximum diameter of the wire).

Potential Issues

As the test is performed at an elevated temperature, it is important for there to be a reflux mechanism to ensure that the fluid is not boiled off too quickly. This ensures that the water levels are maintained, otherwise, the sample is hanging in air exposed to steam or hot dry air. Lastly, the wire or cable should be inspected before the test. Visual examination and pretest voltage breakdown should be done to ensure that the sample is not damaged before the test. Lectromec will typically do a voltage withstand test once the sample is installed to ensure that no damage was incurred during the handling or installation. This does place additional voltage stress on the insulation, but it is done to ensure that thousands of hours of testing are not wasted.

When considering the application of this test, it is important to consider the material properties of the insulators. For example, the original MIL-W-81381 wires had a humidity resistance test as part of the product verification, yet the material was still prone to degradation when exposed to long-term moisture and mechanical stress.

Application Factors

The goal of the forced hydrolysis test is to represent decades of wet/humid environmental exposure on an aircraft (think SWMAP zones). While most aerospace wires will not spend their service lives submerged in water, the test, like many accelerated aging tests, uses conditions that exceed expected service conditions to generate results within a reasonable duration. The impractical test condition is accepted because the results generate data to support service life predictions.

As with any accelerated aging test, the parameters are very important. It is possible to perform the forced hydrolysis with a tighter bend radius or perform the test in a pressure vessel so that the water could be at an even higher temperature; the testing under these more stressful conditions might introduce other failure mechanisms that would not occur under normal conditions.

Conclusion

Forced hydrolysis testing is used for wire/cable evaluation and accelerated aging in numerous industries and product constructions. For aerospace, the use of this test method is typically limited to wires/cables where polyimide is part of the insulation system. While the test is frequently a long-term test taking thousands of hours to complete, it is a necessary part of product verification to ensure reliability when installed on aircraft. To find out more about this test, contact Lectromec.

Michael Traskos

Michael Traskos

President, Lectromec

Michael has been involved in wire degradation and failure assessments for more than a decade. He has worked on dozens of projects assessing the reliability and qualification of EWIS components. Michael is an FAA DER with a delegated authority covering EWIS certification and the chairman of the SAE AE-8A EWIS installation committee.