Why is PN25 used instead of PN16 when the temperature and pressure of liquefied hydrocarbons are not high? Where is this specified?
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Why, when the temperature and pressure of liquefied hydrocarbon media (butadiene) are not high, are pipes designed to be PN25 instead of PN16? Where is this specified?
This is probably due to the fact that when liquefied hydrocarbons are transported through pipelines, they tend to vaporize locally; this vaporization process absorbs a large amount of heat, which causes any moisture present in the medium to freeze into ice. Smaller pipelines are prone to ice blockages, while larger pipelines are less susceptible to such issues. Additionally, larger pipelines can absorb and dissipate heat more easily, making it less likely for there to be sudden changes in local temperature. Personal opinion; not intended as an authoritative reference.
With years of experience in production sites, I have never seen hazardous chemical pipelines use PN16; the minimum standard is always PN25； PN16 is only used for media such as process water, circulating water, and compressed air. Experts in design, please share your opinions.
Consider the pressure under extreme conditions; moreover, choosing a pressure rating one level higher ensures greater safety.
At least, a material that can withstand the vapor pressure at 40 degrees should be selected
The previous version of the petrochemical regulations required that the pressure rating for liquefied hydrocarbons be no less than 2.0 MPa; this requirement was removed in the 2018 version. Butadiene is an extremely hazardous medium. According to GB50316, for Class A1 fluids, in addition to the use of weld lip gaskets, a margin of 25% or more should be reserved when selecting the flange nominal pressure, which shall not be lower than 2.0 MPa.