Flowline
Hammer unions
Hammer unions join flowline iron in minutes: a wing nut on the male sub is struck up onto the female sub, and the seal holds pressure. Supplied by figure, size, end and service.
A hammer union is a three-piece pipe connection: a male sub carrying a wing nut, and a female sub with an external thread and a seal. Striking the lugs of the wing nut with a hammer pulls the two subs together and seals the joint, so flowline iron can be rigged up and broken down quickly. We supply hammer unions from FIG 100 to FIG 2002 with threaded, butt weld or hose ends, for standard or sour service, complete with wing nuts and seals.
How a hammer union works
The two subs are welded, threaded or machined onto the pipe or equipment they join. The male sub has a shoulder that the wing nut bears on; the female sub has the external thread the nut engages and the seal face or seal groove. As the nut is hammered tight, the subs are drawn together and the seal is compressed. Because no flange bolts or torque wrench are needed, unions are the standard connection for temporary iron on frac, cementing, flowback and well test jobs.
Figures and pressure
The figure number identifies the union design, and halves of different figures must never be connected, even when they thread together. These are the ratings union makers publish:
| Figure | Standard service | Sour gas service | Typical use |
|---|---|---|---|
| FIG 100 | 1,000 psi | - | Water, air and other low-pressure lines |
| FIG 200 and 206 | 2,000 psi | - | Low-pressure lines and hose connections |
| FIG 400 | 4,000 psi | - | Medium-pressure lines |
| FIG 602 | 6,000 psi | - | Mud, cement and production lines |
| FIG 1002 | 10,000 psi | 7,500 psi | Cementing, acidizing and well service |
| FIG 1502 | 15,000 psi | 10,000 psi | Frac, flowback and well test iron |
| FIG 2002 | 20,000 psi | - | Very high-pressure well service |
| FIG 2202 | - | 15,000 psi | High-pressure sour gas service |
Ratings as published by union makers, for example TechnipFMC for its Weco figures and Kuriyama for figures 100, 206 and 400. Confirm against the drawing for the exact part.
End connections
| End | How it joins | Where it is used |
|---|---|---|
| Threaded | Line pipe or NPT thread machined in the sub | Low and medium-pressure lines, where the thread rating suits the line |
| Butt weld | Beveled to the pipe schedule for a full-penetration weld | Manifolds, skids and permanent piping with union break-outs |
| Hose | Shank for a hose with a crimped or clamped ferrule | Hose connections on low-pressure figures; for transfer hoses, see camlock couplings |
| Integral | Sub machined from the pipe or fitting body, no weld | Pup joints and integral fittings at the highest ratings |
A threaded or welded end can limit the rating of the joint below the union figure. The marked rating is the lower of the two.
Seals
Low-pressure figures often seal metal to metal on a ground face; medium and high-pressure figures use an elastomer seal, an O-ring or a lip seal, in the female sub. Nitrile seals suit standard service; for sour gas, high temperatures or aggressive fluids, fluoroelastomer or other compounds are chosen for the fluid. Seals are wear parts: carry spares, and replace any seal that is cut, swollen or flattened.
Sour service
Unions for hydrogen sulfide service are made from material heat treated to the hardness limits of NACE MR0175 / ISO 15156-2, 22 HRC maximum for 4130, and carry the sour version's lower rating and a sour service marking. Order the service on every line, because a sour union is not a standard union with a different label.
Marking and safe make-up
Each sub and nut is stamped with the figure, size, cold working pressure and heat number, so crews can check both halves before make-up and inspectors can trace each part to its certificate.
Some unions of the same size but different figures will thread together, then fail far below either rating. Check the stamped figure on both halves before every make-up, keep figures apart in the yard, and retire parts whose marking can no longer be read.
We make these parts to the API 6A and API 16C 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
Hammer union, 2 in FIG 1502, complete (male sub, wing nut, female sub, seal), butt weld ends for 2 in XXS pipe, AISI 4130 quenched and tempered, 15,000 psi CWP standard service, EN 10204 3.1, 20 sets
Hammer union, 4 in FIG 206, complete, threaded 4 in line pipe, 2,000 psi CWP, nitrile seal, EN 10204 3.1, 10 sets
Frequently asked questions
What does FIG 1502 mean?
FIG 1502 is a hammer union design, one figure number in a series that identifies the thread, the seal and the cold working pressure. FIG 1502 is rated 15,000 psi in standard service and 10,000 psi in its sour gas version. The full chart is in hammer union figures explained.
Which half carries the wing nut?
The male sub. The wing nut rides on the male sub and threads onto the external thread of the female sub, which also carries the seal. Order unions as complete sets, or state male or female for each half.
Do you supply spare seals and wing nuts?
Yes. Seals, wing nuts and retainer segments for each figure can go on the same order as the unions. Tell us the service so the seal material matches it.
Can you weld the union to our pipe?
Butt weld subs are supplied with ends beveled for your pipe schedule, ready for your welder. For a union that needs no field weld at all, see our integral pup joints, where the union ends are part of the pipe.