Electricity + Control March 2019

PLANT MAINTENANCE, TEST + MEASUREMENT

Inspecting steam systems to maintain optimum efficiencies

A Fluke application note – Information supplied by Comtest

Steam is used in wide-ranging applications in industry to heat raw materials, for ex- ample, and to treat semi-finished products. It is also a power source for equipment as well as for building heat and electricity generation. But steam is not free: it comes at a cost of millions of rands annually when the fuel feed to boilers and associated factors involved in generating the steam are taken into account.

Take Note! Generally speaking, steam is a highly efficient way to transport heat energy. Sight, sound and tem- perature are the main factors to be considered in checking steam trap performance.

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G enerally speaking, steam is a highly ef- ficient way to transport heat energy be- cause the amount of latent heat required to produce steam from water is quite large and steam is easily moved in pressurised piping sys- tems that can deliver that energy at manageable costs. When steam gets to its point of use and gives up its latent heat to the environment or to a process, it condenses into water, which can be returned to the boiler for re-conversion to steam. Several condition-monitoring technologies are useful for monitoring steam systems to determine how well they are functioning. Among those tech- nologies is infrared (IR) thermography, in which technicians use thermal imagers to capture two-di- mensional images of the surface temperatures of equipment and structures. Thermal images of steam systems reveal the comparative temperatures of system components and in that way indicate how effectively and effi- ciently steam system components are operating. What to check Using a combination of ultrasound and thermal in- spections significantly increases the detection rate of problems in steam systems. All steam traps and steam transmission lines should be checked, including any underground lines. Heat exchang- ers, boilers and steam-using equipment should be scanned. Every part of the steam system should be examined with a thermal imager.

densate and air from the system. During inspec- tions, both thermal and ultrasonic testing should be used to identify failed steam traps and whether they have failed open or closed. In general, if a thermal image shows a high inlet temperature and a low outlet temperature (< 100°C) this indicates that the trap is functioning correctly. If the inlet temperature is significantly lower than the system temperature, steam is not getting to the trap. This usually indicates an up- stream problem – a closed valve, pipe blockage, or similar. If the inlet and outlet temperatures are the same, the trap probably has failed open and is ‘blowing steam’ into the condensate line. This keeps the system operating but with significant energy loss. Low inlet and outlet temperatures in- dicate that the trap has failed closed and conden- sate is filling the trap and the inlet line. The thermal imager can also be used while the steamsystem is operating to scan specific elements. • Steam transmission lines should be scanned for blockages, including closed valves, and un- derground steam lines for leaks. • Heat exchangers should be checked for block- ages. • Boilers should be checked, especially their re- fractories and insulation. • Steam-using equipment should be checked for any anomalies. • Recent repairs should also be assessed to con- firm their effectiveness.

Thermal images of steam systems reveal the comparative temperatures of system components to indicate how effectively they are operating.

What to look for Steam traps are valves designed to remove con-

A regular inspection route that includes all key steam-system components in the facility, should

32 Electricity + Control

MARCH 2019