When Is PP Pall Ring Not Suitable for a Packed Tower?

Polypropylene Pall Ring is widely considered for scrubbers, absorbers and other packed towers because it is lightweight, corrosion-resistant in many aqueous chemical services and usually more economical than higher-performance fluoropolymers or corrosion-resistant metals.

However, PP Pall Ring is not universally suitable for every corrosive packed-tower application.

The decision should not be based only on statements such as:

• “The liquid is acidic.”
• “The pH is low.”
• “Plastic is corrosion-resistant.”
• “PP is cheaper than PVDF.”

PP suitability depends on the complete operating environment, including:

• chemical species;
• chemical concentration;
• operating temperature;
• oxidizing conditions;
• solvent exposure;
• mechanical load;
• expected service life.

The key product-selection question is:

When should PP Pall Ring be removed from the candidate list before a packed tower is specified or purchased?

The short answer is:

PP Pall Ring may not be suitable when the process exceeds the polymer's chemical, thermal or mechanical limits, or when the required long-term reliability justifies a more resistant packing material.

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1. PP Pall Ring Should Not Be Selected Based on pH Alone

One of the most common material-selection mistakes is using pH as the primary compatibility criterion.

Two liquids can have similar pH values but interact very differently with polypropylene.

Material compatibility depends on:

Chemical Species + Concentration + Temperature + Exposure Time

—not simply:

Acidic / Neutral / Alkaline

PP performs well in many aqueous chemical environments, but this does not mean that every acidic or alkaline process is automatically suitable.

For preliminary selection, identify the actual chemicals first.

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2. Elevated Temperature Can Become a Major Limitation

Polypropylene is a thermoplastic.

As temperature rises, its mechanical behavior changes.

Possible effects include:

• reduced stiffness;
• greater deformation under load;
• increased creep;
• reduced dimensional stability.

This matters because random packing must retain an open geometry to provide:

• gas-flow passages;
• liquid drainage;
• usable mass-transfer surface.

If PP Pall Rings soften or gradually deform, the packed bed may become denser.

That can contribute to:

• increased pressure drop;
• reduced void space;
• reduced hydraulic capacity.

Therefore, high-temperature service should trigger a more careful material review.

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3. There Is No Single Universal Maximum PP Packing Temperature

A single temperature limit should not be applied to every PP Pall Ring application.

The practical limit depends on:

• resin grade;
• chemical environment;
• continuous vs intermittent exposure;
• mechanical load;
• expected operating life.

For example, a temperature that may be acceptable in one aqueous service could be less appropriate in another chemical environment.

Therefore, the better question is:

Is the selected PP grade suitable for this chemical system at the actual continuous operating temperature?

For high-temperature applications, alternatives such as:

• PVDF packing;
• ceramic packing;
• suitable metal packing

may deserve evaluation.

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4. Strong Oxidizing Conditions Require Particular Caution

“Corrosion-resistant plastic” is too broad a description for material selection.

Some oxidizing chemical environments can be much more demanding for polymers than ordinary aqueous acid or alkali service.

When the process contains strong oxidizing species, engineers should confirm:

• chemical identity;
• concentration;
• temperature;
• exposure time.

PP should not be assumed suitable simply because it performs well in another acid service.

The actual process chemistry matters.

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5. Certain Organic Solvents May Exclude PP

A common mistake is applying experience from:

• water;
• acids;
• alkalis

directly to organic-solvent service.

Polymer compatibility with organic chemicals can be very different.

Some organic media can affect polymers through:

• swelling;
• softening;
• loss of mechanical strength;
• dimensional change.

Therefore, if a packed tower handles significant concentrations of:

• hydrocarbons;
• organic solvents;
• mixed organic streams,

PP compatibility should be checked specifically for that fluid system.

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6. Mixed Chemical Systems Need More Care Than Single-Chemical Tables Suggest

Real process streams are often mixtures.

A scrubber liquid may contain:

• acid;
• salts;
• oxidizing species;
• dissolved organics;
• reaction products.

A compatibility table for one pure chemical does not automatically describe the behavior of the complete process stream.

When several aggressive components are present, the material review should consider the combined exposure.

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7. Chemical Concentration Can Change the Decision

A polymer may behave well at one chemical concentration but less favorably at another.

Therefore:

“PP is resistant to chemical X” is not a complete engineering statement.

The relevant question is:

“Is PP suitable for chemical X at concentration Y and operating temperature Z?”

This is especially important for:

• concentrated process streams;
• evaporative systems;
• scrubber recycle loops where concentration can increase over time.

