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Hot Tap Question

05/30/2012 10:17 AM

Fellows,

What is, where is the calculation for minimum allowable wall thickness for preforming hot taps?

(I lobster and I can a flounder.)

-A-

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#1

Re: Hot Tap Question

05/30/2012 10:54 AM

Er, it can be done at practically any wall thickness, as it is routinely done to fit washing machine adapter-valves to 15mm nb domestic copper water pipe in the UK <spits on the practice>. The lowest acceptable wall thickness of any pipe is determined by:

  1. the pipe material and
  2. the maximum test pressure and temperature of the substance inside it.
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#2

Re: Hot Tap Question

05/30/2012 1:27 PM

During my time in petrochem, we did countless hot-taps, so my first thought was with regards to that environment. The Wikipedia article is pretty complete, notice the API RP it references.

But Slack reminds us of the domestic taps, done with clamp-on fittings I've heard them referred to as 'cold taps'.

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#9
In reply to #2

Re: Hot Tap Question

05/30/2012 6:57 PM

"bigg"

Definitions:

"Hot-Tap = Means the line being accessed is still flowing and or is still under operating pressure and temperature.

"Cold-Tap = Means the line being accessed is shut down, drained and steamed out or otherwise made "safe" for welding or flame cutting.

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#3

Re: Hot Tap Question

05/30/2012 3:13 PM

A hot tap can be done on any pipe type and wall thickness containing a non-flammable and pressurized liquid.

I'm most familiar with the hot-tapping of pressurized water mains and water processing pipes in water treatment plants, usually done to install an inline water meter or to cut in a new water main service lateral or branch......in those cases you usually need a Mechanical Joint wet-tapping sleeve w/ retainer glands or a saddle, and a Mechanical Joint wet-tapping valve w/ retainer glands. All MJ's must have set screws to prevent movement of the sleeve, valve and the pipe barrels.

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#4

Re: Hot Tap Question

05/30/2012 3:32 PM

Thank you all so far.

I know that a hot tap can be preformed on pressure pipe. I know that the wall thickness is dependent upon material and pressure. Unfortunately, pointing this out does not come close to answering my original question, "What is, where is the calculation for minimum allowable wall thickness for preforming hot taps?"

THERE IS AN EQUATION IN ASME **SOMEWHERE** THAT SPECIFIES MINIMUM ALLOWABLE WALL THICKNESS GIVEN PIPE MATERIAL AND PRESSURE DIFERENTIAL.

Is there anyone out there who happens to remember what the equation is or where it can be found?

Ideally, the next post will suggest that I look it up in ASME. . .

-A-

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#5
In reply to #4

Re: Hot Tap Question

05/30/2012 5:04 PM

tm = (PD)/(2S+2yP) + C

(ANSI/ASME B31)

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#6
In reply to #5

Re: Hot Tap Question

05/30/2012 5:44 PM

Thanks Bigg,

We're almost there. . .

Now all I need are the units, and more preferably, the location within B31 where I can find the corroborating equation. B31 is, after all, a fairly large file.

I seriously do appreciate everyone's time in helping me out.

I have faith that CR4 is populated by more than trolls giggling as they doll out half answers and sarcasm.

-A-

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#7
In reply to #6

Re: Hot Tap Question

05/30/2012 5:55 PM

inches

PSI (pounds per square inch)

inches

PSI

[dimensionless]

PSI

inches

Now 'look it up in ASME. . .' (You don't have it, do you? You haven't told us what you're wanting to hot-tap.)

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#8
In reply to #7

Re: Hot Tap Question

05/30/2012 6:34 PM

Never mind. It will be easier for me to find it myself than to ask CR4.

B31.1 = 352 pages

B31.3 = 386 pages

B31.4 = 122 pages

Total = 860 pages.

I spent a 20 minutes or so paging through the files and then I thought, why don't I ask CR4? This is a genuine Engineer's forum, right? I might be able to save some time, right?

This is my penance for trying to take a short cut. I apologize. I am going to look it up myself. I know it will do me good. I should have better familiarity with the standards anyway.

I seriously have no idea why I asked in the first place. Just another reminder as to why I am a member of this site.

Thank you,

-A-

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#13
In reply to #8

Re: Hot Tap Question

05/31/2012 8:36 AM

Great, you thought there are thousands of donkeys in CR4 who can work for you free of cost to do your homework to scan 860 pages to find a one line equation which is not related with your question (the equation is to calculate minimum thickness), not to find minimum thickness for hot tapping.

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#11
In reply to #6

Re: Hot Tap Question

05/31/2012 3:21 AM

Hold the faith. Trolls don't respond well to full descriptions of the problem; the original post doesn't fall into that category.

