Stainless Bolts

[Pulpboy]

I'm trying to replace an HH Bolt A325 with a stainless equivalent. What about the nut?

Would that be a a grade 8.8 or 10.2?

 

[NickE]

Often times stainless bolts and nuts have a lowere rating, since high strength bolts are usually Q&T alloy steel. To produce similar strength levels in a SS bolt A martensitic alloy such as 410 must be used. Even then the corrosion resistance is not incredible. If this is for initial design you may have to go to a larger diameter fastener. If its a swap out to gain corrosion resistance you my not be able to get exactly what you want.

(For further note, I've under taken a project to replace all of the carbon steel fasteners underneath my car with 18-8 or A2-70 fasteners, this is an annoying project since the A2-70 M10 coarse fasteners I'm using have a different wrench size than what I'm replacing, I have to keep swaping wrenches.)

Nick
I love materials science!

 

[CoryPad]

Stainless fasteners similar to ASTM A 325M include property class A2-80 according to ISO 3506-1 (bolts/screws) and ISO 3506-2 (nuts). These are similar to property class 8.8 according to ISO 898-1, but not an exact substitute. Stainless fasteners are prone to galling, so use a lubricant.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[EdStainless]

Galling is problem one.
A close second issue is the galvanic corrosion of the joined items. I would never bolt carbon steel with stainless fasteners. Protecting the less corrosion resistant material becomes very difficult.
The higher strength SS bolts are usually cold worked (rolled threads, not cut). This helps galling some, but anti-sieze agents are still needed. If you need strength and corrosion resistance you may need to look at 17-4PH (or 15-5 or 17-7) age hardened stainless.

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Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[NickE]

Ed Stainless- I guess you might be right, however I find that after a winter in detroit with the salt an slush I cna change out different exaust components, and prototypes from my daily driver, as well as still remove and clean the skid plate with far less difficulty than when I used the original carbon fasteners.

(although I do use plenty of well rubbed in MoS2 adn Ni based anti-sieze on the bolts and threads)

nick

 

[EdStainless]

I remember so many cases that it makes me pause.

The Statue of Liberty is a classic, Fe vs Cu.

Photos of a yatch that used 6%Mo SS for the hull, and Monel rivets. The hole in hull plates corroded out and the whole thing came apart.

In you case Nick, the risk is small and the benifit is big. I would do it too.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[Pulpboy]

Okay here's some more information for your perusal although what I asked for was answered by Corypad - 8.8.

This will be used to secure stainless parts together underwater (fresh). I will be using a loctite to make sure ther bolts never come apart as well as to prevent galling. The manufacturer had A325 cadmium plated bolts but I wanted to go to a stainless because something failed (I don't know what yet until I drain the tank). The bolts probably aren't the problem but I thought why not upgrade them for corrosion if I can keep a similar strength. The tank has only been drained 1 in 12 years so I don't have a lot of oppurtunities to fix loose bolts.

 

[WhiteLotus]

I've retrofitted lots of equipment in the past few years that was originally put together with carbon steel bolts. When I've made the switch to stainless, I always use everdur (Monel?) washers. Stainless bolt w/ stainless washer is impossible to remove once tightened without cutting.

 

[KernOily]

EdStainless -- OK, does that mean I need to use a flange insulation kit when bolting an A182 SS pipe flange to an A105 CS pipe flange? Every time I ask this question I get different answers. Some guys say yes, others no. And would you use B7 stud bolts or B8M for this application? The galvanic table in my materials book does not list SS, only its elements so I don't think that's a good go-by. The Statue of Liberty Fe vs Cu is a case of an elemental galvanic couple, as far as I know. I am not a corrosion engineer - doesn't the presence of alloying elements affect the galvanic properties? Comments?

Thanks!
Pete