Maximum Allowable Internal Pressure During Welding
Maximum Allowable Internal Pressure During Welding
(OP)
Hi -
I'm currently preparing a line for a hot tap and I have been religiously following the API 2201 in the process. Based on that document, I have a clear understand on metal minimum thickness and how to proceed & what precautions to take when welding onto a thin pipe. However, API seems to be silent on determining the maximum allowable internal pressure for welding the hot tap nozzle onto the pipe.
Our refinery uses the formula:
P = (2*t*SE)/(D-2Yt)
where t, measured thickness, is multiplied by 0.4 (how far HAZ is extended during welding), Y = 0.4, D is your pipe diameter, E = 1 and S is the allowable stress at Mean temperature which is significantly lower than my design allowable stress.
So, the result was a maximum internal pressure that is lower than our operating pressure. Seems like the only way to proceed is to lower the operating pressure below maximum.
Here's my pipe data
Design: 500 F @ 400#
Operat: 450 F @ 330#
Stress allowable at Design: 18900#
Pipe Material: A-106B
Size: 14"
THK: 0.375" Nom (assume minimal corrosion)
Any advice would be appreciated.
Thanks.
FYI: I've also looked at API 1104. No info there about Maximum Internal Pressure during welding.
DEX
I'm currently preparing a line for a hot tap and I have been religiously following the API 2201 in the process. Based on that document, I have a clear understand on metal minimum thickness and how to proceed & what precautions to take when welding onto a thin pipe. However, API seems to be silent on determining the maximum allowable internal pressure for welding the hot tap nozzle onto the pipe.
Our refinery uses the formula:
P = (2*t*SE)/(D-2Yt)
where t, measured thickness, is multiplied by 0.4 (how far HAZ is extended during welding), Y = 0.4, D is your pipe diameter, E = 1 and S is the allowable stress at Mean temperature which is significantly lower than my design allowable stress.
So, the result was a maximum internal pressure that is lower than our operating pressure. Seems like the only way to proceed is to lower the operating pressure below maximum.
Here's my pipe data
Design: 500 F @ 400#
Operat: 450 F @ 330#
Stress allowable at Design: 18900#
Pipe Material: A-106B
Size: 14"
THK: 0.375" Nom (assume minimal corrosion)
Any advice would be appreciated.
Thanks.
FYI: I've also looked at API 1104. No info there about Maximum Internal Pressure during welding.
DEX





RE: Maximum Allowable Internal Pressure During Welding
The maximum temperature of the wall when welding should be considered. You may need to calculate a minimum flowrate past the welding area to keep the wall metal below the maximum temperature.
"If everything seems under control, you're just not moving fast enough."
- Mario Andretti- When asked about transient hydraulics
http://virtualpipeline.spaces.msn.com
RE: Maximum Allowable Internal Pressure During Welding
Steve Jones
Materials & Corrosion Engineer
http://www.linkedin.com/pub/8/83b/b04
RE: Maximum Allowable Internal Pressure During Welding
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It's not very cheap, but if you are going to be doing lots of hot tap work it may be worth looking in to.
The Edison Welding Institute (EWI) did quite a bit of work with this and is the basis for the program. I've read through some of the original reports and it's fairly complex and doesn't lend itself to simple formulas and calculations.
What is the fluid that is in the pipeline?
A couple observations from past work are
1. Wall thicknesses greater than .25" are difficult to burn through if you have a moving fluid inside the pipe.
2. A liquid fluid nearly always provides adequate cooling even at very low flow rates.
Something to keep in mind is hydrogen cracking that can be caused by the weld cooling too quickly. Low hydrogen welding rod should be used with enough heat to ensure that it doesn't cool too quickly.
RE: Maximum Allowable Internal Pressure During Welding
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RE: Maximum Allowable Internal Pressure During Welding
We are in the process of doing a UT to determine the line current thickness, but we should have sufficient wall thickness.
We have about 5 ft/s flow in the line.
The service is crude going to our heaters.
SJones: " Item 4 of Table 3 in the Annex A checklists " From what document??
Thanks!
Dex