How do you survey and map the large-diameter flanges at the user’s site?

The following methods are commonly used to measure the hole spacing of large-diameter flanges at the measurement site: 1. **Ruler and caliper**: For valve flanges that can be accessed, a long ruler and caliper can be used to measure the diagonal distance or the distance between the centers of adjacent holes. 2. **Template method**: Create a template that matches the flange hole pattern and spacing, align it with the flange holes for comparison, and verify the hole spacing. 3. **Laser ranging**: Measurements are taken using a laser rangefinder. This method requires a high level of skill from the operator, as precise alignment with the center of the hole is necessary. 4. **Optical/digital measuring instruments**: Such as optical projectors or measuring devices equipped with digital cameras, which enable contactless measurement and allow for accurate data acquisition through image processing. 5. **Portable CMM (Coordinate Measuring Machine)**: A high-precision measurement tool suitable for on-site measurement of large parts. 6. **3D Scanning**: 3D laser scanners can quickly scan the entire flange and create its 3D model; software analysis then enables the accurate determination of the hole spacing. In practice, factors such as the position of the flange, whether it is removable, and the required precision must be considered when selecting an appropriate method. In cases where direct measurement is difficult, professional equipment or technicians may be required. .

Measure the inner diameter of the flange; the resulting value is roughly equal to DN. In addition, the valve body also has markings indicating relevant dimensions, pressure, material, etc.

Valves installed on pipes cannot measure the inner diameter, but generally measuring the bolts is sufficient. It’s mainly the hole spacing of the large flange.

Use a rope to measure: wrap it around the entire bolt area, then wrap it around each screw individually, count the number of bolts, and then go back to the CAD file. There you’ll have a large circle (the diameter of the bolt hole’s pitch circle plus the bolt diameter), with all the bolts’ outer circles being tangent to this circle.

This post was last edited by vszxp on 2024-1-8 at 22:16. 1. First, check the valve nameplate markings to determine the valve model, pressure (PN/CLASS/K), and diameter (DN/NPS). 2. Measure the bolt specifications, the number of mounting bolts, and the thickness of the flange. 3. Use the measured dimensions to draw a diagram for verification in accordance with relevant flange standards

Having conducted on-site surveys frequently, I have a few insights: 1. Make a preliminary assessment based on the markings on the valve bodies of other valves in the pipeline where the flange to be measured is located, as well as the engravings on the outer surfaces of the connecting flanges； 2. Use a thin rope to measure the circumference of the pipe and the flange, in order to preliminarily determine the nominal diameter of the pipe and the outer diameter of the flange ； Then, use a tape measure and calipers to measure the flange thickness, bolt diameter, and the distance from the outer surface of the bolt to the edge of the flange, in order to determine the center distance between the bolt holes; also count the number of bolts ； 3. Return the measurement results to the mapping tool and review them alongside the first set of results.

First, check the valve’s markings to determine the nominal diameter and nominal pressure, then refer to the relevant standards; HG/T 20592 is usually sufficient for this purpose. If it’s a device flange, then the standards specific to device flanges should be consulted. Once the standards are clear, all the dimensional information can be obtained. If no information on the valve is available, it’s possible to measure the more easily accessible dimensions and then compare them with the data in the standard tables to determine the model