Scabs on Cast Iron Sewer Pipe

[Tbbarch]

I have a leak at the bottom of an elevated cast iron pipe, in a crawl space. It is assumed to be a pin-hole leak from internal corrosion since there is no evident damage to the outside of the pipe.
This is only the second time I have worked on a leak in cast iron.
During preparations for cutting out the leaking section of cast iron I found some brown lumps on the outside upper half of the pipe about 18" down stream.
I scraped these brown lumps to get a flush surface and they come off like flesh wound scabs. There is a divot underneath but no apparent hole.
Anyone have insight into what these "scabs" are?

 

[Tuttles Revenge]

Its likely rust coming through from the inside. I would recommend replacing that entire section of pipe if its got multiple failure points.

 

[Sponsor]

 

[Tbbarch]

Its likely rust coming through from the inside. I would recommend replacing that entire section of pipe if its got multiple failure points.

I would have thought it to be rust too except it is not on the bottom half of the pipe. Do you have an idea as to why it is corroding from the outside in as opposed to the inside out?

 

[Tuttles Revenge]

Without seeing the pipe its hard to make any kind of diagnosis. Generally pipe that is above grade and in a relatively dry environment is only going to degrade from the inside out. And I have seen lead pipe degrade from the top of the pipe first likely due to acids in urine.

I would still think that the issue is coming from the inside of the pipe and the visible part on the outside is just the tip of the iceberg.