Hot Tapping in Compressed Air Line

[roker]

Hello,
Hot Tapping in Compressed Air Line (Carbon Steel line Size 8" –penetration 4")in a HI-TECH plant

1)Is it Common and/or Recommended?

2)Is there any possibility of Damage to Final Filter (0.01 um) due to shaving particles( metal chips)

3)Hot Tapping to be placed close to Air Receiver Inlet in Bottom of Vessel ( Outlet 3 mt above inlet nozzle)

4)If Recommended what is the best way to do ( good Practice Engineering ?)

regards and thanks,
roker

 

[BigInch]

You will find most of what you need to know here at TD Williamson's site,

http://www.tdwilliamson.com

and here's the brochure on hot taps,

http://www.tdwilliamson.com/PDF/Catpdf/TDWSbro.pdf

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[dcasto]

Hot tapping any lines are common, but there are risks. You'll need to gather the data recommended by the BigInch sites and discuss the pro's and con's. It's going to cost a little to do all this planning, but the alternatives make hot tapping a profitable and safe course of action.

 

[rconner]

I think all good information. I'd only like to add one thing that I didn't happen to see on first glance at the linked references. If the tapping operations involve e.g. weld heat on a blanked off section of any gas piping, making it at that time not unlike a closed vessel, there would likely be some increase in pressure as the gas is heated, in accordance with the gas laws. While perhaps this would not be of any signficance if the volume/length of piping was large compared to a small heated area, I would think it could get significant if e.g. the blanked off area represented very small volume, the gas was already at pressure challenging the strength of the vessel, and the gas was then subjected to a very high delta T increase etc. from welding heat If this is the case (and while I don't have specific experience in such hot tapping of gas lines), I suspect a calculation of the increase pressure effect of heating the gas might well be in order. [Of course I suspect most all are aware of the additional sensitivity of ignition sources like welding or grinding etc. around flammable gas lines, of which this is not).

 

[STYMIEDPIPER]

The above responses should point you in the right direction.
Also, keep in mind the size, accessibility, and positioning of the tapping machine. If you cannot rig tapping machine for true perpendicular fit-up than you are wasting your time. Remember, the tapping machine will be offset from the 8 inch header by the distance of the 4 inch flanged nozzle and the length of the tapping valve.

 

[BigInch]

Hot taps should (I always thought) be done with a specific minimum flow past the hot tapping area (not closed), thus maintaining temperatures within limits when welding and preventing internal pressure increase. Furthermore, operating pressures must be reduced to very safe levels before hot tapping operations can begin.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[zdas04]

I see a lot of hot tap procedures from various companies, and every one has a specified minimum flow rate (or technique to determine it). The procedures that say "why" talk more about carrying the heat of welding away from the weld than they talk about risks of pressure increases.

In terms of reducing pressure, most companies don't require it. In those companies, they have you compute the hoop strength of the line at the hot tap and if it is above a certain percentage of SMYS they don't allow the hot tap.

David

 

[jte]

My thoughts in regard to rconner's concern about raising pressure are that if the area to be tapped in this 8" pipe can be sealed off pressure tight on both ends... Then how is a hot tap justified? Seal both ends, cut the hole, toss in a tube blowing argon or nitrogen (push enough tube in to reach the seal or at least to provide a "comfortable margin"), blow the purge until the LEL shows near zero, continue the purge and weld on your fitting. 'Course, this may not be necessary for an air line...

On the other hand, if the pipe is long, and cannot be sealed, then a good welding engineer can work some magic to determine whether or not a flow is required and if so, how much. I've done hot taps on 42" flare lines for which establishing adequate flow would have been quite difficult... And if there was a significant flow in the line the hot tappers would probably have evacuated since that flow would have been caused by a major unit upset... I was fortunate to have the support of a good, experienced, practical welding engineer. Easier to conduct the heat away with liquid than with vapors.

jt

 

[RossABQ]

I've read the OP twice or more and I still can't be sure, but it sounds like he is asking if the VESSEL can be hot-tapped???

"Hot Tapping to be placed close to Air Receiver Inlet in Bottom of Vessel..."

 

[BigInch]

zdas, "above a certain percentage of SMYS they don't allow the hot tap." That's about 30% (I think), which usually requires a reduction of the operating pressure, since they should be well above that anyway.

Ross, the way I read it is the filter is located at the entry to the air receiver vessel, both of which are downstream of the pipe to be tapped.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[jte]

Ross-

For what its worth, I've seen several vessles hot tapped and have engineered such taps a few times myself. Not much different from hot tapping a pipe except for the obvious involvement and approval in advance by the AI.

But my interpretation of the OP was that the proposed hot tap was a 4" branch onto a 8" pipe near to, but not a part of, the bottom of the air receiver vessel.

jt

 

[packdad]

If this evolution is a big concern, you might consider a mock-up.

I had a vendor perform a mock-up of a hot-tap years ago in our maintenance shop because we were concerned about foreign material entering our system. We wanted to add a 3/4" sockolet connection to a 8" Sch.40 water-filled process pipe. Our results showed a small amount of metallic debris did enter the system - enough that we opted not to perform the hot tap for fear of risking damage to downstream pumps. The debris consisted of fine chips of metal, most of which were no more than 1-2 mm across. We are pretty sensitive about foreign material, so maybe this isn't as big a deal for you.

Regarding foreign material, it's my recollection that smaller drill bits will generate a smaller total volume of debris, but the individual pieces will be larger than you'd get from a larger drill bit (because the larger bit tends to grind up the shavings).

 

[packdad]

Additional notes: When we attached the sockolet to the 8" mock-up pipe prior to the 3/4" hot tap, the 8" pipe was dry and this resulted in some deformation of the 8" pipe around the sockolet. It may also have locally hardened the 8" stainless steel pipe, which may have slowed the drilling (hard to quantify). I think the entire hot tap operation took about an hour and a half, and I remmeber the bit tended to bind a lot.