Reliable fire protection is the requirement for industrial valves in sensitive applications where fire accidents can happen easily. The valves used in the oil and gas, refinery, chemical, and petrochemical industries must guarantee a reliable and safe shut-off in case of fire. Fire-safe design is an important criterion for such industrial valves. The term fire-safe means the ability of the valve to minimize the amount of process lost (leakage) downstream or to the atmosphere after a fire test.
Industrial valves are not an entity of fire hazards. For valves used in the oil and gas industries, the American Petroleum Institute(API) has developed fire tests. After years of refinement, API 607, ISO 10497, API 6FA, BS 6755, and BS 5146 have been accepted as the standards of fire tests of valves. There are a few other standards and procedures like API RP6F, FM 6033, Exxon BP3-14-1, OCMA FSV-1, etc. Using these standards as guidelines, many organizations make their own internal procedure for fire-safe valves.
A universally accepted fire fighting strategy mentions that if a fire is not beaten in a one-half hour, a withdrawal and containment policy is instituted. Structural failures like flange bolt failures, pipe rack collapse, and concrete eruptions will occur. Based on this concept, a fire test duration of a one-half hour (30 minutes) has been established.
Principle of Fire Testing of Valves
The idea behind the fire tests is that any fire-safe valve under pressurized conditions must operate after being burnt at a specified high temperature for a specified period and leakage after burning should be within specified limits. The usual principle of fire testing of valves or fire-safe valve testing is as follows:
The water-filled pressurized closed valve is fully enveloped uniformly in high-temperature flames of around 750 °C to 1000 °C for a period of 30 minutes. When the valve is completely enveloped in fire exposing the seat and sealing areas to burn temperature, the heat intensity is monitored with thermocouples and calorimeter cubes. During this period, the external and internal leakage past the valve is measured. This leakage should be within acceptable limits. Also, once the valve is cooled after the fire test, the pressure-containing capability of the same valve seats, shell, and seals are tested.
- The stem and bore are usually kept in the horizontal position. Check valves are tested in their normal operating position.
- The temperature is measured using two thermocouples. One is located 25 mm below the valve under test and the other 25 mm from the upper stem packing box on the horizontal centreline.
- The piping to valve end connections for joint leakage is not part of valve fire testing.
API 607 vs API 6FA
The most widely used standard for fire testing of industrial valves is API 607 and API 6FA. Both the standards are devised by the API. So, what are the differences?
API 607 provides fire test criteria for quarter-turn valves and other valves with nonmetallic seating under pressure, whereas API 6FA provides the fire testing requirements for API 6A and API 6D valves. API 6FA is applicable for metal seated valves.
Fire Safe by Design vs Fire Safe Tested
There are some confusing terms often used related to the fire safe valves. They are:
- Fire Safe by Design: A “fire safe by design” valve is designed to make the valve fire safe. However, the valve hasn’t been tested.
- Fire Safe Tested: A “fire safe tested” valve could have been tested. However, the valve has not been approved by a governing third party.
- Fire Safe Approved and Certified: The term “fire safe approved and certified” for valves signifies that the has been tested, approved, and certified by a governing third party following the guidelines mentioned in common standards like API 607, API 6FA, ISO 10497, etc.
Fire-Safe Ball Valves
For applications involving explosive or fire-risk environments, fire-safe ball valves are produced. These valves are specially designed to limit the spread of fire. The fire-safe ball valves are normally fire-tested to API 607, API 6FA, and BS 6755-Part 2.