Limitation on pipe size for hot tap 1

[vesselguy]

Hi,
I'm new on this subject of hot tap.

Does anyone know if there is a rule of thumb or design guideline in an industrial standard that says what is the maximum diameter (size) of branch you can hot tap onto a run? I have read one company's standard that says you can only hot tap and install a pipe that is no more than 70% of the run's diameter.

I have read API RP2201 but this document does not say there is a limit. Any insight would be useful. Thanks.

 

[STYMIEDPIPER]

Advance Valve Installation catalog lists tap size to 36 in 600 lb

 

[pennpiper]

This is a question you should ask a responsible Hot Tap vendor.
Try:

http://www.tdwilliamson.com

 

[jte]

vesselguy-

Size-on-Size hot tapping is feasible, but quite a bit more risky than hot tapping reducing branches. The issue with a Size-on-Size is that there is relatively little tolerance for error on the part of the cutter. The operator who is running the cutter must be very accurate with how far he runs the cutter in since he has to go far enough to cut the desired coupon... but a fraction of an inch more and now he's starting to cut a hole on the backside of the run pipe. A reducing size hot tap, on the other hand, has a bit more "play" before the cutter starts to cut the inside of the pipe on the side opposite the desired cut.

I've heard of a 70% rule of thumb, but in my work we just kept the branch one size smaller than the run. In some cases I made two (or more) hot taps and connected them with a header in order to get full flow into the branch.

jt

 

[Zoobie]

I agree with pennpiper and jte. Williamson has the expertise you need. They have a horizontally split tee/sleeve for doing size-on-size hot taps. There is still risk involved (it is a hot-tap after all). We were going to go this route last year but it turned out to be cheaper to take the line out of service (the endless debating of the piping engineers was costing money).

 

[dcasto]

Every where I worked we used the 50% rule of thumb, a 3" on a 6" is okay, but no 4" on 6". If you look at the pressure drop of a 3" on 6" tap, you can probably live with it, then expand up to a 4".

We could do a larger than 50% tap, if it was pre engineered by one of the tapping companies. The <50% we ran our own tapping machines.

 

[dtn6770]

http://www.plidco.com/public/products/hot_tapping_saddle.php

They advertise full size branches and in any range of sizes and pressures, with threaded, welded or flanged outlets.

 

[rconner]

Just a general comment for any that may not be familiar with the process, as I'm not sure whatever codes specifically address all technical issues:

It should be obvious that drilling or trepanning etc. a hole in the wall of any working pipeline material will weaken or create a location of stress concentration in the wall/barrel of that pipeline. Again, the larger the hole, the greater the weakening effect. It follows that there must be provision in the design, mechanisms and/or support/ construction procedures used to prevent damage in working/excavation around working pipelines and to adequately/dependably resist all loads that come to bear on the piping in construction and future service at that location.
Demands on the penetrated piping may include of course internal pressure, axial thrust loads from any adjacent thrust foci (any valves, fittings, etc.?), as well as potential bending and shear loads on the piping of whatever origin (including supporting the weight of quite heavy tapping equipment, at least when one gets to the larger sizes). Obviously, a strand of remaining original pipe on the backside of a large tap is likely not to handle all this by itself in many cases, and due to the complexity of the matters I discuss I suspect specialists or folks with experience in this field as mentioned by others may be particularly important in large tapping operations.

 

[rconner]

Oops (I see I should have also mentioned that tapped piping must also handle thermal effects, that I suspect might particularly be substantial in much petro-chemical work)

 

[vesselguy]

Hello,
Thanks to all that reponded.

Rconner, it is exactly those issues that are formost on my mind when I approached the problem of hot tap. That is why I try to look for any experienced input on size limitation. Jte's input concures with a standard I have read from a major oil sands producer here in Alberta. I agree with a 70% limit because you will still have more than 65% of the pipe material left to help hold it all together. I don't like a size on size hot tap because welding and cutting (especially the cutting part) is difficult.

50% rule is way too conservative. Keep in mind that the new nozzle or branch (plus any reinforcements) will be welded to the run before the tap and drill process. Hence strengthening is available.

Hot tap is never to be considered as a common activity. As such, of course we will have HAZOP with the Hot Tap Contractor participating and provide input into the planning of the whole thing. I just needed to grasp the major design rule before hand. I think I got it by reading your inputs couplied with my own reasearch. Thank you.

 

[davefitz]

as I recall, asme code ( and EU codes) indicate that add'l reinforcement of the main branch is required if the diameter ratio exceeds 0.7 : 1.

 

[nartz]

vesselguy, I'm from TDWilliamson, please contact me if you need info or support on hot tapping or plugging.

 

[mgtpip]

I agree with davefitz, having a 0.7 diameter ratio is enough to proceed with the hot tap. However, if you want to apply a 3" hot tap over a 4" line, it is possible to apply an "Split tee", reinforcing the existing line to avoid overstresses and wakening on the line and adjusting the ratio because is a procedure where you apply a doble schedule over the part you are working on. Obviously you have to have a minimum schedule of 5mm in the existing pipe to proceed with the drilling.

Industry codes and standards are: ASME B31.3, ASME SEC VIII D1 and to vessels: API 650

However, the minimun schedule, combined with the type of material, the position of the machine, diameter to proceed with,etc.. are too many variables to take in consideration, not defined in any code or standard. Only experience on this area, can tell you if over a CS or a SS or galvanized lines are hard enough to do a size-on-size hot tap or a lees than 0.7 diamter ratio one. Hot tap vendor as TDWilliamson, TBL, Claxon or Plidco will help you.