- Fire testing to ISO 10497 or API 607 proves that a quarter-turn valve design can contain a hydrocarbon fluid at line pressure after being subjected to a defined fire exposure — it does not prove that any individual production valve will perform as well, which is why fire-safe certification must be combined with production quality controls to have real safety value.
- The distinction between a tested valve design and a certified design matters enormously: a valve manufacturer can claim their valve is based on a fire-tested design while making substitutions in seat material, body tolerances, or assembly procedures that void the tested design’s performance in a fire, and buyers must verify that the actual valve supplied matches the certified configuration.
- ISO 10497 and API 607 use different test sequences, different failure criteria, and different leakage measurement methods, meaning a valve certified to one standard is not automatically certified to the other — understanding which standard applies to your specific application and jurisdiction is the first step in fire-safe valve specification.
Why Fire Testing Matters
A hydrocarbon process plant represents an enormous inventory of flammable material, and a fire — once started — can escalate rapidly if isolation valves fail to contain the process fluid under fire conditions. A valve that performs perfectly under normal operating conditions can fail catastrophically during a fire if its seats, seals, or body materials soften, burn, or distort under flame impingement. The purpose of fire testing is to verify that the valve design maintains adequate containment of process fluid even when directly exposed to fire, ensuring that the isolation function remains available at the moment it is most needed.
The primary failure mode of quarter-turn valves in fire conditions is seat seal degradation. Standard soft-seated ball and butterfly valves use PTFE or polymer seat inserts to achieve bubble-tight shutoff. At temperatures above approximately 260 degrees C, PTFE begins to soften and above about 327 degrees C it melts. Under fire conditions, the external temperature of a valve body can reach several hundred degrees within minutes, and the temperature gradient through the valve wall means that even if the bulk body metal is at an acceptable temperature, the seat material at the flow bore can be at destructive temperature within a short time. A burning PTFE seat releases fluorine compounds that are acutely toxic, and the loss of the seat material leaves the valve with only the metal-to-metal contact between ball or disc and body as the sole remaining sealing element — contact that was never designed as the primary seal.
ISO 10497 Test Procedure
ISO 10497 — Testing of valves — Fire type-testing requirements — specifies the fire test procedure for all valve types intended for use in flammable fluid service. The standard applies to quarter-turn valves (ball, butterfly, plug) as well as rising-stem valves (gate, globe), though the specific failure modes and test configurations differ between valve types. For quarter-turn valves, the test sequence is as follows.
The valve is fully assembled with all standard production components and installed in a representative piping assembly. A line pressure equal to the rated pressure of the valve is applied upstream. The valve is closed. The test rig is then exposed to a calibrated hydrocarbon fire that achieves a minimum flame temperature of 650 degrees C on the valve body surface, sustained for a minimum of 30 minutes. During the fire period, external leakage (past the packing or shaft seal) is measured, and through-seat leakage (past the closed seat) is measured. Both leakage rates must remain below the maximum permissible values specified in the standard throughout the burn period.
After the 30-minute burn period, the fire is extinguished and the valve is cooled by water spray — simulating the deluge system activation that would accompany fire suppression in a plant. The thermal shock of rapid cooling on a hot valve body creates additional stress on all components. Following cool-down, the valve is operated — opened and then reclosed — and the seat leakage is measured again at the rated pressure. The requirement to operate after fire and cooling is a critical element of ISO 10497: a valve that survived the fire but seized solid during cooling is not fire-safe, because the isolation function must be available after the fire event to allow controlled shutdown.
API 607 versus ISO 10497
API 607 — Fire Test for Quarter-turn Valves and Valves Equipped with Nonmetallic Seats — is the American equivalent of ISO 10497 for quarter-turn valve fire testing. While both standards test valves under fire conditions and measure leakage during and after the fire, there are meaningful differences in the test procedures and acceptance criteria.
The fire temperature requirement differs: API 607 specifies a minimum fire temperature of 760 degrees C on the valve body surface, compared to 650 degrees C in ISO 10497. This 110-degree difference means a valve tested to ISO 10497 may not achieve the API 607 fire temperature requirement, and the test should not be considered equivalent unless specifically verified. The burn duration is similar — 30 minutes in both standards — but the cool-down procedure and the post-fire operational test differ in detail between the two standards.
The leakage acceptance criteria also differ. ISO 10497 uses a leakage rate in cubic centimetres per minute per unit of nominal bore diameter, while API 607 uses a maximum leakage volume over the test period. The practical effect of these differences is that a valve design that passes one standard may or may not pass the other, and the certificate must state specifically which standard the test was conducted to. Specifying fire testing to both ISO 10497 and API 607 is possible and provides maximum coverage, but requires the manufacturer to have conducted tests under both protocols — a requirement that should be stated explicitly in the purchase order if both certifications are needed.
Fire-Safe Design Elements
A valve design that passes fire testing incorporates specific engineering features that maintain containment after the primary seal material is destroyed. Understanding these features allows the engineer to assess whether a claimed fire-safe design is genuinely so, rather than relying solely on a certificate.
