Pipe Deterioration Formula

There might be actuarial data on this, but I bet the standard deviations would be so large as give low predictability. (Though low might be better than none.)

Exterior or interior corrosion can occur in any pipeline. Both types can be occurring at the same time. The electropotential galvanic cell is really referring to a battery cell and the degree of corossion that could be expected. You might try googling cathode protection for better information and solutions.

Interior corrosion would be a function of the water quality and can be quite variable. The standard for corrosion caused by water quality is to use Langlier's Index at various temperatures. There are many calculators for the index that can be found on line but it does require some good chemistry parameters to apply. Once you know what these parameters are (the water could be considered encrustative and not corrosive), appropriate prevention is usually applied.

Sorry I cannot be of help getting a general formula for pipeline corrosion but these are the tools used when correction is applied. Corrosion of pipelines has many causes including the above. You can add microbial, galvanic cell, physical, as well as chemically polluted soils. I am not a specialist in pipeline corrosion but did provide details of water quality to include Langlier's index at cold, ambient, and very hot temperatures. At least that way you would know the potential. I am not sure how to apply a rate of deterioration or even if there is a specific formula. Such a formula would be a great tool for someone managing long runs of pipeline.

Thanks for these links and the insight.

The failures that we encounter are a combination of failure due to internal material flow and the Langlier information is noted. We also are aware of the impacts of acid sulfate on pipe exterior of some pipe materials, then "beam" effects on brittle pipes in reactive soils subject to drying/wetting cycles (Fortunately no frost heave here), abrasion of protective films from thermal expansion, even variation in pipe laying methods and so on.

The equation provided for AC pipes was extracted from some studies in Canada and provided a generic predictive failure for that type of pipe.

As the other response indicates, the standard deviation for the data may well be huge, but with the distances that I have to provide prediction for, hopefully "Central Limit Theorem" will balance out across the totals involved.

I'm looking to predict total maintenance crews required for the whole network (man hours per year) rather than try to predict which specific pipes will fail.

Being able to predict that will also provide tools to predict the impact of renewal of parts of the network and associated payback traded off against levels of service.

I must consider myself fortunate, we have details for around 17,000 pipe sectors including diameter, year laid, failures already observed (for last 10 years), material, depth, soil types and so on.

If I cannot get independant equations, then I can develop predictive ones based on our data, but local management will want to have some external reference for comparison.

Get in touch with the Australian Water Association. They have been developing these algorithms for many years and should be able to provide the information you seek.

I am solidly in touch with AWA (Employer is a registered member) and there are some proposed and untested ideas in the wind but nothing anyone is prepared to publish yet.

Thanks for the suggestion

I am not sure if AWA is linked to the American Water Works Association (AWWA) but you may want to fire an email to them ( www.awwa.org ) for reference material. You can check out their information on distribution systems at their store . I am a retired member of the Ontario WWA which is a member of AWWA. Unfortunately, I have not kept up my membership.

Oh there is electropotential galvanic cell formed with Asbestos CONCRETE pipe, tell me is the concrete the anode or cathode??? Don't post your google search results you waist our time.

Try google'ing corrosion rates of metals in seawater. I have a corrosion handbook that shows carbon steel corrodes at 5-10 mils/year and austentic nickel cast iron corrodes at 2 mils/year (sorry it's a reference book not a details list). Try a metals handbook for more detailed corrosion rates and for more metals.

The formula is simple: initial pipe wall thickness minus corrosion rate times years in service.

t-(CR)(yr)

This will tell you when you have a hole in the pipe. If there's pressure (which I'm sure there is) you'll need to look at the minimum pressure thickness. Over here we use ASME B31.3 for that but you may use a different code. Essentially, all codes will use some form of the hoop stress equation.

Try looking up NACE RP 0169 and RP 0275. These might help.

But will it be helpful for buried pipes?

Buried pipes corrode too right? I'm sure if he checks some of the handbooks or references he might find better corrosion rates for buried pipe.

I'm trying to lead him in the right direction not do it for him.

This is not a good practice, to govern pipe replacement by some arbitrary equasion. Check your head loos to determin the amount of barnicals and other deposits, once your C value drops below a value say 100 (based on in field testing, i.e. hydrant flows) then your are loosing way too much pressure due to friction.

AC pipe should be replaced after 50 years because the pipe becomes very brittle. YOu can go and use sleeves to patch blowouts but, over torquing can crush the already brittle pipe material. New transition sleeves are not stock made for use on AC pipe in the water industry (special order item).

2500km of pipe thats it?, pull it all out and use Ductile Iron whos life expectancy is over 100 years. US Pipe and Foundry, Atlantic Pipe, or Griffen pipe are the best pipe makers, never use anything from China in your water system they do not test there products they do not have any quality control. I tried to use a Star 1/8 bends on a 12-inch DI and the bends was not circular so the pipe wouldn't seat in (Mechanical Joints not Flange pipe).

Thanks for all the replies so far. Each is contributing to the general body of knowledge.

Internal friction is one indicator of internal condition and yes, we monitor flow rates at specific hydrants on a regular basis. However many pipes are attacked from the outside soil conditions.

Corrosion rates are great for metalic pipes, but we also have plastic and some metalic pipes are protected by "wrapping" systems to exclude external oxygen attack.

Ductile is wonderful in the right locations, but ripping out 90 years of infrastructure is not a one year budget job.

Everyone is contributing where they have expertise and I can recognise that and sift the gems.

I never expected one individual to have all the answers (Otherwise the results would have already been published) but our collective knowledge may take us well along the path.

That's why I love this site.

Corrosion rates on plastic pipes in seawater are very low compared to metal. That's why I didn't look it up or mention it.

As a NACE certified corrosion engineer working in the U.S. you will find that this question has many answers, but few facts to back them up. Certain pipe vendors will claim their material will last for >200 years, yet they've been making this material for less than 50 years. External corrosion prediction (up to this point) is best predicted by using soil corrosivity data coupled with actual failure rates to emperically derive time-to-failure models. Moving forward, asset management is the key since most municipal utilities don't know what they have in the ground, so they have no idea of when it will fail.

I can provide more information/external references for these statements upon request.

Lots of advice above, but no-one has considered the most common causes of failure: damage by movement of ground, either by human action - building works, excavations, etc - or root invasion which can cause ingress through joints or simply push the pipe out of alignment causing leakage.

You are indeed correct that ground movement can also be significant.

For reactive clay, there is even movement caused when roots (en\ven when not touching the pipe) cause localised drying of the soil with associated movement.

There is also pipe mevement from poor construction techniques where thrust blocks are incorrectly anchored, or omitted from pipelines.

I am looking for a formula that people are using that provides an indicative failure rate that is the combination of all the effects nominated so far, plus a few others.

Thanks for the input.

No fresh comments on this thread for a few days, so I'm signing out. If you feel that yuo have additional material that could help me, then please send via the personal mail system as I'm unsubscribing from this thread that I started.