absolute roughness for 56 inch diameter ASTM A106 pipe used for natural gas pipeline

[A. H.]

I`m trying to find out the pipe friction coefficient for 56 inch ASTM A106 pipe used for natural gas pipeline. I need the absolute roughness of such pipe (an old pipe used more than 3 years). Can any one help me in providing this info? Also it is appreciated if you can give me external link on internet?
addit. Info. : absolute pressure in this line is between 80.4 bar at inlet to 58.1 bar at outlet at maximum flow rate. temperature is :maximum 48 C at inlet to 32 c at outlet. length = 80 km= 80000 m
have no idea about the cleanliness on inside the pipe.

 

[georgeverghese]

To be able to help you, pls tell us the following:

a) What does the internal surface of the pipe currently look like - rough, somewhat clean, or clean

b) Is this pipeline in natural gas service with water dewpoint temp above the minimum ambient soil temp, or is the water dewpoint temp below? Pls note this water dewpoint temp must be estimated at the corresponding max operating pipeline packing pressure at no flow conditions, not at normal operating pressure. This will tell us if liquid water can condense in this pipeline. This also must take into account the max water content in this gas if your company permits short term export of water wet gas for some operating emergencies.

c) How long is this line and what is a rough estimate of current pressure drop through the whole line at max flow?

 

[A. H.]

Addit. Info. : absolute pressure in this line is between 80.4 bar at inlet to 58.1 bar at outlet at maximum flow rate. temperature is :maximum 48 C at inlet to 32 c at outlet. length = 80 km= 80000 m
have no idea about the cleanliness on inside the pipe.

 

[georgeverghese]

Reponse to (b) is critical. In relation to (b), also tell us if there is an established program for corrosion inhibitor injection and / or routine operational pipeline pigging to address short term water wet gas export (since this is a carbon steel line) or to clear out debris /solids that may have accumulated in the line.

 

[LittleInch]

There are some good past discussions on this here

http://www.eng-tips.com/viewthread.cfm?qid=409077

and

http://www.eng-tips.com/viewthread.cfm?qid=322259

also

http://www.eng-tips.com/viewthread.cfm?qid=418278

is similar to your question.

A pretty universal "basic" default number used for pipeline design has been 46 micron which is a metric version of 1.8 x 10_3 inches.

A number of people now take a "new" pipe as around 20 - 25 micron.

Internally coated (which a lot of gas transmission lines are) are about 5 micron.

If your line is existing and you have good and accurate operational data for a few different flowrates, then you should be able to "calibrate" your analysis and determine the roughness factor as it is an easy number to vary to get the analysis to match reality. Of course this can mask the inherent inaccuracies of the analysis so don't get too exited, but so long as your roughness does go lower than 20 or more than 150 then you're in good shape.

If you just want a number to use, then use 46 micron and no one will blame you. Do some sensitivities around this down to 25 and up to 70 and see what impact it has.

There is no definitive answer or reliable reference AFAIK. I've been looking for 20 years and never found it, so if you do please let us know.

If the line is heavily corroded or has deposits which reduce the diameter, this will throw all your calculations into chaos.


Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[georgeverghese]

Answers to (b) will tell you if you should use a roughness value greater than 0.046mm. Higher values will be the case when water can condense.

Run a pipeline hydraulics simulation with current flow / terminal pressure data to see what friction factors currently apply. That will also give you some indication of how much higher it will be in the future.

 

[BigInch]

0.0018in is a conservative pipeline design value used to account for future needs when the system is 10-20 years old.

What you are likely to see depends as much on where the pipe is located and its service conditions as it is old, perhaps more. Sometimes even better than new pipe values will be found in old pipe if it is a dry gas transmission line far away from the gathering systems. Close to gathering systems it can be far worse than on clean gas transmission pipelines far away from gathering systems. Gathering pipelines with warm water and CO2 or H2S can go totally bad in a few years.

Without specific information on pipe condition, I use,
0.02mm new steel pipe, ranging to
0.05mm for old pipe (10-20 years)


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