Flush Patch placement
Flush Patch placement
(OP)
Is is prohibited to install a flush patch across a girth seam?
Example: vessel is 10ft dia. carbon steel and has had multiple repairs at same area in circumferential girth seam weld. Repair company would like to install a 2ft x 2ft flush patch in shell at area of prior multiple repairs. Can the portion of the girth seam weld and some shell material on each side be cut-out and replaced by a single flush patch? Or would you have to have a 1ft x 2ft flush patch on each side of the girth seam forming new section of circumferential girth seam to be welded? Long seams and girth seams result in "T-joints" as would be created by the patch across the seam. When installing a nozzle in a weld seam there is NDE (RT) that must be performed on either side of the weld seam (but material is removed in that case). The NDE for this Repair will be 100% (RT or possibly UT)of the flush patch butt-welded seams.
Example: vessel is 10ft dia. carbon steel and has had multiple repairs at same area in circumferential girth seam weld. Repair company would like to install a 2ft x 2ft flush patch in shell at area of prior multiple repairs. Can the portion of the girth seam weld and some shell material on each side be cut-out and replaced by a single flush patch? Or would you have to have a 1ft x 2ft flush patch on each side of the girth seam forming new section of circumferential girth seam to be welded? Long seams and girth seams result in "T-joints" as would be created by the patch across the seam. When installing a nozzle in a weld seam there is NDE (RT) that must be performed on either side of the weld seam (but material is removed in that case). The NDE for this Repair will be 100% (RT or possibly UT)of the flush patch butt-welded seams.





RE: Flush Patch placement
RE: Flush Patch placement
Since this is an in-service vessel you would be following either API 510 or the NBIC (NB-23). For either in-service repair code, a flush patch plate can be installed across existing shell weld seams (girth or long seam).
The flush patch requires full penetration welds and the plate should match the contour of the vessel.
Second, the Nondestructive Testing (NDT) requirements for the repair welds should follow the requirements of the original code of construction. If this is not practical or none was performed, or only partial NDT was performed based on the original code of construction, I would recommend you do the following;
1. After the flush patch plate has been tacked into position, deposit the root pass and perform a dry powder MT and visual.
2. After the weld joint deposit has reached 1/2 wall thickness, perform a dry powder MT and visual.
3. After the flush patch weld is completed and ground flush, perform a final wet fluorescent MT. This would be your final acceptance of the flush patch repair weld.
OR, if you prefer a volumetric examination, I would perform shear wave UT as final acceptance or you can RT. In either case the dry poweder MT across various points of weld deposition should be acceptable.
Run the above by your Inspector.
RE: Flush Patch placement
If RT must be performed, the owner would have to shutdown production as personnel working within a certain proximity of the vessel would have to stop and move out of the area? So, therefore it is more practical to perform volumetric exam using UT (shear wave).
RE: Flush Patch placement
RE: Flush Patch placement
RE: Flush Patch placement
RE: Flush Patch placement
RE: Flush Patch placement
In regards to the new patch, I would imagine that root and final MT or PT would be sufficient examination to avoid a hydro and full volumetric inspection.
Our AI recently accepted these inspection criteria on a flush patch crossing a seam in a RT-1 vessel without a hydrotest.
RE: Flush Patch placement
RE: Flush Patch placement
I suggest you search the internet using the keywords such as "asme vessel restoration by encapsulation" Let me now if you need any further help on this method of restoration for which I am extremely familiar.
RE: Flush Patch placement
While NB-23 covers administrative and technical requirements for inspection repair and alteration for any construction code, ASME PCC-2 only provides technical methods for repair on ASME designed piping and vessels.
ASME PCC-2 can be used for technical reference on repairs under NBIC. While NBIC generally tends to tell you to repair to original code of construction, PCC-2 will give more detailed requirements for the repairs so that the repair is adequate for safe operation.
RE: Flush Patch placement
I have seen butt-weld caps used to cover pinhole leaks due to MIC in raw water (class 3) piping systems....so it is kind of the same philosophy I guess.
RE: Flush Patch placement
RE: Flush Patch placement
Encapsulation component are designed to satisfy ASME Code stress acceptance criteria. This can be done, depending on encapsulation component size and configuration, using hand calculations or finite element analysis.
2. how do you know how thick encapsulation material has to be? Would you use same thickness as original shell material?
Total thickness finished component, including material removed for the internal machined undercut, is dependent on the design pressure but an average thickness of the starting material would be in the range of 1 ¼” to 1 ½”. However, thickness of encapsulation component material where full penetration welded to shell is the same thickness as the shell material.
3. What about corner welds...do you have to create some sort of ogee type seam?
Typically the Category D Hub to shell full penetration corner weld (typically beveled at 45 or a J weld bevel) is the same thickness as the shell. This weld is typically reinforced with a fillet weld. Total weld deposition to attach and encapsulation component is generally less than that required for a Flush Patch and no removal of degraded shell material is required. Encapsulation components have no size limitations whatsoever and can be constructed to encapsulate large areas of degraded shell or nozzles – only being limited by the size of the milling machine.
4. I have seen butt-weld caps used to cover pinhole leaks due to MIC in raw water (class 3) piping systems....so it is kind of the same philosophy I guess.
They are undercut to form a hub (skirt) that results in an attachment weld configuration that is identical to that of a set-on nozzle – see Figure UW-16.1(a) of ASME Section VIII, Div. 1). Code NDE of the attachment weld would be that required for a Category D weld for which there is generally no code mandated NDE.