Monday, October 24, 2016



There have been a number of fluid discharge incidents and other accidents at gas production sites throughout the United States.  Based on our forensic investigations, quite a few of these releases have been caused by the failure of hammer unions or hammer joints.  Considering the skyrocketing increase in the number of these gas production sites, and since this is an on-going and recurring issue in the Oil & Gas, the chemical and steel industries, it is important to advice the insured and the insurers on the critical issue of mismatching and subsequent failure of hammer unions.

The danger of mismatched hammer unions
Hammer unions are connectors for flowline and temporary pipe installations.  Sometimes people use them instead of the flanged connection called for in the design. 
Property damage, injury and environmental release reports continue to come in involving pressurized lines and the unions used on these lines.  Workers have been observed mismatching unions.   In addition, workers have been observed hammering on lines while still under pressure.  Several accidents within the industries that use these unions, including fatalities, have occurred due to pressurized lines being improperly connected or being hammered on while under pressure.

FMC acquired the original Weco company that used to make these unions in the 1950s. The design is old, and used in steel and chemical plants, marine dredging vessels, strip mines and the oil & gas industry.  The problem is that Weco had made quite a few of these unions using different design standards they developed; in addition, there is no industry-wide standard.  There is a real potential for mismatch of the most commonly used hammer unions in the oil & gas, chemical and steel industries:  2-inch Figure 402, 2-inch Figure 602, 2-inch Figure 1002, and 2-inch Figure 1502.  The 2” Figure 1502 will make-up with 2” Figure 602 and 1002 and Guiberson 607.

You can eliminate the hazards involved with the mismatching of the various unions, by destroying 2″ 602 & 1002 Weco unions or old Guilberson Unions found in your operation and use only 1502 Thread Halfs (female sub) Use only Unions supplied by FMS and in good condition to ensure they hold rated pressure.

Recent representative releases caused by mismatched hammer unions at gas sites

·         A failed hammer union resulted in (21) gallon spill of production fluid that impacted the surface of the ground on the Well Pad. The spill was discovered around 3:40 PM on 11/30/2013.

·         One incident occurred when a 1502 wing nut male sub union holding a pressure sensor was attached to a 602 female union on the mud pump. The 1502 union and pressure sensor blew off the discharge of a mud pump. Another incident occurred when one service company’s 1502 wing nut for the male sub was made up to another service company’s 602 female half. While attempting to test the surface casing, the rams were closed and the standpipe pressure was slowly brought up. The intended test pressure was to be 1500 psi. When the pressure reached 1300 psi, the 1502 union stripped out and blew off and struck a third party service employee causing serious injury.

·         A spill occurred on 1/8/13.  An unknown amount of re-use water was released onto the ground.  A hammer union was leaking into the secondary containment of the frac tanks.

·         A spill occurred on 11/21/12 at 12:54 PM.  According to the incident report, the result of the release was due to a hammer union coming apart on the line to the production tank associated with the E Bunnell 6H Well. 

·         A drill crew was drilling ahead when a third party pressure sensor attached to the stand pipe stopped working. The sensor was made up to the standpipe with a size “602″ hammer union rated at 6,000 psi working pressure. The crew removed the faulty sensor and replaced it. The hammer union on the new pressure sensor had a size “1502″ wing nut rated to 15,000 psi. The “1502″ female threads in the wing nut appeared completely made up to the “602″ male threads coming off the standpipe

·         A spill occurred on 2/1/2014 when a dump line froze which caused a hammer joint to loosen and subsequently release production fluid to the ground.  Reported spill volume was 42 gallons. 

Figure 1.  FMC Hammer Union

The dangerous problem

The thread (or male half) of a 2” 602 and 1002 hammer union will make-up to the wing nut (or female half) of a 2” 1502 hammer union leading a worker to believe he has mated two compatible components that will withstand fluid pressures up to 6,000 psi.  As the threads on the two halves are of the same pitch and design, they will actually screw together.  However, because there is a 5/16” difference between the diameters of the thread and wing-nut halves described above, the two mismatched components will not actually hold high pressures very long.  The hammer unions will eventually separate.  When the union halves blow apart three immediate hazards are created:

1.                  The wing-nut becomes an 8 lb. Projectile that moves in an undetermined direction, maybe at personnel.

2.                  Uncontrolled release of high-pressure fluids that may or may not strike an employee in its path.

3.                  Uncontrolled release of potential toxic fluids (acids, oils, fuels, diesel base mud) that may cause harm to persons or the environment.

Figure 2.  Differences between the 1502 and the 602 female sub

These hammer union components have a history of failing under pressure due to incorrect matching of components (pressure ratings and/or incompatible geometry).

The above list is not meant to be all-inclusive and users should establish controls to ensure hammer union combinations are safe, especially when more than one manufacturer’s components are used.

The Recommended Procedure by the American Petroleum Institute

The recommended procedure (RP) alert by the API is intended to raise awareness of the incompatibility and dangers of these hammer unions.  Even though these parts mate up, they are likely to fail below the working pressure of the hammer union segments (male and female). Failures typically result in personnel injury or death in addition to extreme equipment damage.

Figure 3.  Compatible hammer unions.  Note the smaller diameter of the lips of the male sub.

The RP also describes a recommended procedural solution to the industry that will reduce the likelihood of a 2-inch Figure 402, 602, and/or 1002 hammer union component being made up inadvertently to a 2-inch Figure 1502 hammer union.

Additionally the RP describes and proposes an engineering solution to the industry that makes impossible the mating of female 2-inch Figure 402, 602, and/or 1002 subs with the wing nut of the 2-inch Figure 1502 hammer union.

It is important that all users and suppliers adopt the procedural solution as it could possibly be a number of years before the new hammer union designs are implemented and the original hammer unions taken completely out of service.

Briefly, the procedural proposals include using one or more of the following measures depending on the fleet or equipment package:

        Replace all 2-inch hammer union components to a 2-inch Figure 1502.

        Use Go/No-Go gauges on all 2-inch female subs to determine whether the component is acceptable for use with a 2-inch Figure 1502 male sub and nut.

        Perform inspection and marking to ensure all hammer unions are repaired or removed from service as required. Marking should be either by stamping or branding and large enough to easily see.

        Train all personnel on the hazards of mismatched hammer unions and include identification of all components, wear and tear, and out of service criteria.

        Management of change process should be utilized.

        Permit-to-Work (PTW) and/or Job Safety Analysis (JSA) should be used in all work requiring hammer unions.

        Jobsite inventory of hammer union component.


The RP also notes that the engineering design solution is in three areas of the female sub:

1)      reduced thread major diameter,

2)      raised shoulder, and

3)      a mark indicating the design.

Other areas covered in the RP include mitigating the effects of mismatched components parting, as well as several general safety recommendations.

The dangers of mismatched hammer unions have been in the patch for far too long.  But by following the recommended procedural solution contained in this RP, as an industry, we can protect our workers to the best of our ability while using hammer unions. It is of the utmost importance that all employees are trained and retrained in the proper handling, use and make-up of hammer unions.

Figure 4.  Incompatible hammer unions.  Note the almost same diameter of the male and female lips.

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