When Should Plastic Pall Rings Be Replaced with Metal Pall Rings?

Replacing Plastic Pall Rings with Metal Pall Rings is not a simple material upgrade. Even at the same nominal 25, 38, 50 or 76 mm size, changing from plastic to metal can dramatically increase packed-bed weight and alter void fraction, packing factor, mechanical behavior and chemical compatibility.

A metal replacement becomes worth evaluating when the existing plastic packing is limited by:

• operating temperature;
• mechanical deformation;
• structural durability;
• process changes;
• hydraulic requirements.

But plastic should often remain in service where:

• corrosion resistance of the selected polymer is appropriate;
• temperature remains inside the verified polymer limit;
• low packed-bed weight is valuable;
• existing tower performance is satisfactory.

The correct question is therefore:

What problem is the material change supposed to solve?

If there is no defined problem, changing Plastic Pall Ring to Metal Pall Ring may add cost, structural load and corrosion risk without providing meaningful benefit.

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1. Direct Answer

Consider replacing Plastic Pall Ring with Metal Pall Ring when:

• operating temperature has moved beyond the confirmed capability of the existing polymer;
• plastic elements are deforming, softening or mechanically deteriorating;
• the tower needs greater metallic mechanical robustness;
• process conditions have changed and the polymer is no longer appropriate;
• a hydraulic review shows that the selected metal geometry offers a useful operating advantage;
• the existing tower internals can safely carry the much heavier metal bed.

Keep Plastic Pall Ring when:

• its chemical compatibility is proven;
• operating temperature is suitable;
• the bed remains mechanically intact;
• hydraulic performance is acceptable;
• low tower weight is important;
• there is no engineering reason for a material conversion.

The central principle is:

Replace the material only to solve a verified process, mechanical or compatibility constraint.

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2. Same Geometry Family Does Not Mean Like-for-Like Replacement

Both products are called:

Pall Ring

and both use an open ring structure.

But the material changes how the element can be manufactured.

DAIER's verified Plastic Pall Ring catalog includes molded dimensions such as:

• 25 × 25 × 1.2 mm;
• 38 × 38 × 1.4 mm;
• 50 × 50 × 1.5 mm;
• 76 × 76 × 2.6 mm. 

The Metal Pall Ring catalog includes:

• 25 × 25 × 0.4 mm;
• 38 × 38 × 0.5 mm;
• 50 × 50 × 0.5 mm;
• 76 × 76 × 1.0 mm. 

So even at the same nominal diameter:

the physical construction of the element is different.

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3. DAIER Plastic vs Metal Pall Ring Data

 

These supplier-specific data reveal something important:

Surface area remains surprisingly similar, but bed openness and especially packed-bed weight change dramatically.

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4. Surface Area Changes Much Less Than Many Buyers Expect

At matched sizes:

25 mm

Plastic:

213 m²/m³

Metal:

212 m²/m³

38 mm

151 vs 145 m²/m³

50 mm

100 vs 106 m²/m³

76 mm

73.2 vs 69 m²/m³. 

The differences are relatively small.

Therefore:

A Plastic → Metal Pall Ring conversion should not normally be justified by claiming dramatically more geometric surface area.

That is not what these catalog data show.

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5. The Real Difference Is Void Fraction

Metal Pall Ring has substantially higher verified free volume at every matched size:

 

This gives the metal geometry a significantly more open catalog bed structure.

But:

higher void fraction does not automatically mean lower actual pressure drop or higher tower capacity.

Operating conditions still matter.

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6. Why Metal Pall Rings Can Achieve Higher Void Fraction

Metal can be formed into relatively thin:

• walls;
• tabs;
• structural sections.

For example:

50 mm Plastic Pall Ring

approximately 1.5 mm wall geometry

versus:

50 mm Metal Pall Ring

approximately 0.5 mm metal thickness. 

Less solid volume inside each packing element can create greater bed free volume.

That is an important material/manufacturing advantage of metal construction.

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7. But Metal Pall Rings Are Dramatically Heavier

The dry bulk-density difference is enormous.

