Just a guess, but for gravity sewers where H2S gas is likely to be present, along with other aggressive chemicals, a cement mortar lining would seem to offer little protection.
The epoxy lining is the standard lining for sewer service.
Epoxy lining for DIP sewer use is the standard for every utility I am aware of (about 15).
As usual, RWF7437 is correct. A cement mortar lining offers no protection due to the H2S.
I've also run into the DIP only restriction. I don't understand it, because PVC is appropriate for sanitary sewer use in most situations.
in this case, existing sewers are being permanently supported by replacement with DIP in order to allow a large storm drain to be constructed below. Only other option is to use reinforced concrete encasement and the contractor does not want to do that.
Beyond that, I believe iron piping (with and without cement mortar lining etc.) has many engineering attributes, including a generally successful record in many sewer services for a couple hundred years or more.
It is true that if there are some specific conditions in gravity or pressure sewer applications (these are not necessarily omnipresent conditions, they involve many factors/variables, and these variables are now pretty well-discussed in many authoritative ASCE, WEF, and EPA etc. publications) that result in continuing biological/biogenic conversion of H2S gas to extremely low pH sulfuric acid, this can be aggressive to a great many materials, including even good quality cement mortar linings and iron. Among the design considerations that are reportedly involved in evaluating such conditions e.g. according to ASCE MOP #’s 60 and/or 69 are high wastewater temperature, high sewage concentration (or lack of dilution), “very slow” flow velocities, waste solids intermittingly agitated, in effect sort of aged sewage in very large, long trunk lines, high concomitant H2S concentrations, and also must have areas/head space etc. that are non-full for extended period of time etc. It is also true that e.g. extremely acidic chemical/industrial waste discharges might also have direct effect, though in that case one would think e.g. most on the bottom side of the sewer, but I suspect such discharges are now discharges largely prohibited (into modern municipal systems) by regulatory organizations such as EPA or state etc. agencies.
Where per Engineering analyses such very aggressive conditions (as the biological conversion of H2S to very low pH sulfuric acid etc.) might occur, I believe the linings now most frequently applied to DIP are types of quite high-build epoxies such as "ceramic epoxy" (as can be searched from many portals, including previous responses).
We have a 3.9 mile section of 42" DIP with an epoxy liner that goes through a swamp to feed our WWTP. The main was installed in 1993 and was inspected last year. With the exception of a few small bedding issues the pipe was found to be in excellent condition. The manhole rings and covers were highly corroded from gas, but the interior of the pipe looked great.
If the pipe stays full always there will be minimal corrsion even with a cement mortar lining. However, I would spec all the DIP to be used with a protecto 401 lining, or equal.
I have been retained as an expert on a half dozen PCCP and DIP force main failure lawsuits and claims from CA to NJ to MO to AL. The main problem is the researchers do not test the linings at an appropriate pH, which needs to be down to 0.5 for an extended period. In one case, the Protecto 401 did not extend into the bells or spigots far enough and they corroded, in another the 401 was blown out by sewer cleaning jet of water, then corroded to failure (holes in the wall) in one year or so, cement mortar is gone in a few weeks, John Redner, former operations superintendent for LA County Sanitation said in an ASCE committee meeting minutes that any linings that are brushed on, sprayed on, etc last up to 5 years before failure in an H2S environment. Most of the force main failures occur just over the hill where the line goes to gravity flow. See ASCE Manual #68 "Sulfide in Wastewater Collection Systems". AMIDE-cured Coal Tar Epoxy lining is an energy source (i.e.,FOOD) for the sewer bacteria and is good for 3 to 12 years before pipe failure in a sulfide environment. Amazingly, some associations and manufacturers still recommend it for sanitary sewers. Good luck.
pipeexpert - are you talking about just force mains? or have you seen claims involving ordinary gravity sewers? I'm not talking about long, large diameter interceptors which tend to go septic, but just your ordinary 8, 10 or 12" city sewer.
CVG: We have seen as many or more gravity sewer H2S failures as force mains, in the gravity sewers the failure point is sometimes just downstream of a force main or pump station discharge into a gravity sewer. The size of the failed pipe is not limited to large pipe, one of the H2S related failures was in an 8 inch DIP, the smallest size we have encountered as a sulfide failure. Many of the failures are related to coal tar epoxy lining failures. Correction: see ASCE MOP #69, not #68. Another good publication is the 1985 EPA Technology Transfer Manual #EPA/625/1-85/018 "Odor and Corrosion Control in Sanitary Sewerage Systems and Treatment Plants."
You are correct in thinking that the sewer must go septic (oxygen deficient or anaerobic) but if the source of the H2S is another intercepting sewer, the size is not an issue, all sixes will corrode, unless they flow full and are kept full.
