These Methods » 
Are Used 
For Tests 
Man-Hours Involved (Relative to Dye Test) 
Here's How They Compare | 
MASS SPECTROMETER—HOOD TEST. Tests entire 
surface; sums total leakage; can be used to localize leaks. 
Procedure: Draw 50-micron vacuum in test volume; 
introduce helium into rubber or plastic bag over test 
surface. Draw sample of evacuated gas into mass 
spectrometer. Ultimate sensitivity reached by evacu- 
ating all gas through tester. Leak pin-pointed by using 
fine helium jet as blanket. 
Comments: Sensitivity depends on proportion of gas 
passing through tester; properly applied, method devel- 
ops full inherent sensitivity of tester. When attempt- 
ing full sensitivity on large volume, response is slow 
and outgassing is time consuming; cleanliness require- 
ments stringent to avoid outgassing problems. 
MASS SPECTROMETER—SNIFFER TEST. Useful step 
in approaching high degree of leaktightness. 
Procedure: Pressurize test volume with helium and 
air so that pressure differential drives helium through 
leaks; helium concentration is 20% or greater. Probe 
outer surface with nozzle in short hose leading to tester; 
mark leaks. When leaks are repaired, repeat test. 
Comments: Efficiency depends on operator’s experi- 
ence and diligence; careful probing is tedious. Cleanli- 
ness is essential to avoid masking leaks. 
MASS SPECTROMETER—BOOT TEST. Localizes indi- 
vidual leak; permits rapid repetitive testing of parts for 
which specialized boots can be developed. 
Procedure: Introduce helium into test volume; apply 
cup or boot to portion of outside surface; evacuate gas 
between boot and surface of tester. 
Comments: Sensitivity comparable to previous method. 
Response unaffected by size or configuration of test 
volume; almost as rapid as sniffer test. Outgassing 
time short. Cleanliness only sufficient to avoid mask- 
ing leaks being sought since large-volume outgassing 
problems are avoided. Probably does not develop full 
tester sensitivity; sealing boot to test surface is major 
problem. Single boot not applicable to every test. 
HALOGEN SNIFFING. High-sensitivity test. 
Procedure: Pressurize system to 100 psig with halo- 
gen-air mixture; generally use halogenated hydrocarbons, 
e.g., Freon-12 at 20% conc. Cover test surface with 
probe at }4 in./sec. Fan draws continuous air samples 
into detector containing halogen-vapor-sensitive element. 
Portable control unit contains power supply, amplifier, 
indicator, and loud-speaker. 
Helium sniffing 
2 Halogen sniffing ; 
B crenen eecton | 
7 Isotope testing — 
15 Hydrostotic 
face wetting 
10 WOE ae: 10> Bo 10% 
” Relative Sensitivity 
Comments: Less expensive than mass-spectrometry 
testing, but less satisfactory; may leave traces of halogen 
in system; sensitivity to airborn contaminants gives false 
leak indications under field conditions. 
SOLUBLE-DYE TEST. Visual observation of leak. 
Procedure: Fill system with water containing fluo- 
rescent dye, e.g., Caleco uranine B-4315 (American 
Cyanamid); much smaller fluorescent-dye concentration 
with u-v light pin points leak than possible with ordinary 
dye. Raise system to 1.5 X design pressure and hold for 
6-8 hr. Depressurize and inspect under u-v. 
SURFACE-WETTING TEST. Hydrostatic water test; 
generally used for component and subassembly tests 
where volumes are relatively low. 
Procedure: Fill system with water to 1.5 X design 
pressure. Isolate system. Drop in pressure indicates 
leak rate. Detect leaks by noting weeping at surface. 
CHEMICAL DETECTION. 
Procedure: Introduce tracer compound inside test 
volume, explore outside with ‘‘detector.” Suitable test 
is white fumes given off by acid-base reaction between 
ammonia and carbon dioxide or hydrogen chloride; or 
halogen torch, whereby halogenated hydrocarbon as 
tracer imparts green color to torch flame. 
Comments: Several chemical methods have about same 
sensitivity. 
SOAP-BUBBLE TEST. Finds larger leaks in assembled 
system before employing more sensitive methods. 
Procedure: Pressurize test volume with air. Paint 
leakage areas with soap solution. After repairing leaks, 
repeat. 
Comments: Relatively high sensitivity with propor- 
tionally low expenditure of mah-hours. 
RADIOISOTOPES. Used after repairing major leaks. 
Procedure: Fill system with radioisotope solution 
(Rb®* often used); initial concentration generally about 
0.01 uc/ml of water. Using weld numbers as guide, wrap 
all pipe welds, valve bonnets, vent plugs, etc. with ab- 
sorbent 34-in.-wide absorbent tape. Raise filled system 
to 1.5 X design pressure and hold for 6-8 hr; then gener- 
ally cycle several times, depressurize system, remove 
tapes, and count. With tapes giving 150 cpm or more 
with standard-geometry G-M tube, welds are inspected 
and repaired. 
Comments: This is variation of standard water hy- 
drostatic testing procedure to achieve greater sensitivity. 
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