Acoustic Emission testing

Acoustic emission detection of large spherical tank

Update time：2008-05-14 13:19　　　 Viewed：次

Pressure test acoustic emission detection

Spherical tank shall be conducted with pressure test using water or air as the medium after completing manufacturing to review and confirm the safety and quality. For some special requirements of spherical storage tank, it also need to carry on the acoustic emission monitoring at the same time to detect crack initiation and extension may occur in the process of spherical tank pressure test and to evaluate the structural integrity of the spherical tank in the process of pressure test.

Acoustic emission testing generally adopt multi-channel acoustic emission instrument and probe array adopts the triangle time positioning method for integral realtime monitoring of spherical tank, spacing between acoustic emission sensor is commonly 3 ~ 5 m. For example, the most common 400 m3 spherical tank adopt 16 channels, 1000 m3 spherical tank with 24 channels.

Hydrostatic test load for the first time, the newly installed spherical tank spherical shell welding and assembly produce residual stress to the gradual release, acoustic emission signal is very rich, acoustic emission location source will be more evenly dispersed spherical shell parts, but the manhole and pillar fillet weld, wrong side, uneven heat treatment and have defects such as cracking area of stress concentration is bigger, is easy to appear acoustic emission location source group. Usually distinguish between residual stress release and cracking defects caused by acoustic emission signal source, metal materials with KAISER effect characteristics, from the test pressure stepdown to the design pressure and then the second step up to the test method of residual stress release area second booster almost silent emission signal, second booster cracking defects parts usually repeated acoustic emission location source signal. Acoustic emission testing technology, active defect location can be determined, but to determine acoustic emission source within specific what property defects, is still need to conduct re-inspection the conventional NDT methods.

To ensure the safe operation of the pressure vessel, countries around the world adopt regular inspection system for pressure vessel during the operation. There are two kinds of pressure vessel inspection: one is external inspection under operating condition; another is internal and external comprehensive inspection after stopping the running state. External inspection cycle is usually 1 ~ 2 a (years), internal and external comprehensive inspection cycle is usually 5 ~ 10a. According to relevant regulations of our government, external pressure vessels inspection cycle is 1 a, internal and external comprehensive inspection cycle is up to 6 a.

New uses of new spherical storage tank, if made of materials whose standard tensile strength limitσb≥540MPa, should be opened to conduct a comprehensive inspection after one year’s use; Otherwise the inspection can be postponed to 3 year later. Annual spherical tank pressure vessel inspection contents includes the inspection of user units’ pressure vessel safety management, spherical tank ontology and running condition inspection and safety accessories inspection, etc. Check method is mainly macro inspection, and also the thickness and content of corrosive medium if necessary. For example, spherical tank welding seam of existing overweight weld defects acoustic emission monitoring method can be used to identify whether the defect is active; If you need to determine whether certain high stress concentration areas of fatigue damage, magnetic memory testing method can be used. If you need to check whether there is fatigue crack on external surface of the spherical tank or stress corrosion crack, surface crack electromagnetic detection method can be used.

With spherical tank can comprehensive inspection cycle is 6 a commonly, but for security rating is class 1 or 2 levels of spherical tank, the measured medium on the material corrosion rate per year is lower than the O.l mm internal thermal spraying coating metal (aluminum stainless steel powder), and 1 ~ 2 times a comprehensive inspection to confirm slightly corroded, comprehensive inspection cycle cans can be extended to 12 a. Spherical tank can fully test the key is in the process of running by the medium, temperature, load and environmental factors such as corrosion, erosion and stress corrosion cracking, fatigue crack and material degradation, in addition to the macro inspection, but should also include magnetic particle testing, penetrant testing, ultrasonic testing, radiographic testing and acoustic emission testing NDT methods. Spherical tank the installation using the field test, the testing conditions, and the nondestructive testing method is suitable for field application technology, the instrument is suitable for non-destructive testing field portable measurement instrument.

At present, there are two modes of comprehensive inspection: conventional nondestructive testing and acoustic emission testing method. For conventional NDT methods model, the internal and external surface of weld and welding scar parts 100% magnetic particle or liquid penetrant, butt weld to 20% ~ 100% internal ultrasonic testing, radiographic testing of ultrasonic testing found that excessive internal deficiencies in to determine the nature of the defect, and to determine the specific parts of repair; This test method is generally used in internal no known excess welding defects or paint defects rarely spherical tank, but this kind of test method of the test time is relatively long. The model of acoustic emission detection method for the spherical tank stopped after the hydrostatic test and acoustic emission testing first, then the acoustic emission testing specified active source parts for testing and ultrasonic testing on the surface of the reinspection do not coincide, and appropriately expand the surface detection ratio above 20%, radiographic testing of ultrasonic testing found that excessive internal deficiencies in camera to determine the nature of the defect, and to determine the specific parts of repair; This test method is generally used in the known inside weld deposit or spherical tank may save a lot of paint defects, acoustic emission testing can from a large number of super Identify the active defects in the defect to repair; Without excessive flaw spherical tank, the use of this model, also can greatly reduce open tank inspection time, reduce the loss. , value to remind is, the smaller surface crack, in the process of pressure testing and location of the source signal may not produce acoustic emission and acoustic emission detection can't find small surface cracks.
(Editor：admin)

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