1.Overviews
Heat exchanger is general equipment for electric power, petrochemical, and other many industrial departments, and occupies an important position in production. Now, vortex testing technique is mainly used for in service and pre-service detections of heat exchanger pipes such as brass, titanium, stainless steel tubes, boiler steel pipes in the departments such as boiler test, electric power, and petrochemical.
2.Detection plans
1)Aim at pre-service testing
Conventional vortex testing technique matches with the outer traverse type or inner traverse type sensor for testing. For ferromagnetic new tube detection, should cooperate with outer traverse magnetic saturator for testing, this can reduce magnetic noise interference and improve the detection depth.
① For testing non-ferrous metal pipes with outer traverse type probe, pipe should pass through from probe inner hole.
② For testing non-ferrous metal pipes with inner traverse type probe, probe should pass through from pipe inner hole.( focus on internal wall defects)
③ Ferromagnetic steel tube detection, matches with magnetic saturator detection and reduces magnetic noise interference and improve detection depth. A full set of test schematic diagram below (according to actual situation, to see if need marking alarm and demagnetization device, etc).
2)Aim at testing in service
For non ferromagnetic materials(such as brass, titanium tube, stainless steel tube, etc.),using conventional vortex testing technology, cooperating with inner through probe for testing. For ferromagnetic material, using far field vortex testing technology and matching with special far field inner traverse probe for testing. The site inspection photos as shown in the figure below.
3.Detection technology and characteristics
1)Common vortex testing technology
Vortex testing technique is based on electromagnetic induction, can detect the defects such as corrosion pits, inclusions, cracks, air holes, deformations from tested parts. Testing heat exchanger non-ferrous metal pipes with common vortex inspection technology, having high detection speed, low cost, and high detection sensitivity for testing surface and near surface defects, now it is the most reliable and efficient detection technology. Using cooperatively multi-frequency vortex testing technology, can effectively suppress the influence of various interference factors,(such as support plate signal, etc,) and achieve the purpose of eliminating false and retaining true, improve detection sensitivity, accuracy and reliability, make a right evaluation for tested parts.
2)Far field vortex test technique
Far field vortex testing technique is a kind of low-frequency vortex testing technology which can penetrate metal tube wall, and can overcome the affects of common vortex to ferromagnetic pipe. Due to the effect of skin effect, it can only detect pipeline surface defects, improve penetration depth of detection.
Compared with the magnetic leakage and ultrasonic nondestructive testing, the far field vortex nondestructive testing has the following advantages:
① The surface of tested steel pipe don't need to clean;
② Probe do not contact with steel tube surface, the clearance changes between probe outer diameter and pipe inner diameter have little impact on test results. Allow maximum clearance is 30% of the steel tube diameter, the best clearance is less than 15% of the steel pipe inner diameter.
③ The technology has same sensitivity when testing the corrosion pits existed in steel pipe inner surface and outer surface.
④The technology has high detection sensitivity for testing uniform thinning, gradual thinning and eccentric wear thinning detections.
⑤ Whether uniform of probe detection speed is no effect to the detection result.
⑥The gas and liquid medium in steel pipes have not influence to test results.
⑦The testing equipment is small in size, light weight, easy to flexible application in site.
4.Recommend instruments and accessories
1)The testing instruments apply to in service and pre-service inspection of non-ferrous metal materials are:EEC-35++ 、EEC-39 , etc.
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