Piping steam hammer

Steam hose leading to a steam hammer or jet pipe shall be securely attached to the hammer with an adequate length of at least V4-inch diameter chain or cable to prevent whipping in the event the joint at the hammer is broken. Air hammer hoses shall be provided with the same protection as required for steam lines. 

The cause of water and steam hammer is the same sudden deceleration of water in an enclosed system. In the examples cited above, the rapid and localized condensation of steam accelerates a slug of steam condensate upstream by producing a localized area of low downstream pressure. The high-velocity water slams into a piping elbow or an exchanger channel head and produces the clanging sound associated with water hammer. 

Equipment loads include dead weight, restrained thermal expansion and dynamic effect such as pressure transients, changes in momentum, water and steam hammer in the equipment and earthquake. They also may include the effect of the restraint of attached piping. The effect of such phenomena must be considered in the design check. 

I was told by an attendee at one of my seminars about the method used at his plant in Delhi to suppress steam hammer. A screen that looks like a pump suction filter is inserted between pipe flanges. As 1 have never used such a device myself and do not know how to calculate the required hole size or percent of open area of the screen, I have not included any further details in this text. My Indian colleague noted that this screen retrofit was quite effective in reducing steam hammer in this facility. 

Water hammer results from the collapse of this trapped steam. The localized sudden reduction in pressure caused by the collapse of the steam bubbles has a tendency to chip out pipe and tube interiors. Oxide layers that otherwise would resist further corrosion are removed, resulting in accelerated corrosion. 

To control differential shock, the condensate seal must be prevented from forming in a biphase system. Steam mains must be properly pitched, condensate lines must be sized and pitched correctly, and long vertical drops to traps must be back-vented. The length of lines to traps should be minimized, and pipes may have to be insulated to prevent water hammer. 

A fire, followed by an explosion at Huddersfield in 1900 was also caused by detonation of iron picrate (presumably Fe++). The iron picrate had been formed on the surface of steam pipes located in the Picric Acid drier shop. It ignited when a plumber, unaware of the fact, struck one of the pipes with a hammer. The flame spread along the pipe and set the drying Picric Acid on fire... 

Steam traps are automatic mechanisms that remove low heat-content air and condensate from the steam delivery system. The lack of steam traps or use of traps that fail to function properly leads to a gradual decline in heat-transfer efficiency, waterlogged heat exchangers, and water hammer (which may in turn result in ruptured pipes). When adequate maintenance of steam traps is neglected, this ultimately leads to a serious overall loss of operating efficiency. There are various types of steam traps, each designed for a specific function. Some common variations are discussed in the following sections. 

Instantaneous surges of water under pressure caused by sudden interruptions in water flow in a pipe or water system, producing a hammering sound and leading to metal stress and possible eventual failure. Water hammer can develop where a steam main is incorrectly pitched, has un-drained pockets or where steam flows up and meets draining condensate flowing down causing a temporary interruption in both flows. 

The major problem with steam distribution is condensate removal. If steam traps are working properly while significant steam loss stiU occurs, the c ause may be inadequate drainage in condensate discharge locations (CDLs). The consequence is condensate backing up in the system due to blocked traps and plugged drains. The water falls to the bottom of the pipe, which could cause water hammer and lower heat transfer efficiency. 

The design of the System 80+ Main Steam system adequately addresses dynamic loads caused by condensation-induced water hammer and has piping arrangement and drainage provisions to protect against water entrainment. These are described in CESSAR-DC, Sections 10.3.2.2D, M, N, and P. 

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