The ones on the left look like staining from the wash water.
Any scale or tint on a stainless is bad news as it ties up Cr reducing the local corrosion resistance.
How were they supposed to be descaled?
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First, if your analysis is high precision then this is 7050.
There is a tolerance for the product analysis vs the standard chemistry.
When they did the tensile test did they cut a strip sample or test the tube?
What makes me suspicious is the high UTS and good elongation.
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I have seen people ground things to the wrong piping.
And then a poor power supply (or a failure) allows full mains voltage through the system.
The 420 should resist CSCC.
You could try clips made of 17-4PH, those should be common.
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P.E. Metallurgy...
If the process fluid is conductive then you have the potential for accelerated attack at the inner edge of the CS flange against the 316/Graphite gasket. This would be very localized.
If you allow it to get wet from the OD then you could see attack of the CS flange and outer ring where they meet...
I was at a plant once a few days after they lost a full tank car of pure Cl.
I had to find their safety person and shake their hand, no one hospitalized
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And this works because the thick baffle marked 'drains subcooling zone enclosure' uses very tight-fitting holes for the tubes to minimize bypass.
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Look at the chart with categories of service.
You need to respect the H2S pressure, pH, temperature, and Cl content when making these choices.
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The two plants that I did some work in that scared me;
one had a unit making sulfur chloride,
and the other had a hydrogen cyanide unit .....
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Considering that large scale development began in the early 1920's there is quite a range of structures.
Many of the old ones are very good (except for windows and doors) because they were very scared of storms.
By the 1950's fast and cheap was the order of the day.
So you get a bit of...
I'll ad that he only time that I have seen this as an issue is doing manual weld overlay using NiCr on the inside of a vessel.
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You need to do biological control at the intake.
I would suggest using a bar screen for big stuff and then a fine wedge-wire screen for finer trash.
Often biocide is injected between the two screen systems.
Sand separators will save a lot of pain and maintenace costs down the road.
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It is common to have the tools touch a reference before machining to assure positioning.
We usually programed it to do so after machining as well.
If the tool/machine combination didn't hold zero, then we know that the part has issues.
This let us pull a fairly loose AQL and still get excellent...
Pointless. If they are in a confined area, then they need positive ventilation.
The reason is related to Cr vapor.
The EU is big on this, but I have tested and never seen levels that were even detectable.
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They swapped a tool that was the wrong size.
These machines swap tools frequently during the machining process.
The other possibility is that there was debris that interfered with the zeroing of the tool position.
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If you want the pipe rejected, then tell them to clean it back to white metal (grit blast and/or pickle) and then you will inspect it.
They won't want to put work into it knowing that they still risk rejection.
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And if the coating is meant to actually protect the piping then there needs to be Zn rich primer, a protection layer, and a sealant.
It needs to go onto a clean surface of the correct profile.
The thicknesses need to be according to the manufacture.
And the cure is important.
The real problem is...
Try reading this.
MS-1: Materials Selection for Sulfuric Acid
Converters
The converter operates at high temperature (up to 625ºC [1,157ºF]) in an oxidizing
atmosphere. Sulfur dioxide from the burners enters the top of the converter through
Al-coated steel or type 304 ducting...
I would hope that there is no PWHT on this.
The weld procedures for these alloys are very rigorous.
I have helped write some and we could get properties that would be acceptable in mill annealed plate.
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