Relief Valve API Standards
API 2000 Standard:
The basics segregation of relief valves in API standards is done as per how much pressure the relief valve needs to handle.
If the equipment is having a MAWP (maximum allowable working pressure) less than 15 Psig then API 2000 standard is applicable.
It has a little less stringent requirements as compared to other API Relief valves standards mentioned below.
API 521 Standard:
In simple words this standard caters towards selection of pressure relief device (Relief valves, Rupture disk, their combinations etc) based on various process scenarios.
It guides on the most appropriate device for the risks and circumstances involved in various installations.
The standard provides the guidelines on the following points
1. Examining the principle of overpressure
A practical example:
In Midland resource recovery accident on May 24, 2017 CSB found out that just a relief valve would not have been sufficient to prevent the explosion inside the vessel.
The CSB investigation added an interesting observation as follows
“In Fact, a safety relief valve may not be capable to react quickly enough to protect equipment from rapid pressure increase by an explosion inside a vessel”
So, for such requirement where we need rapid relieving of pressure, we could select a rupture disk.
Note: This is as per my current understanding and process engineers can give us a better idea with respect to typical process requirements.
2. Determining individual relieving rates
In simple words, the relief valve must be “fast enough” to relieve the extra pressure in case of mishap.
Else, what use would the relief valve be if the equipment burst due rapid increase in overpressure.
Thus, the relieving rate is also extremely crucial parameter for relief valve design.
3. Selecting and designing disposal system
The relief valves handling services such as air could be relived to atmosphere.
However, Hydrocarbons cannot be released in such a manner.
Also, the disposal system must be adequate to contain the service released.
API 520 Standard Part 1:
This standard deals with the Relief device itself.
In simple words we could say this standard deal with the operational characteristics and sizing procedures.
API 520 Standard Part 2:
This aspect is sometimes taken lightly but can lead to fatal consequences.
And that is “Installation details”.
A lot of times and incorrect installation has been the root cause of a fatal incident.
Thus, as per my humble opinion extreme consideration should be given to API 520 Part 2.
API Standard 526:
This standard deals with the purchase aspect of Pressure Relief devices.
API Standard 527:
One peculiar consideration for valves and especially relief valves is leakage consideration.
Thus API 527 comes handy and is one of the most frequently cited standards for relief valves.
This standard deals with the Relief device itself.
In simple words we could say this standard deal with the operational characteristics and sizing procedures.
API 520 Standard Part 2:
This aspect is sometimes taken lightly but can lead to fatal consequences.
And that is “Installation details”.
A lot of times and incorrect installation has been the root cause of a fatal incident.
Thus, as per my humble opinion extreme consideration should be given to API 520 Part 2.
API Standard 526:
This standard deals with the purchase aspect of Pressure Relief devices.
API Standard 527:
One peculiar consideration for valves and especially relief valves is leakage consideration.
Thus API 527 comes handy and is one of the most frequently cited standards for relief valves.
Conclusion
Let us try to summarize these standards as solution to different question that arise with respect to pressure relief devices.
Q) Which Pressure relief device should be selected (Relief valve, Rupture disk, Multiple relief valves, Combination of relief valve and rupture disk etc) and how should it be selected based on various process scenarios?
Answer: API 521
Q) How to size and understand the operation characteristics of Pressure relief devices?
Answer: API 520 Part 1
Q) How to correctly install these pressure relief devices?
Answer: API 520 Part 2
Q) How to get guidance on purchase of relief valves?
Answer: API 526
Q) What are the guidelines on seat tightness requirements of relief valves?
Answer: API 527
Q) Is there a separate standard for relief valve on equipment’s handling low (less than 15 Pisg MAWP)?
Answer: API 2000
