Stainless steel on stainless steel is notorious: stems seize in stem nuts, threads lock up, and seats or wedges tear when they slide under load. Once it starts, galling usually gets worse every cycle. Prevention means pairing dissimilar or hardfaced materials, keeping threads lubricated, and controlling seating loads, which is why valve trim specs pay so much attention to hardness differences.
Stem nut is galled to the stem, it took both of us on the wheel to move it and now it's chewed.
A dab of nickel anti-seize on stainless stem threads and stud bolts prevents most galling for the cost of a few seconds.
Also heard as
- galled
- galled up
Related terms
Trim
The replaceable internal parts of a valve that touch the process fluid, such as seat, disc or plug, stem and cage.
Stem
The rod that carries motion from the handwheel, lever or actuator through the bonnet to the closure member.
Seat
The surface inside a valve that the closure member presses against to stop flow.
Torque out
For a motor-operated valve to stop on its torque switch because it met more resistance than expected.