Muffler

How do I fix this? How did this hapoen? How do I prevent it from happening again?

 

aftermarket muffler welded in? thats what it appears to be. could be welded in a way that it put stress on the weld and eventually cracked.

 

Can I fix this myself or should I take to mechanic?

 

exhaust shop can fix it up.
unless you know how to weld.

 

I believe @dirtydeeds is still having their group buy going on right now....

 

Can you show a wider shot of where this is? If you want to DIY, you'll probably want to cut that whole muffler out and fit a replacement.

 

It's called intergranular corrosion or "weld decay" in the HAZ (heat affected zone, see diagram in linked article). This occurs when stainless steel is welded improperly. This outcome was built-in from the day the muffler was welded in. Post weld heat treatment would be one way to avoid. You can repair it yourself if you replace components back to a bolted joint.

https://www.corrosionclinic.com/types_of_corrosion/weld_decay_weldment_corrosion.htm#:~:text=Weld decay is a form,heat affected zone (HAZ).

Edit: Or, it could be poor post weld cleaning. The corrosion is definitely from the welding, but given it's gradual distribution from the HAZ, it's probably this:

"...(A)ccording to Chester Collier, senior vice president of global distribution at Windsor, Conn.-based Walter Surface Technologies. 'Stainless does not react well to a lot of heat,' he said, 'so when you’re welding thin material, even TIG welding, you get a lot of bluing and discoloration of the stainless. That’s cosmetic, but here’s something even worse. [Welding] has burned off a layer of chromium oxide, the element that prevents stainless steel from rusting.'

He added that when stainless steel is cleaned properly, its chromium exhibits a kind of creeping action. 'In a sense, [the stainless] heals itself,' Collier said. 'It’s a little like cutting your hand. If you let the cut get dirty, it will take a long time for the cut to heal, and it won’t heal very well. But if you clean the cut and protect it, the cut will heal itself and not leave too much of a mark. Stainless steel heals itself the same way.'

If bluing or other debris left by the welding process remains, the chromium layer won’t creep and seal the weld. If the oxide layer hasn’t sealed the weld, you get oxidation and rust."

 

Can't weld rust, that area is toast. Is that an echo tip? just cut the tubing back to where it's not rusted and weld a new tip or turn down on. Muffler shop can fix that right up. May be time for a new exhaust system if all the pipe is corroded. My Flowmaster muffler and associated added pipe have begun to show signs of rust. Mostly the pipe that isn't factory. Starting to rust through like yours. It is 15 years old though......