LD rupture disc: composite with fluoropolymer or metal seal

In short: The LD is a composite rupture disc made up of a scored metal dome and a seal on the process side, which can be fluoropolymer or metallic. It serves as primary or secondary relief and as valve isolation in corrosive processes, with operating pressures of up to 80 % of the marked burst pressure.

How it works

The idea behind the LD is to separate two functions that, in a solid disc, fall on the same piece. The scored metal top section is the one that withstands the pressure and determines the burst point. The seal, placed on the process side, takes care of tightness and of protecting the metal from the fluid. This way the metal can be chosen for its mechanical behavior and the seal for its chemical compatibility.

The option of choosing between a fluoropolymer or metal seal is what gives the model its flexibility. A fluoropolymer offers very broad chemical resistance and low-adhesion surfaces, but has the temperature limits typical of plastics; a metal seal may be preferable when temperature or fluid permeation is the main concern. The decision depends on the process, not on the disc.

The dome incorporates seven holes at the apex and six radial pre-cut sections. Those lines guide the opening and, with the right seal, allow the disc to open without releasing fragments. According to the manufacturer, this allows sturdier materials without dropping below an 80 % operating-to-burst ratio. The model accepts static, cyclic or pulsating service.

When it makes sense (and when it does not)

• Suitable when a composite disc is needed and the seal material is to be chosen according to the fluid.
• Suitable for protecting a pressure relief valve from continuous contact with the process; the non-fragmenting option avoids damaging its seat and helps control fugitive emissions.
• Suitable for corrosive fluids or those prone to fouling.
• Not suitable without vacuum support if the equipment may reach full vacuum; the LDV variant exists for that case.
• Not recommended if the operating pressure exceeds 80 % of the marked burst pressure.

Data to specify it

• Marked burst pressure and coincident temperature.
• Maximum operating pressure and nature of the service (steady, cyclic or pulsating).
• Seal material: fluoropolymer or metallic, depending on fluid and temperature.
• Nominal diameter and disc holder.
• Whether it must be the non-fragmenting version.
• Whether there is a vacuum risk, in order to add the corresponding support.

In sizes of 1" (25 mm) or larger the disc carries a flow direction tag, useful for quick installation and inspection.

To go deeper: How to select a rupture disc and Materials for rupture discs.

Descriptive sheet for educational purposes. For availability and a quote for this model, consult P&V Control Devices.