Common Failure Modes in Vessel Roller Systems: Identification, Root Cause Analysis, and Prevention

A pipe-laying vessel returns to port after a 14-month campaign. The maintenance engineer inspects the roller system and finds five different types of damage across 200+ pad positions: uniform abrasion on the stinger rollers, edge tearing on two tensioner tracks, a delaminated pad on a guide roller, surface cracking on three topside pads, and a compression-set pad that no longer springs back to its original thickness. Each failure tells a different story — and each demands a different corrective action.

Vessel roller failure follows predictable patterns. The five most common failure modes in polyurethane roller pad systems are abrasive wear, delamination, compression set, hydrolytic degradation, and thermal or UV-induced cracking. Identifying which failure mode caused a pad to degrade — through systematic root cause identification rather than assumption — determines whether the corrective action is a material change, a process adjustment, or a design modification. Treating every failure as a material problem misses the operational and environmental factors that often drive premature polyurethane pad degradation.

This article provides vessel engineers with a diagnostic framework for each failure mode: what it looks like, why it happens, and how to prevent it.

1. Failure Mode 1: Abrasive Wear

What It Looks Like

Gradual, progressive material loss across the pad contact surface. The pad gets thinner over time with a smooth, polished wear face. Wear is typically most pronounced at the center of the contact zone and tapers toward the edges. This is the most common and most predictable vessel roller failure mode.

Root Cause

Abrasive wear results from pipe contact — specifically, the concrete weight coating or anti-corrosion coating sliding across the polyurethane surface under load. The wear rate depends on pipe coating roughness, contact pressure, sliding distance per lay cycle, and pad hardness. Harder pads (Shore 90A–95A) resist abrasion better but absorb less impact. Softer pads (Shore 70A–85A) offer better pipe protection but wear faster.

Prevention

Abrasive wear cannot be eliminated — it is inherent to the application. The goal is to manage it. Specify pad hardness matched to the pipe coating type: harder grades for rough concrete coatings, softer grades for smooth FBE or 3LPE coatings. Ensure pads start at adequate thickness to provide the required service life. Track wear rate through periodic thickness measurements during the campaign and schedule replacement before pads reach minimum thickness thresholds.

2. Failure Mode 2: Delamination and Bond Failure

What It Looks Like

The polyurethane separates from the steel roller core. Early signs include a visible gap at the pad edge, a slight lifting of the coating, or a hollow sound when the pad is tapped. Advanced delamination produces a loose or shifted coating that moves under pipe contact — an immediate safety hazard.

Root Cause

Delamination traces back to one of four causes. The most common is inadequate surface preparation during manufacturing — steel not blasted to Sa 2.5 standard, primer applied over oxidized surfaces, or insufficient flash-off time between primer and polyurethane application. The second cause is environmental attack on the bond line: seawater moisture migrating through pad edges to the metal-polyurethane interface, corroding the bond from within. Third, stress concentration from sharp geometric transitions (corners, undercuts, rapid thickness changes) focuses load at the interface rather than distributing it through the pad body. Fourth, thermal cycling — the mismatch between steel and polyurethane expansion rates — fatigues the bond over repeated temperature cycles.

Prevention

Prevention starts at manufacturing. Require minimum bond strength of 6 MPa per ASTM D4541 and specify cohesive failure testing — meaning the polyurethane should tear before the bond fails. For in-service prevention, protect pad edges from mechanical damage that opens pathways for moisture intrusion. Inspect the bond line during between-campaign maintenance using a feeler gauge at pad edges. Catch delamination early, because once it starts, it accelerates under load.

3. Failure Mode 3: Compression Set

What It Looks Like

The pad does not return to its original thickness after load removal. A flat spot or permanent indentation appears at the contact zone. The pad feels harder and less resilient than new material. In severe cases, the pad’s reduced thickness creates an uneven roller profile that affects pipe tracking.

Root Cause

Compression set occurs when polyurethane is held under sustained load beyond its recovery capacity. Two conditions drive it on vessel rollers: static loading during extended standby (pipe resting on rollers without movement) and incorrect hardness specification (pad too soft for the load). Temperature amplifies the problem — elevated heat reduces elastic recovery. Poor storage practices contribute too: spare pads stacked under heavy loads develop compression set before installation.

Prevention

For operational compression set, relieve static loads during extended standby. If a pipe must remain on rollers for weeks, rotate which rollers carry the load periodically. Specify hardness grades appropriate to the load — tensioner pads carrying thousands of kilograms require Shore 85A–95A, not softer grades designed for light-duty guide positions. For stored spares, follow proper storage guidelines: flat, unstressed, on cradles that support the steel core rather than resting on the polyurethane surface.

