Bolts

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 Bolts:

To complete any flanged assembly, two additional items are required: Bolts & Gaskets. Bolts obviously hold mating flanges, nozzles, or valves together.
The pressure rating of flange will determine the size, spacing, and number of bolts required.
As the nominal pipe size and pressure rating change so will the diameter, spacing and number of bolts.
Flanges are designed to match the bolt circle and bolt hole dimensions of other flanges that are of the same diameter & pressure rating. It is critical that drawings convey the exact orientation of flanges to the fabricator.
ANSI standards require all flanges straddle either the horizontal, vertical or north-south centerlines of pipe and equipment.
To assure that bolt holes on flanges, nozzles, or valves align properly, holes are equally spaced around the flange.
The following formula makes bolt hole location and alignment quick and simple:
Angular location = 360°/number of holes
for example:
Angular location = 360°/8 = 45°
So it should be spaced 45° apart for a 8 hole flange. The holes must be positioned 221/2° on  each side of the centerline.




Bolts are available in two types, Machine & Stud.

  • Machine bolts have a hexagonal head on one end and threads on the other end. It is used with a hexagonal nut and a round washer
  • A Stud doesn't have head and is fully threaded. It is used with two hexagonal nuts & washers.
  • The length and diameter of studs / bolts required for flange joints of all pressure classes are specified in ASME B16.5.

THE MOST COMMON BOLTING MATERIALS USED IN THE PETROLEUM INDUSTRY :

  • ASTM A193-Alloy steel bolts for high temperature service
  • ASTM A 194-Alloy steel nuts for high temperature service
  • ASTM A 320-Alloy steel bolting materials for low temperature service.
  • ASTM A 307- Low carbon steel bolting material.
The dimensional standards for bolts are
  • ASME B 18.2.1- Square and hexagonal head bolts
  • ASM B 18.2.2-    Square and hexagonal nuts 



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