# The Impact of Operating Ratio on the Static and Fatigue Life of Forward-Acting Rupture Discs

## TL;DR

This study examines how operating ratio affects the lifespan of rupture discs under different conditions, offering a framework for predicting their replacement intervals.

## Contribution

A predictive framework for rupture disc life based on operating ratio and material behavior under various conditions is proposed.

## Key findings

- Life decreases as operating ratio increases for both materials and all test conditions.
- Inconel 600 shows longer life than 316 L stainless steel at matched operating ratios.
- Failure analysis reveals progressive plastic deformation and thinning leading to reduced bursting pressure.

## Abstract

Rupture discs are critical safety devices for pressure vessels, yet defining replacement intervals for discs that have not ruptured remains challenging due to limited quantitative life-prediction methods. This study investigates forward-acting rupture discs made of 316 L stainless steel and Inconel 600 under three test conditions: low pressure at room temperature, low pressure at elevated temperature, and ultra-high pressure at elevated temperature. Static hold life and fatigue life were measured over a range of operating ratios R = Pw/Pb. To model life–ratio relationships while avoiding far-reaching extrapolation, static life was fitted with a log-normal accelerated-life (AFT) model and fatigue life with a Basquin relation following ASTM E739, reporting 95% prediction bands. Predictions were restricted to validated domains (static: R ≥ 0.86) and truncated at five times the groupwise maximum observed life/cycles. Results show a consistent trend for both materials and all conditions: life decreases as R increases, with steep sensitivities within the observed range. At matched R, Inconel 600 generally exhibits longer life than 316 L. Qualitative failure analysis under constant and cyclic loading indicates progressive plastic deformation, local thinning, and a concomitant reduction in bursting pressure until failure. The proposed in-range predictive framework provides actionable guidance for determining conservative replacement intervals for rupture discs.