Hi Danielle, I see no one has yet tried to answer your question, nor yet tried to help you. I guess what you are really talking about is what types of pipe are best suited for a specific, though potentially some different, water main applications. There are of course many types of piping now available for installation in water systems. There are advantages (you can find many with various degrees of completeness and objectivity in e.g. a web search of all the various pipe manufacturer and trade organizations like DIPRA, Uni-Bell, and PPI etc.) and disadvantages that can be talked about concerning all types. While it appears e.g. the plastic pipe folks are trying in some cases to sell/claim innovation or state-of-art to folks new in the field, most commonly utilized basic types of piping have actually now all been around for many decades, and most very large large water providers (at least some of the “old heads” among them) already have some experience with all of them.
From a detail perspective, however, and irrespective of the fact that all of these materials have their own ASTM and/or AWWA specifications etc. that convey some suitability for conveyance of water and pipes and might not be magnitudes different in installed cost, I think it is most important to understand that these pipes are indeed much different (in many properties/respects), and they are thus in fact not technically “equal”. While it is certainly possible to compare e.g. pressure ratings and explicit minimum safety factors etc. for the predominantly only two-dimensional basic design say contained in many AWWA standards for the various materials, this does not tell the whole story. The actual safety factors vs pressure and various loadings/ exposures/impacts/other vulnerabilities etc. that result from different furnished pipes can be far from these numbers. Direct comparative testing and experience of various representative pipes is thus a better indication of relative security. All materials can additionally be adversely affected by different environments e.g. metallic materials in some corrosive soils where they are not adequately protected from same, and plastics etc. by other forms of corrosion/degradation, heat, cold, various environmental stress cracking agents, aging/embrittlement, creep, permeation etc. Additionally, in spite of the claims to the contrary all pipe materials in fact have “joints”, and all also must be connected to laterally by various means, whether they be gasketed, welded or fused etc. These joints all have inherent features, capabilities, and potential problems that can be compared. There are many other factors, many of which may be some non-obvious to particularly young folks, for comparison/consideration in a selection process for piping materials, including but may not be limited to the following:
1. Of course, the overwhelming majority of states in the USA, and many other entities elsewhere, require all materials in contact with potable water to be at least deemed suitable for that application as a result of some sort of formulation/normalization product reviews (e.g. NSF 61 listing)
2. The selection of piping should otherwise provide reasonably for public safety and protect water quality, and e.g. even when confronted with incidence of known, unknown but discovered in construction, and maybe even in the event of future possible soil/groundwater contamination (as with volatile, petroleum, fuel etc.), including effects of “permeation”. Permeation refers to some perhaps rather non-obvious (at least to lay folks phenomena, whereby some volatile (e.g. quite bad actor, deemed carcinogenic) constituents will pass from an unpressurized contaminated outside water/soil environment through the walls of some specific types of previously potable pipe and gaskets and end up inside, in some concentration, in even highly pressurized water! [Such effects can be read about e.g. in the references at
and at
]
3. Other experience/durability records of comparable pipelines (but it is important that any statistics consider EVERYTHING that can happen out there to pipes) in various areas and environemnts. At least some level of disaster event performance e.g. in earthquakes etc. is even also now of consideration in more areas than perhaps many folks realize.
4. The ability of the pipes to be shipped and delivered in sufficient volume and on time to (and maybe even beat around?) the project site, and yet remain reasonably intact for effective installation/service
5. The otherwise strength and robustness of pipes and joints for actual field installation and bedding etc. service, with consideration also for the available abilities and conscientiousness of labor, equipment, inspection etc.
6. The actual long-term load, pressure and thrust resisting where necessary (both tensile and compressive) capabilities of the piping, including effects in joints (to allow for proper installation and service of the pipe systems e.g. pushing and pulling through casings, pipe-on-supports and also bi-directional thrust forces from closed isolation valves etc.)
7. Engineering economic analysis based on the actual internal flow area of the pipe (despite all the hoopla over claimed smoothness/flow coefficient of surfaces, the actual hydraulic performance and head loss/pumping energy consumption of modern lined etc. comparative pipes is primarily dictated by the inside diameter, which varies between types of pipes)
8. The ability for the life of the piping to handle all transient conditions such as surges, pressure and temperature (including effects of expansion/contraction) fluctuations incl. fatigue etc.), and maybe at some point in their life in even the cases of the strongest of pipes eventual collateral effects of “line breaks”. In my opinion, it is unrealistic to assume that there will be only very small surge pressures in systems that are composed of all different kinds including inevitably some quite inevitably high-stiffness or encased pipes.