4. Failure Mode 4: Hydrolytic Degradation

What It Looks Like

Surface softening, tackiness, or a gummy texture. In advanced cases, the material crumbles or tears with minimal force. The degradation often starts at the outer surface and progresses inward. Hydrolysis typically manifests after extended service in warm, wet environments — often becoming apparent only when the pad is loaded and the weakened material fails under stress that it previously handled.

Root Cause

Hydrolysis is a chemical reaction where water molecules attack the polymer chain, breaking bonds and reducing molecular weight. Polyester-based polyurethanes are highly susceptible. The ester linkages in the polymer backbone absorb moisture and degrade progressively, with the rate accelerating at temperatures above 50°C (122°F). This failure mode is almost entirely preventable through correct chemistry selection.

Prevention

Specify polyether-based formulations for all marine roller applications. Polyether linkages resist hydrolytic attack, making them the industry standard for vessel roller coatings exposed to seawater. If a pad on a marine vessel fails through hydrolysis, the root cause is almost certainly a formulation error — polyester material specified where polyether was required. This is a supplier and specification issue, not an operational one.

5. Failure Mode 5: UV and Thermal Cracking

What It Looks Like

Surface cracking, crazing, or a network of fine fissures across the exposed pad face. Surface chalking — a white, powdery residue — often precedes visible cracking. Hardness testing reveals the pad has stiffened beyond specification. Cracks propagate under cyclic loading, eventually reaching the bond line and triggering delamination.

Root Cause

UV radiation breaks polymer chains at the pad surface, creating a brittle layer that cracks under mechanical stress. UV photons generate free radicals that initiate chain scission and crosslinking reactions, stiffening and embrittling the surface. Thermal aging works through a slower pathway — sustained elevated temperatures accelerate oxidation that degrades the polymer. Both mechanisms affect topside pads more than submerged or shaded positions.

Prevention

Use UV-stabilized formulations for all topside roller positions. HALS (Hindered Amine Light Stabilizers) and UV absorbers extend outdoor service life significantly. Between campaigns, cover exposed pads with opaque sheeting to halt UV accumulation during idle periods — a simple measure detailed in our preventative maintenance guide. For pads on vessels operating in tropical environments, aliphatic isocyanate-based topcoats provide superior UV resistance compared to standard aromatic systems, though at higher cost. More detail on weathering mechanisms is available in our article on environmental durability and UV resistance.

6. The Root Cause Identification Process

When a pad fails, resist the impulse to simply replace it and move on. A failed pad is a diagnostic opportunity. Photograph the damage, record the pad position, note the pipe type and campaign duration, and preserve the failed pad for analysis if possible.

Ask three questions. First, is this failure premature or expected? Normal abrasive wear after 14 months is expected. Delamination after three months is not. Second, is the failure isolated or systematic? A single delaminated pad suggests a manufacturing defect; multiple failures at similar positions suggest alignment, loading, or specification issues. Third, does the failure mode match the environmental exposure? Hydrolysis on a topside pad points to contamination or incorrect chemistry, not environmental degradation. This structured approach — consistent with the failure mode and effects analysis (FMEA) methodology described in the SAE J1739 standard — turns each failure into actionable data that guides specification improvements and maintenance priorities across campaigns.

7. Frequently Asked Questions

What is the most common vessel roller failure mode?

Abrasive wear accounts for the majority of replacements. It is also the most predictable and manageable — pads wear at measurable rates that allow scheduled replacement. The most costly failure mode is delamination, because it occurs suddenly and often forces unplanned vessel downtime.

Can I determine the failure mode from visual inspection alone?

In most cases, yes. Abrasive wear produces smooth, thinned surfaces. Delamination shows as edge lifting or coating shift. Compression set creates flat spots. Hydrolysis causes softening and tackiness. UV cracking produces surface fissures and chalking. When evidence is ambiguous, hardness testing or laboratory analysis can confirm the mechanism.

How do I prevent multiple failure modes simultaneously?

Specify polyether-based, UV-stabilized polyurethane at the correct hardness for each position. Ensure proper surface preparation and bond strength during manufacturing. Follow documented inspection and maintenance protocols during campaigns. Cover pads between campaigns. These four practices address 90% of preventable failures.

Does hardness affect which failure modes are most likely?

Yes. Softer pads (Shore 70A–80A) are more susceptible to abrasive wear and compression set but less prone to cracking. Harder pads (Shore 90A–95A) resist wear better but may crack under impact if formulated without adequate tear resistance. Matching hardness to each position’s demands is the foundation of failure prevention.

When should I involve the pad manufacturer in failure analysis?

Involve the manufacturer when failure occurs prematurely, when multiple pads fail in the same pattern, or when the failure mode suggests a material defect (hydrolysis, widespread delamination). Reputable manufacturers welcome failure data — it improves their products and strengthens the supplier relationship.

Pepson has manufactured high-performance polyurethane elastomers since 1998, serving industries worldwide from our Dongguan, China facility. Our material science expertise and quality manufacturing deliver solutions optimized for demanding applications.