Of course it follows that any time there are system modifications or tie-ins is also a good opportunity to examine the condition of the pipe.
Examinations of any existing pipeline when exposed can of course include visual observations of the surface, pecking any suspect areas with something like a welding (flux etc.) “peck hammer”, or even ultrasonic thickness measurements (that use a special small sonar-like instrument coupl(ant)ed intimately to the outside surface of the pipe, and subsequently the speed of sound in the specific metal to deduce the thickness from travel time of reflections etc.) Any kind of saw-cut etc. through the pipe metal will of course also reveal a fresh metal-edge that is indicative of the soundness of that cross-section. Also, when any kind of connections or “cut-ins” of valves etc. or sizeable “taps” are made in the pipeline e.g. for service connections, miscellaneous pipe pieces or “coupons” from these operations are sometimes retained by Owners and Engineers for detailed examination, of course that is possible inside and outside with such samples.
While it is a somewhat more disruptive procedure, as has been mentioned small investigatory coupons can even be cored or cut from an existing pipeline with or without pressure on the line, and a dependable tapping sleeve, saddle, or repair clamp etc. can thereafter be assembled for a pressure-tight closure over the hole. Safety is of course paramount when digging etc. around working pipelines.
While I guess rust or isolated tubercles might be observed in some aggressive waters in internal inspections, it may be unusual with this somewhat unique lining system to see perforation from the inside-out or even significant internal corrosion depth penetration of cement-mortar lined iron pipes in most normal potable water services, even at small damaged or metal sliver/thin areas of such linings.
In the case of ultrasonic readings appropriate procedures for outside surface coupling must be followed, and the instrument in these cases must be appropriately calibrated for the specific metal involved to obtain accurate readings. Obviously also, even an accurate ultrasonic thickness measurement is at best a snapshot of the thickness at the time, and unless prior accurate measurements were taken at the location or ongoing measurements are taken one would not really know if the thickness was somehow pre-existing at that location, or instead indicative of some sort of meaningful deterioration over time. Ductile iron pipe from the factory has been available and might be installed at any particular location with a great many different classes and wall thicknesses per size, and even modern individual pipes are subject to some allowable thickness variations according to standard, from end-to-end as well as circumferentially.
Likewise, I am aware that many enterprising folks/entrepreneurs are working on many other sorts of in some cases much more complicated technologies, it appears hoping to “cash-in” on real needs (and maybe even now some hype?) over condition assessment and asset management regarding the huge amount of existing piping out there. I believe there will likely be some real value to some of these technologies in some circumstances. Speaking however of any kind of indirect instrumentation readings including ultrasonic, care should be taken in the analysis of and decisions made from the results obtained. Seemingly alarming indirect observations or readings obtained should probably be verified by some direct hands on the pipe/physical observations as previously discussed, the cause for any problems analyzed as best possible, and the remaining strengths/reliability of the system for present/future service conditions analyzed (e.g. strength-of-materials and otherwise) before decisions to replace are made. In other words, “trust but verify” may be good philosophy in this as well as many other matters.
