The sudden contact of low-temperature water droplets on high temperature steel leads to what are commonly called thermal impingement stresses. These tensile stresses can be very, very high and lead to yielding of the steel; resulting in visible, local bulging of the pipe and/or cracking of the internal wall. Frequent incidences of this problem with associated failures are observed in thermal power plants; they often occur in Main Steam Bypass and Hot Reheat Bypass Power Piping or in attemporator sprays.
Good control logic and operator awareness is crucial to ensure that spray water doesn't build up when valves are closed, that sprays are not exceeding their proper flow range or that there is over-spraying into the steam.
Inspection techniques vary depending on access but may include Ultrasonic Testing (UT) and Remote Visual Inspection (RVI) by videoscope, as well as hardness testing of sensitive materials. Tetra prepares an Inspection Plan for O&M staff to follow to ensure that the condition of the relevant components is sufficiently monitored to mitigate risks.