Tubing Weld Repair Procedures 1

[boo1]

Our welders have been TIG repairing damage (corrosion and physical) on some of our high, medium and low pressure process tubing, alloys welded were AA5000 series Al, Cres 300 series and Inconel 625. Fuilds are hydraulic fluid, and #2 fuel oil. They are certified for 1/8" plate SST and AL all position. They use the damaged area size dictates repair methods (metal build up, patch or section replacement). The tubing is test to the new tubing requirements (proof pressure test, flush, and systen checkout). They asked me to document the repairs w welding procedures.

I was thinking about
1. Remove tubing section
2. Clean
3. Repair (TIG) damged area governs repair method
a. Pin hole <.25" clad repair
b. area >.25" and <1/2 tube dia - over lay patch same thickness as tubing
c. area > 1/2 tube dia - cut out section to clean metal, replace removed section and butt weld
4. Pressure test
5. Flush/clean
6. Reinstall
7. Leak test system

What are other required parameters for this type of procedures or thoughts?

 

[metengr]

I would add surface NDT after step 3 to ensure no defects in the repair region. Second comment, I would not use a scab path to repair a damaged area on tubing. Either pad weld or install a pup (new) piece with a full penetration butt weld. Scab patches are attached using fillet welds which have lower fatigue strength in comparison to a full penetration butt weld or even a pad weld, which should be ground flush with the tube OD surface.

 

[Tmoose]

Depending on the geometry of the patch and the working pressure I'd be wondering if I was possibly creating a weld strength (like metengr said) or hydro forming experiment.

http://www.youtube.com/watch?v=ppXRMTeR2NQ

 

[berkshire]

Tmoose.
That video is scary, Its like doing a rain dance over a hand grenade with the pin pulled. All they need is a little air pocket in there.
B.E.

You are judged not by what you know, but by what you can do.

 

[EdStainless]

A scab patch on a CRA is troubling also since you are forming a serious crevice under it and you are likely to get greatly accelerated corrosion.
Either cut out a portion or replace a section of pipe would be my vote.

I am glad to see that you at least have a process for this.

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Plymouth Tube

 

[boo1]

Our corrosion is from external sources usually at band clamps, internally the tubes are clean. The tubing is ~20 years old, were looking at ~15 years service life remaining. What do about just allowing scab patch on the low pressure (<150 psi) fuel and lube oil lines?

 

[EdStainless]

That I could probably live with. As long as they are not in the 6 o'clock position.
There can be a lot of trash in the bottom of oil lines.

I have seen where people have used any old plastic or rubber under clamps to protect the pipe, and in the process picked something very high in Cl and assured that the pipe would corrode under it.

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Plymouth Tube