Rupture Disks and safety valve

[Mohamed]

when we use Rupture Disks and when we use Safety Valve

[mohan]

i not able to get the link for the title "Rupture disc & safety valve"

[Mohamed]

i not able to get the link for the title "Rupture disc & safety valve"

i only ask question not give link to download ,if you have answear to this question i will be thankful

[sumit.alok]

PRESSURE RELIEVING / SAFETY DEVICES

There are basically two type of safety devices used for relieving pressure in a system. These are —Safety/Relief valves and Rupture Discs. Safety/Relief Valves may be conventional type, balanced bellow type & pilot operated type.

SAFETY/RELIEF VALVES

Conventional

Conventional safety/relief valves are susceptible to both superimposed and built-up back pressure and are not recommended when the total back pressure exceeds 10% of the set pressure. For these reactions, these should be used only in system relieving to atmosphere like steam, air or other non-toxic and non-flammable materials.

Balanced Bellows

Balanced Bellows valves are not susceptible to back pressure and should be used for back pressure upto 50% of set pressure.
Pilot-operated

In pilot-operated safety valves, the main safety valve opens through a pilot valve. Both the pilot and the main valve contain flexible membranes, which can withstand only ordinary service temperatures. Because of this and the risk of fouling, their use is limited to very clean services and are generally not recommended in hydrocarbon services.

RUPTURE DISCS

Rupture Discs are thin metal diaphragms held between flanges and are designed to bust at the set pressure. Once bust, these are not reusable and have to be replaced. Their set pressure cannot be tested without destroying them. After the test, the rupture disc has to be replaced but there is no guarantee that the second rupture disc will burst at the same pressure. This is a major disadvantage of rupture disc, especially when the bursting pressure is low. For these reasons, rupture discs alone shall not be used. However, they should be used between the vessel and a relief/safety valve for fluid of highly corrosive or fouling nature. Prolonged expose of safety valve directly to such conditions may cause damage to valve components.



SET PRESSURE OF RELIEF VALVES
(a) Relief valves should usually be set at 10% higher over the normal operating pressure to allow a reasonable margin so that the valves do not op frequently with minor process upsets. The difference between the set pressure and the normal operating pressure should not be less than 2 Kg/CM2. This is to account for operating contin-gencies and the fact that spring setting of safety valve at lower pressure is not of high precision. This aspect should be considered for selecting the design pressure (maximum allowable working pressure) of the equipment. The design pressure or maximum allowable working pressure is the highest pressure at which the pressure relief is set to open.
(b) The safety valve set pressure in trunk pipelines should be set within 10% above the maximum allowable operating pressure.
(c) When rupture disc is used, the bursting pressure of the rupture disc should be kept 5% lower than the safety valve set pressure. In order to have a reasonable margin between the bursting pressure and the normal operating pressure, the relief valve set pressure should be 15% higher than the normal operating pressure. A pressure gauge/bleeder between rupture disc and relief valve helps to indicate the health of the rupture disc.


Hope it willl be useful! Sir
i am very thankful for this wonderful website as it helps the new professional.

[Mohamed]

thanks for your reply

but in the external pressure cylinder at fire extinguisher why the manufacture install rupture disk not safety valve

[nskvc]

Good writing and explanation. Good lead by elhagar. Keep it up.

[Mohamed]

Good writing and explanation. Good lead by elhagar. Keep it up.

thanks nskvc
and i still have the question

[dariush]

thank you

[Processor]

Rupture Disks and Pressure Relief Valves are two different safety devices which are used in the following combinations, depending upon the application and service:

* Relief Valve as primary protection with no secondary protection
* Relief valve as primary protection with another relief valve as secondary protection
* Relief valve as primary protection with Rupture Disk as secondary protection
* Rupture disk as primary protection
* Rupture disk as well as relief valve installation in series, both being working as primary protection (generally rupture disk is installed upstream of relief valve). This combination is generally used when small vapors leakage (i.e. actual pressure has not attained set point) may corrode the metallic relief valve. So relief valve is exposed to vapors only when actual pressure builds up.
Please refer to API 520 / 521 to see the set points requirement particularly when more than one safety device is used.
Please also refer to the following link.

Rupture Disks for Process Engineers

[link Point to another website Only the registered members can access] It is Part-5 of series of articles on the same topic. Just change the "7" in link to get other articles.

Thanks

[polaris44]

Rupture disc is normally installed on heat exchanger to cater for tube rupture scenario. Rapid pressure rise and high pressure surge will result from a tube rupture in a heat exchanger operating with an incompressible fluid (liquid) on the LP side and a significantly higher pressure on the HP side. Protection by pressure relief valve is then not adequate, and rupture disks should be used as they react faster.

Rupture disk devices also may be installed upstream of pressure relief valves in systems containing extremely valuable or toxic materials to guard against leakage of the valve or in systems handling materials likely to make the pressure relief valve inoperative because of fouling, plugging or corrosion.

Rupture disks are also used occasionally on the downstream side of pressure relief valves where conditions make an upstream installation impractical or where valves are connected to a header and it is designed to protect the valve mechanism against corrosion from this source. This arrangement requires the use of a valve whose set point is unaffected by a back pressure equal to the rupture disk bursting pressure, or a vent between valve and disk similar to that described above. This arrangement is not allowed by the French and Italian Codes.