Water Hammer & Thermal Expansion Threat
In the run-up to the heating season, start-up dangers are a serious problem for many heating systems using steam as a source of heat, largely due to the fact that they have been lying dormant over the summer.
John Pickering, an expert in safe procedures for steam distribution systems at Spirax Sarco, warns boilerhouse operators that they must therefore be wary of the threat posed by water hammer and thermal pipework expansion when restarting their boilers this autumn.
With the heating season just around the corner, John explains that new operators of steam systems may underestimate the care and time required for steam system start-ups following an extended period of shut down.
“After a long, dormant period over the summer, both water hammer and thermal expansion pose a real threat to steam pipework when systems are fired back up again,” says John.
He continues: “Water hammer may be viewed largely as an acoustic problem, but the consequences can be much worse. The entry of steam into a pipe that already has a build-up of water can lead to condensation, which results in a vacuum forming. This will mean water rushes through the pipe, and its momentum is capable of causing extensive mechanical damage to pipework and fittings.”
According to John, thermal expansion is an equally serious issue. “Expansion occurs when the steam system is heated too quickly, and the pipework quite literally buckles under the pressure of the steam as it hits the weakest point in the distribution line. I have seen instances where pipework has bent and expansion bellows have become twisted and distorted – all of which could have been avoided if the correct procedures had been followed.”
Spirax Sarco recommends an 11-point procedure for warming pipework from cold, which is outlined by the National Industrial Fuel Efficiency Service (NIFES) in the organisation’s handbook.
“The Boiler Operator’s Handbook outlines a clear procedure that includes checks to the boiler and valves and that, crucially, stresses the need for the gradual warming of the system pipework to increase the pressure and purge it of air and condensate,” John says. “I cannot stress enough how important it is to open the steam valve incrementally.”
Steam valves should be opened very slowly. If there is any indication of water hammer in the surrounding pipes, the steam isolating valve should be shut immediately and kept closed until the pipes have been drained. The start-up procedures for steam pipework are complex and require an experienced operator. Those with any doubts over the correct procedure to follow should call an expert.