Engineering Evaluation Case: Plastic Packing Is Chemically Compatible but Becomes Vulnerable During Very Cold Startup and Maintenance

Plastic packing selection often focuses on the maximum operating temperature.

That makes sense because high temperature can reduce polymer strength.

Cold service creates another type of question.

At sufficiently low temperature, some polymer systems can become:

• less flexible;
• more sensitive to impact;
• more vulnerable during handling.

The process may operate successfully once warmed up while still suffering mechanical damage during winter startup or maintenance.

Project Situation

Consider an outdoor scrubber using lightweight plastic packing.

Normal operation is:

• moderate temperature;
• continuous liquid circulation;
• chemically compatible service.

During winter shutdown, the tower cools to a very low ambient temperature.

Maintenance personnel then:

• open the tower;
• remove packing;
• walk equipment nearby;
• reload material.

Broken pieces are found during the next inspection.

There is no evidence of chemical attack.

The mechanical condition during cold handling should be reviewed.

Chemical Resistance Does Not Equal Cold Impact Resistance

A polymer can be completely resistant to the process chemistry and still change its mechanical behavior as temperature falls.

Properties such as:

• toughness;
• flexibility;
• impact resistance

can be temperature dependent.

The correct resin should therefore be evaluated over the full temperature envelope, not only normal operation.

Loose Random Packing Experiences Impact During Loading

Random packing is poured or placed into the tower.

Pieces contact:

• each other;
• the support grid;
• vessel wall.

At normal temperature, a flexible polymer may tolerate this easily.

At very low temperature, the same handling can cause more cracking or edge damage.

Maintenance Is Often the Critical Event

The packing may remain perfectly stationary during process operation.

Damage can occur when:

• frozen or cold packing is removed;
• tools are dropped;
• personnel handle brittle sections;
• material is dumped from excessive height.

This is why operating history alone may not reveal the true risk.

Large Fabricated Plastic Internals Need Separate Review

A random packing piece and a large plastic:

• distributor;
• support panel;
• demister frame

do not experience the same stress.

Fabricated panels may contain:

• welds;
• corners;
• bolted connections.

Low temperature can reduce the tolerance for mechanical shock at these locations.

Startup Creates Thermal Change

Cold internals may suddenly receive:

• warm liquid;
• hot gas.

The resulting temperature gradient can cause differential expansion.

For large plastic components, support clearances and restraint should allow the intended movement.

Do Not Confuse Ice Damage with Polymer Brittleness

Cold-climate towers can experience both:

• material-temperature effects;
• water freezing.

They are different mechanisms.

Ice can physically expand or block internals.

Low-temperature polymer behavior can make an otherwise dry component more susceptible to impact.

Troubleshooting should separate them.

Storage and Shipping Can Matter Too

Replacement packing may arrive at site during winter and be stored outdoors.

If cold material is immediately:

• dumped;
• compressed;
• stepped on,

damage can occur before installation.

Handling instructions should therefore consider ambient storage temperature.

Material Grade Matters

“PP packing” does not describe every possible PP resin formulation.

The supplier should know whether the project has:

• unusually low design temperature;
• outdoor winter exposure;
• impact-sensitive installation.

A specific polymer grade may need confirmation.

Inspection Should Look for Mechanical Fracture

Useful evidence includes:

• clean brittle-looking fractures;
• cracked ribs;
• broken welds;
• lack of chemical discoloration or swelling.

The pattern can help distinguish:

• mechanical cold damage;
• chemical degradation;
• long-term creep.

Metal Packing Is Not Automatically the Answer

Metal may provide better low-temperature toughness in many conditions.

It introduces different questions:

• corrosion;
• weight;
• cost.

The correct choice remains a multi-variable material decision.

Engineering Takeaway

Packed-tower material selection should include the conditions under which the internals are installed, maintained, and restarted—not only the normal process condition.