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8. Process Upsets Should Be Considered

Normal operating conditions are not always the highest exposure the packing will experience.

Possible upset conditions include:

• temperature excursions;
• temporary concentration increases;
• loss of dilution;
• abnormal chemical feed.

If occasional upset conditions could push PP outside its acceptable range, the material may not provide the desired operating reliability.

For critical service, selection should consider credible operating excursions, not only normal conditions.

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9. Deep Beds Can Increase Mechanical Demand

PP Pall Ring is lightweight, which is often an advantage.

However, very deep packed beds still create sustained mechanical loading.

The lower packing layers carry:

• packing weight;
• liquid holdup;
• additional load during abnormal hydraulic conditions.

At elevated temperature, long-term polymer creep may become more important.

Therefore, very deep PP packed beds deserve mechanical as well as chemical review.

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10. Long-Term Creep Can Matter Even Without Immediate Failure

Plastic deformation does not always happen suddenly.

A PP Pall Ring may appear acceptable at startup but gradually deform under:

• sustained load;
• elevated temperature;
• long operating time.

This behavior is generally described as creep.

Possible long-term effects include:

• reduced bed height;
• distorted packing geometry;
• increased local packing density.

A project requiring long service life at elevated temperature may therefore justify a more mechanically stable material.

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11. High Liquid Holdup Can Increase Bed Load

Under normal operation, the packing bed contains process liquid.

If the tower experiences:

• high liquid loading;
• severe foaming;
• flooding,

liquid holdup can increase substantially.

This increases effective load on:

• the packing;
• the support grid.

A PP bed that is mechanically comfortable under normal operation may experience more severe conditions during repeated hydraulic upsets.

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12. PP Is Not a Substitute for Correct Hydraulic Design

PP Pall Ring selection should not be used to solve an unrelated hydraulic problem.

For example, if a tower has:

• insufficient diameter;
• excessive gas velocity;
• poor liquid distribution;
• severe foaming;

changing to PP because it is lightweight does not automatically solve the problem.

Packing material and tower hydraulics are separate decisions.

The DAIER Tower Packing Engineering Assistant can be used for preliminary hydraulic and packing screening when the project requires broader engineering evaluation:

https://www.pxdaier.com/tower-packing-engineering-assistant.html

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13. PP May Not Be the Best Choice for High Mechanical-Abuse Service

Some towers are exposed to conditions such as:

• severe vibration;
• repeated packing movement;
• aggressive maintenance handling;
• unusual mechanical impact.

PP can offer useful toughness, but a polymer packing should not automatically be selected where very high mechanical rigidity is required.

The actual failure mode should be considered.

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14. High Gas Velocity Can Create Packing-Movement Concerns

PP Pall Rings have low density compared with:

• ceramic packing;
• metal packing.

That low weight is attractive for:

• support load;
• handling;
• installation.

But in some high-gas-velocity or upset conditions, lightweight packing may be more susceptible to movement.

Where this risk is significant, the tower may require:

• proper hold-down design;
• adequate hydraulic margin.

If the operating regime repeatedly moves the packing bed, simply adding stronger restraint without correcting the hydraulic cause is not enough.

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15. PP May Not Be Suitable Where Fire or Extreme Thermal Exposure Is a Design Concern

PP is an organic polymer.

Applications involving abnormal thermal hazards or high-temperature exposure may require materials with different fire and thermal behavior.

This does not make PP unsuitable for normal chemical tower service.

It means material selection should reflect the complete process safety and temperature environment.

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16. High-Purity Processes May Have Additional Material Requirements

Some applications impose cleanliness or extractable requirements beyond ordinary chemical resistance.

Examples may include certain:

• pharmaceutical processes;
• electronic-chemical processes;
• high-purity production systems.

In these cases, engineers may need to confirm:

• resin grade;
• additives;
• contamination requirements;
• project-specific material documentation.

Standard industrial PP should not automatically be assumed acceptable for every high-purity process.

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17. PP May Not Be Suitable When the Required Material Documentation Cannot Be Met

Some projects have specific QA requirements.

For example:

• resin traceability;
• material declaration;
• specific test documentation;
• regulatory requirements.

A PP Pall Ring can be chemically suitable but still fail the procurement requirement if the required documentation cannot be provided.

Therefore, product suitability includes both:

Technical Suitability + Project Specification Compliance

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18. PP vs PVDF: When Does PP Lose the Advantage?

PP generally has a major economic advantage over PVDF.

But the lower purchase price matters only when PP can provide adequate service life.

PVDF may deserve consideration when the process presents more demanding:

• temperature;
• chemical resistance;
• oxidizing conditions

than PP can reliably handle.

