Rupture disc fragmentation

We describe what fragmentation is, what ASME has to say about it, and what operations and maintenance engineers can do to mitigate the risks.

Tuesday, March 15, 2022

What is fragmentation?

Fragmentation occurs when a rupture disc shatters into multiple fragments upon bursting. Older rupture disc designs were traditionally all fragmenting. Unscored, forward-acting (also known as ‘tension-loaded’) rupture discs of any type of metal can be prone to fragmentation. Graphite rupture discs will always fragment, graphite being a very brittle material.

This high-speed video shows what happens when three types of rupture disc burst:

  • Graphite
  • Flat metal composite disc
  • Reverse acting metal disc

As you can see, the graphite disc immediately shatters into tiny pieces. The flat metal composite disc, however, does not fragment. The scoring around the periphery of the disc helps control the burst and prevent fragmentation. The reverse-acting design and the peripheral scoring of the third disc prevent fragmentation. The entire disc lifts away from the ‘hinge’ at the top but does not release any fragments into the downstream pipework. 

Why is fragmentation a problem?

When a rupture disc with a fragmenting design bursts, the pieces of disc enter the downstream pipework along with the contents of the vessel or piping. At best, these fragments contaminate the product and may be difficult to remove; at worst, they can clog up, foul or damage downstream pipes and valves, causing safety issues and necessitating a shutdown for repair, cleaning and maintenance. To avoid these issues, ASME states that any discs used below a pressure relief valve or safety valve must have a non-fragmenting design.  

 What can you do to mitigate the problem?

 If fragmentation is likely to be an issue in your plant or process, there are several steps you can take to mitigate the problem:

  • Upgrade any graphite discs to metal ones
    The video clearly shows the difference in levels of fragmentation between graphite and metal rupture discs. If corrosive substances are present in the process, most metal discs can be made of corrosion-resistant materials such as Hastelloy or Inconel. If this is not enough, or if price is a particular consideration, the discs may be lined with a fluoropolymer liner to protect them.  OsecoElfab’s FAS and Safe-Gard bursting discs are both available in corrosion-resistant metals and can both be lined if required.
  • Select the right disc design
    The safest option for reducing or eliminating the risk of fragmentation is to use a disc specifically designed not to fragment. Examples include cross-scored, forward acting discs, such as the FAS and Safe-Gard mentioned above, and peripherally scored reverse acting discs. Many reverse acting disc designs, such as the PRO+KRGL or Opti-Gard are also designed to eliminate fragmentation at both low and high pressures.
  • Check that the specifications of any disc you use below a pressure relief valve or safety valve state that is a non-fragmenting design
    ASME states that any discs used below a pressure relief valve or safety valve must be non-fragmenting. Phrases that the product information might use include: "non-fragmenting design", "suitable for relief valve isolation", "excellent for safety valve isolation", "designed for relief valve protection". Examples of non-fragmenting designs that are excellent for relief valve isolation are OsecoElfab’s PRO+KRGL or the multi-purpose Opti-Gard.
If you would like to learn more about reducing fragmentation in compliance with regulations, our Design Engineers are ready to help you with a a no-cost and no-obligation consultation or a site survey. During a survey, our engineer will inspect all the rupture disc installation points in your plant or application(s). The resulting report can be used to demonstrate compliance with ASME Section XIII and to identify opportunities for stock consolidation and cost reduction.

 Contact us now to request a consultation or site survey.