Knowledge of the leakage detection limits for leakage test methods to prove “tightness”. Absolute “tightness” does not exist.
Permissible limit values for leakages are defined for technical applications. The applied regulations and product standards usually contain information on the method to be used to verify the tightness or contain specific leakage rates.
A typical leak test is the immersion method, in which the product is filled with nitrogen or air and immersed under water for a certain time (usually 30 or 60 seconds). If no bubbles form, the product is “tight”. With this test method, leakage rates greater than 10-4 mbar*l/s can be detected.
The helium leak test is used for higher tightness requirements. The product to be tested is placed under vacuum and exposed to a helium atmosphere from the outside. With the help of a detector (mass spectrometer), He atoms that have entered the vacuum can be detected. The detection limit is up to QL=10-7 mbar*l/s.
The following table contains an overview of the leakage rates (Standard conditions deltaP = 1 bar, 20°C):
| Leckage rate QL [mbar•l/s] | Leakage rate QL [Pa•m3/s] | leak dia. [µm] | Volume flow [l/s] | Volume flow [l/a] | Remarks/ example |
|---|---|---|---|---|---|
| 10-10 | 10-11 | 0,001 | 10-13 | 3,15*10-6 | Detection limit |
| 10-8 | 10-9 | 0,01 | 10-11 | 3,15*10-4 | Highly vacuum-tight* |
| 10-7 | 10-8 | 0,03 | 10-10 | 3,15*10-3 | Gas-tight* |
| 10-6 | 10-7 | 0,1 | 10-9 | 0,032 | |
| 10-5 | 10-6 | 0,33 | 10-8 | 0,315 | |
| 10-4 | 10-5 | 1 | 10-7 | 3,15 | Vapor-tight* |
| 10-3 | 10-4 | 3,3 | 10-6 | 31,5 | Watertight* one air bubble (ø 1mm) per sec |
| 1 | 1• 10-1 | 100 | 10-3 | 31500 | Water tap drips |
| *Colloquial, no exact definition |
In technology, various methods have been developed that enable both qualitative (good/bad) and quantitative (leakage rate) testing.
Test methods for leakage tests
In technology, various methods have been developed that enable both qualitative (good/bad) and quantitative (leakage rate) testing. This enables technical products with practicable methods (as good as necessary) as well as with more precise methods to fulfill requirements that only allow a certain leakage rate, e.g. if leaking substances endanger people, affect the environment or if processes are changed as a result. The permissible leakage rate is also an important aspect in vacuum technology.
A basic distinction is made between the procedures:
| Test procedur | Standard | Methode | Detection limit |
|---|---|---|---|
| Tracer gas test method – Sniffing method – Helium leakage test (integral, partial or local) | ISO 20485 | – overpress vacuum | – 10-7 Pa m3/s 10-12 Pa m3/s |
| Pressure change test – pressure decay method – pressure rise method | EN 13184 | overpress | – 10-6 Pa m3/s 10-5 Pa m3/s |
| Bubble test – with foaming mediums – immersion test method | EN 1593 | overpress | 10-3 to 10-7 Pa m3/s |
Leakage rate unit conversation
| Unit | mbar·l/s | Pa·m3/s | Pa· l/s | std cm3/s | mol/s | atm•ft3/min |
|---|---|---|---|---|---|---|
| 1 mbar·l/s = | 1 | 1·10–1 | 1·102 | 9,87·10–1 | 4,403·10–5 | 2,097•10−3 |
| 1 Pa·m3/s = | 1·101 | 1 | 1·103 | 9,87 | 4,403·10–4 | 2,097•10−2 |
| 1 Pa·l/s = | 1·10–2 | 1·10-3 | 1 | 9,87·10–3 | 4,403·10–7 | 2,097•10−5 |
| 1 std cm3/s = | 1,013 | 1,013·10–1 | 1,013·102 | 1 | 4,461·10–5 | 2,12•10−3 |
| 1 mol/s = | 2,271·104 | 2,271·103 | 2,271·106 | 2,24·104 | 1 | 4,749•101 |
| 1 atm•ft3/min | 4,78•102 | 4,78•101 | 4,78•104 | 4,72•102 | 2,105•10−2 | 1 |
