yamoffathoo
Mechanical
- Sep 19, 2008
- 87
A leaking control valve stem packing requires on-line sealant injection through the existing leak-off port at the lantern ring.
I calculated the maximum stuffing box pressure using thick shell formulae and area replacement methodology (for the injection hole) and got approx. 10,000 psig based on allowable stress for cast steel.
The graphite packing requires 6,000 psig to seal and this can be generated with only 10 ftlbs on each of two, high strength gland packing studs.
These studs could easily generate 4x my calculated maximum stress at their yield torque.
Why would the valve manufacturer install high strength studs with no stated limit on maximum torque?
Is failure not possible because the packing and sealant are non-Newtonian fluids and do not generate a hydraulic pressure?
I calculated the maximum stuffing box pressure using thick shell formulae and area replacement methodology (for the injection hole) and got approx. 10,000 psig based on allowable stress for cast steel.
The graphite packing requires 6,000 psig to seal and this can be generated with only 10 ftlbs on each of two, high strength gland packing studs.
These studs could easily generate 4x my calculated maximum stress at their yield torque.
Why would the valve manufacturer install high strength studs with no stated limit on maximum torque?
Is failure not possible because the packing and sealant are non-Newtonian fluids and do not generate a hydraulic pressure?
