about coupling nuts

[STEVE LIU]

hello
I have a question, because of i need M20 HEX a563 coupling nut to extend anchor.
can i replace it with material it is coupling for pipe (FULL COUPLING, CL3000, FNPT, CS ASTM A105N GALV., ASME-B16.11 ).

 

[BridgeSmith]

If I'm not mistaken, A563 is the spec for nuts for high strength (Fy up to 105ksi) bolts, which means an A563 coupling nut has sufficient hardness and threaded length to transfer a force equal to the ultimate tensile capacity of a solid high strength threaded bar. I seriously doubt any coupler for pipe is adequate to transfer anything close to an equivalent force, so I would say not just no, but hell no!

 

[STEVE LIU]

hi HOTROD10 :

I also doubt too, but I don't have ASTM a105/a10n so I cant compare what different it is
thank for your reply .... hell no

 

[BridgeSmith]

ASTM A105 specifies a minimum yield strength of 36 ksi and a minimum tensile strength of 70 ksi. The lowest proof load stress for any type of nut in A563 is 49ksi, going as high as 175ksi for DH and DH3 types, which are required for high strength bolts and anchor rods.

You should have justification to reject the pipe coupling just based on the fact that a threaded bar has a much larger cross section than a pipe of the same size, and therefore a much larger force capacity, even with the same tensile strength. If you're using high strength anchor rods, that only makes the discrepancy even greater and the pipe coupling inadequate by an even larger margin.

 

[SteveWag]

The thread form is completely different. The thread form of a M20 bar is straight and Metric dimensioned while the FNPT is tapered and NPT threads are inch. As to diameters, well M20 is M20 while NPT, or pipe diameters, are wildly different.
Steve

 

[BridgeSmith]

Any particular reason for trying to avoid using the correct coupling, and instead trying to substitute something that A) Will most likely be inadequate, and B) probably won't fit?