Hammer Unions

How a Hammer Union Works

A hammer union is a quick make and break pipe connection consisting of three parts: a male sub with a spherical or conical nose, a female sub with a matching seat, and a wing nut that draws the two together and is tightened with a hammer, which is where the name comes from. Sealing is by metal to metal contact of the two noses, or by an elastomer seal in some designs, and the wing nut provides the axial force that holds the seal in compression. The advantage is that a joint can be made and broken in seconds with a hammer, without threading or bolting, which is why hammer unions dominate cementing, fracturing and other oilfield manifold applications where lines are rigged up and down repeatedly. The trade-off is that the seal quality depends on correct make-up force, and hammer unions should not be used where a leak would be catastrophic without proper inspection and torque control.

Reading the Figure Numbers

The figure number identifies the design and the pressure rating of the union. The common oilfield figures run from FIG 100 through FIG 2202, with the higher numbers generally indicating higher pressure capacity. FIG 100 is a low pressure general service union, FIG 200 and FIG 206 are intermediate, FIG 400 and FIG 602 cover higher pressures used in mud and cement service, and FIG 1002, FIG 1502 and FIG 2202 are the high pressure unions used on fracturing and high pressure well servicing manifolds, with FIG 1502 rated to 15000 psi working pressure and FIG 2202 rated to 20000 psi. One practical caution: the same figure number from different manufacturers is not necessarily dimensionally or pressure interchangeable, so confirm the specific manufacturer standard before mixing brands in a manifold.