Use of smaller stud size

[rahim16]

Hi guys,
This is first time I am here. I found it very great & helpful in this engg. business.

In short my question is that in one of our flow lines, we have installed an insulation kit for cathodic protection. Due to slight misalighment of bolt holes, the insulating sleeve becomes cracked & the circuit becomes shortened.

Before going for cutting of pipes to get perfect alignment, I wanna discuss one option in the forum that can we try option of using one smaller stud size to give a little bit more space for sleeve?

I have 16"-1500# RTJ WN flange with standard 2-1/2" stud dia. I suggest one smaller stud dia size of 2-3/8".

Is this normal practice & safe? Am I taking too much risk keeping the joint integrity in mind?

This is an urgent decision, need expert comments at their earliest. Thanks in advance.

Imran

 

[ApC2Kp]

Imran,

The CL1500 flange rating would suggest that the system pressure rating must not be compromised by using all 16 smaller diameter bolts. In practice if only one bolt of 16 in flange were to be a smaller diameter there would be little difference.

There would be several possible remedies to consider before cutting and re-fitting the piping. The quick remedy would be to grind down the bolt threads in the middle of length, leaving the ends of bolts with approximately 2-1/2" length of full threads at each end of bolt. These bolts would have same strength as same diameter bolts. Second, the flange bolt holes with interference might be modified slightly larger (or oval shape) to get more clearance if necessary. Third, if there are flanged spools that could be rotated, there might be sufficient re-alignment of holes to get clearance for the bolts and insulating sleeves.