As long as there are no oils on the surface - then power washing and priming the surface with an acidic wash primer - no matter how long it has weathered - would seem to fill the bill for a standard pretreatment of the zinc.
The type of primer I'm thinking of is a single pack, polyvinyl...
The black paint inside has high absorption/emissivity and so absorbs more heat, which transfers into the housing steel and dissipates on its external surface. Pretty elementary.
If you want the 3CR12 housing to emit even more of that heat away, you would also paint it a matt black. However...
By your consideration of HDG, the structure is NOT immersed. Therefore there are many protective coating systems that will provide acceptable performance. Devoe has no special products I'm aware of that would outperform those from PPG, Carboline, Sherwin-Williams, International Paint, ...etc...
Your first option - welding the 304L to the CS and then PWHTing the whole thing - is common in many industries. 309 electrodes are commonly used to do this. Make sure however, if the service is in SCC-causing environments, that the 304L is clean before the PWHT. C from oils and organic matter...
Sounds like a red herring to me.
Fatigue properties relate so strongly to the mechanical properties that I suggest this is where to pay all your attention. After all, there may be many more of these shafts that have not broken and have the same microstructure. You need to do a detailed...
Hold on now. In reality there will be no significant galvanic corrosion between zinc and Al (6061) in regular ambient weather exposure - assuming only occassional wetting and moderate time of wetness. This is mostly because the Al alloy forms an oxide surface layer, conditions will not turn...
K200/201 is an Acrylic urethane primer surfacer made by PPG.
I have trouble seeing how it works here - it's a common surface smoother for body work on cars. Nevertheless, the notion of finding a convenient protective coating (none more convenieint than paste in my experience) is valid...
There is no basis for suspecting that B7 bolts cathodically protect the CS flanges. I suspect this "folk lore" may arise because the bolts are likely to corrode to failure sooner (because they get thinned all around and break because they are loaded). Galvanizing the bolts will...
Stainless steel HX tubes (and carbon steel, copper, etc.) can be seated/sealed in tubesheets by mechanical rolling expansion or by hydraulic expansion.
The latter is really slick (GM now makes some auto frames by hydrostatic shaping) and you can learn more about the Hydroswage process at...
It's hard to tell from your description if the problem is with incomplete coverage with the zinc plating - which possibly could be remedied by hot-dip galvanizing the piece or using an organic or inorganic zinc-rich primer - or if the protective system is inadequate.
In relation to the...
The surface preparation for hot dip galvanizing (HDG)involves caustic degreasing and rinsing; acid pickling and rinsing, and fluxing - all in a series of baths. You do not need to shot blast, unless someone has devised a HDG process that is entirely different from the norm.
A good property of...
The well-respected ASME Boiler and PV Code stipulates the same max. allowable stress for carbon steels of this type up to 350C.
You should take this to indicate that the yield and tensile strengths - which are the basis for the max. allowable stress - are essentially unchanged, i.e.,do not...
Rerating of pressure vessels requires a fairly standard set of questions be answered:
what are the materials?
what are the allowable stresses?
what condition is the vessel in?
what damage mechanisms threaten its integrity and are they in effect?
what testing or inspection methods apply...
Perhaps your standard is not set by considering all the relevant factors. Fitness for service assessment can indicate the minimum thickness for different sizes of thinned areas. So you set a "rule" and now you have the choice of enforcing it or stipulating when it truly should be...