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#10

Re: Hot Tap Question

05/30/2012 10:59 PM

If B31.n is in PDF format, you could ask your computer to trawl through it in accord with suitable search criteria....

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#12

Re: Hot Tap Question

05/31/2012 5:06 AM

The minimum wall thickness has nothing to do with whether or not it is "hot tapped". The minimum wall thickness is governed by material, diameter, temperature and pressure.

tm = (PD)/(2S+2yP) + C

(ANSI/ASME B31)

When hot tapping, the assumption is made that the flowing liquid, (it can and often is flammable) or the stored liquid will dissipate the heat generated by the welding process. Confirm the heat carrying capacity of the fluid before striking an arc!

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#14

Re: Hot Tap Question

05/31/2012 8:55 AM

ASME B31.3 Para. 304.3 is for branch connection wall thicknesses. I'll do a little reading to see if it applies for hot taps too as I'm sure there are other things to consider for a hot tap vs a typical branch connection.

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#15
In reply to #14

Re: Hot Tap Question

05/31/2012 9:31 AM

Thanks. I have just been through all of B31.1 chapters 2-5 (about a hundred pages)and didn't see anything on pressurized pipe.

I will check your suggestion next.

I am seriously taken aback by the lack of technical help and trolling on this site. I have been hanging out for the last couple of years reading and commenting. Only recently have I turned to CR4 for help or insight and all I have received so far, with your post as the exception, are comments of little or no technical value.

I know my question was vague, but frankly I was hoping to pique the interest of someone who was familiar with the subject matter who could, with little effort of their own, point me in the right direction.

I am not going to let a few incidents (or individuals) drive me away from this site. Still, I can't help but feel that there must be many (thousands of?) people driven away from this sight by trolls.

There are other engineering forums on the web, but this on is (fairly) spam free and I like it. I can only justify staying if there are actual benefits, other than reading all the snarky comments.

There have been some good folks who have commented on this, and my last few questions, thank you. Still, it feels like the waste-of-time to helpful ratio is about 10:1. Maybe that ain't bad for the internet. . .

-A-

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#16
In reply to #15

Re: Hot Tap Question

05/31/2012 9:46 AM

Try

API Publication 2201, Safe Hot Tapping Practices in the Petroleum and Petrochemical Industries

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#18
In reply to #15

Re: Hot Tap Question

05/31/2012 9:50 AM

I only read one response that was anywhere near as threatening as what you described. That was anonymous.....

I hope I wasn't a contributor to any of these perceived violations.

I was trying to give you some advice on how to ease your reading burden.

Your inquiry is pretty specialised sport, so don't be surprised if somebody who has actually needed to know what you want to know doesn't just blurt out the answer.

Sometimes you'll encounter a capable person whose interest you have aroused who may delve deeper with you. Cingold is a top bloke for helping you with some reading.

Have you found your answer yet?

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#20
In reply to #18

Re: Hot Tap Question

05/31/2012 10:24 AM

Thank you for your comments Wal. I was not offended by your comment. I am sure you are a great guy. However, if you search B31 for "hot tap" you will find ZERO hits in the document. Therefore, while not malicious in any way whatsoever, your post was of absolutely no help. I really do not mean to offend. You are a smart and capable guy, er, person.

cingold (my friend in real life who, if I remember correctly, I introduced to this site) is, as always, very helpful. Also, davesets seems to be pointing to some helpful info. I will check as soon as I finish this response.

3 of 15 comments above say, "you might check here. . . "

Thank you again. Now, it looks like I have some reading to do.

-A-

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#22
In reply to #20

Re: Hot Tap Question

05/31/2012 10:34 AM

Yep you introduced me to this place. I have some stupid meetings all day but when I get a chance I'll look at B31.3 and see if I can find a copy of the API 2201 suggested as well. Let me know if you don't have a copy of these.

I'm not sure where your application is but I would think most of the piping at that plant falls within B31.3. B31.1 is for boiler piping and (I really hate this line in the code) "all other piping covered in this code but not boiler piping."

Side rant...what the **** does that mean ASME? Other piping covered in this code? Does that mean that any and all piping could be covered by B31.1? Anyway, I'm out...

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#19
In reply to #15

Re: Hot Tap Question

05/31/2012 9:55 AM

Did you try B31.3

304.1.2 Straight Pipe Under Internal Pressure

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#21
In reply to #19

Re: Hot Tap Question

05/31/2012 10:26 AM

Thank you, I will check now.