9. The dependability, cost/ease, and safety of future tapping/tie-ins etc. to the pipeline
10. The impact/gouge/service tear-out etc. resistance of the pipeline to outside force and third-party damage (at least fully comprehensive studies indicate this is by far the single greatest threat to modern pipelines) and when same occurs the availability to repair same with available devices/labor in all sorts of weather etc. (and maybe even underwater!) conditions
11. The locally available ability/knowledge to dependably “locate” the pipeline once buried (I think this probably relates particularly to Item 10 damages)
12. A weight/bulk density and outside surface texture of the pipeline sufficient to keep it in place in the ground [while “lightweight” is often touted as an advantage of plastic pipes, in at least the very smallest sizes where the weight of the pipe is below OSHA labor-lifting limits, this may not necessarily be helpful in the more long-term engineering perspective and maybe particularly in larger sizes e.g. to prevent the pipeline from moving from its intended position in a soil (water) or concrete encasement mass]
13. Does the piping offer sufficient selection, and strength/dependability, of joining structures for installation and service, including unrestrained and restrained joints when necessary?
14. Does the piping provide electrical conductivity (where this is needed or desired for whatever purpose)?
15. The ability to repair or connect to piping in contaminated soil areas (petroleum derivative absorption contamination can adversely effect quality of some types fusion etc)
16. Some specific types of pipes or what is required to install them have been implicated in incidences of explosions from welding/cutting arcs etc., static electricity discharge, and also failures due to lightning strikes that may be a concern in some areas/environments
17. Where the pipeline goes across bridges or other supports (where it will be exposed to the elements, including sunlight/UV etc.) where applicable, is the pipe material and its joints suitable for long-term exposure in that environment?
All of these things could impact which pipe might be best for specific applications. There are even some other issues that I think may be a little harder for some engineers to get a clear handle on, but that may be viewed and even weighed with some degree of importance by others. In this regard, are the pipe manufacturers (and their organizations etc.) available and willing to help at least to some reasonable extent provide support with issues and inquiries involved with the piping and applications etc. of same? Does history show that they will likely be around/available to help in the future? Based on history etc. will gaskets likely still be available for connections to old (plugged etc.) pipes/fittings etc.? In this regard, at least a few materials are typically left over from jobsites, and in other cases installation of even large quantities is even intentionally or unintentionally delayed for long periods of time (sometimes years). This also goes for pipes kept on hand by utilities etc. for emergency repairs. History has shown some types of pipes have been successfully installed (with new gaskets etc.) even many decades after they were originally manufactured, whereas others have obviously more limited “shelf life”. In a similar vein, other “life cycle” issues are becoming of at least some local importance. E.g. does the piping material consist of recycled materials, and can itself (likely/practically) be re-used or recycled (instead of having to consume precious landfill space, or worse eventually becoming “hazardous” waste as some already have in areas)? What are the basic feedstocks for the piping material, and what are all the long-term impacts of their production? What will be the total energy consumed in use of the product in its life cycle, including actual long-term pumping energy (not necessarily based on very high or unrealistic, not proven long-term in the field flow coefficients)?
Lastly, I have heard of some past practice wanting to allow multiple types of pipes as “equal” in specifications (that are in fact not technically equal, as I hope I’ve previously supported) for the purpose of more beating bid prices down. While I guess this is in general some well-meaning, and while not commenting on nor knowledgeable of actual temporary or long-term effectiveness of such practices to this end, I will state that there are individually multiple manufacturers of all the various common types of pipes. I will also state that if inferior pipe is allowed in the specifications, there is certainly a chance in a competitive bid environment that it will be chosen for installation on even a multi-million dollar project, and even if it is only one cent cheaper than another that may have several times the strength or other security level! While installed cost is no doubt a practical consideration/fact of life, I guess it is even possible such practices as discussed in this latter paragraph could at some point eventually bring in questions of mission, principles, canon, practice or ethics etc.
Also, while I think one can learn something from virtually all studies and information, with regard to item 3 above I would also suggest you be some wary of some crafted, partial performance studies, and particularly those that for whatever reason exclude some manners of in-service pipeline breaks or maintenance incidents etc. from their statistics. It is my opinion everything (see e.g. all previous features, including third-party damage/loading incidences etc. listed) should be “on the table” for most objective comparison of different types of piping, lest products inferior in those respects prove not to be in the long-term interest of tax/rate payers nor public health/safety.
Sorry for the very long post (I think this is a question that defies easy answers, and I have probably unintentionally even left out some other considerations in this quick composition!), but I hope this information is of help. If you have read this far, have a good weekend!
