Views: 0 Author: J-VALVES Publish Time: 2026-10-29 Origin: Site
Many leaks blamed on the seat happen at the joint instead. The end connection decides how the valve meets the pipe, how much bolt load reaches the gasket, and whether the assembly can be broken and remade on site without machining. Three families cover almost every specification: raised face flanged, ring type joint flanged, and butt weld. They are not graded by quality. They are graded by what the line can tolerate, and choosing one above the duty of the piping around it buys cost without buying reliability. The end also settles one of the two leak paths a valve has without involving the seat, the other being the stem seal and its emission class.
A raised face joint seals because a gasket, spiral wound, graphite sheet or PTFE, is compressed between two machined faces by bolt load and flows into the surface finish. The seal depends on stress staying inside a band: too little and the joint weeps, too much and the gasket is crushed or the flange yields. That is why the raised face joint is cheap, quick to break and re-make, and intolerant of a fitter who tightens one bolt at a time instead of crossing the pattern in stages.
An RTJ joint replaces the soft gasket with a solid metal ring seated in matching tapered grooves cut into both flange faces. Bolt load drives the ring into the groove until it yields against the two conical faces, so the seal is metal to metal and does not depend on gasket creep or on the joint staying at one temperature. The ring is softer than the groove by design: the ring is meant to deform, the groove is meant to survive. That single rule explains most RTJ failures, because a groove scratched or hammered during maintenance is no longer a sealing surface and no new ring will rescue it.
The joint carries higher pressure because nothing inside it can extrude. A soft gasket at Class 1500 has to be confined, and the confinement is what eventually gives way; a metal ring is already confined by its groove. This is why RTJ becomes the default from Class 900 upward in most project specifications, and why it appears on hydrogen, high hydrogen sulphide and hot steam lines at lower classes too. The cost sits in the detail: the ring is single use in practice, the grooves must be inspected every time the joint is broken, and the two flanges must align closely enough for the ring to enter both grooves without being cocked.
A butt weld end removes the gasket and the bolting altogether, replacing them with a full penetration weld at a prepared end. Nothing can leak through an interface that no longer exists, which is why welded ends dominate small bore high pressure piping, cryogenic lines and services where a flange would be a leak path or a weight penalty. It also moves the risk into the weld: root defects, incomplete penetration and bore mismatch become the failure modes, and none of them is visible from outside. B16.25 defines the end preparation; the weld itself belongs to the piping code.
Bolts tightened in a circle rather than a cross pattern leave one side of a raised face joint under-stressed. A spiral wound gasket reused after compression has lost the spring that made it work. An RTJ ring of the wrong number, or a ring pulled from a used joint, sits high in the groove and never seats. And welding a valve into line without shielding the packing and the seat sends enough heat through the body to destroy both, which is a valve failure caused by a piping decision.
| End type | Seals by | Best fit | Re-makeable | Dominant failure |
|---|---|---|---|---|
| RF flanged | Gasket compressed between raised faces | General process, steam and water at moderate class | Yes, with a new gasket | Uneven bolt load, gasket creep |
| RTJ flanged | Metal ring yielding into tapered grooves | High class, hydrogen, hot hydrocarbon | Yes, with a new ring | Damaged groove, reused ring |
| Butt weld | Full penetration weld, no gasket | Small bore high pressure, cryogenic, buried line | No, cut and re-weld | Root defect, bore mismatch, welding heat |
The valve should follow the piping specification rather than lead it. Face-to-face dimensions come from B16.10, so a change of end type changes the space the valve occupies and the spool pieces around it. Flange drilling must match the mating flange, including the series for sizes above 24 inch, where B16.47 divides into two bolt patterns that do not interchange. A welded line feeding a flanged valve needs a welded neck flange of the same material rather than a threaded adapter, and an insulated joint wherever cathodic protection makes pipe and valve different electrical systems.
Name the end type, the facing standard and the mating flange series, then state what the valve must survive. For a flanged valve that means the gasket type and the bolt material; for an RTJ valve it means the ring number and whether spares are wanted; for a welded valve it means the end preparation, the bore match and the non-destructive examination required on the finished weld. J-VALVES supplies gate and check valves from 1/2 to 56 inch and globe valves from 1/2 to 48 inch, ASME Class 150 to 2500, with raised face and ring type joint flanges to ASME B16.5 and butt-welded ends to B16.25; the butt welded globe valve range and the pressure seal gate valve range are listed separately.
Can an RTJ ring gasket be reused? In practice, no. The ring has already yielded against the groove, and a second make up relies on a deformed shape meeting a groove that may have been marked in the first assembly. Rings are low cost compared with the downtime of a leaking joint, so spares should be ordered with the valve and the grooves inspected each time the joint is opened.
When should a valve be butt welded instead of flanged? When the line is small bore and high pressure, cryogenic, buried, or when the piping class rules out flanges as a leak path or a weight penalty. The trade is maintenance access: a welded valve cannot be lifted out on site, so it suits a line that is expected to stay closed for years rather than one that is opened for cleaning every month.
Does the end connection change the pressure rating of the valve? The body rating comes from the design standard and the class, so the end connection does not raise it. What the end must do is match or exceed that rating and match the mating pipe exactly, because a Class 2500 valve with a Class 900 flange pattern is a mismatch that no gasket will cover.
