17-4 PH material for actuator valve keys 1

[ProcEng2]

One of our vendors is selecting 17-4 ph cond. 1150 material for a valve actuator key. This material strength of 140 ksi min, seems to border on being too strong in that brittle fracture may be a consideration or fatigue.

My experience is that the high strength materials sacrifice toughness.

This is not a corrosive environment, so corrosion resistance is not a concern. The key material strength is being chosen strictly for strength to provide sufficient margin to account for increased torque as time goes on.

Does anyone feel we would be better served with a 4140 material? Keeping in mind, I have no real feel for what impact loads, if any, are transmitted through a motor operated valve actuator to the key.

 

[unclesyd]

We use 17/4 H1125 for keys on all our valves requiring same. This includes both ball and plug valves to 12". We also use 17/4 H1125 for the the stems on the Ball valves and use Nitronic 50 as stems on the plug valves, with a few exceptions where we use Ti stems due to process considerations. We went to 17/4 valve components due to failures of the OEM components leaving the valve inoperable. For our process the valves have to operate.

We use 17/4, Aquamet 17 or Aqualoy 17, for pump shafts. Nearly all our vertical turbine pump shafts under 12" have been changed to 17/4. While all the larger pumps have been changed to Aquamet 22, 22-13-5.

I have never seen any of above mentioned 17/4 PH components fail in a brittle manner. The only problem we have with 17/4 is in one part of our process we continually thermal cycle all the components and we have had some 17/4 parts that failed in a brittle manner. All of the failed parts had hardness ranges in the upper 40's where the original was in the mid 30's.

 

[ProcEng2]

Thanks for this:

"The only problem we have with 17/4 is in one part of our process we continually thermal cycle all the components and we have had some 17/4 parts that failed in a brittle manner. All of the failed parts had hardness ranges in the upper 40's where the original was in the mid 30's. "

This is what I suspected about 17-4 ph, it's brittle only at certain temperatures (like above 570 F or something). Since that's not our application, we should be OK.

Thanks, again.

 

[EdStainless]

The strength vs ductility properties for each class of alloys is slightly different. You need to look at the properties of each alloy.

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[ProcEng2]

Edstainless said:
"The strength vs ductility properties for each class of alloys is slightly different. You need to look at the properties of each alloy. "

PE:
Thanks. The Alloy is heat treated condition 1150 F of SA-564 Gr. 630.
There does seem to be a difference in strength between aged and double aged:

http://www.amcastle.com/Download/QG160F.pdf