Steel tape measure, a commonly used inspection tool for pressure vessels

Thread Content

Introduction: A steel tape measure is one of the most commonly used length measurement tools for checking geometric dimensions at pressure vessel manufacturing sites. A steel tape measure, also known as a tape or box tape, is a measuring tool with marked scales on it; by comparing it to the dimension being measured, the value can be read directly from the scale. It is a common tool for measuring length. Depending on their structure, tape measures are classified into reel-type tape measures, automatic tape measures, brake-type tape measures, and depth-measuring steel tape measures, as shown in the figure below. Image: The main component of a steel tape measure is an elastic steel strip with grooves on it, which is wound around a case or frame made of metal or plastic. Ordinary steel tape measures have a hook or pull ring at the end, while depth-measuring steel tape measures have a steel weight at that end; the connection between this weight and the tape can be either hook-type or fixed. The frame and the weight are numbered identically, and the weights are available in two weights: 0.7 kg and 1.6 kg, depending on their usage importance. The braking tape measure is equipped with a button mechanism to control the reeling in of the tape. Nominal length of steel tape measures: For steel tape measures under 10m, it should be an integer multiple of 0.5; for those over 10m, it should be an integer multiple of 5. Steel tape measures are divided into two grades: first grade and second grade. Usage requirements: When using a steel tape measure, it is first necessary to check all its parts. For self-winding and brake-type tape measures, the tape should extend and retract smoothly and flexibly, without any sticking ； The button mechanism of a brake-type tape measure should be able to effectively control the reeling in of the tape, with no obstruction or malfunction occurring ； Box and rack-type tape measures should be flexible when rolling the tape ； The surface of the scale band must be free from rust, obvious spots, or scratches, and the lines must be clear. When using a tape measure, the \"0\" mark should be used as the reference point for measurement, which makes reading easier. When using a non-zero point as the measurement reference, special attention should be paid to the numbers on the lines at the starting end to avoid misreading. When using a tape measure, just as with a metal ruler, it must not be tilted in any direction, and the measuring tape should be stretched tight. The tape of a steel tape measure is usually coated with chromium, nickel, or other coatings; therefore it needs to be kept clean, and it should not come into contact with the surface being measured to avoid scratches. When using a self-winding or braking tape measure, do not pull the tape out too forcefully; instead, pull it out slowly, and also let it retract slowly after use. For a braking tape measure, press the brake button first, then slowly pull out the tape. After use, press the brake button to automatically wind up the tape. The tape measure can only be rolled, not folded. It is not allowed to place the tape measure in humid areas or those with acidic gases to prevent rust. To facilitate use at night or in low-light conditions, the scale surface of some steel tape measures is coated with a luminous substance that emits light in darkness, allowing the scale markings and numbers to be seen clearly. It is important to take care to protect this coating during use. In addition to measuring length, steel tape measures are also often used to determine the diameter of cylindrical components such as cylinders and end caps. Before making a measurement, it is necessary to select a steel tape measure with an appropriate measurement range based on the diameter of the component being measured. When measuring the outer circumference, a flat steel tape should be used. A steel tape measure in use must not have any defects that could affect its performance; the surface of the workpiece being measured as well as the working surface of the tape measure should be cleaned thoroughly. The usage method is to wrap the tape measure around the circumference of the radial cross-section of the workpiece being measured, pull the tape measure taut with both hands, slide it back and forth along the surface of the workpiece several times, and then take a reading. The method for reading a steel tape measure is the overlapping method: when the tape is wrapped around the object to be measured, the ends of the tape overlap. The value indicated by the markings at the point where the tape ends overlap is the measurement result, which represents the outer circumference of the cylindrical object being measured. By dividing the measured value of the outer circumference by π, it is possible to convert it into the outer diameter value of the cylindrical workpiece being measured (such as a cylinder or a hood). If using a steel tape measure to measure small-diameter cylindrical workpieces, the measurement can be carried out directly ； When measuring large-diameter cylindrical workpieces and the operation is to be carried out by a single person, it is necessary to use magnets to press the tape against the workpiece (this is only applicable when the workpiece is made of a ferromagnetic material) in order to conduct the measurement, or two people must work together to do it. When using a steel tape measure, special attention should be paid to whether it has passed calibration; there have been many cases of problems arising from the use of low-quality tape measures with large errors. Secondly, when measuring the length of the same workpiece multiple times, the same steel tape measure must be used.