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Pressure ratings of carbon pipes, tables and some irony? 3

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IJR

Structural
Dec 23, 2000
774
Pals

Where can I find pressure ratings of carbon steel pipes, both seamless and welded?

I found from the net some tables. Strange thing from these tables is that whereas some plastic pipes show pressure , carbon steel pipes eg ASTM 53 and 106B show relatively lesser capacities. Is this possible? I mean you easily find a small diameter pipe rated as PN16 (metric= 160MPa= 23ksi capacity) but you have trouble finding a similar rating for even seamless carbon steel pipe.

I will appreciate a well shared knowledge and references. Metric or US customary units are both fine.

respects
ijr
 
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IJR

Equations for calculating required wall thicknesses for pipe (pressure design) vary from one Code (or Standard) to another. The allowable stresses tables will also vary depending upon the "built-in" factor of safety associated with the various Codes. The best thing to do is to make a spreadsheet that allows you to include a table of allowable stresses AT TEMPERATURE for each material from the Code and includes various equations from the Codes that you want to address. Remember that you must allow EXTRA WALL thickness for mill tolerance (seamless pipe), corrosion, erosion, etc.

I use a suite of spreadsheets called "Piping Office" (by Ben Nottingham) that covers the ASME B31 Codes (Ben keeps these updated as Codes change). Be careful of the tables that you can find in various sources. Some of the older publications include pressure-temperature tables for pipe that were calculated BEFORE changes were made to the Code allowable stresses and of course these tables will no longer be accurate.

We are currently looking at changing over to a single wall thickness equation to cover all the ASME Codes. But again, since there are differences in the allowable stresses from one Code to another, the required wall thickness at temperature can differ.

Regards, John
 
Since hoop stress is twice as high as longitudinal stress, hoop stress formula is the one that is used to calculate wall thicknesses or pressures. Basic formula for Hoop stress ( s=pD/2t) s-working stress;p-pressure;D-diameter(inside or outside with no appreciable error; t-thicness; ASME codes has variants of this basic formula based on end conditions of the piping.
Lesser flow capacities of steel pipes in comparison to plastic tubing is probably due to the higher roughness values of the steel piping.
 
I do no business in Europe and am not knowledgeable in regard to European components or design codes, so the PN (pressure number) designation system is foreign to me. I hope someone who IS knowledgeable about this system will respond to this thread.

Doing a basic web search on the topic out of curiosity, I've seen occasional references to PN16 having something to do with 160 MPa as repeated by the OP, but the source of this information is unclear. What is certain is that this is NOT an internal pressure rating for PN16 piping components nor is it a safe allowable stress for the materials used to make these components.

What what I've seen elsewhere on the web, PN16 is a flange or valve/fitting CLASS rather than a pressure rating per se. The flange class is very roughly equivalent to the pressure rating of the flanges in BAR, not 10s of MPa. There is no difficulty in finding either A53 or A106 pipe schedules serving pressures in this range.

As to tables for the internal pressure ratings of piping: the reason you rarely find these for metallic piping is that they are DANGEROUS in the wrong hands. The pressure rating of a piping system is not determined purely by the pipe and is seldom limited by the pipe itself: it is determined by the pipe, fittings and other pressure-retaining components, AND by the joining method, in accordance with a design code.

In regard to the maximum allowable working pressure of the pipe itself, chicopee is correct in that the minimum required wall thickness is calculated based on the hoop stress versus a safe allowable stress for the material in question at the service temperature. Manufacturing tolerances, thickness reduction due to threating etc., joint efficiencies for welded seams, brittleness, and corrosion allowance are also taken into account in these calculations.
 
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