CORRECTIVE MAINTENANCE : BENDING OF VALVE STEM / SPINDLE 1

[GAL02]

Dear All, Good afternoon !
If any Plug spindle/ stem of valve (short length,1Ft approx.)is got detectable / Visual bend from head onwards
What is to be done to it to make it straight if material is SS316L (Urea Grade / stellated / Chrome plated)?

With regards

 

[gerhardl]

GAL02,

New valve! ... or at least new spindle and full check and certification of the complete valve if originally required.
Check routines for operation and limitations for stroke!

I actually cannot think of a single case where I would recommend a mechanical straightening (with or without heating) and be sure of structural strength and geometrical accuracy afterwards. At your own responsibility you might of course try fastening in both ends and correct with a jacked wooden block, possibly locally heated by a blowtorch. Check straightness by fastening and rotate in a turning lathe.

 

[MikeHalloran]

New valve, and hide all the hammers.


Mike Halloran
Pembroke Pines, FL, USA

 

[GAL02]

Dear all, Good morning!
Some of the times when plant is about to take startup action & such matter arises,
at such moment when you don't have any other option than to go for straighten up.
As Urea grade material takes 3 to 5 months to prepare and later 1 month for delivery during that period it is unwanted solution to go for.
If we go for force straighten up the spindle then it is chance of crack ta the head / weak portion & if we go for heat treatment it's Grain structure will get affect as well as chrome plating / hard facing of head will get damaged? what are the losses on the basis of macroscopic point of view?

With regards

 

[Danlap]

Dear GAL02,

Totally agree with MikeHalloran and gerhardl. Highly suggest to replace at least the spindle.
Been there done that, it will bend again in the near future. And if now the "TurnAround" is multi disciplines related, the next will be only this valve related.
Its structure already experiences plastic deformation especially at the bent area, straightening it (with or without heating) will not repair this.
Once the valve back in operation and after several strokes, the torque/tension will find its weakest spot which is "the already straightened use to be" bent area.

Re-engineered / re-fabricate the spindle from a forged bar with similar or stronger material e.g. Alloy 625, 17-4PH, or standard SS316 which will be hard facing afterwards. might do the trick.

But if you choose the path of straightening, hopefully it will survived.

Regards,
MR

All valves will last for years, except the ones that were poorly manufactured; are still wrongly operated and or were wrongly selected