Rupture Disk Working Principle and Type

In this article, we will discuss the Rupture Disk Working Principle and Type and accessories of rupture disk. Before we start, we will see the basic of rupture disk.

What is Rupture Disk?

A rupture disk is a non-reclosing type of pressure-relief device. It’s used to protect vessels, piping, and other pressure-containing components from excessive pressure and/or vacuum. Once the rupture disk burst out the entire vessel or system pressure will be relieved. The system will resume its function after replacing the burst rupture disk.

Advantages of the Rupture Disk

• Rupture disk installed with either a single or multiple relief devices to protect the vessels.
• Rupture disk reacts quickly enough to relieve the pressure spikes.
• With no moving parts, rupture disks are simple, reliable, and faster-acting when compare with other pressure-relief devices.
• The rupture disk is lightweight when compared with other pressure-relieving devices.
• The rupture disk used for both gas or liquid handling application for relieving the excess pressure.
• No maintenance cost for rupture disk.

Disadvantage of Rupture Disk

• Once the rupture disk burst out, we need to replace the whole rupture disk.
• The complete system as to shut down after the rupture disk failure, for rupture disk replacement.
• High care required during installation and handling, a small scratch even damages the rupture disk.
• During installation, improper bolt torque also affects the disk burst pressure.

Impact due to temperature

In rupture disk, the burst pressures can vary significantly with temperature. If the temperature of the operating medium change, as a result, the temperature of the disk increases. This increase in temperature will decrease the burst pressure of the rupture disk. It’s lead to premature failure of rupture disk.

Rupture Disk Types

The rupture disks are classified as three major types of
a. Forward-acting (Tension loaded)
b. Reverse-acting(Compression loaded)
c. Graphite (Shear loaded)

Forward-acting

The forward-acting rupture disk in which the concave side installed against the system pressure (Refer below figure). As the process pressure increases beyond the allowable operating pressure, the rupture disc starts to expand. This expansion continues with an increase in pressure until the tensile strength of the material reaches the maximum value and rupture occurs. This rupture disk also called as “Tension-Type Rupture Disk”.

Based on the disk configuration the forward acting type disk further classified into three types. They are

• Solid Metal Rupture Disks
• Scored Rupture Disks
• Composite Rupture Disks

Solid Metal Rupture Disks

This type of rupture disk typically contains an angular seat design. Hence it will provide a satisfactory service life when the operating pressure up to 70% of the marked burst pressure of the disk.

If the vacuum or backpressure condition present, then the disk furnished with support to prevent reverse flexing.

During burst out of the rupture disk the opening configuration is random and fragment design. Due to this, they are not suitable for install in the upstream of a Pressure Relief Valve (PRV).

Scored Rupture Disks

The scored forward-acting rupture disk, the concave portion of the disk designed to burst along the scored lines(Refer below figure) at a rated pressure applied on the concave side of the disk. This design provides a satisfactory service life when the operating pressure up to 85 % to 90 % of the marked burst pressure of the disk.

This type of rupture disk will withstand the vacuum conditions without vacuum support. But in the case of backpressure conditions are present, the disk furnished with the necessary support to prevent reverse flexing.

The scored mark in the rupture disk determines the opening of rupture disk. During bursting, the disk will not be fragmented. Hence this type of disk used in the upstream installation of the PRV.

For the same burst pressure, the scored type, forward-acting rupture disk material thicker than the non-scored design. Also, it provides additional resistance to mechanical damage.

Composite Rupture Disks

The composite rupture disk is a flat or a concave type with multi-piece construction disk (see Figure). The concave type rupture disk designed to burst at a rated pressure applied to the concave side. But for the flat composite rupture disk designed to burst at the rated pressure in either or both directions. Some designs of composite rupture disks are non-fragmenting and it is acceptable for use in the upstream of a PRV.

The burst pressure controlled by the combination of slits and tabs in the top section and a metallic or nonmetallic seal member under the top section. Composite rupture disks burst pressures usually lower than the standard type rupture disks. Composite rupture disks may offer a longer service life as a result of the corrosion-resistant properties of the seal material selected.

The slits and tabs in the top section provide a predetermined opening pattern for the rupture disk. If vacuum or backpressure conditions are present, composite disk furnished with support (optional) to prevent reverse flexing(refer above figure).

The composite rupture disk generally provides satisfactory service life when the operating pressure is 80% or less of the marked burst pressure (80 % operating ratio).

The flat type composite rupture disk used for low-pressure vessels. This disk usually comes complete with gaskets and designed to install between companion flanges rather than within a specific rupture disk holder. Flat composite rupture disks generally provide satisfactory service life when operating pressures are 50% or less of the marked burst pressure.

Reverse-acting Rupture Disks

Reverse Acting Rupture Disk installed in a system with the process of media pressure against the convex side of the disk(refer figure). The rupture disk is subjected to the burst pressure, the compression loading act on the rupture disc causes it to reverse and open disk at the predetermined scoring pattern. This disk also called Compression loaded type disk.

These disks provide a satisfactory service life when the operating pressures of 90 % or less than the marked burst pressure.

Because a reverse-acting rupture disk operated with pressure applied on the convex side, thicker disk materials shall be used. Thereby lessening the effects of corrosion, eliminating the need for vacuum support, and providing longer service life under pressure/vacuum cycling conditions and pressure fluctuations.

Graphite Rupture Disks

Graphite rupture disks are typically machined from a bar of fine graphite that has been impregnated with a sealing compound to seal the porosity of the graphite matrix (see figure). The disk operates on a pressure differential across the center diaphragm or web portion of the disk.

Graphite rupture disks provide a satisfactory service life when operating pressures, up to 80 % of the marked burst pressure. These type of rupture disk used for both liquid and vapour services.

If vacuum or backpressure conditions are present in the system. Then the disk furnished with support to prevent reverse flexing. These disks have a random opening pattern and are considered fragmenting design. Hence it’s not suitable for installation on the upstream of a PRV.

A metallic ring called armouring often added to the outside diameter of the disk. It’s used to prevent the uneven piping loads acts on the disk. Also, minimize the potential for cracking of the outer graphite ring.

Basic Components of Rupture Disks

The most basic components of rupture disks are the rupture disk holders and rupture disk accessories.

Rupture Disk Holders

Rupture disk holder used to clamp the rupture disk in place and effect a leak-tight, metal-to-metal seal. The seating area of the holder typically unique to specific manufacturers and styles of rupture disks.

Rupture disk holders are available in a variety of configurations including full bolting, weld neck, threaded, etc. The most common configuration is the insert type that fits between standard pipe flanges, and the outside diameter of the holder fits inside the flange studs. Rupture disk holders are available in a variety of materials and coatings.

 Rupture Disk Accessories

A variety of accessories available with the rupture disk in various applications. The following accessories are widely used with a rupture disk.

a) Rupture Disk Types

These devices typically provide an electrical or mechanical signal which can indicate the opening and/or leakage of a rupture disk.

b) Alarm Monitors

Alarm monitors used to raise an alarm then the rupture disk open or leakage. The monitor always associated with the rupture disk indicators or sensors.

c) Heat Shields

It’s generally installed in the upstream of the rupture disk in high-temperature processes to reduce the temperature act on the rupture disk.

d) Baffle Plates

When the rupture disk opened, the excess system pressure vented to atmosphere. For protecting the personnel and equipment from the burst pressure a baffle plate used to deflect process discharge away. Baffle plates also commonly used to assist in absorbing the recoil forces of an activating rupture disk.