-A-

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#23
In reply to #19

Re: Hot Tap Question

05/31/2012 11:01 AM

As a side note to all of this, more often than not pipe reaches a failure point not from pressure considerations but stuctural integrity considerations. The pipe will maintain the internal pressure but will not sustain its own weight suspended over gaps in the supports.

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#26
In reply to #15

Re: Hot Tap Question

05/31/2012 3:13 PM

* My first reply contained a link to just about all I remember about hot-tapping

Later, you wrote, 'I know my question was vague, but frankly I was hoping to pique the interest of someone who was familiar with the subject matter who could, with little effort of their own, point me in the right direction.'

* You did, and I think my first reply did exactly that.

Then you wrote, 'THERE IS AN EQUATION IN ASME **SOMEWHERE** THAT SPECIFIES MINIMUM ALLOWABLE WALL THICKNESS GIVEN PIPE MATERIAL AND PRESSURE DIFERENTIAL.'

* I think my second reply did exactly that. Although as I did so, I knew you would still have to find S and y for your situation, and that minimum wall thickness is only one consideration for a safe hot-tap.

Thinking that with reasonable effort on your part, and egged on by 'Ideally, the next post will suggest that I look it up in ASME. . .' and 'I have faith that CR4 is populated by more than trolls giggling as they doll out half answers and sarcasm.', and feeling a bit gnarly,

* I made my fateful third reply. I apologize for the snide remark.

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#27
In reply to #26

Re: Hot Tap Question

05/31/2012 3:39 PM

Hey Bigg, I love you man. Any one who says they feel "gnarly" is a friend of mine.

BUT, variables without nomenclature are not helpful. Telling me to look it up in B31, also not helpful.

Between Davesets and cingold I was able to go right to what I was looking for. Even though I had already read the sections they were directing me to, the fact that they were sending me back to the same passages led me to understand that it wasn't that I hadn't found something yet, it was that I had overlooked something. Very helpful.

Look, no harm, no foul. I hope you have a wonderful day. And, the next time you feel gnarly, i hope it's for the right right reasons.

-A-

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#17

Re: Hot Tap Question

05/31/2012 9:46 AM

In a situation where the wall thickness is a concern, use a full-body tapping sleeve, that provides structural integrity for the portion of the pipe where the coupon is removed. There are several manufacturers of these items. Call and ask them to spec one for you.

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#24

Re: Hot Tap Question

05/31/2012 12:29 PM

Thank you Davesets and Cingold. With your help I have found it.

ASME B31.3 para 304.1.2 specifies minimum material for pressure pipe with no deferance to welding.

API 2201 specifies 3/16" minimum thickness + 3/32" SF with no deference to pressure in the line.

I had looked at these two several times thinking that they were not applicable to my needs.

Now I will use them both to specify a maximum penetration on the branch connection making sure to leave a cross section of material below the puddle that exceeds the minimum thicknesses specified above.

Thank you.

-A-

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#25
In reply to #24

Re: Hot Tap Question

05/31/2012 12:37 PM

A side note here is that a lot of companies now are requiring someone to put a PE stamp on hot tap and pipe clamp calculations. Be careful doing the calculations yourself.

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#28
In reply to #25

Re: Hot Tap Question

05/31/2012 3:51 PM

If you don't mind mentioning it, what's the process or fluid in the line you're looking at? B31.3 is for process piping, B31.4 is for pipelines (which I doubt this will apply to you), and B31.1 is boiler piping.

Although all of the codes essentially use hoop stress plus complicating modifiers, you still have to pick the right one to do the calculations.

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#29
In reply to #28

Re: Hot Tap Question

05/31/2012 3:53 PM

LP N2

100psig

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#30
In reply to #29

Re: Hot Tap Question

05/31/2012 3:57 PM

Ok B31.3 is good.

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#31

Re: Hot Tap Question

06/08/2012 12:29 AM

"Minimum allowable wall thickness for performing hot tap?"

there is no restriction. You can carry out tapping on a pipe with 1mm thickness. I think your question should be more related to welding. API 1104 guidance restricts the minimum thicness to 4.6 mm (minimum level). For any thickness below this, there should be a specifically established PQR and ofcourse an agreement with the pipe owner.

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#32

Re: Hot Tap Question

06/16/2012 12:39 PM

I don't believe that the pipe being hot tappet is the place to start. You must know how much reinforcement for opening is needed.. You may choose to use a weldolet, a saddle or full wrap connection. These will have flanged pipe, a valve, and a drill. The valve and drill may be attached later. these are welded to the pipe using an approved WPS, are welded to the pipe. The branch material must reach pressure and temperature requirements of the original pipe material. During welding preheat and interpass temperatures must be closely monitored.

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