Root Cause Failure Analysis of Failed Rubber Grommets

Root Cause Failure Analysis of Failed Rubber Grommets

Background & Client Challenge

A global manufacturer of water and wellness equipment approached our laboratory to investigate premature failures observed in rubber sealing components used in water-handling applications. During field service, multiple EPDM rubber grommets developed visible surface residue described as an "oily substance," accompanied by discoloration, cracking, and localized fracture after extended operation. The failed components had been exposed to warm chlorinated water environments during service. Since these components were critical for sealing performance and long-term product reliability, the client required a failure analysis.

The client required a comprehensive characterization of a representative failed grommet to distinguish between formulation-related degradation, environmental aging, additive migration, and external contamination, and to identify opportunities for improving material performance and product reliability.

Our Analytical Methodology & Diagnostic Testing

Our laboratory performed a comprehensive failure analysis using complementary analytical techniques to evaluate the polymer composition, surface degradation, additive distribution, thermal behavior, and mechanical properties of the failed EPDM component.

This integrated approach enabled differentiation between material formulation issues, environmental degradation, and external contamination sources.

Analytical Results & Key Findings

The investigation determined that the observed oily residue was primarily caused by additive migration (blooming) from the EPDM matrix, which was accelerated by environmental degradation during service.

• Microscopic examination identified surface cracking, brittle fracture features, dark residue, and white powdery deposits on the failed grommet. SEM/EDS analysis confirmed increased concentrations of inorganic additives, including calcium-, zinc-, and sulfur-containing compounds, on the affected surfaces compared with cleaned areas, supporting additive migration as the source of the residue.
• FTIR analysis confirmed the material as EPDM rubber and identified a small amount of foreign polyether-based contamination, which was determined not to be the primary failure driver. Thermal analysis showed evidence of material aging, including an elevated glass transition temperature, indicating reduced polymer flexibility after prolonged environmental exposure.
• TGA characterization confirmed the material composition was consistent with a filled EPDM rubber formulation, including polymer matrix, carbon black, and inorganic additives. The detected inorganic constituents corresponded with the surface residues identified during chemical analysis, supporting the conclusion of additive migration. Mechanical testing confirmed the material remained consistent with EPDM rubber while exhibiting signs of long-term environmental degradation.

Root Cause Determination

Based on the combined analytical evidence, the failure mechanism was determined to involve two interconnected processes:

1. Additive Blooming and Surface Migration

During service, lower-density additives within the EPDM formulation migrated toward the surface due to incomplete compatibility and solubility within the polymer matrix. This blooming phenomenon produced the observed oily residue and white powdery deposits.

2. Chlorinated Water-Induced EPDM Degradation

Continuous exposure to elevated-temperature chlorinated water accelerated EPDM degradation, causing embrittlement, cracking, and fracture. The cracks exposed internal additive materials and accelerated their migration to the surface, increasing the visible oily appearance.

The overall failure mechanism was therefore concluded as:

EPDM degradation → surface cracking → additive exposure → additive migration/blooming → oily surface residue formation

Engineering Recommendations

To improve future product reliability and reduce similar field failures, the following recommendations were provided:

• Optimize EPDM formulation compatibility: Select additive systems with improved solubility and reduced migration tendency within the EPDM matrix.
• Consider peroxide-cured EPDM materials: Compared with sulfur-cured EPDM, peroxide-cured formulations generally provide improved chemical resistance, lower compression set, and reduced blooming potential.
• Reduce chlorine exposure severity: Minimize prolonged exposure to high-temperature chlorinated water or optimize chlorine concentration where possible.
• Implement preventive inspection programs: Regularly inspect grommets for early signs of surface cracking, discoloration, or residue formation.
• Perform periodic surface cleaning: Routine removal of migrated surface additives may delay visible bloom accumulation.

Value Delivered

By combining advanced surface characterization, chemical analysis, and thermal evaluation, our laboratory successfully identified the root cause of the rubber component failure and distinguished material-related degradation from external contamination. The findings provided the client with actionable guidance for material selection, formulation optimization, and reliability improvement, helping reduce future field failures and enhance product durability.