High Tech Pressure Safety knows well about the behaviors of rupture discs through design/manufacturing, research/development and applications. Quality of our rupture discs exceeds the requirements set by various industry codes. Our products are simple, accurate, dependable, reliable and competitive in price. We are setting up a higher technical standard for the rupture disc industry. Our goal is to lead the industry in both design/manufacturing and applications of rupture discs, to meet or exceed customer’s requirements.

Rupture discs are unique mechanical devices. The uniqueness lies in the way by which rupture discs are designed.--- Rupture discs are designed to make sure they fail under the specified conditions while many other mechanical devices are designed to make sure they will stand under some conditions.

Over-pressure in pressure vessels or pipelines can cause explosions or system shut down. Sometimes normal operation or malfunctions can cause pressure built-up in a pressurized system. Rupture discs can be installed in the pressurized system to relief the over-pressure before any explosions or damage occurs.   

Rupture discs are safety devices that are designed to burst at a specified pressure, which is called rupture disc burst pressure. ASME (American Society of Mechanical Engineers) Section VIII, Division I specifies that rupture disc burst pressure can be set as 110% of MAWP (Maximum Allowable Working Pressure). This burst pressure is the base of the rupture disc production. Rupture discs manufactured by High Tech Pressure Safety are more accurate on burst pressure due to our unique statistical quality control process and other control processes.

The burst pressure of rupture discs depends on many factors, such as disc size and type, disc material and material thickness, temperature, boundary conditions, manufacturing methods, just to name a few. The bursting of a rupture disc, from mechanical points of view, is a process of material failure. The first important step to understand rupture disc is that one must understand that rupture disc burst pressures are random variables. That is to say no one can tell exactly what the burst pressure is before the rupture disc bursts. The dilemma is all the rupture discs with burst pressure known already burst (can not use anymore), and the rupture discs (from the same lot) sent to customers, are the ones with burst pressure unknown. But we are very confident that our rupture disc will perform well, as we expect, in customer's process because, together with other theories, statistical theory is applied in our design/manufacturing process.

To understand how the statistics is applied to the rupture disc quality control process, let us first understand some relative nomenclatures.  For example, a customer is ordering M rupture discs form High Tech Pressure Safety, additional N discs will be manufactured for testing purpose. That is, total (M+N) rupture discs are manufactured. In statistics, N is called sample while (M+N) is called population, or a lot in factories. According to the burst pressure specified by customers, (M+N) rupture discs will be manufactured. N of them will be test by burst and the average burst pressure will be calculated and stamped on all M rupture discs (sent to customers).

 The average burst pressure of the N rupture discs is called sample mean. It can be shown theoretically that the mean of sample means is equal to population mean, and that the variance of sample means becomes smaller as sample size becomes larger. For the purpose of engineering convenience, this average burst pressure (sample mean) is usually treated as the average burst pressure of the total (M+N) rupture discs (population mean). With that in mind, we can claim that the average burst pressure of the N rupture discs is the average burst pressure of the lot but remember that they are not exactly the same. The ideal situation is that average burst pressure of the lot is equal to the burst pressure specified by customers. For a manufacturer, to achieve the ideal situation is very difficult (sometimes impossible) and unnecessary for industry purpose. So the difference between the average burst pressure of the lot and burst pressure specified by customers must be recognized. This difference is called Manufacture Range in ASME codes.

 According to statistics, a good quality control should control two areas, i.e. average burst pressure and individual disc burst pressure. That means the diversity of the individual disc burst pressure must also under control to produce high quality rupture discs. This control is called Burst Pressure Tolerance in ASME codes.

 So far, we have illustrated the first step to produce high quality rupture discs. It has been seen that some misleading theories and practices exist even in some codes. High Tech Pressure Safety has a tighter control in rupture disc burst pressure than that specified in various codes. The next step is the design and manufacturing process. A good control in this step will guarantee our tighter control in the first step can be achieved. This step includes holder design, torque load determination, sealability and boundary condition treatment. It needs to point out that some people claimed their rupture discs are non-torque sensitive. Strictly speaking, rupture disc burst pressure always depends on torque value form the standpoints of mechanical engineering. High Tech Pressure Safety's design has largely minimized the effect of torque value to boundary conditions. This is another way to guarantee an accurate burst pressure.

Rupture disc sizing has long been an issue in the industry. Many rupture disc sizing methods have been recommended by professional organizations, manufacturers and other sources. All those methods require a given flow rate (Q) into the vessel before the size of a rupture disc can be determined. Furthermore, those methods do not, or can not, take the volume of the pressure vessel into consideration. The obvious faults in those methods can be seen. As a result, the application of those methods is very limited; because many customers could not predict the flow rate (Q); or in some cases, flow rate into the vessel does not exist. Actually, the job of a rupture disc is not only to protect equipment from overpressure due to a known source but, more importantly, also to protect it from overpressure due to unknown sources, such as system malfunctions or other unpredictables.

High Tech Pressure Safety has done research on rupture disc sizing and created a new method--- Huang’s Equation--- to determine rupture disc sizes. Advantages in our method are that we can size rupture discs without the flow rate into the vessel, and that the volume of the pressure vessel is also taken into consideration, making our method more reasonable and applicable.

Huang’s Equation can be expressed mathematically in the form as,

    A = f (Pi, Ti, V, Ft, Kd, Kc, Ke, z)

Where,

A     The required area of the rupture disc

Pi    Upstream and downstream pressures

Ti    Upstream and downstream temperatures     

V     The volume of upstream pressure vessel

Ft        Fracture empirical coefficient, proved by tests and scientific calculations

Kd    Rupture disc discharge coefficient

Kc    Capacity coefficient due to viscosity

Ke    Extension of release

z    Compressibility

This Equation can be applied to liquids or vapors (gases).

It is worthwhile to point out that something called “head loss” of a rupture disc is currently popular in the rupture disc industry.  Head loss is relative to rupture disc sizing. However, one should understand two important points. 1). Burst of a rupture disc is a statistical event; therefore, opening areas would be different from one other, and 2). Rupture disc opening configuration depends on many factors, such as rate of pressurizing, disc materials, upstream volume and downstream conditions, etc. It is clear that a lab test can not include all possible real situations in rupture disc applications. Therefore, one lab tested head loss of some rupture discs to be applied to all circumstances in industry is very questionable.

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Last modified: 05/11/04