To use telecom cable in steel conduit

Hello,

I brought up with my problem that I'm not sure I can discuss about here.
If you know better board than here, let me know.

I'm working in plant engineering industry and working as an electrical engineer. I encountered some problem with my customers on using steel pipe with telephone cable.

Telecom Cable - 50 Pair (refer to the file attached)
Steel Pipe - PVC Coated steel pipe (pvc is coated and outside of steel conduit, so basically it's all insulated from the air)

Pipe runs around 600m through underground. For cable pulling, there are kind of manhole between every 50m steel pipe and steel pipe stops at each side. so continuity of steel pipe stops every 50m.

The thing is, customer wouldn't allow us to use steel pipe even though it is coated with pvc
. They're saying steel material of pipe will have an effect on signal running through the telecom cable. But they couldn't show exact reason or principle for this.

I tried to find standard regarding this issue, but couldn't.

Are there anybody who can help me or make me understand with principle or standard.

I'd appreciate your help in advance.

I think it could be matter of shielding.

The pipe is not continuous so it cannot act as a shield against the external electric field. However even it case you can connect the various chunks, the steel has a less conductivity with respect to aluminium (roughly 0.7 instead of 0.03 ohm*mm^2/m) so it's a worse shield.

My opinion.