API 687 2001 pdf free download
API 687 2001 pdf free download.Rotor Repair.
B.3.3.2 Precautions For Use of Magnetic Field Since poor indications are produced when discontinuities are perpendicular to the current flow (parallel to the magnetic field) the parts shall be magnetized in at least two different directions approximately at right angles to each other. To pro- duce satisfactory indications, the magnetic field in the part must have sufficient strength. For the indications to be consis- tent, this field strength must be sufficient to develop the pat- tern of the field indicator (pie gauge) over the entire area to be examined. As this inspection method induces a magnetic field in the component, care must be taken to ensure that the component is demagnetized (degaussed) to a maximum level of ±2 gauss residual magnetism. If left magnetized, the components could be damaged. Residual magnetism in the shaft vibration probe track area could also adversely affect the vibration signal. B.3.3.3 Surface Condition Maximum sensitivity can only be achieved on a smooth surface. This is often not possible or practical. A light grind- ing of the suspect surface or in most cases just a good wire brushing brings about considerable improvement. B.3.3.4 Spacing of Prods For most applications, spacing of 15 to 20 centimeters (6 to 8 inches) are most effective. B.3.3.5 Temperature of the Surface being Inspected 1. Wet magnetic particle work should not be performed on surfaces above 60°C (140°F). CAUTION: Above this temperature may cause flashing of the penetrant. 2. Dry magnetic particle work should not be performed on surfaces above 315°C (600°F).
B.5.1 BRINELL SCALE The term “hardness” is ambiguous; glass will scratch hard- ened steel, but would never do as a machine tool. The hard- ness data of any material is only valid when the particular type of hardness test is understood. There are several scales to indicate just how hard or soft a specific material is. One method was devised by Dr. J. A. Brinell of Sweden in 1900. He reasoned that the hardness of a metal could be determined by measuring the diameter of an impression made by a steel ball forced into the metal under definite static loads by means of hydraulic pressure. A scale of Brinell numbers is based on the diameter of the indentation, and the hardness of the metal on this scale also shows the approximate ultimate tensile strength.
B.4 Ultrasonic Inspection Ultrasonics is capable of economically revealing sub-sur- face discontinuities in a variety of materials and shapes. A piezoelectric crystal is excited with a high voltage pulse, causing the crystal to vibrate and emit a short pulse of sound introduced into the test material. The sound travels through the material and is reflected back to the crystal from the oppo- site side or from any location in the material where there is an abrupt change in acoustic impedance. The crystal converts the sound vibrations to electrical energy and the reflected pulse is displayed on a Cathode-Ray Tube (CRT). Signal amplitude and elapsed time are very important. Knowledge of the sound beam angle and elapsed time permits the flaw to be located. Ultrasonic inspection is particularly useful when only one surface of the test item is accessible, when heavy sections of material must be inspected for internal flaws, or when results must be immediately available. Another advantage of ultra- sonic inspection is that reflections from indications can pro- vide specific information regarding size and distance from the surface of the indication. Ultrasonic inspection has disadvan- tages too; (1) the test surface must be relatively smooth, and (2) the couplant used between the crystal and the material limits its use to under 55°C (130°F). Surface indications will not be detected because of near field signals. B.4.1 STRAIGHT-BEAM TECHNIQUES The straight-beam technique is accomplished by projecting a sound-beam into the test specimen perpendicular to the test surface to obtain reflections from the back surface or from discontinuities. The crystal in most cases acts as both trans- mitter and receiver of the sound-beam. The straight-beam technique is also used to inspect steel plate for laminar indica- tions. This method works well on shafting material.