The decision should not be:

PP is cheaper, therefore choose PP.

It should be:

Is PP sufficiently resistant for the complete operating envelope?

If yes, PP may be the more economical choice.

If no, lower initial cost can create higher replacement and shutdown cost later.

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19. PP vs Ceramic Packing

Ceramic random packing may be considered where:

• high temperature;
• aggressive chemical exposure;
• polymer compatibility

makes PP less attractive.

Ceramic also has limitations.

It is:

• heavier;
• brittle;
• more sensitive to impact during installation.

Therefore, moving from PP to ceramic is not automatically an upgrade.

It is a different material trade-off.

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20. PP vs Metal Packing

Suitable metal packing may provide:

• higher mechanical strength;
• higher temperature capability.

But metal can introduce:

• corrosion risk;
• higher material cost;
• greater packing weight.

A stainless-steel packing should not automatically replace PP unless the selected alloy is compatible with the process chemistry.

Material selection remains application-specific.

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21. Low Price Should Not Override Compatibility

One of the main reasons PP Pall Ring is attractive is cost.

However, packing price is only one part of lifecycle cost.

Consider:

Packing Cost + Installation + Shutdown + Replacement + Lost Production

If an unsuitable PP bed must be replaced after a short operating period, the low purchase cost can become irrelevant.

For demanding service, compatibility has higher priority than initial unit price.

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22. When PP Pall Ring Is Still a Strong Candidate

A limitation page should not imply that PP is generally unsuitable.

PP Pall Ring can remain a very practical choice when:

• process chemistry is compatible;
• temperature is within a suitable range;
• mechanical conditions are reasonable;
• corrosion makes conventional metals unattractive;
• lightweight packing is beneficial;
• project economics favor plastic random packing.

This is why PP is widely considered for many:

• scrubbers;
• absorbers;
• gas-treatment systems.

The correct selection depends on actual conditions.

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23. Corrosive Scrubber Service Does Not Automatically Mean PVDF Is Required

It is also a mistake to move directly to the most expensive polymer.

If PP is fully compatible with:

• chemical species;
• concentration;
• temperature,

then selecting PVDF may provide little practical benefit relative to its additional cost.

The purpose of material selection is not:

“Choose the most resistant material available.”

It is:

Choose a material with sufficient resistance and reliability for the actual duty.

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24. PP May Be More Attractive in Large Packed Towers

Because PP has relatively low density, it can reduce:

• packing-bed weight;
• support loading;
• handling effort.

For large packed volumes, this can be a significant practical advantage.

However, tower size does not eliminate the need to review:

• temperature;
• chemistry;
• mechanical stability.

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25. Packing Size Still Matters After PP Has Been Selected

Choosing PP determines the material.

It does not determine the correct packing size.

For example, smaller PP Pall Rings may provide:

• higher surface area;

while larger PP Pall Rings may provide:

• lower pressure drop;
• greater fouling tolerance.

Therefore, material selection and size selection should remain separate engineering decisions.

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26. Fouling Service May Change the Preferred PP Pall Ring Size

A chemically compatible PP packing may still perform poorly if:

• passages are too small;
• solids accumulate;
• deposits form rapidly.

For dirty scrubber service, a more open packing geometry or larger size may deserve consideration.

The problem in this case is not necessarily PP material.

It may be the packing geometry.

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27. Do Not Confuse Material Failure with Fouling

If PP Pall Rings are removed from a tower and appear:

• covered in scale;
• coated with solids;
• blocked by deposits,

the problem may be fouling rather than chemical degradation.

By contrast, signs such as:

• softening;
• swelling;
• severe warping;
• embrittlement

may justify a material-compatibility investigation.

The failure mechanism matters before choosing a replacement material.

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28. Do Not Confuse Material Failure with Installation Damage

Deformed PP packing can also result from:

• compression;
• poor storage;
• rough handling;
• excessive mechanical loading.

Therefore, a damaged piece is not automatic proof that PP is chemically unsuitable.

Review:

• damage location;
• operating temperature;
• chemistry;
• installation history.

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29. When Replacing Failed PP Packing, Do Not Automatically Use the Same Material

If an existing PP bed has failed, identify the root cause first.

Possible reasons include:

• excessive temperature;
• chemical incompatibility;
• hydraulic overload;
• fouling;
• mechanical compression.

Only then decide whether to:

• reinstall PP;
• upgrade to PVDF;
• use ceramic;
• evaluate suitable metal packing;
• change packing size or geometry.

