Can anyone tell me why the EGR pipe on my '92 SSE */c has a ribbed outer metal pipe and a smooth inner metal pipe?

I assume that the smooth inner pipe carries the exhaust gas from the exhaust manifold to the EGR bracket base, but there'* also exhaust gas flowing through the channel between the inner smooth pipe and the outer ribbed pipe (I know because the ribbed pipe on mine has a leak and is blowing out exhaust gas). Which direction does the exhaust gas flow between the smooth inner pipe and the ribbed outer pipe, and why isn't there just one flow path for the gas?

Any experts out there?

Not an expert, but I thought the EGR inlet & outlet pipes were ribbed indicating that they are flexible pipes. Just my guess. Are you saying there is another pipe within the ribbed (flex) pipe?

The outter pipe is the heat shield, the inner pipe is exhaust gas.
Your gasket may have a leak or the pipe has a hole?

Thanks, that what I thought - the inner pipe should carry the exhaust gas and the outer pipe is just a heat shield. Where my outer ribbed pipe is damaged I can see thru to the inner pipe, and it looks to be solid. The damage was there when I bought the car several years ago, and it looks like it was eaten away by acid or something. I didn't notice it at the time when I bought it, but this car has always had a rough idle since I've owned it. No EGR error code, though.

A few days ago I patched the outer ribbed pipe with a piece of a steel sheet rolled over it and clamped on, and sealed the gaps with thermo-steel but the rough idle is still present.

I gues it'* time to get a replacement EGR pipe assembly.