HEAVY STEEL NUTS
Steel nuts are available in multiple forms and shapes, the most common are: hex nuts, heavy hex nuts, square nuts, hex jam nuts, heavy jam nuts, hex coupling nuts, sleeve nuts, lock nuts. To build pipelines and process plants, heavy hex nuts are the most used type. In the petrochemical and oil & gas industry, hex nuts are used to tighten the stud bolts that join flanges.
The ASME B18.2.2 standard sets the dimensions and the tolerances for heavy hex nuts used in conjuction with stub bolts for flanged connections. This type of nuts is defined "heavy", as they are slightly larger and thicker than traditional steel nuts (standard finish hex nuts). These bolts need to withstand significant mechanical forces and are key to prevent leakages in flanged connections. Depending on customer’s specification, nuts may be both sites chamfered or with on one side a washer-face. When ordering bolting sets, compatible material grades for stud bolts and nuts shall be choosen. The table below shows the most commonly matching grades of bolts and nuts.
On the market, heavy steel nuts are generally available in the size range 3/8 inch. -2 3/4 inch. and in both plain metal or galvanized. Special heat treatments and coatings are also possible for specific applications.
ASME B18 2.2 (STEEL NUTS DIMENSIONS)
|WIDTH ACROSS FLAT||WITH ACROSS CORNERS||NUTS THICKNESS|
STUD BOLT / NUTS MATERIALS
The table shows the compatibility between ASTM stud bolts and nuts materials:
|ASTM A193 Stud Bolt Material||ASTM A194 Steel Nut Material|
|A193 Grade B7||A194 2H or 4 or 7|
|A193 Grade B8 (Class 1 and 2)||A194 8*|
|A193 Grade B8M (Class 1 and 2)||
|A320 Grade L7||A194 4 or 7|
|A320 Grade B8 (Class 1 and 2)||A194 8*|
|A320 Grade B8M (Class 1 and 2)||A194 8M**|
* Stainless steel nuts, grade S304
** Stainless steel nuts, grade S316
Washers offer a smooth bearing surface underneath the head of a steel nut or a bolt. ASTM F844 sets the standards for flat washers. Steel washers are available in the size range 1/2 inch to 4 inch and supplied either in plain metal or galvanized (as the steel nut).
Washers can have a circular, oval and rectangular shape.