Check out ASME PCC-2 Repair of Pressure Equipment and Piping I believe part 2 covers welded repairs such as split sleeves, part 3 covers mechanical clamps, and part 4 covers non-metallic repairs i.e. epoxy wraps. When in doubt there are several organizations that provide piping enclosures. For each design they should also provide an engineering package that covers the equations and method of their designs. Most calculations will be per the required piping code.