25 mm

Plastic:

68 kg/m³

Metal:

288 kg/m³

38 mm

60 vs 246 kg/m³

50 mm

44.5 vs 185 kg/m³

76 mm

48 vs 265 kg/m³. 

This is one of the most important retrofit constraints.

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8. A Material Change Can Multiply the Tower Packing Load

Consider 50 mm Pall Ring.

For a 20 m³ packed bed:

Plastic Pall Ring

20 × 44.5 ≈ 890 kg

of catalog dry packing weight.

Metal Pall Ring

20 × 185 ≈ 3,700 kg

of catalog dry packing weight.

The metal bed adds approximately:

2.81 tonnes of dry packing load.

This calculation addresses dry bulk packing only.

Final mechanical review must also consider:

• liquid holdup;
• deposits;
• support weight;
• dynamic operating loads.

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9. Why Support Grid Review Is Mandatory

If an existing tower was originally designed for Plastic Pall Ring, its:

• packing support;
• support beams;
• shell attachments

may have been sized around a much lighter bed.

Replacing plastic with metal without structural review can significantly increase load.

Therefore:

Plastic → Metal Pall Ring should automatically trigger a support-load check.

This is not optional engineering housekeeping.

It is part of the replacement decision.

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10. 76 mm Shows the Weight Difference Most Dramatically

At 76 mm:

Plastic Pall Ring

48 kg/m³

Metal Pall Ring

265 kg/m³. 

That is more than a fivefold difference in catalog dry bulk density.

One reason is that the verified Metal Pall Ring uses approximately:

1.0 mm metal thickness

at this size.

Therefore:

“larger metal packing is always lighter per cubic meter” is not valid.

The exact product construction must be checked.

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11. Packing Factor Usually Favors Metal—but Not Always

The verified dry packing factors are:

 

At:

• 25 mm;
• 38 mm;
• 76 mm,

Metal Pall Ring has the lower catalog packing factor.

But at 50 mm:

Plastic = 127 m⁻¹

Metal = 128.5 m⁻¹

They are essentially the same, with the plastic value slightly lower.

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12. Why the 50 mm Result Is Important

It prevents another bad generic claim:

“Metal Pall Ring always has a lower packing factor than Plastic Pall Ring.”

The catalog does not support that.

At 50 mm, the two are essentially equal.

Therefore the hydraulic justification for changing 50 mm Plastic Pall Ring to metal must come from:

• actual process data;

not from a generic material assumption.

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13. Packing Factor Is Not Operating Pressure Drop

Even where Metal Pall Ring has a lower dry packing factor, actual tower pressure drop depends on:

• gas or vapor velocity;
• liquid rate;
• gas density;
• liquid viscosity;
• packed height.

Therefore:

Do not calculate a percentage ΔP reduction directly from the packing-factor ratio.

The physical data tell you that the packing geometry changes.

They do not tell you the final operating pressure drop without process conditions.

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14. When Temperature Is the Real Reason to Change

One of the strongest reasons to move from plastic to metal is:

operating temperature beyond the verified capability of the selected polymer.

Plastic temperature capability depends heavily on the actual material grade.

For example:

• PP;
• PVC;
• CPVC;
• PVDF;
• PTFE

have very different usable temperature and chemical envelopes.

Therefore:

Do not describe “plastic Pall Ring” as having one universal maximum temperature.

The existing polymer must first be identified.

If operating temperature exceeds its verified continuous or peak limit, another polymer or metal may need to be evaluated.

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15. Temperature Does Not Automatically Mean Metal Is Correct

Higher temperature may eliminate one plastic material.

But it does not automatically establish:

SS304 or SS316L is compatible.

The metal alloy must still tolerate:

• chemical composition;
• concentration;
• chlorides;
• oxidizers;
• corrosion mechanism.

The correct sequence is:

Existing Polymer Limit → Required Temperature → Chemical Compatibility → Candidate Metal Alloy

not:

Hot Process → Stainless Steel Automatically.

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16. Mechanical Deformation Can Justify a Metal Retrofit

Plastic elements may experience problems if exposed to inappropriate:

• temperature;
• mechanical load;
• long-term service conditions.

