Strong gas swirl entering an existing packed tower can bias flow toward the wall and reduce use of the full cross-section. Retrofit should identify the upstream swirl source, evaluate inlet-plenum length, use low-resistance flow straightening where justified, and consider interaction with the packing support and wall region.

A high-velocity side inlet can create severe gas maldistribution even when average tower velocity is acceptable. Retrofit should consider nozzle velocity, jet direction, distance to the bed, low-resistance flow conditioning, drainage, structural jet load, and evidence of localized hydraulic stress.

Uneven existing support rings can distort new tower internals and create hydraulic problems. Retrofit should survey the full circumference, verify structural condition, use suitable secondary leveling where necessary, preserve load distribution and open area, and record the final installed elevations.

A slightly tilted packed tower can create major maldistribution in gravity-dependent internals even when the vessel remains structurally usable. Retrofit should measure inclination, independently level distributors where practical, review collectors and demister drainage, and monitor whether foundation movement continues.

When the vessel top head cannot be opened, replacement tower internals should be redesigned as modular systems that can enter through existing manways, turn inside the shell, assemble with practical field joints, preserve structural and hydraulic performance, and remain removable during future maintenance.