TomC wrote:I can't speak for Ray, but blueing is just a pettier version of rust ( oxidization), with the added perk that it helps inhibit further rusting. If you were to use a mild steel and not stainless, blueing would add the corrosion resistance, with the added strength of it not being stainless, as described above.

I've never heard of bluing used in food safe- potable water applications myself, but I'm also not a metalurgist. I think you've got your ground covered perfectly the way you are with your food safe thread gaurd.

Bluing is generally used when you don't mind keeping a thin coat of oil on stuff. Blued metal will rust, especially when in contact with water. On the scale of durable finishes, bluing (even hot bluing) is nothing to write home about.

Usually if you really need to protect mild steel or something steel which doesn't have natural resistant properties in its alloy, then you'd use like some sort of Mil spec black oxide or perhaps some sort of grey or black parkerizing. Powder coating is also popular and cadmium isn't half bad (but again, with cadmium it will still usually eventually rust if left exposed).

The acid test is usually whether or not your finish can be exposed to salt water spray for XXXX hours and still hold up. If it can, then you are good. If not, then make sure there is a layer of oil to keep the oxygen molecules at bay

Ray

and then there's Titanium and inconel and crazy stuff like that - for when DrGary decides to build a space shuttle or jet plane, etc.

and of course Gold can be left at the bottom of the ocean for 500 years and it will pop up just as shiny as the day it was minted.

It all basically boils down to how well the metal holds onto its atoms.

Ray

Thanks for your input, guys. As noted these are specced by an experienced Conti repair tech who's seen them hold up over time. I'm not doubting that Ray's suggestions are likely to be ultimate, but practicality's a concern at this moment. Total cost for the screws, nuts, washers is $12.93 plus tax, no shipping cost, and I have them. Total cost at McMaster-Carr would be about $23 for the screws alone at grade 8, probably more for SS, plus extra for nuts and washers, plus shipping, and I would have very many left over cluttering my workspace as some of these are ordered by lots of 50 or 100.

The tech who's coaching me is recommending a regime of progressive tightening of the group bolts with a torque wrench at 10 - 15 lbs., no more than 20. So I should tighten once, heat and tighten hot, check again at 24 hours of heat, tighten hot again after a week, then again at 6 months until they don't tighten any more. He gives similar instruction for progressive tightening of the group studs but there suggests I should be fine with a 6" wrench, which I can lean on pretty hard with one hand but don't overdo it or lean in with my body weight. He writes that for the group studs Conti still makes this group and uses 18-8 stainless steel with plain steel nuts. He has those in stock, so I'll buy them and will coat them with anti-seize compound.

I was thinking last night, after I logged off, that button cap allen head screws might look nice too.

When it comes to torquing down the gasket, you probably wanna use a star pattern, similar to how you torque down lug nuts on a car wheel or head bolts on a motor.

Ray

Wouldn't have thought of that. Thanks, Ray!

What kind of gasket material did you finally settle on?

Ray

drgary wrote:Wouldn't have thought of that. Thanks, Ray!

I definitely would not start at one side and go around to the other. You could introduce uneven sealing or warp the flange if you aren't careful.

And do the torquing in stages. 120 in/lbs, 240 in/lbs, etc.. up to whatever the torque you want is.

Keep in mind, usually more damage results from over tightening than under tightening. So don't go crazy over there with 200 ft/lbs per bolt or anything.

Ray

Hi Ray,

Per above, I'm getting gaskets that are pre-made for the Prestina out of fiber. Torqueing will be pretty low intensity, about 20 lbs at most.

Sounds good. I was going to say you might want to use some cooper coat spray on them, but maybe not since it's in contact with food, etc.

If you know anyone with a surface plate, you might check the flatness of the flanges. I have a granite grade B surface plate, but I am not sure it's large enough for your boiler. Have you checked to see if the flanges are perfectly flat or have you surfaced them or anything?

I think if it were me, I would at least sand them on glass (with emery cloth) or have them precision surfaced maybe. Just so you are dealing with perfectly true, flat surfaces when you bolt everything together.

Ray

Ray,

You and Paul Pratt both use this step. Yet when I took apart the boiler I noticed casting irregularities that hadn't been smoothed out and the seal had held. It's a large flange for a boiler not under a lot of pressure. I'll think about your suggestion and check with the guy who fixes these and similar all the time. I wonder whether the choice of gasket material can also make the seal more forgiving if the material fills in surface imperfections.