Possible field symptoms can include:

• deformation;
• distortion;
• collapse of element openings.

If the existing plastic packing is physically losing geometry, a metal alternative may deserve stronger evaluation.

However:

first identify why deformation occurred.

Changing material without correcting abnormal operating conditions may simply move the problem elsewhere.

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17. Metal Can Provide Stronger Element Rigidity

Thin formed metal can provide substantial structural stiffness while maintaining large openings.

That can be useful where:

• mechanical integrity;
• long service life under appropriate conditions

are important.

But metallic rigidity introduces other considerations:

• greater packed-bed weight;
• corrosion;
• cost;
• sharper handling edges.

So “stronger” is not equivalent to “better overall.”

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18. Corrosive Service Often Favors Plastic

One of the strongest reasons not to switch to metal is chemical compatibility.

A properly selected polymer can be valuable in many corrosive aqueous systems.

A metal alloy can fail if:

• corrosion mechanism is underestimated;
• chlorides are high;
• oxidizing/reducing conditions change;
• temperature accelerates corrosion.

Therefore:

A Plastic Pall Ring that already has proven chemical compatibility should not be replaced with metal merely for mechanical prestige.

The corrosion review comes first.

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19. Polymer Selection Can Solve the Problem Without Moving to Metal

If the current plastic material is unsuitable, the alternative may not need to be metal.

Depending on the actual stream, another polymer may be evaluated, such as:

• PVDF;
• PTFE;
• CPVC;

where manufacturing availability and compatibility are confirmed.

DAIER already treats PP vs PVDF Pall Ring as a separate material-selection decision.

Therefore:

Plastic → Metal is only one possible material pathway.

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20. Existing Hydraulic Performance Matters

Suppose an existing Plastic Pall Ring tower already has:

• acceptable pressure drop;
• sufficient capacity;
• required removal efficiency;
• stable operation.

Then changing to metal simply because metal has:

• higher voidage;

may provide little practical benefit.

A successful existing tower has real engineering value:

proven operating history.

Do not discard it without a defined improvement objective.

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21. When Hydraulic Capacity Can Justify Metal Review

Metal Pall Ring may deserve evaluation when:

• gas throughput needs to increase;
• pressure-drop margin is tight;
• the matched metal model's higher void fraction is useful.

For example at 38 mm:

Plastic

91% void220 m⁻¹ packing factor

Metal

96.7% void151.7 m⁻¹. 

That creates a legitimate reason for hydraulic engineering review.

It does not by itself guarantee the retrofit will solve the capacity problem.

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22. Why 38 mm Is a Strong Retrofit Candidate for Evaluation

38 mm has:

• similar geometric surface area;
• much higher metal void fraction;
• considerably lower metal packing factor.

Surface area:

151 plastic vs 145 metal m²/m³

is relatively close.

So compared with other sizes, this can create an attractive preliminary situation:

similar geometric area with a more open metal bed position.

But the metal bed weight rises from:

60 → 246 kg/m³.

That structural penalty cannot be ignored.

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23. 25 mm Gives a Similar Hydraulic Story

At 25 mm:

Surface Area

Plastic:

213 m²/m³

Metal:

212 m²/m³

Almost identical.

Void Fraction

90% → 96.2%.

Packing Factor

285 → 229.8 m⁻¹. 

Again, Metal Pall Ring creates a more open physical position without sacrificing much geometric area.

But dry bulk density changes:

68 → 288 kg/m³.

The retrofit therefore exchanges:

hydraulic openness

for:

much higher structural load.

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24. 50 mm Is Different

At 50 mm:

Plastic

100 m²/m³91.5% void44.5 kg/m³127 m⁻¹

Metal

106 m²/m³97.5% void185 kg/m³128.5 m⁻¹. 

Metal provides:

• more voidage;
• slightly more surface area.

But the dry packing factor is essentially unchanged.

Therefore:

A 50 mm Plastic → Metal conversion requires a stronger justification than simply “metal has lower packing factor.”

It does not in this catalog comparison.

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25. Same Nominal Size Does Not Guarantee the Same Packed Height Is Correct

Even where surface areas are similar, the material change alters:

• wall structure;
• voidage;
• wetting characteristics;
• hydraulic behavior.

