Pressure Testing Tools & Equipment
Helium leak testing is never, if ever, used to demonstrate that the system can safely stand up to the design stress score. Any leakage of helium from the encompassing chamber into the component will de drawn into the helium leak detector by the vacuum it is producing. The helium leak detector incorporates a mass spectrometer configured to sense the presence of helium molecules.
In most instances a strain larger than the design pressure score is utilized for a short duration, say a minimum of 10 minutes. The magnitude of this preliminary take a look at strain is usually no less than 1.5 occasions the design stress rating for a hydrostatic test. However, it could be totally different, relying upon which code is applicable and whether the test is hydrostatic or pneumatic. Helium leak detectors will not be successful to find leaks unless the component or piping system is totally dry.
It may be a single temperature, or an envelope of acceptable working temperatures as a operate of stress. All stress vessels have their very own peculiar hazards, together with nice saved potential force, factors of wear and tear and corrosion, and attainable failure of overpressure and temperature control safety units. Pressure vessel and piping methods are widely used all through business and include a very large focus of vitality. Despite the fact that their design and set up adjust to federal, state and native rules and recognized industrial standards, there continue to be severe stress gear failures. The chosen test method and fluid test medium, together with the relevant code, may even set up the principles to be adopted in calculating the required take a look at stress.
Field situations are usually not free of the chance for contamination of the leak detector. A giant leak also can flood the detector, temporarily rendering it ineffective until all of the helium is removed from the mass spectrometer. The helium stress used in all these methods is generally one or two atmospheres, which is enough to detect the presence of very small leaks. The low strain also serves to scale back the amount of helium required for the check.
This closed-system testing methodology is able to sensing leaks as small as 1X10-10cc/sec (6.1X10-12 cubic in/sec), standard atmospheric air equivalent. The closed-system methodology is not acceptable to measuring a big leak that would flood the detector and render it useless for further measurement till every helium molecule could possibly be withdrawn from the detector. The hood mode of helium leak testing is probably the most delicate technique for detecting leaks and the only technique accepted by ASME Code Section V as quantitative. Manufacturers of elements requiring a airtight seal will use the hood methodology of helium leak detection as a production leak take a look at.
Liquid contained in a small leakage path, due to capillary action, may seal the leak because of the low strain of the helium and the surface pressure of the liquid. Therefore nice care is required to use this method underneath fully dry conditions. Otherwise this system could also be even less sensitive in detecting a leak than a high-strain hydrostatic take a look at. Furthermore, the helium leak detector is definitely contaminated by oils and different compounds and rendered inaccurate.
Minimum Allowable Metal Temperature (MAMT) - The minimum temperature for an current vessel to maintain the testing or working situations with a low threat of brittle fracture. The MAMT is set by an analysis for pressure vessels constructed prior to 1987. This term is utilized in API RP 579 for the brittle fracture evaluation of current equipment.
So per the code, a leak take a look at utilizing air may be carried out if the system proprietor considers the hydrostatic test to be impractical. Where the proprietor considers a hydrostatic leak test impractical, both a pneumatic take a look at in accordance with para. 345.5 or a mixed hydrostatic-pneumatic check in accordance with para. 345.6 may be substituted, recognizing the hazard of power stored in compressed fuel.