As a manufacturer of hammer union by API flange and/or hub adapters,
WOODCO USA strongly supports the creation of an API Standard
Specification for Figure Number designated hammer unions. Presently operators and users of Figure
Number designated threaded, butt weld and integral, wing nut hammer unions have “Mostly
Learned” that they can connect any male Figure Number half union to any
female Figure Number half union, as long as both halves have the same Figure
Number and size designation.
Reported incidents resulting from accidentally connecting
incompatible 2" Figure Number 1502 male half unions, to 2" Figure Number
602 female half unions, which engage improperly when threaded
together and fail explosively when placed under pressure, prompted the
creation of API Recommended Practice 7HU1, 1st Edition, May, 2009.
To purchase a copy of Recommended Practice 7HU1,
To see a free example of the solution offered by Recommended Practice
The task group activity to create Recommended Practice 7HU1 resulted
in questions about the safety and interchangeability of all sizes and
pressures of Figure Number designated hammer unions for 6,000 psi and higher
A new API Task Group 5 Subgroup, had its first meeting on December,
2011, and a new effort began to create an API Standard for Figure Number
designated hammer union connectors.
Investigation has revealed that over time manufacturers of Figure
hammer unions have created a “Defacto Standard” for these unions, that
will allow them to reliably join, test, and function, but with small and
not-so-small dimensional differences. Manufacturers cannot explain these
differences to the satisfaction of one another, or other interested
parties. This has resulted in some manufacturers issuing various
warnings that include a caution not to attempt joining similarly marked
and rated Figure Number hammer unions together unless made by the same
Based upon the number of these unions in the field, and the fact that
no single manufacturer can satisfy the demand for the quantity or
configurations of equipment with these connectors, a strong need for an
API Standard exists.
If your company owns or uses Figure Number designated hammer union
connected equipment, please contact the manufacturer identified on the
equipment and urge them to participate in, or support, the current API
effort to standardize these unions. The standardization effort does not
intend to obsolete, or make unusable, any current Figure Number designated
hammer unions, but rather to bring the current compatible designs into
future uniformity of dimensions and materials.
You can contact any of the hammer union manufacturers by searching the internet
using their company name to find their website and then click on their
In the interest of safety and productivity, we
urge your company to participate in the current API effort to
standardize the identification designation, material, and dimensions of
Figure Number designated hammer unions.
Please add your company name
and your personal contact information.
Should you want to contact API directly, to comment on or make suggestions,
concerning the task group currently working on this project, send an email