Steam hammering is the sound that is heard as a pinging, rattling, or banging in a steam system under conditions of Start-up, shutdown, changing loads or even in few cases, steady state full load operation.
Causes of steam hammering
Steam hammering is the phenomenon which occurs in steam charging in the pipeline while there is a presence of condensate in the line. This is because of sudden drop in pressure of steam as it comes in contact of condensate.
This can also occur due to poor heating of steam network before the steam enters into the system. Piping network remains cool and as soon as the hot steam enters, condensation takes place and water gets accumulated in the lines forming a Slug. As the steam flow increases, steam carries the water with it and lot of momentum is created and it hammers the line loops with tremendous forces creating a lot of stress. Steam hammers can blow flange joints and can damage piping supports and even piping itself.
Poor condensate drainage in pipeline leads to this steam hammering. Where air filled traps are used, these eventually become depleted of their trapped air over a long period of time through absorption into the water. This can be cured by shutting off the supply, opening taps at the highest and lowest locations to drain the system and then closing the taps and re-opening the supply.
Effects of steam hammering
The effect of steam hammering can result in following:
- Cracking of steam traps and pressure gauges
- Break pipe welds and even rupture piping systems
- Bend internal system mechanism
- Causes valve failure
- Cause heat exchanger equipment tube failures
- Failure of pipe supports.
Prevention of steam hammering
Steam hammering condition exists in a steam system where condensate coexists with generated steam or flash steam. Typical examples include heat exchangers, tracer lines, steam mains, condensate return lines and sometimes, pump discharge lines.
A common example of steam hammer occurs during start-up or energizing of a steam system. If the steam line is energized too quickly without proper warm up time and condensate created during the start-up is not properly removed; steam hammer will be the result.
There are few design or system changes that can be implemented to prevent or eliminate steam hammering:
- Ensure correct steam and condensate design.
- Have documented SOP’s (standard operation procedures) for steam system start-ups and shut downs.
- Proper training for plant personnel.
- Have installation standards for steam components.
- Correct condensate connections of branch lines to the main condensate header and entry only from the top of the header.
- Use steam traps that are properly sized and appropriate for application.
- Use warm up vales as steam line isolation valves larger than 2 inch. Do not “crack open” large steam isolation valves.
- Check or repair the pipe insulation. It saves energy and reduces accumulation of condensate in the piping system