1. Quenching Too Close to Saturation & Blind Temperature Flooding
Attempting to control steam temperature within 5°C (10°F) of saturation (T_out ≈ T_sat) causes unevaporated water droplets to coat the downstream RTD thermowell. The liquid film blinds the sensor, which reads cold and signals the spray valve to shut, then dries, reads hot, and floods the line. The accumulated water creates devastating thermal shock and explosive water hammer. Always maintain at least 10°C to 15°C (20°F to 25°F) of superheat.

2. Thermal Fatigue Cracking & Pipe Wall Rupture (No Thermal Sleeve)
Omitting an internal thermal sleeve liner inside the desuperheater spool piece is a fatal error. When 120°C (250°F) boiler feedwater droplets impinge directly on a 400°C+ (750°F) chrome-moly pipe wall, the cyclic thermal quench induces severe circumferential thermal fatigue cracks that propagate through the wall, causing catastrophic high-pressure steam rupture.

3. Droplet Impingement on First Pipe Elbow (< 20 Pipe Diameters)
Liquid water droplets take time to vaporize in high-speed steam. Installing a 90-degree pipe elbow closer than 20 to 30 pipe diameters downstream of the spray nozzle results in centrifugal droplet throw-out. Water droplets crash into the elbow extrados at 35 m/s (115 ft/s), eroding the pipe wall from the inside and causing pinhole leaks within months.

4. Wide Turndown Control Valve Hunting & Seat Wiredrawing
Steam boilers frequently operate between 10% and 100% load, requiring 10:1 or 20:1 turndown on spray water. Using a single standard globe valve results in operation at 2% to 4% valve stroke during low load. High differential pressure (ΔP > 15 bar) causes severe cavitation and seat wiredrawing, destroying the valve plug and causing persistent leakage into the steam pipe when the unit is idling.

5. Spray Water Mineral Deposition on Steam Turbine Blades
Spray water mixes directly and permanently into the steam header. Using untreated plant service water, softened water, or unpolished condensate introduces dissolved solids (silica, sodium, chlorides). As droplets vaporize, minerals precipitate as microscopic glass crystals that travel downstream, baking onto high-pressure steam turbine blades, destroying aerodynamic efficiency, and inducing rotor unbalance. Only high-purity demineralized boiler feedwater is permitted.