4 replies to this topic

[Carlos Massucci]

Hello

I'm doing a pressure drop calculation and I cant find the roughness for used (or old) commercial steel.
I need the old data because the factory is old.

Does anyone know a good souce?

And I need references. So internet isn´t so trustful.

Thank all.

[Art Montemayor]

Carlos:

Since we don’t know the scope of work under which you are doing your pressure drop calculations, it is rather difficult to recommend any one pipe roughness we believe would “fit the bill” – or be appropriate for what you are doing.

Although you don’t state it outright, what we are discussing here is the actual, existing, absolute pipe roughness of the internal surface of a pipe. The reported measurements for pipe roughness in such acknowledged and recognized expert publications such as Crane’s Tech Paper #410 state the following values for absolute roughness (in feet):

Drawn tubing = 0.000005
Commercial Carbon steel = 0.00015
Asphalted Cast Iron = 0.0004
Galvanized Iron = 0.0005
Cast Iron = 0.00085
Concrete = 0.001 to 0.01

Crane does not specify the age or condition of the materials. I have always assumed the above values are for NEW material. However, Crane (and the ASME report by L.F. Moody, where this data originated) is about as good a reference as you can get.

Please be aware that the above values represent a “best effort” in measuring representative samples and the measurements are random and represent an “average”. The measurements are also subject to an unreported error (which is expected). I have always used the above values with a 25% contingency added to them. In other words, I multiply them by 1.25. And that is for NEW material. For older, rusted, worn, eroded, or contaminated material I always add another contingency – depending on the circumstances, the scope of work, and the need for being conservative in design.

No one in his/her right mind expects you to be accurate in estimating the absolute roughness existing inside a pipe that no one can actually see – or accurately measure. The actual, existing absolute roughness of any pipe IS and ALWAYS WILL BE an estimate based on the engineer’s experience and knowledge of the process in question. That’s as much as anyone can hope for. Fortunately, real-life calculations and applications prove the method to be acceptable within good engineering judgment – as long as the calculations take into consideration the application of the results and the need (or lack of need) to be conservative.

[ankur2061]

Carlos,

Look in section 6.1 of Norsok P-001 edition 5. The free download link is:

http://www.standard....er.exe?id=13264

The value given for carbon steel (corroded) is 0.5 mm. Seems fairly conservative but it is from a respected reference.

Regards,
Ankur.

[JoeWong]

It really subject to corrosivity of fluid, type of material, maintenance activitity, life of the pipe, etc.

Is this a real plant ? You may consider to re-establish roughness value from actual flow condition (if you can).

[sheiko]

See attachment

Attached Files

•  roughness.xls   37.5KB   174 downloads