Enlarging Bolt Holes - Routine or R-1 1

[UKCats]

I have a heat exchanger bonnet that has twenty-four (24) 3/4-inch holes in its flange. I need to enlarge the bolt holes to 7/8-inch to match a new shell.

I have run the calc, and the code supports the larger holes. Would enlarging the holes be considered an Alteration???

 

[metengr]

The NBIC is concerned with alterations that affect the pressure retaining capability of the component where "welding" is performed. Alterations, where no physical work is performed, deals with re-rating issues. If the calulation shows the pressure retaining item can withstand larger stud holes without affecting the pressure retaining capability, and no rerate of the item is performed, and no welding is required, in my opinion this is a REPAIR.

Mechanical repairs that do not affect the re-rating of an item are NOT addressed in the NBIC. Of course, your Authorized Inspector has the final say regardless of the answers in this forum.

 

[deanc]

No sure I agree with you metengr. See NBIC Appendix 4-Glossary-Alterations. Also see Appendix 6- C. Examples-4.

 

[metengr]

deanc;
Ah, the wonder of code interpretations. This is what makes my day (haha) in dealing with the NBIC main comittee. Anyway, the issue is "affecting the pressure retaining capability" because the example given in Appendix C-6 is a change in the original design of a heat exchanger head to a pressurized jacket design.

The information given by UKcats is sketchy in detail. If the replacement head is not changing the original design of the heater and all that is required is to drill larger bolt holes in the original head for a new, replacment shell (that is the same design as the old shell), I still believe this is a repair. All that has changed is larger bolt holes in the head - nothing else.

However, if the existing head is being placed on a new shell that is different in design - size, wall thickness etc (not an in-kind replacment of the original shell), this would be an alteration because the pressure boundary of the heater shell has been changed.

 

[UKCats]

The MAWP for the shell or bonnet is not changing. The original U-tube bundle has/had a double tubesheet. The shell side MAWP is 300 psig and the tube side 150 psig. We have purchased a new U-tube bundle with a single tubesheet and now must sandwich the tubesheet with the shell and bonnet flange. The shell and bonnet flanges have 2 different bolt hole diameters and but drill out the smaller (bonnet).

As a repair, it is my understanding an R stamp Nameplate is not required???

 

[metengr]

UCats;
Based on your additional information I believe this is an alteration to the original heat exchanger design per the 2001 NBIC, 2003 Addendum. The change in configuration from double to single tubesheet design(if this is indeed the case and you eliminated the original two tubesheet design to combine into one tubesheet) falls under a change in internal contour/dimensions of the pressure retaining item.

 

[Christine74]

Are you enlarging the bolt holes because you are changing the flange bolting from 5/8" studs to 3/4" studs? If so, then that would be an alteration. The existing flange may not calculate for the increased bolt load.

-Christine

 

[deanc]

What fun! Things are never as simple as they seem.

UKCats-Strongly suggest you contact your local Jurisdiction and your Insurance carrier.

 

[UKCats]

I thought the new U-tube bundle, since it's removable, would be a U-2 part...stand alone???

With the old U-tube, double tubesheet design...there are 2 different flange sets... bonnet to first tubesheet (with 3/4-inch holes) and a second tubesheet to shell (with 7/8-inch holes). With the new single U-tube bundle (U2 Part), 2 flanges will sandwich the new tubesheet but we have a mismatch in holes. We are enlarging the bolt holes on the bonnet from 3/4-inch to 7/8-inch to match the shell's bolt holes. We have performed a code calculation and the bonnet will pass with the larger 7/8-inch holes.

I don't have a copy of the original U-1 on me but I don't think bolt holes/stud sizes are on there. That's why I don't think it's an Alteration... but we are changing the U-1 with the new tubebundle which forces us to increase the holes... I think I need to contact the local AI..it's just they're not right all the time either.