What is the background for these valve threshold 3

[Danlap]

Dear All,

There are so many information often taken for granted. Up to this day, I am still puzzled with this two numbers. Appreciate if someone know the background or can elaborate where these numbers were coming from:
a.ASME B16.34, and related standards.
Flange rating limited to 538^oC (1000°F).
So many comments e.g. “not to be use above 538^oC”, “flanged-end valves terminate at 538°C”,” At temperatures above 538°C, use only if the material is heat treated…”.
What is the risk if we use this flange (material) above 538^oC? Why 1000°F? is it just a nice number for Fahrenheit using countries?
In refineries, we are using more exotic material for more higher temperature due to process demands, and this numbers is often the limiting factor from standard point of view.
If I check the 1981 edition, it is already stipulate 1000°F as maximum threshold, and it seems even with more advance technology and manufacturing capability for the last 37 years, I am wondering whether this number is still valid


b.Industrial recommended practice of valve travel speed shall not faster than 4s/in. valve size, or sometimes 6s/in. valve size. To mitigate the risk of flow surge, etc.
How did valve designer end up with this number? Assumed fluid is water or something else? What sort of differential pressure and flow? Etc.

Thank you in advance for the clarification, my excuse if someone smiling or laughing at this question.

Kind regards,
MR

https://nosuchvalve.com

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

http://www.eng-tips.com/faqs.cfm?&rat1=2&fid=376

 

[gerhardl]

Interesting!

Speculations only:
Perhaps an old limit set because most strength/temperature scales are ending, uncertain (not much measured or with widely variable results?) and/or much weaker at this point. Actually one can observe that steel and iron materials have a marked brake in the strength curve starting well before 1000 deg F. Why was not a lower limit set? And I cannot see a reason for a somewhat larger limit

A standard is valid in the way that is must be followed until the issuer is change the details. Perhaps a revision is timely on reasons given by you.

On valve opening/closing speed: Some limit should be set and be incorporated in a standard. Most such limits are based on common sense, and most often limited flow speed to avoid water hammer. The standards limit are probably referring to 'best practice' or tests based on most common fluid (water?) and most common 'normal' speed limits?