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“Inadequacy of traditional test methods for detection
of non-hermetic energetic components”
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George R. Neff & Jimmie K. NeffIsoVac Engineering, Inc., Glendale, CA
Barry T. NeyerPerkinElmer Optoelectronics, Miamisburg, OH
Karl K. RinkUniversity of Idaho, Moscow, ID
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The Authors Competency
Many decades of experience in leak detection and failure analysisManufacture of ordnance devicesFundamental research in ordnance device designs and performanceAcademic research in leak testing theory and applicationPreparation of Military Standards & Commercial Test Specifications
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The Hermeticity Test Problem
Poor understanding of leak test theoryMisapplication of test methodologiesFailure to understand device geometryCommitting to traditional practicesIgnoring MIL-STD limitationsLack of Field FeedbackInferior failure analysisWeak Statistical recordkeeping
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The Hermeticity Callouts
Most Ordnance Devices have “Seal-Test” callouts of:Visible to 5 x 10-6 std cm3/sec
(The “Gross-Leak Rate Range”)
Many Ordnance Devices have Small & Zero-Cavities that are:
0.01 cm3 through 0.000001cm3
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Test Methodology Reviewed
Helium Mass Spectrometry
Radioisotope Test Method
Red Dye Penetrant Failure Analysis
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Typical Leak-Rate Distribution
Over 98% of leakers
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Test Methods
Helium ‘Mass-Spec’ leak test method, (HMS)
Being misapplied for “Gross-Leak” testingRequires “Caution” with small ordnance devicesMIL-STDs limit HMS to Fine leak testing only, and not allowed for Gross leak testing.Unreliable to detect “gross leaks” in “Small & Zero-Cavity” devices
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Helium Mass Spectrometry
“Back-Pressurization”Various bomb times and pressuresParts measured IndividuallyParts are evacuated prior to measurementHelium is lost during evacuation
Tracer-Gas loss During Evacuation:0.0001cm3 cavity with 10-4 std cc/s leak- 99.99% of Helium tracer gas in 10 sec.
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Helium Mass Spectrometry
A “Leakage passage” Usually has short length and a ‘passage’ volume: < 10-5
cm3
Therefore: With a 10-4 cm3/s leak rate: “Helium is gone in Less than 1 second”.Then: Detectable helium is only from:“Interparticulate” cavities or “He Dissolved
in Binders”, very slowly released.Result is an “Indicated-Leak” less than the
spec, and an “escaped leaker”.
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Radioisotope (Kr85) leak testing
Called out in MIL-STDs for Gross & Fine leak testing
Testing small (0.02cm3) to large cavities.
Testing “Small” & “Zero-cavities” with charcoal gettering.
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Radioisotope Test Method“Back-Pressurization”
0.01% Kr85 tracer-gas mixture
Measured “In-Place” (In Device Cavity)
Detectability: ~ 1011 molecules Kr85
Bomb Times:“Gross-Leaks” ~36 sec. (> 5 x 10-6)“Fine-Leaks” ~6 min.
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Technical theory of the testThe gamma rays from Kr85 gas trapped within a leaker, will penetrate the walls of normal devices, and are easily detected by the scintillation crystal at the counting stations.
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Dye Penetrant Failure Analysis
Purpose”Verification of gross leakageDetectability to ~ 1 x 10-7 std cm3/sIsolation of leak sites
Glass header cracksGlass-to-metal sealsWeld defects
Destructive test
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Vacuum Decay Equation
Pt = Po e -kt
Where:Pt =Partial press Kr85 at time “t”Po =Original partial press Kr85 k= leak rate (std cm3/s)
cavity vol. cm3
t = time in vacuum (sec)
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The “Gettering” Technology
“Charcoal Gettering” of Kr851. Steam Activated Charcoal2. High surface area: 500m2/gm3. Mixed with ordnance4. One Particle of Charcoal:
0.003” size, 0.243 µgm, vol. ~10-7 cm3
“Provides 133 mm2 surface area”.
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“Gettering” of Kr85
“Steam-Activated Coconut-Shell Charcoal”
1. “Adsorbs” Kr85 tracer gas2. Holds Kr85 by van der Waals forces3. Does not effect ordnance materials4. Adsorbs 27% by wt of water5. Assures detection of ‘wide open leak’6. Used in 50+ million Ordnance parts/year
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Leak Test Standards
MIL-STD-883MIL-STD-750MIL-STD-202
MIL-STD-S-19500MIL-13474c-Squibs
S-113 Ordnance+ Others, (Military & Company Specs)
Mostly: based on MIL-STD 202
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Mil Std. 883
Bubble or Dye Penetrant Test
0 10-510-8
Leak Rate std-cc/sec
Leak Test Ranges for U.S. Specification Callouts
Gross Leak Fine Leak
Radioisotope Gross
Radioisotope Gross Leak Test & Fine Leak TestHelium Test
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Bubble or Dye Penetrant Test
0 10-5
Leak Rate std-cc/sec
Radioisotope Gross Leak Test & Fine Leak Test
Leak Test Ranges for U.S. Specification Callouts
Gross Leak Fine Leak
Mil Std. 750
Helium Test
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Bubble or Dye Penetrant Test
0 10-5
Leak Rate std-cc/sec
Leak Test Ranges for U.S. Specification Callouts
10-8Gross Leak Fine Leak
Mil Std. 202
Helium testRadioisotope Test
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MIS-13474C (Missile Inspection Systems-Squibs)
0 10-5
Leak Rate std-cc/sec
Leak Test Ranges for U.S. Specification Callouts
Radioisotope Gross Leak Test
10-8Gross Leak Fine Leak
Radioisotope Fine Leak Test
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Red-Dye in “Header Gross-Leak”
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Pin-Glass “Gross-Leak”
Bridge-wire
Header
Glass
Pin Red-Dye penetrant
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“Pin-Glass Gross-leaks”
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“Fungus-Growth” on Ordnance
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Charcoal mixed in ordnance
Compressed ZPP
Bridge-Wire Impression
Charcoal Particles
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Impulse Cartridge
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Residue of corroded bridge-wire
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Need to Establish a Guaranteed Leak Test Method
Leak testing of energetic products is inherently more complicated than a simple vacuum decay equation impliesNeed to research known leakers with proposed approach to ensure that the method works.
Investigate devices with known leaks in glass-to-metal seals and defective welds.Verify that the method can detect such leaks
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Use of Academia
University of Idaho has developed some Unique Engineering Capabilities
Fully equipped for “Fundamental Research”Skilled in Ordnance technologiesSophisticated Ballistic testingAll leak testing methodologiesHermetic seal mechanics studiesGas and Moisture transfer through leaksOrdnance material behavior
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The authorsThank You for Your Time
May we answer any Questions?