Establishing repair priorities based on safety, steam/energy loss and possible impact on production and quality is a sensible approach to a steam system management programme, says test and measurement tools supplier Comtest.
Water boils at 100 ºC making steam, which is routinely transmitted at high pressure, which is extremely hazardous, so any condition that poses a safety risk should take the highest repair priority. In many situations, the next most important kinds of problems to deal with are those that can affect production capabilities.
To check steam trap performance, sight, sound and temperature are the dominant techniques. Implementing a basic annual inspection of the steam traps and associated equipment with infrared inspections will likely reduce steam losses between 50% and 75%.
The cost to an operation that completely loses its steam system varies from industry to industry. Among the industries that use the most steam are chemicals, food and beverage processing and pharmaceuticals.
If the facility has performed no maintenance of steam traps for three to five years, expect 15% to 30% of the traps to have failed. Therefore, if there are 60 medium-sized traps on the system, losses from ‘blow by’ are estimated to be between R500 000 and R850 000 yearly.
Using a combination of ultrasound and thermal inspection significantly increases the detection rate of problems in steam systems. All steam traps and steam transmission lines, including any underground lines should be checked. In addition, heat exchangers, boilers and steam-consuming equipment should be scanned. In other words, every part of the steam system with a thermal imager should be examined.
The company insists that, when a problem is discovered using a thermal imager, the associated software is used to document the findings in a report, including a thermal image and a digital image of the equipment. It is the best way to communicate the problems found and to suggest repairs.
Comtest adds that steam traps are valves designed to remove condensate as well as air from the system. During inspections, both thermal and ultrasonic testing is used to identify failed steam traps, and whether they have failed to open or close. In general, if a thermal image shows a high inlet temperature and a low outlet temperature – less than 100 ºC – that indicates that the trap is functioning correctly.
If the inlet temperature is significantly less than the system temperature, steam is not getting to the trap. The company needs to look for an upstream problem – a closed valve, pipe blockage and so forth.
If both the inlet and outlet temperatures are the same, the trap probably has failed to open and is ‘blowing’ steam into the condensate line. This keeps the system operating but with significant energy loss. Low inlet and outlet temperatures indicate that the trap has failed closed and condensate is filling the trap and the inlet line.
Comtest suggests that a company can use the thermal imager to scan steam transmission lines for blockages and all steam-using equipment for any anomalies. This includes looking at closed valves, underground steam lines for leaks, heat exchangers for blockages, and boilers, especially their refractories and insulation.
Comtest puts forward that comvpanies must consider creating a regular inspection route that includes all key steam-system components in the facility, so that all traps are inspected at least yearly. Larger or more critical traps should be inspected more frequently, as the potential for loss is greater.
Comtest concludes that, over time, this process will help determine whether a hot or relatively cool spot is unusual or not and help to verify when repairs are successful.