ET16.pdf

Potential heat exchanger tube material damage

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Potential Heat Exchanger Tube Material Damage Mechanisms Feedwater heat exchanger carbon steel axial cracking nickel copper alloy circumferential cracking stainless steel condensate grooving loose part damage pitting roll transition cracking steam erosion vibrational wear Generator stator cooling system alloy of 90 percent copper and inside surface pitting 10 percent nickel Generator hydrogen cooler aluminum brass; alloy of 90 percent inside surface pitting and copper and 10 percent nickel outside surface damage Lubricating oil cooler admiralty brass inside surface pitting Main condenser stainless steel copper nickel alloys; inside surface pitting and admiralty brass; titanium vibrational wear
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rejectable grading units. Sizing accuracy is based on correlation of the eddy current parameters and on a standard error of regression at an interval where there is a 90 percent probability that discontinuity sizing is accurate to within 50 percent of discontinuity depth. The demonstration results and techniques are peer reviewed by a panel of experts. The industry guidelines specify a number of personnel qualification requirements. 1 Before becoming qualified data analysts, personnel must be certified as a Level II or Level III (as defined in the guideline) and attend additional data analysis training. They must pass written and practical examinations and attend annual training. In addition, utilities have established a site specific performance demonstration program for all prospective analysts. To prepare for the next steam generator inspection, personnel should attend training that will provide practice analyzing indications of interest for that site. A site specific practical examination must be passed for each planned outage and written examinations may be required. The sampling plan for the inspection may be prescriptive or performance based: inspections and additions to the test object sets are partly determined by previous inspections. The inspection results and operating history of other power plants are also considered. Balance-of-Plant Heat Exchangers In a nuclear power plant, heat exchangers that do not carry reactor cooling water from the containment vessel are commonly referred to as balance-of-plant heat exchangers. Most of them have counterparts in fossil fuel power plants and are tested with similar techniques. Some of the tubing materials are ferromagnetic, so techniques other than conventional eddy current are required. These other techniques include magnetically biased eddy current, remote field eddy current and magnetic flux leakage testing. Table 1 lists routinely inspected heat exchangers, potential damage mechanisms and the tubing material. Nonferromagnetic tubing is usually tested with multifrequency eddy current techniques in the differential and absolute modes using bobbin coil probes. In most cases, phase angle analysis is used and relies on a flat bottom hole reference standard. During calibration, the operator may decide to set the 100 percent hole response at about 40 degrees. As the
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  • Fall '19
  • Test, Magnetic Field, Nondestructive testing, electromagnetic testing

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