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And there you have it from a "Tire Engineer" (is that right Capri?). You should replace your tire any time you have a flat.....
I'm afraid you misunderstood what I was trying to say.
But let's take a different approach, something along the lines of sharing experiences and see if we can learn something along the way.
Since we've started this discussion about plug-type repairs, let's continue down that path.
Here's what I've experienced:
I used to do tire testing at a courier service - a scheduled pickup and delivery service that operated on predetermined routes and stops. They had a fleet of cars that were based in several locations, but the cars were absolutely controlled by that location. I would supply tires to them and they would mount them and return the tires when they were finished with them. I inspected the tires about once a month - wear profile and pressure. They put on over 8,000 miles a month and once a month went in for oil change and routine maintenance. I saw pretty close to 100% of the tires I supplied. From that I was able to understand the wide range of things that happens to tires and to be able to put percentages to these.
While I wasn't happy that they used plugs to repair punctures, it gave me an opportunity to observe how many they used and what happened to the tires. This fleet experienced about a 10% puncture rate - which has since been confirmed from other sources as being typical.
The one part of the equation I couldn't know directly was how many plugs had to be replaced because they leaked. But I was able to ask the mechanic. He said about 10% of the plugs had to be replaced - most of them in the initial repair, but about 25% of those at a later date. He mentioned that the need for replacement seem to be tied to a particular batch of plugs and when he experienced this he tossed the remaining plugs and bought another batch.
There are a couple of interesting statistics that come out of this experience:
Punctures occur in about 10% of the tires.
Plugs leak about 10% of the time.
That means that 1% of the tires had a leaking problem. I was able to connect some of the plugs leaking to the pressure checks I made. This is especially significant in that virtually none of the tires that I supplied leaked.
Occasionally I would encounter a tire that had been run flat. 90% of the time I could find the puncture - some of those had plugs. I assumed at the time that the other 10% were punctured in an area that has since been damaged by running the tire flat - basically the sidewall. I have since found other studies that confirm this figure.
I never saw a durability problem with the tires I supplied. Looking back I determined that even though I supplied hundreds of tires, the statistics on durability failures would say that I needed to supply 1,000's of tires to get some. I am sure some of this was due to the locale - Florida, which is only #5 on the states most likely to experience a durability failure not factoring in the effect of vehicle population.
I should mention that because I inspected the tires every month, I had a good handle on the inflation situation and pointed out to the mechanic which vehicles needed attention. I am sure this had a very positive affect on the popluation of tires.
OK, that's just a taste of where I am coming from. I'm sure that will generate questions, so……………
