We have a high temp valve that was 1

[Hush]

We have a high temp valve that was returned on warranty. Upon inspection the gate, stem, gate guides were all warped. Customer claims the operating temperature was 350 F but I suspect considerably higher. My question what temperature do you have to reach to discolor alloy steel (4130 Q&T) blue.

 

[CdotS]

What is the real problem? I assume warping, rather than the change in color is the real problem.

Warping can be due to any reasons -(1) residual stress from processing which got relieved in service, (2)mechanical overload ether during installation or service, etc.

Was it a welded structure?

Measure hardness of the area where it has discolored. If there is huge difference between the supplied valve hardness and warped material, it might have tempered more. Generally 4130 is suplied around 35-45HRC (25 for oil and gas applications due to SCC). See the microstrcure change, if any.

Refer to a heat treatment book where color change with temperature could be found. If everything fails, call your materials vendor for help.

I am sorry I can't think of any more.

 

[arunmrao]

Bluing is a condition which cannot go unnoticed duringthe valve assembly stage. This might have occurred during service when it was put to disabuse. Warping and bluing can have resulted due to stress relief in 4130 grade steel or due to wrong fitment or assembly of valve.Alternately if it is a manually operated valve it could probably have been over stressed during operation,or some foreign matter could have got lodged in the guides which might have caused the seizure resulting in bluing.

 

[Hush]

This occured in service obviously due to external application of heat. What I need to know is what temperature is required to turn steel blue. I'm estimating at least 1050F to warp the parts and I'm hoping the dicoloration backs me up.

 

[Kenneth]

Under "Tempering" my Machinery's Handbook has a table for "Temperatures as Indicated by the Color of Plain Carbon Steel." Note the "Plain Carbon" (as opposed to "Alloy&quot in the title and a further warning that because ..."colors are affected to some extent by the composition of the metal, the method" (using color to determine tempering temperature) "is not desirable." That having been said, the pertinent part of the table shows:

Light Purple: 530° F
Full Purple: 540° F
Dark Purple: 550° F
Full Blue: 560° F
Dark Blue: 570° F
Light Blue: 640° F

If you need it, you might borrow a copy of Machinery's Handbook to see the rest of the table.

If you're the manufacturer, and have some parent material, you may wish to heat some of it (immersed in the media used in the value?) at increasing temperatures to see what temperature is required to duplicate the discoloration...

 

[Hush]

Thanks Kenneth, I never even thought of going to the bible, much appreciated.