Nearly 10% of boilers and pressure vessels inspected in the second quarter of 2008 were slapped with violations, which means that the violations put workers and equipment in danger, according to a quarterly report released by the National Board of Boiler and Pressure Vessel Inspectors.
The "Report of Violation Findings" indicated problem areas and trends related to boiler and pressure vessel operation, installation, maintenance, and repair. The highest percentage of violations was detected in boiler controls, followed by boiler piping and pressure-relieving devices. A portion of the violations can be attributed to lack of knowledge and training on Section 1 of the American Society of Mechanical Engineers’ (ASME’s) International Boiler and Pressure Vessel Code.
Properly functioning control or safety devices are absolutely essential for any boiler. The only way you can be confident they will work when called upon to do so is to regularly perform required maintenance and testing while adhering to ASME code requirements. Here’s a quick reminder of some of the key requirement updates.
Code Updates for Water Level Indicators
ASME has specific minimum requirements for direct (visual) and indirect (instrument) water-level indicators, which must be installed on every power boiler manufactured in accordance with the code (Figure 2).
2. Easy boiler water level monitoring. The DuraStar Flat glass gauge illuminator—approved for use in Class 1, Div 1, Group B, C, and D environments—uses LEDs for high-intensity imaging of the water line. Courtesy: Clark-Reliance
A gauge glass is the only form of direct water level indicator found on steam boilers. The various types are:
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Tubular glass (for pressures up to 250 psig), which displays the water level meniscus.
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Prismatic (reflex) glass (for pressures up to 350 psig), which displays black color up to the water level and white above the level.
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Flat glass or transparent (for pressures up to 2,000 psig), which displays a clear color for both the water below and steam above the meniscus line.
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Ported glass gauges (for pressures up to 3,000 psig), which display green color for water and red color for steam by using the principle of light refraction.
There are multiple code requirements for gauge glasses to ensure the safety of boiler operation and plant workers. For example, the code states that all boilers operated up to 400 psig must have at least one direct-reading water gauge glass in service at all times. This allows the operator to view the actual water level with no interface mechanisms or sensors, which could distort the display of actual water level.
The code also requires that tubular and transparent gauge glasses with multiple sections will overlap by a minimum of 1 inch to prevent the loss of visibility of the actual water level. This is especially relevant for flat glass gauges so the steam and water level interface meniscus can always be seen.
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