Return to Answer

Believe it or not, the causative agent is the Ascorbic acid from the pineapples, which is known to cause pit corrosion (explained here) with stainless steel! Here is a source "Effect of ascorbic acid on the pitting resistance of 316L stainless steel in synthetic tap water", to quote:

"Above the 10^-4 M of A.A concentration, A.A generates soluble chelate rather than absorbs on the steel surface and it causes passive film deterioration and severe pitting corrosion."

And per the question: "why are there concentrated spots of rust on the wall", which supports not normal rusting, but pit corrosion, which I have experienced. I actually did a related thread on it in another forum. Others reported similar experiences, with my experience starting with mango juice exposure to stainless steel steak knives left unwashed in a sink.

Apparently, in the presence of moisture, oxygen, iron, Ascorbic acid (a source of H+ and a chelate) and tap water minerals (electrolyte), an electrochemical based pit corrosion reaction can proceed with time.

Believe it or not, the causative agent is the Ascorbic acid (presence in pineapple juice), which is known to cause pit corrosion (described here) with stainless steel! Here is a source "Effect of ascorbic acid on the pitting resistance of 316L stainless steel in synthetic tap water", to quote:

"Above the 10^-4 M of A.A concentration, A.A generates soluble chelate rather than absorbs on the steel surface and it causes passive film deterioration and severe pitting corrosion."

And per the question: "why are there concentrated spots of rust on the wall", which supports not normal rusting, but pit corrosion, which I have experienced. Interestingly, I actually did a related thread on it in another forum when my cutlery was unexpectedly (and seemingly, unexplainedly) attacked. Others reported similar experiences, with my experience starting with mango juice exposure to stainless steel steak knives left unwashed in a sink.

Apparently, in the presence of moisture, oxygen, iron, Ascorbic acid (a source of H+ and a chelate) and tap water minerals (electrolyte), an electrochemical based pit corrosion reaction can proceed with time.

Believe it or not, the causative agent is the Ascorbic acid from the pineapples, which is known to cause pit corrosion (explained here) with stainless steel! Here is a source "Effect of ascorbic acid on the pitting resistance of 316L stainless steel in synthetic tap water", to quote:

"Above the 10^-4 M of A.A concentration, A.A generates soluble chelate rather than absorbs on the steel surface and it causes passive film deterioration and severe pitting corrosion."

I actually did a related thread on it in another forum. Others reported similar experiences, my experience started with mango juice exposure to stainless steel steak knives left unwashed in a sink.

Apparently, in the presence of moisture, oxygen, iron, Ascorbic acid (a source of H+ and a chelate) and tap water minerals (electrolyte), an electrochemical based pit corrosion reaction can proceed with time.

Believe it or not, the causative agent is the Ascorbic acid from the pineapples, which is known to cause pit corrosion (explained here) with stainless steel! Here is a source "Effect of ascorbic acid on the pitting resistance of 316L stainless steel in synthetic tap water", to quote:

"Above the 10^-4 M of A.A concentration, A.A generates soluble chelate rather than absorbs on the steel surface and it causes passive film deterioration and severe pitting corrosion."

And per the question: "why are there concentrated spots of rust on the wall", which supports not normal rusting, but pit corrosion, which I have experienced. I actually did a related thread on it in another forum. Others reported similar experiences, with my experience starting with mango juice exposure to stainless steel steak knives left unwashed in a sink.

Apparently, in the presence of moisture, oxygen, iron, Ascorbic acid (a source of H+ and a chelate) and tap water minerals (electrolyte), an electrochemical based pit corrosion reaction can proceed with time.

Believe it or not, the causative agent is the Ascorbic acid from the pineapples, which is known to cause pit corrosion (explained here) with stainless steel! Here is a source "Effect of ascorbic acid on the pitting resistance of 316L stainless steel in synthetic tap water", to quote:

"Above the 10^-4 M of A.A concentration, A.A generates soluble chelate rather than absorbs on the steel surface and it causes passive film deterioration and severe pitting corrosion."

I actually did a related thread on it in another forum. Others reported similar experiences, my experience started with mango juice exposure to stainless steel steak knives left unwashed in a sink.

Believe it or not, the causative agent is the Ascorbic acid from the pineapples, which is known to cause pit corrosion (explained here) with stainless steel! Here is a source "Effect of ascorbic acid on the pitting resistance of 316L stainless steel in synthetic tap water", to quote:

"Above the 10^-4 M of A.A concentration, A.A generates soluble chelate rather than absorbs on the steel surface and it causes passive film deterioration and severe pitting corrosion."

I actually did a related thread on it in another forum. Others reported similar experiences, my experience started with mango juice exposure to stainless steel steak knives left unwashed in a sink.

Apparently, in the presence of moisture, oxygen, iron, Ascorbic acid (a source of H+ and a chelate) and tap water minerals (electrolyte), an electrochemical based pit corrosion reaction can proceed with time.