Measuring and testing – Surface and cutting edge testing
Patent
1994-07-27
1996-09-10
Williams, Hezron E.
Measuring and testing
Surface and cutting edge testing
738658, 738665, G01N 2191, G01N 2190
Patent
active
055548008
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a device and to an instrument for the non-destructive testing of tubular members, by discovering, localizing and reproducing surface flaws and faults such as cracks that may be present in the inner surfaces of the tubular members. The invention finds particular application in the inspection of tubular members of small inner diameters.
TECHNICAL STANDPOINT
Heat exchangers such as steam generators in nuclear power stations are equipped with high-load heat exchanger tubes having an internal diameter of 15-20 mm. The tubes are secured by rolling the tubes in end walls which form tube attachments and partition walls that mutually separate the heat-carrying media passing through the heat exchangers. The vulnerability of the tubes to load caused by pressure and heat and by changes in these factors, vibrations, corrosion, etc., can result in flaws and faults, such as the formation of cracks in the tube walls. If these flaws are not rectified in time, the flaws may become so serious as to cause the tubes to rupture, resulting in serious consequences. It is therefore important to constantly monitor the tubes, so that necessary measures can be taken in time. In the case of steam generators, damaged tubes can be plugged at the time of making an annual inspection.
Different non-destructive testing techniques are used to detect surface flaws, of which techniques inductive testing has been one of the few techniques applied for testing deep into small bore pipes and tubes. In this technique, there is inserted into the tubular member to be tested a probe which is equipped with a coil to which alternating current is supplied and which functions to induce eddy currents in the wall of the tubular member which retroact on the coil. Because the eddy currents are influenced by flaws in the tubular member, some information can be obtained as to whether or not a flaw exists and, if so, the size of the flaw, by measuring the retroactive effect of the eddy currents on the coil. One pronounced drawback with this known method of inspection, however, resides in the difficulty experienced in determining the nature of the flaw, and in that the signal interference ratio is small. Not only small flaws are hidden by interference noise. For instance, if the probe is constructed to produce good indications of the presence of longitudinally extending cracks, which are the most common, equally as large transversely extending cracks will only result in small readings (output signals) which are difficult to distinguish in the interference noise.
DISCLOSURE OF THE INVENTION
Technical Problem
The object of the present invention is to provide a device and an instrument for detecting internal surface flaws in tubular members. The device is intended to provide a more accurate understanding of the flaws than has hitherto been possible with known methods.
Solution
This object is achieved with an inventive device and an inventive instrument.
In the case of one known method for the non-destructive testing of surfaces, flaws which are otherwise invisible are treated so that they can be seen with the naked eye. A so-called penetrant, i.e. a liquid which is able to penetrate into very fine cracks, is applied to the test surface with the aid of a brush for instance. The penetrant also has the ability to remain in the surface fault when the test surface is subsequently washed to remove excessive penetrant that has not penetrated into the surface faults. When a coloured penetrant is used, the test surface is sprayed with a so-called developer which contains a fine-grain white powder. The penetrant is drawn out of the cracks by the powder layer and disperses in the layer so as to form contrasting indications on cracks having a width down to 0.001 mm. On the other hand, when a fluorescent penetrant is used, it is possible to observe indications directly with the aid of ultraviolet light. This method, however, presumes that the test surface can be easily reached. Consequently, it has not been possible to apply
REFERENCES:
patent: 2667070 (1954-01-01), Sockman et al.
patent: 3049752 (1962-08-01), Jorda et al.
patent: 3830094 (1974-08-01), Leger
Larkin Daniel S.
Vattenfall AB
Williams Hezron E.
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