Views: 0 Author: J-VALVES Publish Time: 2026-10-26 Origin: Site
A soft-seated valve seals because a polymer seat conforms to the closure. That same polymer is the first thing a fire removes: PTFE melts at about 327 °C, and EPDM or NBR seat inserts are gone well before that. A valve whose only sealing element has burned away cannot be described as fire-safe no matter how well it held Class VI on the test bench the week before. Fire-safe design starts from that sentence. The valve has to keep isolating, with the line still under pressure, after the seat is ash. Nothing in the requirement says the valve must be reusable afterwards. It says the valve must not feed the fire.
API 607 is the American fire test for quarter-turn valves with soft seating. ISO 10497 is the international fire test method, and the current editions follow the same burn-and-retest sequence, so most projects accept either certificate for the same valve. Two neighbours are worth knowing because they are constantly confused with them: API 6FA covers API 6D pipeline valves, and API 6FD covers check valves. A 6FA certificate is not a 607 certificate, and a supplier who offers one when the specification asks for the other is offering a document that will not be accepted at inspection.
The valve is mounted in a test loop, usually closed, and burned for 30 minutes with the flame averaging 761 to 871 °C. It is then cooled, often with a water spray, and pressured again. Shell tightness and seat tightness are both checked after the burn, at the pressure class the valve is qualified for. External leakage past a body joint, a bonnet gasket or the stem seal decides pass or fail; seat leakage is measured against a limit written into the standard, not against zero. That distinction matters commercially. A fire-safe certificate is not a claim of bubble-tight shutoff after a fire, and no supplier should present it as one.
| Component | Soft-seat default | Fire-safe build | Job after the burn |
|---|---|---|---|
| Seat insert | PTFE, RTFE or EPDM | Graphite or metal-backed secondary seat | Holds a sealing line once the polymer is gone |
| Body gasket | PTFE or elastomer sheet | Flexible graphite laminate | Body joint stays tight at flame temperature |
| Stem packing | PTFE V-ring | Flexible graphite rings | Stem seal survives cool-down |
| Stem | Plain stem through the gland | Blowout-proof stem with collar | Pressure cannot eject the stem |
| Backseat | None or decorative | Lapped metal-to-metal shoulder | Second barrier at full open |
| Stem bearing | PTFE-lined bushing | Metal or graphite bushing | No polymer collapse at the shaft |
Every row in that table is a polymer being replaced by something that does not melt. The secondary seat is usually a stainless ring loaded by a spring or by line pressure, so that when the soft insert has burned away, metal lands on metal with enough force to hold the class. This is also why a fire-safe butterfly valve carries a higher operating torque than the same valve with a plain soft seat. The metal backup has to be preloaded before the fire, not after it.
Three failures repeat in the field. The first is a valve that survives the burn and fails the cool-down: the body distorts when the quench hits it, and the bonnet joint opens. The second is graphite that keeps sealing but loses its gland load, because the packing oxidises above roughly 400 °C in air and the ring volume shrinks; the stem seal then weeps at the next thermal cycle. The third is the soft seat that melts and flows into the flow path, blocking the disc from closing at all. That valve is fire-safe on paper and jammed in fact. A good design gives the melted polymer somewhere to go.
A fire test is a design qualification, not a batch test. The certificate therefore names a valve model, a size range, a pressure class, a material combination and an end connection, and it covers nothing outside that envelope. Ask four questions. Which standard and which edition. Which sizes and classes were actually burned. Was the valve tested in both flow directions, if it is bidirectional. And who witnessed the test. A certificate issued for a 6 inch Class 150 lug butterfly does not qualify a 48 inch triple offset valve, even from the same factory and even with the same seat material.
Four lines are enough. State the fire test standard and edition, the size and class range to be covered, both-directions testing where the valve is bidirectional, and the documents to ship with each valve: the fire test certificate, material certificates to EN 10204 3.1, and the seat test record to API 598 at 1.1 times rated pressure. Then add the line the standard does not contain, which is whether the valve has to remain operable after the burn. That is a different and much harder requirement, and it changes the design rather than the paperwork.
J-VALVES builds the soft-seated valves where this question usually appears: butterfly valves from 2 to 112 inch (DN50 to DN2800) up to Class 900, sleeved plug valves, and gate valves from 1/2 to 56 inch (DN15 to DN1400) in Class 150 to 2500. Graphite body gaskets, graphite stem packing, blowout-proof stems and metal-backed secondary seats are quoted as a stated build on the order, with the fire test documentation issued against the valve serial number. Shell tests run at 1.5 times and seat tests at 1.1 times rated pressure.
What is the difference between API 607 and ISO 10497? API 607 is the American fire test standard for quarter-turn valves with soft seating, and ISO 10497 is the international fire test method. Current editions follow the same burn-and-retest sequence, so most projects accept either certificate for the same valve. The certificate still has to match the valve model, size and pressure class, and that is where most mismatches are found at inspection.
Does a fire-safe certificate mean the valve is leak-tight after a fire? No. The test proves the valve still isolates within the leakage limit the standard sets for the seat, and that no external leakage appears at the body joint or the stem seal. That is a survival limit, not bubble-tight shutoff. A valve that has been through a real fire is normally replaced rather than returned to service.
Which parts of a valve have to change for a fire-safe build? Every polymer in the pressure boundary and every polymer in the sealing path: the seat insert, the body gasket, the stem packing, the stem bearing and, in a butterfly valve, the disc-to-stem seal. A metal-backed secondary seat and a blowout-proof stem complete the change. Replacing only the seat insert gives a valve that survives the burn and then leaks at the gland.
