Hydrostatic Testing Weldolet Branches 1

[PipingEIT_CAN]

Hello,

We are currently working on the tie-ins of a facility expansion. ASME B31.3 is the design code for the piping system, and none of the fluids are Category D so we know we need to hydro test all the branch connections. The existing lines are quite large (24" & 30") and we don't have nearby flanges to hydro against. Because the existing pipe is old we'd like to avoid a large test which could create unexpected work during our turnaround window. For that reason, the idea has been passed around that we can simply "test against the skin." Essentially, what we're thinking is that we attached our weldolet and accompanying flange without cutting the coupon out of the header, then we test against the external surface of the pipe before finally cutting the coupon out with a drill.

My questions are,
1. Is that test sufficient per ASME B31.3.
2. Does it ensure the complete integrity of the weld.

I am concerned that this testing method may not fully guarantee the integrity of the weld on the header.

Other suggestions were to break in flange pairs on the header and perform a simple plug test or perform a closure weld for the olet. However, if this test method is acceptable, it would be cheaper than both alternatives.

Thank you in advance for any input you may have.

 

[pmover]

yes, when conducting hot taps, a hydro test is done before removing/cutting the coupon.

take a look at API 2201.

 

[GBTorpenhow]

IMO the test you describe meets the requirements of B31.3 because it will detect any leaks in the completed weld. B31.3 pressure test isn't a proof or strength test, its to detect leakage.

Make sure to check the header WT against the external pressure applied during the test if the branch is of any appreciable size.

 

[LittleInch]

Have a look at this

https://www.eng-tips.com/viewthread.cfm?qid=418243

and also the post referenced within it. Then come back with any questions.

The biggest issue is that it is difficult to get to 1.5 x MOP B31.3 test pressure without exceeding the collapse pressure of the run pipe, especially if you can't put a static pressure equal to the MOP on that run pipe at the same time if you're doing this in a shutdown to reduce the differential external pressure.

FEA is the only way to prove you can do it.

what size and wt are we talking here for run pipe and size of branch?

Plus this is then a golden weld so you need extra NDT - Dye pen or MPI or something else.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[RVAmeche]

Does the "closure welds" section of B31.3 345.2.3 answer your question?

 

[PipingEIT_CAN]

Hello All,

Thank you for your inputs, its much appreciated. After further discussion internally we've decided that we'd like to seek input from a hot tap contractor. The way I see it we have two options,

1.If the header would be able to sustain an external pressure of 1.5 times design pressure, we proceed with the procedure described initially
-The problem with this option is we don’t have a way to justify our decision without more detailed analysis of the branch and would possibly require FEA.
2.If there is a risk of causing damage to the header, we perform a hydro at a reduced pressure (perhaps follow API-2201 recommendation) and perform additional NDE (MPI/DPI/UT).
-The problem with this option is we’d like to know the cost associated because if it’s going to be too costly, we might be better off simply breaking in new flanges on the headers.

For reference, I've attached a photo with details about the tie-ins,

I will post an update when I have one,

 

[LittleInch]

Pretty sure that 30" x 16" won't be strong enough, but the other two might.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[mk3223]

This is typically a "Hot Tap" work to test the welded branch connection on the pipe header on the live line prior to cutting the coupon. Or, it's a "Cold Tap" if working on the shutdown Line.

You need to perform an UT on the Header at the tie-in location to ensure the proper wall thickness as needed for the process. And, use it to calculate the external hydro test pressure for weldolet and flange of the branch piping before cutting. Note that the testing pressure may be equal or less than the typical 1.5 times the design pressure of the B16.5 flange class rating.

 

[GD2]

Piping EIT CAN,

In hot tap, you don't hydrotest at 1.5P for fear of collapse of the pipewall as LittleInch has pointed out. For a hydrotest, API 2201 recommends it at equal or 10% higher than the Line Pressure (NOT Design Pressure) at the time of hot tap. Usually, the line pressure and flow will be controlled during the hot tap to minimize the effect of hard microstructure formation during welding. You need to be very cautious for the Test Temperature to avoid any shock chilling and brittle fracture depending on the process temperature. Alternately, you can use air/nitrogen test with soap solutions. Again, be careful with test temperature if you are using air (if there is a burn through, there could be possibility of a flammable mixture, if your process is a hydrocarbon).

GDD
Canada