Hammer union figure numbers explained: pressures, seals and sour service from Figure 100 to 2202

A hammer union joins two lengths of pipe or iron with a wing nut that is struck tight with a hammer, which is why it is the connection of choice on temporary lines that are rigged up and down every job. The figure number cast or stamped on it is the single most important fact about the union, because unions of different figures can look alike while being rated thousands of psi apart.

/01The figures on our listings.

/02Where the rule breaks.

Three things catch people out. Some figures lose pressure with size: Figure 400 is listed at 4,000 psi from 2" to 4" and 2,500 psi from 5" to 12", and Figure 1002 at 10,000 psi to 4" and 7,500 psi at 5" and 6". Some figure numbers break the pattern: Figure 2202 is a 15,000 psi union for sour gas. And sour-gas versions of a familiar figure are derated — see section 4. The test pressure on our standard-service listings is one and a half times the working pressure: 22,500 psi for Figure 1502, 9,000 psi for Figure 602.

/03Special-purpose figures.

A few figures exist for a job rather than a pressure class. Figure 207 is a blanking cap (2,000 psi, 3" to 6"). Figure 211 is an insulated union, used to isolate one side of a line electrically, at 2,000 psi in 2" and 3". Figure 1003 is a misaligning union that accepts up to 7.5° off the centre line — 15° included — except the 2" size at 3.5°; it is rated 10,000 psi in 2" and 3" and 7,500 psi in 4" and 5". Figure 1004 is a 10,000 psi butt-weld union in 5" and 6".

/04Sour gas service.

Hydrogen sulphide embrittles hard steel, so a union for sour gas is made from hardness-controlled material and usually carries a lower rating than its standard twin. On our sour-gas listings, Figure 1502 is 10,000 psi rather than 15,000; Figure 1002 is 7,500 psi to 4" and 5,000 psi at 5" and 6"; Figure 1003 is 7,500 psi in 2" and 3" and 5,000 psi in 4" and 5"; Figure 1004 is 7,500 psi; Figure 602 stays at 6,000 psi. Figure 2202 is the sour figure for 15,000 psi, butt weld from 2" to 6", with a lip seal and a stainless steel anti-extrusion ring.

/05Ends, seals and ordering.

Unions come with threaded line-pipe ends or butt-weld ends; for butt weld, the weld schedule must match the pipe (Schedule 40 and 80 on Figures 200 and 206, Schedule 80 and XXS on 602, XXS on 1002 and 1502). On the elastomer-sealed figures the seal ring is a service item — replace it whenever it is cut, flattened or hardened. To order, give the figure, size, end connection and schedule, and whether the service is standard or sour. Unions are part of the wider treating-iron picture in flow iron explained.