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30. A Material Upgrade Does Not Fix an Undersized Tower

Suppose PP packing repeatedly floods because gas velocity is excessive.

Replacing it with:

• PVDF;
• metal;
• ceramic

does not automatically increase tower diameter.

The hydraulic problem remains.

Material and hydraulic decisions should not be confused.

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Quick Decision Table

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Common Selection Mistakes

Mistake 1: Selecting PP Because the Liquid Is Acidic

Acidic service alone does not prove compatibility.

Confirm:

• actual acid;
• concentration;
• temperature.

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Mistake 2: Using Only a pH Value

pH does not identify:

• oxidizing behavior;
• solvent exposure;
• chemical species.

It is insufficient as the sole material-selection input.

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Mistake 3: Selecting the Cheapest Polymer

PP may be economical, but only when service life is acceptable.

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Mistake 4: Assuming All Plastic Packing Has the Same Resistance

PP, PE, PVDF and other polymers have different:

• chemical;
• temperature;
• mechanical

performance.

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Mistake 5: Using a Generic Maximum Temperature

A single generic temperature value can ignore:

• process chemistry;
• load;
• resin grade;
• exposure duration.

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Mistake 6: Upgrading to PVDF Without Checking Whether PP Is Already Sufficient

A more expensive material is not automatically the better economic decision.

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Mistake 7: Blaming PP for a Hydraulic Problem

Flooding, fouling and maldistribution are not automatically material failures.

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What Data Should Be Confirmed Before Ordering PP Pall Rings?

Before final material selection, provide:

Process Fluid

• chemical names;
• concentration;
• major impurities;
• oxidizing components if present.

Operating Conditions

• normal temperature;
• maximum credible temperature;
• pressure.

Tower Data

• internal diameter;
• packed height.

Hydraulic Conditions

• gas flow;
• liquid flow;
• expected turndown.

Packing Requirement

• Pall Ring size;
• required volume;
• existing packing if replacement.

Service History

For replacement projects:

• previous packing material;
• service life;
• reason for failure;
• photographs if available.

This information allows PP to be screened against the real duty instead of selected from a generic corrosion chart.

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Frequently Asked Questions

Is PP Pall Ring suitable for every acid scrubber?

No.

Suitability depends on the specific acid, concentration, temperature and other chemicals in the process.

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Can PP Pall Rings be used at high temperature?

PP temperature suitability is application-specific. Elevated temperature reduces polymer stiffness and can increase creep, so actual chemistry, load and continuous operating conditions must be reviewed.

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Is PP Pall Ring suitable for strong oxidizing chemicals?

It should not be assumed suitable. Strong oxidizing environments require specific compatibility review.

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Can PP Pall Rings be used with organic solvents?

Some organic chemical environments may affect polypropylene. Compatibility should be checked for the actual solvent or solvent mixture and operating temperature.

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When should PVDF Pall Ring be considered instead of PP?

PVDF may deserve consideration when process chemistry or temperature requires a higher level of polymer resistance than PP can reliably provide.

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Is ceramic packing always better than PP for corrosive service?

No.

Ceramic has different strengths and limitations, including higher weight and brittleness. Material choice depends on chemistry, temperature and mechanical requirements.

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Is stainless steel better than PP?

Not automatically.

A metal alloy must also be compatible with the process. PP can be more suitable than metal in many corrosive aqueous services.

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Can PP Pall Rings deform inside a tower?

They can if exposed to unsuitable temperature, sustained mechanical load, chemical attack or excessive compression.

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Does a failed PP bed always mean the material was wrong?

No.

Other causes may include:

• flooding;
• fouling;
• poor installation;
• mechanical compression;
• packing movement.

The root cause should be identified before changing materials.

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Selection Takeaway

PP Pall Ring is a strong candidate for many corrosive packed-tower applications, but its low cost and broad chemical resistance should not be interpreted as universal suitability.

PP should be reconsidered when the application involves:

• elevated continuous temperature;
• strong oxidizing conditions;
• uncertain organic-solvent compatibility;
• severe long-term mechanical loading;
• repeated temperature excursions;
• demanding purity or material-documentation requirements.

The correct preliminary selection sequence is:

Chemical Species → Concentration → Temperature → Mechanical Conditions → Operating Upsets → Required Service Life → Material Cost

The key question is not:

“Is PP corrosion-resistant?”

It is:

“Is this specific PP Pall Ring suitable for the complete chemical, thermal and mechanical operating envelope of this packed tower?”

If the answer is uncertain, compare PP with alternative materials before issuing the purchase order rather than after the tower has already been commissioned.