Evaluation of the aging of elastomeric acrylonitrile‐butadiene rubber and ethylene‐propylene‐diene monomer gaskets used to seal plates heat exchanger

Abstract

Acrylonitrile‐butadiene rubber (NBR) and ethylene‐propylene‐diene monomer (EPDM) gaskets are used as seals in plates heat exchangers due to their elasticity and resilience. However, contact with fluids, oxygen, ozone, and heat lead to permanent deformation. This study investigates the degradation of gaskets submitted to similar service conditions: compressed in a groove for up to 360 h at 100 and 120°C. The analysis was carried through compression set (CS), compression stress relaxation, surface morphology, Shore A hardness, indentation modulus profile, crosslink density, and Fourier transform infrared region with attenuated total reflection analysis. For EPDM, in thermo‐oxidative aging there is a counterbalance between chain scission and crosslinking, which increases CS while hardness and crosslink density remain low. For NBR, diffusion‐limited oxidation causes heterogeneous oxidation, creating a crosslinking network near the surface. The values for CS, Shore A hardness, and crosslink density raised to 50%, 10%, and 75%, respectively. Furthermore, the side thermo‐oxidation was reduced due to the presence of the groove, which reduces oxygen access. Using FITR analysis, a thermo‐oxidative interaction mechanism was proposed for the EPDM and NBR gaskets. It was concluded that EPDM presented a more reliable behavior for the gasket and seal applications under the analyzed conditions.

Service lifetime prediction of nitrile butadiene rubber gaskets used in plate heat exchangers

“…It is important to point out that the hardness measurements were obtained from the top of the gasket. This region was in contact with compression plates during aging, which hinder the oxygen contact and diffusion in this region 6 . Thus, hardness evolution may be influenced by the oxygen access and thus oxidative reactions, which depend on aging parameters.…”

“…The modulus is obtained by the ratio of the observed force and displacement [N mm −1 ] in a range of force, from 3 to 5 N that comprehends a linear correlation between these measurements. This test was based on the examinations presented in previous studies 6,27 . Figure 3(b) illustrates all the 14 scanning points across the sample cross‐section.…”

“…A two-direction displacement system was coupled to an Instron 23-30 universal machine test to scan the stiffness along the middle cross-section of the samples to identify oxidation profile. 6,15,27 The test was carried out in a 5 mm thick slice from the central cross-section of the test piece. Thus, this specimen was positioned with aligners in its seat (see Figure 3a).…”

“…To the best of the present study authors' knowledge, studies on long aging tests, sealing behavior and lifetime prediction in gaskets are rare in the literature. Recently, Souza et al 6 evaluated the influence of an accommodation groove and the aging behavior of NBR and EPDM gaskets used in plate heat exchangers during the aging time.…”

“…4 At higher temperatures (125-150 C) crosslinking reactions between rubber chains were also observed. 5 Souza et al 6 studied the oxidation mechanisms for NBR and EPDM gaskets based on chemical, surface, and mechanical analysis. It was proposed that aging in NBR elastomers occurs due to different crosslinking mechanisms, such as secondary carbon and π-bond in C=C unsaturation.…”