Determine continuous service rating
A small needle valve has a pressure rating of 3500 psi and a
temperature rating of 900 F but the manufacturer (who is no longer
around) doesn't indicate if this is a continuous service rating. What
testing must I do to assure myself the stated psi/temp will work in a
continuous 3500-psi, 900 F application?
What's the ASME/ANSI Standard I should buy to check this out?
Typically the maximum pressure listed is not coincident with the maximum
temperature listed and the working pressure rating at maximum
temperature is usually substantially less than at ambient; based on
reductions in the allowable stress values for the materials of
construction at temperature.
However, it is not clear from the
original post if the quoted rating was the coincident pressure
temperature rating at 900 F or not? Since it is quite typical for small
needle valves to have a cold working pressure rating of 6000 psig, it
is possible that the 3500 psig was the rated pressure at temperature.
Needle
valves are not normally made to an ASME or API standard. To the best
of my knowledge they are typically made to MSS SP-99 "Instrument Valves"
or MSS SP-105 "Instrument Valves for Code Applications". Keep in mind
that many needle valves are made to SP-99 (and not SP-105) even though
they are routinely used in Code applications and unfortunately, the
standard is rarely listed on the valve.
I looked at a couple of
needle valve catalogues and in one the 900 F rating was only 33% of the
cold rating (Anderson Greenwood) but in the other it was 83% of the cold
rating (Century) so not much consistency there.
With regards to
testing to determine the allowable working pressure of the valve, if you
wanted to use testing to determine the ratings basis for the valve, you
would want to review UG-101 of ASME Section VIII Div 1 "Proof Tests to
Establish Maximum Allowable Working Pressure".
Without some
traceability back to the original design/manufacturing standard, and
with the manufacturer no longer around, I would rather just replace the
needle valve since they are a very low cost item and replacement will be
cheaper than testing.
MORE NEWS