Opening Steam valves too quickly when the pipes are cold can lead to a phenomenon called ‘Water Hammer’. Water hammer can damage the steam system by erosion and corrosion leading to leakages.

During cold start up, the rate of condensation in the pipework is higher. As a result if the steam valve is opened quicly a large quantity of condensate will be carried by the steam at high velocities, which can lead to water hammer.

Waterhammer is the noise caused by slugs of condensate colliding at high velocity into pipework fittings, plant, and equipment. This has a number of implications:

• Because the condensate velocity is higher than normal, the dissipation of kinetic energy is higher than would normally be expected.
• Water is dense and incompressible, so the 'cushioning' effect experienced when gases encounter obstructions is absent.
• The energy in the water is dissipated against the obstructions in the piping system such as valves and fittings

Indications of waterhammer include a banging noise, and perhaps movement of the pipe. In severe cases, waterhammer may fracture pipeline equipment with almost explosive effect, with consequent loss of live steam at the fracture, leading to an extremely hazardous situation. Additionally, reduced leakage automatically leads to reduced steam consumption and thus a lower fuel bill.

Thus after cold start the steam valves should be opened gradually to avoid such a condition. Good engineering design, installation and maintenance will avoid waterhammer; this is far better practice than attempting to contain it by choice of materials and pressure ratings of equipment.