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What does the meaning on flange pn16 meaning?

What if on hydrostatic pressure testing on water pipe and the pipe flange was marked on pn16 but running test with 25 bar water pressure, does it overload ? What does the meaning of pn16?

發表於 Posted on: 2016-10-04 20:09

Nara08
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What does the PN16 designation on a pipe flange mean?

For BS4504 Metric Flanges, the PN stands for Pressure Nominale and is followed by the Maximum Working Pressure for use from -10°C to 200°C. At lower temperature, the material would become brittle. At higher temperature, de-rating would be needed as the material would get soft. PN16 means it is rated for use up to 16 bars. At 300°C, that drops to 13 bars.

By industry standards such as the ASME Boiler and Pressure Vessel Code, in case of unforeseen circumstances and for aging, the recommendation is for a 4:1 safety factor for Maximum Working Pressure. Hence,

* Burst Pressure is when the assembly fails due to pressure.

* Working Pressure is the recommended maximum pressure to be exposed to during use. It should be less than 1/4 of the burst pressure. PN16 bursts at about 65 bars.

* Test Pressure is what an assembly is tested to for qualification. It is 1.5 times the maximum working pressure. 1.5 times of 16 bars is about 25 bars.

發表於 Posted on: 2016-10-05 2:22

LatentNightCrawler
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Thanks for your quick response !

Further question, a ductile iron pipe (K12) uses slip-on-flange method, which welding on both internal and external on flange (PN16) to pipe, assuming pipe is DN300, if PN16 flange cannot be over 65 bar pressure, how much hydrostatic pressure would that slip-on flange welding method could be taken ?

發表於 Posted on: 2016-10-07 15:26

Nara08
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DN300 = Pipe with 300mm nominal diameter. Actual OD is about 326mm.
K12 for DN300 = Having a wall thickness of about 9.6 mm.

Using the Barlow's pipe internal pressure calculation, the allowable internal pressure (Pi) for ductile iron pipe with 275 MPa yield is (2 x 275MPa x 9.6mm / 326mm), or 162 bars Pi.

From ANSI 31.1, when used with connections and fittings, there is a 25% reduction, resulting in 121 bars Pi.

Using a 4:1 safety factor and allowing for a 10 bar surge pressure (ref. ANSI/AWWA C150/A21.50,) the Working Pressure is (121/4-10) bars, or 20 bars.

Using the smaller of the 20 bars pipe and 16 bars flange, the maximum working pressure for the assembly would then be 16 bars. You should never go over the test pressure of 1.5 times of 16 bars, which is 25±1 bars.

PN designates only the Working Pressure, not the burst. The 65 bars is an implied burst when the manufacturer uses the recommended 4:1 safety factor.

發表於 Posted on: 2016-10-08 7:12

LatentNightCrawler
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