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Max. allowable pressure
2

Max. allowable pressure

Max. allowable pressure

(OP)
(1) Which standard use to figure the data for Maximum allowable pressure and relevant temperature? Standard ANSI/ASME B31.3 or ANSI B16.5?
(2) I found different data of same piping material for Maximum allowable pressure and relevant temperature? Is that possible due to it refer to different version (year) of standard ANSI/ASME B31.3 or ANSI B16.5? Both plant were built in different year.
Thanks.

RE: Max. allowable pressure

2
ASME B16.5 provides the maximum allowable working pressures for flanges.  The ratings that apply to a particular plant are the ratings that were in place at the time the plant was built based on the edition of B16.5 in use at the time.  Different plants can therefore have different flange ratings if they were built at different times.

The flange rating in ASME B16.5 does not tell us what the maximum allowable rating for the pipe that was used might be.  While it is common practice to ensure that the pipe is at least as strong as the flanges, this is not universal.  You would have to calculate the rating of the pipe using ASME B31.3.  Again, this changes from time to time so the rating would be based on the edition in use at the time the plant was built.

B16.5 is used for flanges, B31.3 is used for the pipe.

RE: Max. allowable pressure

(OP)
Thanks Rneill, I have another question. If the table shows T=100, Max.P=6.91;T=150,Max. P=6.26. If T=120, shall I do the interpolation to get Max. Pressure or I just take the nearby value T=150, Max. P=6.26?

RE: Max. allowable pressure

You can go for interpolation (taking the more penalizing upper value adds an extra safety factor not required)

RE: Max. allowable pressure

As mentioned by ione, you would normally interpolate to get flange ratings at intermediate temperatures.  However, you are also free to use the nearby value if you want to since this will be less than the interpolated value.

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