Therefore:

same nominal size + same bed height should not automatically be treated as a guaranteed equivalent retrofit.

Process review is still required.

The need may be smaller than when changing packing family, but it should not be ignored.

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26. Metal and Plastic Wetting Behavior Can Differ

Plastic and metal surfaces can interact differently with liquids.

Effective wetting depends on:

• surface condition;
• fluid properties;
• contamination;
• operating history.

Therefore geometric surface area alone does not tell you:

how much of the available area will actually participate in mass transfer.

This is another reason a material conversion should be evaluated as a process change rather than just a purchasing change.

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27. Fouling Can Change the Decision

Higher void fraction may be useful where moderate fouling exists.

Metal Pall Ring provides higher verified voidage at all matched sizes.

But fouling may also be driven by:

• crystals;
• sticky solids;
• polymerization;
• biological material.

Neither Plastic nor Metal Pall Ring should be described as:

• clog-proof;
• self-cleaning.

Severe fouling may require:

• larger packing;
• another geometry;
• process modifications.

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28. Fire and Process-Safety Requirements May Affect Material Choice

Some projects have material requirements related to:

• combustibility;
• process-safety philosophy;
• equipment standards.

These requirements are project-specific.

Where the specification prohibits a polymer packing for a particular service, metal may become necessary.

But the governing:

• code;
• owner standard;
• hazard review

should define the requirement.

Do not make universal fire-safety claims from packing material alone.

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29. Weight Can Be the Reason NOT to Upgrade

For many existing vessels, the strongest argument against metal may simply be:

mechanical load.

At 76 mm:

• plastic = 48 kg/m³;
• metal = 265 kg/m³. 

For a large bed, that can add several tonnes.

If the support system was designed for plastic, changing to metal may require:

• new support beams;
• stronger support grid;
• structural modifications.

That can change the economics of the entire retrofit.

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30. Cost Should Be Compared as Total Retrofit Cost

Do not compare only:

USD per cubic meter of packing.

A Plastic → Metal project can also affect:

• structural calculations;
• packing supports;
• freight;
• installation labor;
• alloy cost;
• corrosion allowance;
• shutdown work.

Therefore the correct commercial comparison is:

total installed retrofit cost

rather than:

packing purchase price alone.

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Plastic Pall Ring vs Metal Pall Ring Retrofit Decision Table

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31. Quick Retrofit Logic

Keep Plastic Pall Ring when:

• temperature is acceptable;
• polymer compatibility is proven;
• elements remain mechanically sound;
• pressure drop is acceptable;
• bed weight matters.

Evaluate Metal Pall Ring when:

• temperature exceeds the verified polymer limit;
• plastic deformation is occurring;
• process specifications require metal;
• hydraulic review identifies a real advantage;
• structural loading can accept the new bed.

Evaluate another plastic material first when:

• the problem is chemical or temperature compatibility;
• a suitable higher-performance polymer may solve it without the mechanical-weight penalty of metal.

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32. What Data Are Required Before a Plastic-to-Metal Retrofit?

Before requesting a final replacement recommendation, provide:

• existing Plastic Pall Ring size;
• exact polymer if known;
• tower internal diameter;
• packed height;
• operating temperature;
• peak temperature;
• gas/vapor composition;
• liquid composition;
• concentration;
• gas/vapor flow;
• liquid flow;
• operating pressure;
• existing pressure drop;
• reason for replacement;
• current fouling condition.

Also provide internals information:

• support grid;
• support beams;
• hold-down arrangement;
• manway size.

For mechanical review, confirm whether the existing support can carry the proposed metal bed.

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33. What Should the Supplier Confirm?

For both old and proposed packing, confirm:

• nominal size;
• exact dimensions;
• material grade;
• specific surface area;
• void fraction;
• bulk density;
• packing count;
• dry packing factor.

For metal packing additionally confirm:

• metal thickness;
• alloy specification.

For plastic packing confirm:

• polymer grade;
• project-specific temperature and chemical compatibility.

