Study on fretting behavior of rubber O-ring seal in high-pressure gaseous hydrogen

https://doi.org/10.1016/j.ijhydene.2019.02.224Get rights and content

Highlights

  • A model for fretting behavior of rubber seal in hydrogen is developed.

  • Fretting running regime can be obviously changed by swelling.

  • Swelling effect aggravates the fretting wear of rubber O-ring seals.

Abstract

Fretting is a low-amplitude reciprocating movement which may lead to seal failure, it is important to explore the fretting characteristic of a rubber seal in hydrogen atmosphere. In this work, a numerical model considering the effect of hydrogen swelling was presented to study the fretting behavior of a rubber seal. The fretting running condition was analyzed. Results showed that, the amplitude of reciprocating motion made a great effect on the fretting state of rubber seals, the O-ring seal in high-pressure hydrogen atmosphere exhibits a higher propensity to run in the sticking regime because of swelling effect. The fluctuation range of the peak Mises stress in hydrogen was much larger than that in air, leading to aggravating the fatigue failure of the rubber seal. It was more difficult to produce relative slip in hydrogen compared with in air, resulting in exacerbating the fretting wear of rubber seals.

Introduction

Hydrogen has been regarded as the most promising candidate energy for the future [1], [2], [3], [4], [5], [6]. The high-pressure hydrogen gas storage technology nowadays is utilized extensively in hydrogen service systems [7], [8], [9], [10], [11], [12], [13], [14]. The rubber seal is a key part in a high-pressure hydrogen system, e.g. valve and piston seal, which can prevent the leakage of hydrogen gas [15], [16], [17]. Particularly, fretting, low-amplitude oscillatory motion on the sealing contact surface, can commonly occur in a reciprocating O-ring seal. While the rubber seals are imposed with small-amplitude reciprocating displacement, for example rubber dynamic seals with displacement amplitude of smaller than 3 mm for compact tension (CT) testing machine in high-pressure hydrogen environment, there may be various working states on sealing surfaces (including sticking, mixed slip, and gross slip), then seal failure because of fretting damage may happen [18]. Fretting, however, is different from sliding wear [19]. Many studies on wear behavior of rubber have been reported, while few works on fretting wear of rubber have been reported. Shen et al. [20] studied the fretting wear of rubber with the fretting test in air. Baek et al. [21] explored the influence of surface roughness of rubber coatings on the fretting characteristic. Nevertheless, these existing studies are limited to fretting behavior in ambient air. More importantly, the seal failure induced by swelling because of the solute hydrogen in high-pressure hydrogen atmosphere may occur [22]. Therefore we have previously investigated the static sealing behavior of a O-ring seal exposed to gaseous hydrogen and the result showed that the swelling strongly affected the static sealing behavior [23]. Unfortunately, reports on fretting damage of rubber seals exposed to hydrogen gas are scarce, the influence of hydrogen swelling on fretting behavior at a high pressure (up to 100 MPa) still remains unclear.

In this study, a numerical model for exploring the fretting characteristic of a rubber O-ring seal was presented with respect to swelling because of solute hydrogen. The fretting running condition was studied. Both the Mises stress and the contact pressure were employed to discuss the influence of hydrogen swelling on the fretting characteristic.

Section snippets

Theoretical equations

  • (1)

    Hydrogen diffusion model

The equation of hydrogen transport follows Fick's second law [24]:cHτ=DH(2cHx2+2cHy2+2cHz2)where /τ, DH and cH denote the time derivative, the hydrogen diffusion coefficient and the hydrogen content.

  • (2)

    Mechanical equation

The rubber O-ring is considered as hyperelastic material and the constitutive equation with a strain energy density function decided by the Mooney–Rivlin model is adopted in this study to describe the hyperelastic characteristic. The strain energy

Finite element model

The cross-section of the seal component is shown in Fig. 1. It consists of an O-ring and a wedge-ring. The O-ring is compressed by the shaft in the radial direction (x-axis). There are two motion directions in the reciprocating movement, namely, inward stroke and outward stroke. When the shaft moves to the limit of the inward stroke, it is called the first-quarter of a period (0.25 T) for each cycle.

Fretting running condition

As shown in Fig. 1, point O is defined as the origin of the shaft, while point A is a node located on the contact interface of the O-ring. These two points coincide with each other in the initial state. When Da is 0.25 mm, the result of displacement for point O and A as a function of time during two reciprocating cycles is shown in Fig. 3. Because the shaft is assumed to be rigid, the displacement of point O represents the reciprocating displacement of the shaft, which varies from −0.25 mm to

Conclusions

In this study, a numerical model for studying the fretting behavior of the rubber O-ring seal in hydrogen environment is presented by incorporating the influence of swelling induced by the solute hydrogen. The fretting running condition is studied. The influence of hydrogen swelling on the fretting characteristic was discussed in terms of Mises stress and contact pressure. The following conclusions can be drawn:

  • (1)

    The fretting state depends greatly upon the amplitude of reciprocating motion, and

Acknowledgments

This research is supported by the National Natural Science Foundation of China (No. 51705157), the National Key R&D Program of China (No. 2018YFF0215101) and the Fundamental Research Funds for the Central Universities.

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