How to Retrofit Packed Tower Internals After Process Corrosivity Increases

A packed tower may operate reliably for years until process chemistry changes.

Higher acid concentration, more chlorides, stronger oxidants, new solvents, or higher temperature can turn previously acceptable materials into corrosion risks.

If the tower shell remains usable, the retrofit may focus on replacing vulnerable internal components.

Start With the New Corrosion Environment

Material selection should be based on actual process conditions.

Important information includes:

• chemical species;
• concentration;
• temperature;
• pressure;
• contaminants;
• oxidation state;
• cleaning chemicals.

Generic statements such as “acid service” are not sufficient for material selection.

Identify Which Internals Are Exposed

A packed tower may contain multiple materials.

Components include:

• packing;
• liquid distributor;
• support grid;
• beams;
• bed limiter;
• redistributor;
• mist eliminator;
• fasteners.

One material upgrade should not leave another vulnerable component as the next failure point.

Inspect Existing Damage

Corrosion often develops unevenly.

Look for:

• pitting;
• thinning;
• cracking;
• perforation;
• damaged welds;
• crevice corrosion.

Support attachments and fasteners deserve particular attention because structural failure can occur even when large flat surfaces appear acceptable.

Do Not Automatically Upgrade Everything to Stainless Steel

Different environments require different materials.

Depending on service, options may include:

• alternative stainless grades;
• high-alloy metals;
• thermoplastics;
• ceramic components;
• lined structures.

The best material depends on chemistry and temperature.

Stainless steel itself is not universally corrosion resistant.

Consider Nonmetallic Retrofits

In some corrosive services, plastic or ceramic internals may reduce corrosion risk.

But the retrofit must also check:

• temperature limits;
• mechanical strength;
• support loads;
• fire requirements;
• installation methods.

Material compatibility is only one part of suitability.

Check Mixed-Material Interfaces

Introducing new materials can create new issues.

For metals, dissimilar-metal contact may introduce galvanic concerns.

For plastics installed on metal supports, thermal expansion and attachment methods must be considered.

Retrofit design should review material interfaces, not just individual components.

Re-evaluate Fasteners

Bolts, clips, clamps, and small hardware are often overlooked.

A high-grade distributor attached with unsuitable fasteners can still fail.

All wetted hardware should be included in the material review.

Check Mechanical Properties After Corrosion

A corroded support may appear functional but have reduced load capacity.

Thickness loss should therefore be treated as a structural issue.

This is particularly important under heavy ceramic or metal packing beds.

Consider Future Inspection

A corrosion-driven retrofit should make future inspection easier where practical.

Useful improvements may include:

• removable sections;
• accessible fasteners;
• corrosion monitoring points.

This can reduce uncertainty during later shutdowns.

Verify Cleaning Compatibility

Maintenance chemicals can sometimes be more aggressive than normal process fluid.

If cleaning procedures will continue after retrofit, the new material system should be compatible with them.

Retrofit the Weakest Material Chain

The objective is not simply to replace the visibly corroded component.

It is to remove the material incompatibility that caused repeated failure.

That may require reviewing the complete internal assembly.