Stud bolt, nuts, machine bolts and washers are also known as bolting material or fastener. Bolting is the term that used to tighten / create the flange joints connection. Tightening of the flange ensures the leak-proof connection between gasket & flanges.
ASME flanges have a minimum four bolt hole and for higher diameter flanges, the number of bolt holes is always in multiples of four. Selection of number bolt holes depends on the factor such as
- Size of the flange
- Working pressure
- Working temperature
- Flange material
Different Kinds of Fasteners Used in Piping
Stud Bolt
Stud has a thread on full lengths or at both ends. As shown in images. It is having three components if washers are not used (two nuts and stud). If you used washer it would become five. Sometimes additional nuts are used for hydraulic tensioning with larger size stud.
The length of stud bolt should be enough to cover entire Nut plus 1.5 to 3 threads exposed. Long studs must be avoided as it increases the chance of corrosion and other damage to exposed threads, which would make subsequent removal difficult. ASME B16.5 gives the required size of the stud. Length of the stud depends on the type of gasket and the maximum exposed thread requirements.
Machine Bolt
Bolts have a thread at one end and hexagonal head on another end. See the image below. In the process, piping bolts are used with lower strength flange types such as GRE/GRP, bronze. Usually, washers are used with bolt to prevent excessive load to the flange.
Nuts
Commonly Hexagonal Heavy-series nuts used with studs. The nonbearing face of a nut is chamfered, while load Bearing face is finished with a washer face or may be chamfered.
Washers
A washer is a thin plate with a hole at center. Washers distribute the load on flange face; this prevents damage to the flange. Non-metallic flange required washers due to this reason. Different types of washers are used such as Flat, Splits, and Conical Springs.
Conical washers are special washers. Also known as Belleville Springs washers. It Keeps bolted joints tight in an area where vibration, differential thermal expansion, and bolt creep present. These conditions can change the load on a stud which may result in a loose connection. Conical washers provide a spring effect and prevent loosening of a stud. This washer provides High spring loads with small deflections.
Stud Bolt Specification & Standard
Various ASME standards are used for stud bolts and nuts to manufacturing bolting material. List of such standard is given below.
- Diameter and Lengths of the stud and bolt are covered in ASME B16.5 & B16.47
- ASME B1.1 Unified Inch Screw Threads (Cores and Fine thread series- normally Cores thread series is used for stud used in piping)
- ASME B18.2.1 for Square and Hex Bolts and Screws
- ASME B18.2.2 Square and Hex Nuts
- ASME B18.21.1 Lock Washers
- ASME B18.22.1 Plain Washers
Stud Material Grades
Bolting material can be divided into three group
- High Strength
- Intermediate strength
- Low Strength
Stud
List of ASTM Material grade used for manufacturing stud is given in ASME B16.5, which is the Standard for the flanges.
- For high temperature and pressure services ASTM A193 Gr B7, B7M, B5, B8 are used.
- For low-temperature services ASTM A320 Gr L7, L7A, L7B are used.
- ASTM A354 Gr BC, BD is material grades for alloy steel quenched and tempered studs and bolts.
- For special application, ASTM A540 Gr B21 to B24 are used.
Out of these grades, most popular material grades are ASTM A193 Gr B7 & B7M.
Nuts
Nuts may be machined from the same material as stud or may be of a compatible grade of ASTM A194
- ASTM A194 standard lists the compatible material grades for nuts that used with stud & bolt.
- Most widely used material grades are ASTM A194 Gr 2,2H,2HM,8,8M
Washer
Common material grade used for washer manufacturing are
- ASTM F436, ASTM F844, ASTM F959
- If not specified washer can be manufactured from any compatible grade material
Coating on Stud Bolts and Nuts
Sometimes Bolting components are coated with different coating materials to improve its corrosion resistance. This will reduce maintenance cost. Common coatings are
- Chrome Plating
- Galvanizing
- Xylan
- PTFE
- Zinc
Gaskets
In piping, a Gasket is sealing material placed between connecting flanges to create a static seal, which will maintain the leakage proof sealing in all operating conditions. Different types of gaskets are used to achieve the leak proof sealing between the pipe flange. The primary function of gaskets is to seal the irregularities of each face of the flange so that there will be no leakage of the service fluid from the flange joint.
Types of Gaskets
There are three types of gaskets used in process piping.
- Non-Metallic
- Metallic
- Composite
