Repair weld 5

[kslee1000]

What is the detrimental effect on the base metal, for which repair has been repeatively performed over the same, or lengthened, cracks by air arc removal of the defective old weld, and replaced by new passes with minimal, or no, grinding?

 

[stanweld]

kslee1000,
Fatigue cracks love to initiate at 'ugly' welds.

 

[kslee1000]

stan:

Why's that?

 

[racookpe1978]

Mechanical stress likes to "flow" smoothly and simply in wide sweeping arcs through metal.

It's why we like to use (must use!) fillets rather than sharp corners on machined parts, use rounded holes in beams rather than rough-cut square access holes topass wires and pipes, why tank heads are elliptical or rounded in high pressure tanks and vessels, why pipes are round and why tube steel has round edges, and why structral steel has internal fillets where the web meets the flanges.

An ugly, rough weld IS a stress riser, and thus increases the local stresses near the weld from the load. An ugly weld frequently reflects the "care" and "effort" by the welder - who obviuosly has either not been trained to present a professional appreanace, or has not been given the time and material and tools to do a professinal job => Thus, an ugly weld will likely have internal flaws (inclusions or old cracks not removed, heat affected zones where the metal properties have gone bad by too much heat applied too rapidly, and even cold zones where no fusion might have occurred) that themselves create new stress risers.

Besides, an ugly weld offends my highly cultivated sensitivities and delicate nature. 8<)

Seriously, your instincts ARE telling you something - If you "feel" something is wrong with a weld or a weld process or a design or a beam or a load under your crane, you ARE almost certainly "right" even if you can't specifically put your finger on the exact cause of your uneasiness. An elegant design is characteristic of a well-developed, economic, high quality, easily-produced solution to a specific problem with a specific material at a specific time. Nobody would build the Eiffel Tower today with rivets and iron, but it still "looks" like a beautiful work of design brilliance despite the material used.

In this case, an ugly weld is advertising itself as an ugly "solution" hiding very severe future problems.

 

[kslee1000]

Gee, I don't know the "agly" is so attractive . Yes, it made me uncomfortable, and looks like always need re-visit in a very short time frame.

Guys, I am running out of "STAR", but still listening, and all inputs are appreciated.

 

[hogan666]

I believe that post repair volumetric NDT will relieve almost all concerns regarding to "ugly welds". In my experience, performing NDT for the last 18 years, it is not uncommon to have a weld with an ugly cover pass and be totally clean inside. The only way to tell is be performing the testing.

 

[kslee1000]

hogan666:

I think your are correct - it's not how it looks, inside content matters (re after repair's done).

However, as many have pointed out, the irregularities on its (the ugly's) appearance is one the root causes for uneven stress rises/distributions, thus made it vulnerable to repeative/cyclical load with stress reversals. The above matches my experience on this matter - the auglier, the higher chance to crack again. Agreed?

 

[hogan666]

Ugly is acceptable, as long as it meets the codes visual acceptance criteria. The issue of stress risers is typically covered by this. I usually work to D1.1 or D1.5, but I believe that D14.1 is more conservative(I don't have one handy so I could be mistaken).

 

[kslee1000]

Yes, obviously someone has accepted the ugly (sure, it is not the criteria for rejection), then more often than not, it becomes my trouble (to take action), again and again. That's where my concern came from. Thanks for your input though.