1. The end connection is a pressure boundary decision
The end connection is the part of the valve that meets the pipe, and it is a pressure boundary in its own right, not a convenience. Choosing it wrong adds leak paths, pushes up installation cost or forces a weld procedure the site cannot run. A flanged end is bolted and demountable, which makes maintenance easy but adds a gasket and a bolting joint that can leak. A butt weld end fuses the valve permanently into the line and removes the joint entirely, but it cannot be taken out without cutting. A threaded or socket weld end suits small bore instrument and utility lines where the valve is light and the joint can be inspected easily. The selection is made against line size, pressure class, fluid and how often the valve must come out.
2. Flanged ends: raised face, RTJ and the standards behind them
A flanged ball valve bolts to a mating flange, and the face style decides the seal. A raised face flange seals on a gasket held between two machined faces and covers the bulk of refining, chemical and utility service. A ring type joint flange uses a metal ring crushed into a groove and is specified for high pressure, high temperature and hydrogen or sour service where a soft gasket cannot hold. The flange dimensions follow ASME B16.5 up to 24 inch and ASME B16.47 above it, and the face-to-face length follows ASME B16.10, so a flanged valve of a given size and class is dimensionally interchangeable across manufacturers. Flanged ends add weight and a bolting joint, but they are the default because they let the valve drop out for overhaul without touching the pipe.
3. Butt weld ends: removing the joint for high pressure and buried duty
A butt weld end is a prepared weld bevel on the valve body that a welder joins to the pipe with a full penetration weld. There is no gasket and no bolting, so the end connection contributes nothing to the leak path, which is why butt weld ends are standard on gas transmission, buried and high pressure offshore lines. The bevel is machined to ASME B16.25, and the body must be long enough between the ends to carry the heat of welding without drawing the seats. The trade is permanence: the valve cannot be serviced in place without cutting it out, and the weld itself must be made and inspected by qualified procedures. For a soft seated valve the seats are normally removed or protected before welding to keep heat away from the polymer.
4. Socket weld and threaded: the small bore choice
Socket weld and threaded ends cover the small bore world, generally up to 2 inch, and the difference is how the pipe is held. A socket weld end is a socket bored into the body into which the pipe slides, welded around the rim with a fillet weld; a small gap is left inside so thermal expansion does not crack the joint. A threaded end is cut with NPT or BSP threads and the pipe is screwed in with thread sealant, which makes it instantly demountable but not leak free enough for the harshest duties. Both are cheap and fast to install, both suit high pressure small lines, and both are avoided where the fluid is aggressive or cyclic loading can work a threaded joint loose. For flammable service many specifications ban threaded ends above a certain size or pressure class.
5. End connections compared
The table below sets out the practical difference between the four end connections on the values that drive a selection.
| End connection | Typical size | Joint type | Typical duty |
|---|---|---|---|
| Flanged raised face | 1/2 to 56 inch | Gasket, bolted, demountable | Refining, chemical, utility |
| Flanged RTJ | 1/2 to 24 inch | Metal ring, bolted, demountable | High pressure, sour, hydrogen |
| Butt weld | 1/2 to 56 inch | Full penetration weld, permanent | Gas, buried, offshore |
| Socket weld | 1/2 to 2 inch | Fillet weld, semi permanent | High pressure small bore |
| Threaded NPT | 1/2 to 2 inch | Thread plus sealant, demountable | Instrument, utility, clean lines |
6. Face-to-face dimensions and why they are non-negotiable
The face-to-face length is the distance between the two sealing faces, and it is fixed by ASME B16.10 for flanged and butt weld ends and by the manufacturer for threaded and socket weld ends. It matters because a replacement valve must drop into the same gap as the one it replaces. A short pattern valve fits a tight skid but may not match the spool piece drawings, while a long pattern valve will not fit a gap cut for a short one. On brownfield work the face-to-face dimension is checked against the as-built drawing before the order is placed, and the pressure class changes the flange drilling and thickness, so a Class 300 valve is not interchangeable with a Class 600 valve even at the same size. Getting this wrong is the single most common cause of a valve being returned at site.
7. Material matching and weld preparation
The valve end and the pipe must be weld compatible, or the joint will crack or corrode preferentially. A carbon steel WCB or WCC body welds to carbon steel pipe with a matching filler, while a stainless CF8M body to carbon steel pipe needs a dissimilar metal weld procedure and the correct filler to avoid cracking and galvanic corrosion. Duplex bodies call for matching duplex filler and a controlled heat input, and low temperature LCB and LCC bodies need the weld procedure qualified at low temperature so the joint does not lose toughness. For butt weld ends the bevel is supplied machined and the bore is matched to the pipe schedule, so the welder does not have to reform the joint in the field. The material certificate and the weld procedure are settled before the valve ships, not at the site.
8. Specification checklist for the end connection
Five questions settle the end connection: line size and pipe schedule, pressure class and flange standard, whether the fluid is hazardous or clean, how often the valve must be removed, and the pipe material for weld compatibility. Add the face-to-face standard and confirm it against the existing gap on replacement work. J-VALVES supplies ball valves from 1/2 to 56 inch (DN15 to DN1400) in flanged, butt weld, socket weld and threaded ends, ASME Class 150 to 2500, with material and weld documentation built to the project specification, and quotes returned within three working hours.
9. Frequently Asked Questions
What is the most common ball valve end connection?
Flanged raised face, dimensioned to ASME B16.5 up to 24 inch and ASME B16.47 above it. It is the default because it is demountable for maintenance and dimensionally interchangeable between manufacturers.
Can a ball valve be welded into the line?
Yes. A butt weld end with an ASME B16.25 bevel is joined with a full penetration weld, which removes the bolted joint entirely and suits buried, gas transmission and high pressure lines. Seats are usually removed or protected during welding.
What is the difference between socket weld and threaded ends?
A socket weld end slides the pipe into a socket and is sealed with a fillet weld, while a threaded end is screwed together with NPT or BSP threads and sealant. Socket weld is more leak tight and preferred for flammable duty, while threaded is instantly demountable but avoided for cyclic or aggressive service.
