49 CFR §192.275

1. (a)Each caulked bell and spigot joint in cast iron pipe must be sealed with mechanical leak clamps.
2. (b)Each mechanical joint in cast iron pipe must have a gasket made of a resilient material as the sealing medium. Each gasket must be suitably confined and retained under compression by a separate gland or follower ring.
3. (c)Cast iron pipe may not be joined by threaded joints.
4. (d)Cast iron pipe may not be joined by brazing.