Weird plumbing problem

Any fix except replacing the plumbing is temporary. The Sharkbite is one of the easiest to get him up and running again.

 

Agreed. Sorry.

 

Awwwwwwwwww that was mean

 

No, I was only teasing. The timing seemed right for a plumbing joke, and Tom's a kind, intelligent, good-natured guy who wouldn't take that sort of thing personally. Right, Tom?


Uh....Tom?


:brick:

 

Another issue with stainless steel is that welding can cause the formation of chromium carbides and deplete the chromium from the zones near the weld line. This is bad because you now have a small zone where all of the corrosion can occur in an otherwise passivated part. So the local corrosion rate is very high. Bad.

Back to the copper pitting: I wonder if it is a combination of impurities in the copper tubing giving local regions that are anodic (the pinhole locations) and that your local water conditions are providing a nice electrolyte to help promote the reaction. I have a fuzzy recollection of some corrosion reactions which can take place in a material that is homogeneous on a macroscopic level, but has regions on the microstructure level that can be cathodic or anodic compared to the average material.

 

It's only fair to point out there are some drastic variations in grades of stainless steel. The difference between 306 and 316 is dramatic. The really high grade stuff put into the outer clading of nuclear reactors took lots of pressure on the steel industry to establish consistency of the really high end stuff. Even though the specs were clear, the actual delivery of stuff consistently conforming to the specs was surprisingly hard.

 

That's the problem right there. Folks have an opinion, usually it's CLEARLY wrong. Try to explain, just have a casual conversation, you end up offending them

At that point, I usually give them a comment that rhymes with "duck shoe" and walk away. Unless they say "duck shoe too!" in which case it gets ugly ....

Hmmmm. There has to be more to it than that ....

 

Just you wait until you're late-middle-aged and *your* "plumbing" starts to act up. First it will lose its pressure, then it will start dripping all the time.

Then when you *want* it to work, it just won't, no matter how much ... encouragement ... you give it.

Then you will just give up and agree to have the plumbing completely re-worked. Have to warn you, *very* painful process

 

I just *love* it when you talk dirty

It's complex and hard to replicate. There does seem to be a variety of factors, but almost always chlorination combined with certain water chemistries - especially hard water - can cause rapid copper pipe failure.

One must assume if one pinhole has formed, many more are lurking out of sight

The phenomena of copper pipe "pinholing" is well known, at least I thought it was. The Maryland study I linked earlier is very nicely detailed.

Most large utilities understand the problem with potable water pipe corrosion under certain conditions, especially recent use of chlorination (Chlorommine in particular) on a system that had not had any sort of residual disinfectant applied before.

Most utilities will add trace amounts of orthophosphate, which has been shown to significantly reduce or eliminate NEW pinhole reports. Pipes already on the verge of pinholing will not benefit as much from orthophosphate additives

Polyphosphate can also be used, but one must be aware that the addition of polyphosphate to a water distribution system with hard water, that has only recently started chlorination for disinfection, will have problems with odor (Swampy, skanky sort of smell, very noticeable in the shower) and discolored water (Dark red/black water)

 

Not only that, there were a lot of phenomena that were clearly not anticipated or understood at the time

As an example, Atomic Energy Canada has the dubious distinction of having one such phenomenon named after a facility located at Chalk River, Ontario: CRUD (Chalk River Unidentified Deposits)

NRC: Glossary -- Crud

A nice claim to fame. However, some of the best engineering is tombstone engineering and failure mode engineering

 

I always thought the "creeping crud" refered to something you could catch. :madgrin:

Its always interesting to try to figure out why things fail. I would really enjoy forensic engineering I think. I did a fair amount of failure analysis at my former employer.

 

I have one interesting forensic failure story.

I was project engineer for a black box going on F-16 fighter GPS systems. The unit was in full rate production and I thought I had finally got all the engineering to manufacturing issues worked out. Then out of the blue I get called at about production unit 300 and up. Every single unit coming off the production line is totally dead, yet each circuit card going in is 100% tested good. I eventually figure out that every unit is failing due to a CMOS IC issue called latchup. (This is where an integrated circuit internally shorts the power to ground in limited startup situations.)

Why now and never before?

Fortunately our reliability engineer starts examining the issue. (It does not hurt that she is rather attractive, but that would be derailing the thread. More important is that she is most excellent at the job...just watch.) She eventually figures out from the lot codes that there is a manufacturer change. The parts are full mil parts with a military part number and the manufacturer is only extracted with lots of leg work. Production get back on track with a purchasing requirement to only purchase directly from the "good" part manufacturers (Analog Devices and Siliconix).

However, she is not done. She then actually has the failing parts dissected and examined under the electron microscope. What she finds is that the bad parts have a missing silicon dioxide passivation layer compared to the others. That was the actual mechanism of the failure.

However, she is not done. She then calls the manufacturer to see Wth they are doing. Well here it gets interesting. It turns out that the original CMOS switch was made for both commercial and low end military use. However, it was so useful, the military made it a high end part and dedicated a special part number and custom specification/testing requirements. When this is done, any manufacturer that follows all the steps can sell the part to the military. What happened, is that the military spec sheet did not state that the part had to not latchup upon all startup conditions. From this Manufacturer's position, removing the passivation layer was legal and made their part cheaper to manufacture. So once they entered the market, every purchasing department instantly shifted to ordering the cheaper part (as required by government regs, so do not blame the buyers).

Fortunately, she was not done. She put out a warning on the defective parts database and internally explained all details and explicit warnings that manufacturer "M"s parts were to be avoided on this if possible. Lots of lessons learned in this episode.

 

I have similar stories, some involving my former employers products and some involving products that we used from other suppliers, but under the terms of the NDA that I was forced to sign to get my severence pay, I'm not allowed to post anything derogatory about my former employer. Let's just say that not all of the manufacturers in the electronics industry uphold the highest ethical standards.

 

I'm in better shape, the previous employer mailed the NDA to me weeks after I left and had cashed out. They were asking me to sign and mail back. "You are mandated not to blah-blah-blah..." and at the end "We wish you the best of success, but you are required to sign and return..."

I keep it for entertainment.

 

I think I would frame it and hang it on the wall.

 

Would that "M" be under six characters?

 

Yes

 

I'm not going to get into too much detail, but tactical and mission critical systems that *must* continue to operate in a HAEMP environment, are specifically tested against radiation-induced latchup

The GPS navigation is important, but not mission critical. Fly by wire, another story ...

The reason why Soviet era fighter jets relied on vacuum tubes wasn't due to a perceived hardness against HAEMP. Actually, vacuum tube devices are highly resistant to HAEMP

The Soviet Union simply didn't have the technical expertise, or the funds, to manufacture solid state components hardened against HAEMP.