weldolet and hot tapping 1

[twinbrooks]

Hello, there:

To hot tapping into and existing 18" line (Sch. 10. A53 Gr. B, UT shows the wall thickness is 0.25", 300 psig and 200F), using weldolet connection (instead of split Tee).

Please help:
To check whether the weldolet connection is safe , which code should be followed? where could I find the weldolet dimension to check area?

Any advice is appreciated.

 

[metengr]

Depending on the fluid your are conveying in your piping systems and application, check with ASME B31 Piping Codes - either B31.1,B31.3, B31.4, B31.8, etc.

 

[DSB123]

Twinbrooks,
Suggest you ask your weldolet supplier for dimensional details of the weldolet so you can check out the area. Also the weldolet weld to the parent pipe should be pressure tested before you cut the hole in the parent pipe.

 

[dcasto]

The hot tapping company should run the calculations the bending stresses encountered while their tapping machine is set up on the line.

 

[unclesyd]

Have you checked your piping per the above mentioned codes?

I have never seen Sch 10 CS piping used at these pressures. in fact I've never seen any Sch 10 CS in these sizes. The minimum has been Sch 20 with STD being the norm.

 

[dcasto]

B31.3 will have about a 375 psi maop depending on corrosion allowance. under B31.8 375 to 775 depending on class location.

 

[0707]

it is generally much safer, to use a full encirclement fitting on hot tap and line stop operations.

go to

http://www.ceejpublishing.com/Articles/0009.htm

luismarques

 

[doberdorks]

luismarques,

why do you say "generally safer to use a full encirclement fitting"? I don't see anything in that article that says one way or the other.

As to safety, codes etc.... where is the original line, and what is in it? As a start if it's a B31 pipe there's the code it was designed to, API 2201, and internal company standards, and of course, jurisdictional requirements.

in my (limited) experience, hot taps are generally taken very seriously, so choice of what to do and how to do it is often not a low leven engineering one. At the very least you need QC and saftey buy in before continuing.

SLH

orig message
0707 (Petroleum)
6 Aug 07 13:02
it is generally much safer, to use a full encirclement fitting on hot tap and line stop operations.

go to

http://www.ceejpublishing.com/Articles/0009.htm

luismarques

 

[0707]

I totally agree with you doberdorks!

We don’t know the pipe code of the piping where twinbrooks wants to do the hot tapping.

I invite you to read the paper I post with a little bite of more attention.
“A full encirclement fitting will do a couple of things that a simple nozzle will not, it will assist to re-round thin-walled pipe, that may not be round, it will handle the horizontal stresses that the line stop head will place on the pipe, it will also handle the bending stresses applied by the line stop head. For all of these reasons, it is generally much safer; to use a full encirclement fitting on hot tap and line stop operations.”

luismarques

 

[grandnobi]

Reading this thread I had a feeling that it may just not be good enough to ask whether the branch connection will be adequately designed once the tie-in is done. You also have to find a safe way to get there.

Is everybody in this forum really convinced that a welder assigned to the job of welding a weldolet to a pressurized Sched 10 pipe is absolutely safe while performing his job?

 

[JeffLester]

I understand this issue may already be resolved for
Twinbrooks, but for the benefit of those reading this
after the fact, I offer the following:

1. Is the hot tap the last resort? Is it feasible from
a process point-of-view? Some processes can not be hot
tapped. Some, although possible, may not be reasonably
safe. API RP 2201 is an good start in answering the many
questions that can arise.

2. One needs to confirm there are no issues with the
additional piping loads being applied to the existing
line. A pipe stress analysis would be prudent.

3. The existing pipe wall thickness (actual) needs to
be at least equal to the required thickness for pressure
plus a reasonable thickness allowance for welding. If
the actual thickness (preferably confirmed via UT for
example) is barely more than that required for pressure,
then loss of containment at the weld pool is a risk.

4. The configuration of reinforcement needs to be reviewed
and, if necessary, calculated. Full encirclement saddles
for size-on-size hot taps are an example where
reinforcement calculations should be performed.
Reinforcement of branch connections using weldolets are
not generally performed by anyone other than the fitting
manufacturer.

5. Assuming the welded branch is to be pressure tested
prior to the hot tap operation (the "punching" of the
hole), the required thickness of the existing pipe for
the pressure exerted on the OD (within the welded branch
connection) needs to be reviewed. One does not want the
existing pipe to fail while pressure testing the new
connection.

6. Use a reputable hot tap contractor who has experience
in all phases of the project: engineering, procurement,
fabrication, quality control, etc.

Hot taps can be done safely, IF the proper attention is
devoted to each step.

Jeff L

 

[GregLamberson]

As JeffLester, I am jumping in late with some additional FYI’s. As mentioned above, calculations to determine the required wt should come from the hot tap contractor, and will depend on a number of factors - design temp & pressure of the pipe, corrosion allowance, external diff pressure to the existing pipe during testing of the hot tap fitting, loads applied by the tapping equipment.

As far as min wt – you’ll need to do a UT to make sure there are no laminations and the thickness is what you thought and is safe welding. What is safe for wqelding depends on many things, including the material being welded, operating temp & press during welding, weld procedure, produict in the piupeline, etc. Generally though, you’ll want no loess than 5 mm/0.20 in.

And don’t forget flow during hot tapping. For gas, you’ll want to around of 0.4 m/s / 1.3 ft/s of velocity, much more & the weld will cool too fast, much lower & you’ll get heat accumulation.



Greg Lamberson, BS, MBA
Consultant - Upstream Energy
Website:

http://www.oil-gas-consulting.com

 

[deanc]

Well,I know that hot taps can be safe and they are common.

However, the welder would rather be swimming in a pond full of alligators. The split tee at least "feels" better.

 

[GenB]

I do not see anything wrong with the weldo'let
check with bonney-forge for specs, they have reinforcing pads and all.
genb

 

[Ziek]

I didn't see anywhere where the size of the Hot Tap was adressed. There is a pretty large difference between performing a full size 18" Hot Tap on the existing 18" Pipe versus a smaller Hot Tap, such as a 4". If you are making a small branch connection, the weldolet should be a safe bet. If you are getting near a full size connection, standard practice generally is either a split tee or a shaped nipple with full encirclement reinforcing saddle. There are numerous factors that come into play and you should really seek the advice and assistance of a reputable Hot Tapping company as was mentioned earlier. Consider location of the Hot Tap, orientation, design code, flow and safety of welding with the thin wall pipe, stress, vibration, etc. etc. You might even be required to use a large mechanical bolt-on fitting.

Ziek

 

[11echo]

I agree with Ziek. There are two controlling issues here, the size of the hot tap and the wall thickness of the 18" header. IF I had to handle this I would contact T.D.Williams Company, they specialize in hot tapping pipelines and would probably supply you with all information necessary and supplies if needed. My $0.02 anyway, Good Luck!

http://www.tdwilliamson.com/new_servtdw/tdwservices.html

 

[WLLRDQN4]

Where does the internal gas velocity of 1.3 ft/sec come from when doing hot taps? Is there an engineering standard which lets one calculate the required velocity?

 

[pennpiper]

twinbrooks

WHAT SIZE IS THE BRANCH??????