pressure drop in seawater lines HDPE

[fvincent]

HDPE pipe manufacturers sustain that HDPE pipes maintain a very low rugosity even for seawater intakes and pipings (< 0.015 mm)
That sounds non-realistic to me. I was wondering if you have a better figure of the effective rugosity of HDPE pipes after some months/years of use.
The case I am involved - a intake pumping station for 1300 m3/h plus a 2000 m long seawater line up to a power plant (seawater is for make up of cooling towers) - includes for each pump a suction filter (Johnson, 2 mm gap)and means for chlorination (constant and shock). Even then I think some sort of deposits / incrustation will occur either bioufouling or mineral or both. I think pressure drop calculation should take a rugosity of 0.5 mm at least. Do you agree? Any other hint?
Thanks

fabio vincent

http://www.figener.com.br

 

[BigInch]

Pipe values are basically irrelavent. Bio will influence the roughness several orders of magnitude beyond whatever the published values are for the pipe alone.

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus

 

[zdas04]

The surface roughness (yes, I had to look "rugosity" up, not a common term in my world) is a function of the material, not of the product flowing in it. The numbers I see for new, clean HDPE are between 5E-6 ft and 50E-6 ft (0.0015 mm is 49E-6 ft) depending on manufacturer.

Now, whether the pipe will collect scale and slime from sea water, of course it will. A 2-inch accumulation of slime on the inside of the pipe will both reduce the ID and increase the effective surface roughness. Both actions rais the dP.

If I know the dP and the flow rate, then I can adjust efficiency (not surface roughness) to get a measure of the amount that the pipe is fouled. When I've been responsible for seawater piping I did this on a regular basis and I had a minimum acceptable value. When the effeciency reached that point I cleaned up (or replaced) the pipe or I cleaned out the heat exchanger and accepted the slimed pipe.

David

 

[fvincent]

thanks for the answers, BigInch and zdas04

zdas04, do you think a 2 inch accumulation is a reasonable value to consider for such pipe (diameter is 600 mm) or that value is only a "might be"? Have you ever experienced such accumulation in HDPE piping operating with seawater? Can you give me any figures on the rate of accumulation (inch/year) of a well designed pipe and well chlorinated system?

As to the roughness I agree, of course, it will be dictated by accumulation properties and not by the bare clean pipe properties.

regards

fabio vincent

http://www.figener.com.br

 

[zdas04]

Slime build-up has a maximum based on velocity. My experience has been with Naval Brass in untreated systems. A 600 mm pipe in raw sea water can easily accumulate 50-100 mm of stinky junk in raw sea water. I would be surprised if it was that much in a treated stream, but I don't know.

David

 

[BigInch]

Seawater has virtually no limit to the amount of stuff it can accumulate, as long as the velocity remains low enough to not physically bust the stuff off. I've seen 6" of oyster shells and barnacles. And its a very very rough flow coefficient.

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus

 

[willhammett]

I had done research in the past on seawater biofouling of pipes, most of my favorite tabs relating to it were deleted but I was able to find this one. May be of some use

http://www.desline.com/articoli/6246.pdf

 

[stanier]

In the lifetime of the PE pipeline you might expect that the chlorination will not be effective. Encrustaceans will no doubt occur. If chlorination is then effective it will only kill off the living tissue leaving the limestone shells in place.

If you want some accurate information check with operators of desalination plants. Veolia Water or Acciona Agua are two of the largest.

"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.

http://waterhammer.hopout.com.au/

 

[rconner]

A read of the book at

http://books.google.com/books?id=ol...aeo3jkB8chAJBNd13zM&hl=en#v=onepage&q&f=false

might also be helpful. This and other learned responses to this thread indicate there could be more to these issues in some applications (than simply reading or listening to plastic pipe marketing hype or promotion that scale, films, build-ups or clogs etc. don’t occur with such pipe, and then buying same).

While it was not a seawater intake application, I am some sensitive to such issues as I am aware of a specific major water pipeline (60” or ~1500mm diameter) several years ago where a plastic pipe material was chosen (in that case fiberglass/GRP) over other more traditional pipes, it appeared assuming build-ups would not occur and same would thus maintain (as it turned our unrealistic) high flow coefficients as promoted. While I don’t know that build-up was the only problem with the line, it was reported there was a significant slime or scale build-up inside that plastic pipe that later caused flow and/or other problems (more details in prior thread at

http://www.eng-tips.com/viewthread.cfm?qid=196775&page=30).

An equally or maybe even more important question in some applications may be can the chosen pipe handle aggressive e.g. mechanical cleaning means to restore flow capacity and/or re-lining etc., if/when whatever kind of build-ups eventually occur?

 

[stanier]

rconnor,

Sea life does not read standards and will adhere to anything unless it contains copper. In Malaysia I came across an organism that burrowed into the PE material used for pile covers in marina.

If you want evidence of PE with barnacles just visit your local harbour and check out the piles for oysters.

Pe and GRP are used for marine systems but are chemically treated in a regular dosing regime with chlorinated water and sulphuric acid.

"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.

http://waterhammer.hopout.com.au/

 

[rconner]

I had heard a few years ago of rapid attack/failures of some pvc plastic pipelines (some thought, perceived, and/or advertised immune to marine effects) by a general class of organisms referred to as "marine borers". The reference at

http://www.sciencedirect.com/scienc...641269707f03ac2c95da4846ff31ca9d&searchtype=a

says penetration has actually occurred it appeared in working pvc pipelines in as early as one to three years! It perhaps stands to reason that other plastic pipes and substances with similar hardness or penetrability would likely be similarly affected, and your experience appears to substantiate this.
While I guess I understand how something like hypochlorite etc. might be injected (with some bother, expense, and maintenance etc. e.g. at the entrance to an intake to be sucked up?), was just curious how are "regular dosings" applied or helpful to the exterior of submerged piping, as I am not familiar with this application?