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Common Replacement Mistakes

Assuming Metal Is Automatically Better

It can solve specific problems but introduces major weight and corrosion considerations.

Assuming the Same Pall Ring Size Means Like-for-Like Replacement

Material changes element construction and bed properties.

Saying Metal Provides Much More Surface Area

DAIER's matched-size data show surface areas are actually very similar.

Ignoring Bed Weight

Metal can weigh four to five times as much per packed cubic meter in these examples.

Assuming Metal Always Has Lower Packing Factor

The 50 mm catalog comparison does not support that.

Using pH Alone to Decide Plastic vs Metal

Actual chemical species, concentration and temperature matter.

Automatically Choosing SS316L

Alloy suitability must be confirmed for the actual stream.

Keeping the Same Support Without Structural Review

The increase in dry load can be substantial.

Changing Material Without Identifying the Existing Problem

A retrofit should solve a defined constraint.

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Frequently Asked Questions

Can Plastic Pall Ring be directly replaced by Metal Pall Ring of the same size?

Do not treat it as a simple like-for-like replacement. The nominal size may match, but void fraction, bulk density, packing factor, wall construction and material compatibility differ.

Do Metal Pall Rings have more surface area?

Not significantly in DAIER's matched-size data.

For example at 25 mm:

• Plastic — 213 m²/m³;
• Metal — 212 m²/m³. 

Which has higher void fraction?

Metal Pall Ring at all matched 25, 38, 50 and 76 mm sizes in the verified catalog data.

Which is lighter?

Plastic Pall Ring by a very large margin.

What is the 38 mm weight comparison?

• Plastic — about 60 kg/m³;
• Metal — about 246 kg/m³.

Does Metal Pall Ring always have lower packing factor?

No. At 50 mm, the values are approximately:

• Plastic — 127 m⁻¹;
• Metal — 128.5 m⁻¹.

When is metal most worth evaluating?

When polymer temperature capability, mechanical integrity, owner specification or a real hydraulic constraint makes the current plastic packing unsuitable.

When should plastic remain?

When its chemical compatibility and temperature capability are suitable and the existing bed performs correctly.

Can I switch from PP Pall Ring directly to SS316L Pall Ring?

Only after reviewing actual process chemistry, temperature, hydraulics and structural load. SS316L should not be selected automatically.

Does a metal retrofit require a new support grid?

Not always, but the existing support and beams must be checked because dry packing weight can increase dramatically.

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Selection Takeaway

Replacing Plastic Pall Ring with Metal Pall Ring is primarily a material, hydraulic and mechanical retrofit—not a simple performance upgrade.

At 25 mm:

Plastic → 213 m²/m³ / 90% void / 68 kg/m³ / 285 m⁻¹

versus:

Metal → 212 m²/m³ / 96.2% void / 288 kg/m³ / 229.8 m⁻¹.

At 38 mm:

Plastic → 151 m²/m³ / 91% void / 60 kg/m³ / 220 m⁻¹

versus:

Metal → 145 m²/m³ / 96.7% void / 246 kg/m³ / 151.7 m⁻¹.

At 50 mm:

Plastic → 100 m²/m³ / 91.5% void / 44.5 kg/m³ / 127 m⁻¹

versus:

Metal → 106 m²/m³ / 97.5% void / 185 kg/m³ / 128.5 m⁻¹. 

The most important conclusions are:

• geometric surface area can remain almost unchanged;
• metal provides much greater verified void fraction;
• metal dramatically increases packed-bed weight;
• packing-factor benefit is size-dependent;
• polymer and metal corrosion compatibility must be evaluated separately.

Therefore the correct retrofit sequence is:

Why Is the Existing Plastic Packing Inadequate? → Polymer / Temperature / Chemistry Review → Hydraulic Requirement → Compare Exact Plastic and Metal Pall Ring Data → Structural Load Review → Alloy Selection → Internals Compatibility → Final Retrofit Decision

The key principle is:

Do not replace Plastic Pall Ring with Metal Pall Ring because metal sounds more durable or advanced. Replace it only when the metal version solves a verified limitation of the existing plastic bed without creating a larger corrosion, hydraulic or structural problem.