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Hex bolt VS Studbolt

Hex bolt VS Studbolt

Hi everyone,

Could somebody explain/advise me as following detail:

-Why Hex bolt is not widely use in Oil & Gas industries? What is the reason that limit or restrict to use the Hex bolt ?

-When refer to API 570 & 510, Is it state any objection to use the Hex bolt?

-Any advantage and disadvantage to use the Hex bolt instead of Studbolt?

Thanks for any help.

RE: Hex bolt VS Studbolt

Nothing wrong with using hex bolts *if* they are Heavy Hex pattern. The holes in flanges are sized generously, so the heavy hex is required - see B16.5 - for developing the design strength of the flange. With bolts, you have to be pretty exact in the length. With studs, over-length is fully acceptable. And studs + 2 nuts is 'traditional'. Makes the customer nervous when you violate tradition.

FWIW, most of the biodiesel, ethanol, and vegetable oil extraction plants were built using Gr.5 machine bolts, *not* the needed heavy hex bolting. Guess they liked to go shopping at Tractor Supply, etc. instead of an industrial supply that carried heavy hex like B7's.

RE: Hex bolt VS Studbolt

One nice thing about studs and 2 nuts is if one nut rusts shut, you have another that you can break loose.

RE: Hex bolt VS Studbolt

Also some failures occurred in the head of a bolt at the crotch which were not detected until failure. Studs and nuts don't have that issue. Also you can tighten them from both ends. Turning a bolt from the head end is not allowed as it can destroy the groove pattern.

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