The secondary metal-to-metal seat is the most important fire-safe design feature for ball and butterfly valves. When the primary soft seat material (PTFE or other polymer) is destroyed by fire, the secondary seal is the metal seat ring body that continues to contact the ball or disc surface. This metal contact will have higher leakage than the intact soft seat, but it provides sufficient containment to meet the fire test leakage criteria. The geometry of the metal seat ring must be carefully designed so that the metal-to-metal contact occurs even after the soft insert material is gone — the seat must not collapse into the void left by the burned polymer in a way that prevents metal contact with the ball.
Graphite shaft seals replace standard O-ring stem/shaft seals in fire-safe designs. Standard elastomeric O-rings (NBR, FKM) degrade rapidly under fire conditions. Graphite packing maintains sealing integrity to temperatures well above those encountered in a process plant fire and does not burn or emit toxic gases. Many modern fire-safe ball valve designs use a combination of primary elastomeric seals for normal service performance and secondary graphite seals that engage if the elastomeric seals are destroyed by fire. The graphite seals must be pre-compressed to a level that will seal against the operating pressure — simply inserting graphite rings without pre-compression will not provide adequate sealing.
Anti-blowout stem design is a fire safety requirement independent of the fire test — it prevents the stem from being ejected by line pressure if the stem packing fails during a fire. A valve body that is engulfed in fire for 30 minutes will have its packing severely degraded, and if the stem is not physically retained by a shoulder or shoulder ring that cannot pass through the packing bore, line pressure will eject it. ISO 10497 and API 607 both require anti-blowout stem retention, and the test configuration verifies that the stem does not eject during the test.
What Certification Covers and What It Does Not
A fire test certificate from a recognised testing authority — such as Exova, LGAI/Applus, BV, or an equivalent accredited body — confirms that the specific valve design configuration tested, in the size range tested, passed the specified fire test sequence on the date of the test. This is a type test certificate. It does not certify every production valve of that design — it establishes that the design is capable of passing the test when correctly manufactured to the design configuration.
The certificate will specify the valve size range covered (fire-safe certification is not automatically valid for all sizes of a design — testing is required for each size class), the pressure rating tested (typically the maximum rated pressure of the valve), and the valve configuration tested (specific seat material, seal material, packing type, and trim material). Any deviation from the tested configuration — different seat material grade, different packing compound, modified tolerance on seat bore — may void the certification for that specific valve. This is the critical point that buyers sometimes miss: a fire-safe certificate on the design does not guarantee that the actual valve purchased is built to the same configuration as the tested valve.
Purchase orders for fire-safe qualified valves should explicitly require that each valve is manufactured to the certified design configuration, with material certificates for all fire-safe critical components (seats, shaft seals, packing), and dimensional verification that the seat geometry matches the certified drawing. The valve should bear a permanent marking indicating the fire test standard and certificate reference number, and the certificate should be included in the valve documentation package delivered with the valve.
Extended Testing for Special Applications
Some applications require fire testing beyond the ISO 10497 or API 607 standard scenarios. Cryogenic service valves must be fire-tested at cryogenic operating temperatures rather than at ambient, because the thermal shock during fire engulfment of a cryogenic valve (instantaneous change from minus 160 degrees C to fire temperature) is fundamentally different from the gradual heating of an ambient-temperature valve. ASME and LNG industry specifications include fire test requirements for cryogenic valves that supplement the standard fire test protocols.
Offshore safety and ESDV applications may require extended fire test duration (60 minutes or longer rather than the standard 30 minutes) to reflect the longer fire scenarios envisaged for offshore platform designs. Some national offshore safety authorities and major oil companies have issued supplementary fire testing requirements that exceed the ISO 10497 minima — these should be identified in the project fire protection philosophy document and reflected in the valve purchase specification.
Dual-rated valves — those required to meet both fire-safe performance and other specific service requirements such as fugitive emissions or cryogenic performance — require multiple type test certificates, and the test configurations must be compatible. A valve cannot be configured with graphite packing (required for high-temperature fire-safe performance) and also with live-loaded PTFE packing (required for low fugitive emissions at ambient temperature) simultaneously — the engineer must choose a packing system that meets both requirements or accept that the valve needs different packing configurations for different service stages.
Inspection Points for Fire-Safe Valves
Factory acceptance inspection of fire-safe qualified valves should include verification of the following items as a minimum. Confirmation that the valve design drawing reference matches the certified design drawing — any revision to the certified drawing that affects fire-safe components requires re-qualification testing or engineering justification. Material certification review for seats, shaft seals, and packing — the actual materials supplied should be cross-referenced against the certified configuration to verify no substitutions have been made. Dimensional check of the seat assembly geometry against the certified drawing, particularly the metal backup seat face dimensions and the soft seat thickness. Packing inspection — confirm graphite packing rings are present, correctly staged, and pre-compressed to the specified torque. Anti-blowout stem check — confirm the stem shoulder dimension exceeds the packing bore dimension on the approved drawing. Fire test certificate review — confirm the certificate covers the valve size, pressure rating, and configuration as supplied.