Prediction of internal corrosion in sewer pressure mains
Prediction of internal corrosion in sewer pressure mains
(OP)
hey,
i need to find some equations which predict where corrosion will occur in a pressure main. I understand that corrosion occurs at the high points but not always.
i need to find some equations which predict where corrosion will occur in a pressure main. I understand that corrosion occurs at the high points but not always.





RE: Prediction of internal corrosion in sewer pressure mains
ht
Two indices are useful to predict the potential for corrosion or scale-formation of water. These are the Langlier Index and the Ryznar Index.
The American Water Works Association has a very useful calculator for the Langlier and Ryznar
Indices. It can be easily accessed using the following link:
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http:
RE: Prediction of internal corrosion in sewer pressure mains
RE: Prediction of internal corrosion in sewer pressure mains
I am more interested in the gas water phase of sewer mains.
When the sewer main stops pumping air goes to the high puts and starts corroding it. When the pump starts again i need to know weather the flow will be enough to pump out the air bubble from the high point
RE: Prediction of internal corrosion in sewer pressure mains
RE: Prediction of internal corrosion in sewer pressure mains
With regard to your restated or new question about moving the "air bubble", I know ASCE MOP No. 36, Wastewater Treatment Plant Design (1977) contains the statement, "A velocity of at least 1.2 m/s (4 fps) is required in the pipeline to shear the bubble and to keep it moving down grade." However, the subject of flow in various pipeline services for effectively scavenging, scouring, or shearing air bubbles from high points though without working air valves has been the subject of many other discussions on these blogs and others over the years (I think sometimes suggesting more complicated determinations and more/complex parameters). I suspect with a good search and some of these key words you could find much more information and other viewpoints.
RE: Prediction of internal corrosion in sewer pressure mains
There have been numerous posters on this forum inquiring about problems with force mains. If the velocity is inadequate to push the air downstream, you will have trapped air in the force main.
In general, you need a velocity of at least 4 ft/sec to force air down the force main.
Here are a couple of examples:
thread161-237329: sewer forced main problems: sewer forced main problems: sewer forced main problems
http://www.eng-tips.com/viewthread.cfm?qid=270920
See the attachment for a detailed discussion.