Tightening the anchor bolt's nut

[Syahar1975]

Dear experts

Is there any standard / code about how many NM or Ft.Lb required when we are tightening the nut of the anchor bolts on the tank ?

Best regards,

Syah

 

[MJCronin]

I assume that you have an API-650 style metallic storage tank.

Good information here:

http://www.engineersedge.com/civil_engineering/concrete_foundation_anchor_bolts_design_10132.htm

Generally speaking, there is no hard and fast rule for tank anchor bolt torque. " Turn of the nut" method is commonly used.

http://www.civildesignhelp.info/ab.html

Do not torque the tank anchor bolts until the tank has its initial fill of liquid.

More information here: (but its for plastic tanks !)

https://books.google.com/books?id=G...age&q=storage tank anchor bolt torque&f=false

MJCronin
Sr. Process Engineer

 

[Syahar1975]

Thanks MJ Cronin.

 

[IFRs]

API 650 says: "Any anchor bolts shall be uniformly tightened to a snug fit (nuts hand tight in contact with anchor chair top plate plus maximum of 1/8 turn with wrench)... Measures such as peening the threads, or adding locking nuts, or tack welding nuts to chairs, shall be taken to prevent the nuts from backing off the threads."

 

[Duwe6]

Before you lock the anchor nuts, RETIGHTEN! Don't know the mechanism, can't get any good guesses from the eng's I've talked to but:
After the first tightening of anchors in concrete, especially cast-in-place anchors, they loosen themselves up. After the vessel/tank has had a few days after being full, per MJCronin post above, go back and Retighten, then lock the nuts [if you wish].

Don't overthink the 'Snug Tight'. For smaller stuff, it is "Full effort of a man on an ordinary [spud] wrench". For bigger stuff [like anchor bolts], it is "A few blows of an impact wrench". Put a wrench on the nut, hit it a couple of times with an ironworker's 'beater' [4# to 8#], keep hitting until the nut stops turning and the hammer just rebounds, and you are done. Rinse and Repeat.

 

[JStephen]

Note that certain high-strength bolts are required to be pre-tensioned to specific levels, not applicable to normal Grade-36 bolts.