Wellhead and manifolds
Hub and clamp connections
Two hubs, a seal ring and a clamp: a high-pressure joint that makes up with two or three bolts. Hubs, clamps and rings to API 16A for drilling equipment, or to your drawing for process lines.
A clamp hub connection joins two hubs, each with a tapered shoulder behind its sealing face, by closing a clamp over both shoulders: as the clamp bolts are tightened, the taper draws the hubs together and loads the seal ring between them. On drilling equipment the hubs, clamps and rings follow API 16A; on process and pipeline service they follow the connector maker's or buyer's design. We make weld neck, integral and blind hubs, clamps and seal rings in AISI 4130 and 4140, to API 16A dimensions or to your drawing.
Parts of a clamp connection
| Part | What it is | Options |
|---|---|---|
| Weld neck hub | Hub with a tapered neck butt-welded to the pipe or a fitting | Bored to the pipe; weld end to ASME B16.25 |
| Integral hub | Hub machined on the equipment body itself | On spools, blocks and valve bodies, to drawing |
| Blind hub | Hub with no bore, closing a connection | Solid, or with a tapped test port |
| Clamp | Two or three segments joined by bolts | Sized by clamp number to the hub |
| Seal ring | Metal ring between the hub faces | BX or RX rings for API 16A hubs |
API 16A hubs
API 16A, the specification for drill-through equipment, covers the clamp hub connections used on blowout preventer stacks, drilling spools and choke and kill lines. Its hubs are rated 5,000, 10,000, 15,000 and 20,000 psi and seal with BX or RX rings; each hub size and rating has a matching clamp number. Hubs are forged from AISI 4130 and quenched and tempered to the strength the rating needs, and they are made to the material class, temperature class and PSL on your order, with sour service to NACE MR0175 / ISO 15156.
Process and pipeline hubs
Clamp connectors are also used in process piping, on offshore platforms and in pig launchers and receivers, where they save weight and space over flanges. These hubs are often made in low temperature carbon steel such as ASTM A350 LF2 with clamps and seal rings in 4130 or 4140, impact tested at the minimum design temperature. We make them to your drawing and material specification.
Clamp bolts are tightened evenly to the torque in the connector's data, and the hub faces and seal ring are inspected each time the joint is opened. A damaged ring is replaced, never reused.
We make these parts to the API 16A requirements your order calls up: material, dimensions, tests and marking as specified. We do not hold an API license, so the parts do not carry the API Monogram. If your specification requires monogrammed equipment, the quotation says so plainly.
Ordering
Weld neck hub, API 16A, 3-1/16 in 10,000 psi, BX-154 groove, bored for 3 in XXS, AISI 4130, material class DD, temperature class P, PSL 3, with matching clamp and bolting, EN 10204 3.1, 2 sets
Blind hub, API 16A, 2-1/16 in 15,000 psi, BX-152 groove, 1/2 in NPT test port, AISI 4130, PSL 2, EN 10204 3.1, 2 pcs
Frequently asked questions
Why use a clamp connection instead of a flange?
A clamp joint has two or three bolts instead of a ring of studs, so it makes up and breaks out faster, and the hubs are smaller and lighter than flanges of the same rating. It suits connections that are opened often, and tight spaces in manifolds and BOP stacks.
Are clamps interchangeable between hub sizes?
No. Each clamp fits one hub profile and size. API 16A numbers its clamps by hub size and rating; pipeline clamp connectors follow their maker's series. Order the clamp with the hubs, or give us the clamp number or hub drawing.
Do you make proprietary clamp connector designs?
We make hubs, clamps and seal rings to API 16A dimensions, or to a drawing you own or are licensed to use. We do not copy another maker's proprietary connector design.
Which seal ring goes in an API 16A hub?
A BX ring for most sizes and ratings, or an RX ring where API 16A calls for one, of the number that matches the hub. See ring gaskets.