Supporting Large Steel Pipes

Ductile iron, concrete lined and epoxy covered last at least 80 years, with periodic inspection of the external coating for deterioration and appropriate response.

Burried pipes, properly wrapped and concrete lined are at least the same.

The real challenge is the transition point from underground to above ground where the chemistry of protection need to cope with both circumstances.

Most failures of above ground pipes relate to damaged coating allowing localised corrosion of the pipe.

(Depends a little on wall thickness.)

I'm currently working in an area that has 200km plus of steel pipes in sewage system, working on predictive failure process to get renewals done before smelly spills happen across the community. We already have some pipes at 90 years (cast iron) that were concrete lined in situ when they were 40 years old.

(ductile iron ≠ steel)

But that aside, yes, DI coated, lined, and properly installed can work and work well. Speaking from the experience of all the city's I work with though, for every success story of DI in sewer service, there are 10 failure stories (at least here in the US).

The failures that I've seen can all be traced back to "special cause" issues local to the failure.

Things like wrapping damaged by "backhoe" teeth when the pipes were laid. (Failed pipe had corrosion at same centre distances.) We excavated another 10 pieces each 3m long and verified that the rest of the pipe was OK. (1000m rising main 300mm ID.)

Things like coating damaged due to "burning off" the vines that were underneath it.

Things like tapping holes for metering that were not properly coated.

Things like leaking joints where "wrapping" was not done properly. (We are currently exposing and re-wrapping a 25000m long water line because of inferior joint protection.)

Premature failures have all (so far) provided an identified issue that allows decisions about the remainder of the pipe.

You've hit the nail on the head (that's why I was sure to include "properly installed" in my comment). With the appropriate linings and coatings in place, DI pipe can withstand the harshest of sewer gasses and most corrosive soils.

My original comment though is that steel piping is generally not used for sewer service. It appears the OP is using 36" steel gauge piping (not DI).