Pipeline Hydraulics Roughness Benchmarking 1

[Sawsan311]

Dear All,

I would like to inquire on the pipeline roughness adjustments for existing pipeline (for example, water), as part of the hydraulic study, we acknowledge that the pipeline roughness has increased due to scaling and possible deposition of corrosion products, this would impact the calculated pressure drops, therefore:

- For the adequacy check of existing pipeline system, can we tune the roughness factor based on actual field data, would 0.6 mm roughness be reasonable for carbon steel pipeline.
- Is there any rule of thumb (other than the old piping roughness of 10 times new carbon steel of 0.0457 mm). Do pipeline get treated like piping or they are seamless and hence the roughness impact is not accurately credible.
- If you are designing a new pipeline network, and the governing case is 20 years down the road, would you account for a higher roughness in this case?

Appreciate your views on this subject.

regards,

 

[shvet]

- Is there any rule of thumb (other than the old piping roughness of 10 times new carbon steel of 0.0457 mm).

1/ Norsok P-001 5th ed. para. 6.1
2/ Idel'chik's Handbook of Hydraulic Resistance Table 2-1

 

[Mech85]

Hi Sawsan,

Brater and King (Handbook of Hydraulics, McGraw-Hill Professional, 7th Edition) quote a couple of cases where pipe deterioration was observed. One case on galvanised steel pipe indicated a doubling of the roughness value over a 3 year period as a result of moderate conditions of use. In the other case, a number of new wrought-iron pipes and some “old, rusty” wrought iron pipes were tested and the pipe roughness evaluated. The results indicated that roughness may increase 20 to 60 times for very old rusted pipe.

Barfuss, Rahmeyer and Christensen (The Realities of Aged Pipe Friction, Barfuss, S L.; Rahmeyer, W W.; Christensen, R T. AWWA ACE65191, 01-Jun-2007, 20 pages) conducted a study into friction loss in aged iron pipes transporting water. It was found that the headloss due to friction in seven pipes ranging from 30 to 50 years old increased 200% to 2400% as compared with the new condition. Pipes become rougher as they age. However, in many cases they become much rougher than common literature recommendations for aged pipe.

 

[LittleInch]

When "tuning" an analysis to match an existing pipeline, often the roughness is the only thing left if you're confident that the model has the right ID, length, fluid properties, temperature, no of bends etc so the number you come up with is not really the same as if you measured it.

Models usually are conservative, but you have so many factors that it isn't always the actual roughness.

Now predicting the future is quite frankly a mugs game. All sorts of things can change so to make one specific allowance for something which might or might not change is usually not worth it to spend more now to possibly save in the future. The chance of the flow rate / demand or pressure staying constant for 20 years is so low as to be negligible. So why allow for increased roughness?

My philosophy has always been design for what you know now and let the future take care of itself. Anytime I get to retrofit something where an item was identified for "future" it is invariably in the wrong place, wrong size / rating and we just ignored it. Only if you have clear staged increase / decrease in flow can you do this and then in most cases it never happens the way it was predicted.

Depending on if this is potable or other water then you need to allow for corrosion or inject corrosion inhibitor or allow for a future pump connection.

If the line gets that bad then slip line it and use PE to decrease your roughness.

If you pump it fast enough, sometimes the roughness goes down as the line becomes "polished"....

Remember 0.046mm comes from 0.18" and is itself now often seen as being fairly conservative. I often use 20 micron for new pipe nowadays. I've tried to find actual data / mesurements and it's hard to come by, certainly anything new.

BTW can you explain this sentence "Do pipeline get treated like piping or they are seamless and hence the roughness impact is not accurately credible." - I don't understand the question.

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

 

[EdStainless]

Not that it applies in your case, but worked with some people that re-habbed an old line. It was cleaned and then polymer lined. They had a heck of a time getting things to work because the line was now slicker than when it had been new. They ended up putting old, worn impellers back into the pumps (they did turn them to a known diameter).

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P.E. Metallurgy, consulting work welcomed

 

[Sawsan311]

Thank you all for your great inputs,

Mr. LittleInch, I was mainly enquiring in the last statement if pipeline roughness build up tend to behave in a different aspect than piping. Accounting for roughness increase in existing pipeline system is surely a cumbersome and tedious task as no stable operating envelope is ensured.

Mr. EdStainless, do you mean that the existing line which was revamped actually experienced lower roughness than expected, why the team you are referring to decided to put worn back impellers in the pumps? where they targeting lower pressure than what the hydraulics is providing.

Regards,

 

[EdStainless]

Yes, the head loss was so much lower that the pumps were running way off of BEP. Trimming old impeller let them lower the pump head and work closer to BEP.

While there is a lot of noise in your flow data (temp, flow rate, fluid properties) that make calculating the exact effects of roughness difficult this can be approached using statistics. If you calculare enough of these over time you can see trends. Just make sure that you use consistent assumptions.


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P.E. Metallurgy, consulting work welcomed

 

[pierreick]

Hi,
Consider handbook of hydraulic resistance by I.E Idelchick suggested by schvet . my reference is table 2.5 in 4th edition revisited .
Pierre