A193-B8M bolt

[Syahar1975]

Dear experts,

The bill of material states A193-B8M bolts is required to bolt 24" shell manhole. In other engineering notes it is stated the external bolts shall be floro carbon. My understanding A193-B8M is AISI 316 material (stainless steel)

It is possible to floro carbon the stainless steel bolts ?

Thanks and regards,

Syah

 

floro carbon

Suggests a Teflon coating. Why this would be considered necessary on a 316SS fastener I cannot guess.
I am generally skeptical of non-metallic protective coatings on fasteners.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[Screwman1]

We see a lot of B8M bolts with Fluorocarbon coating for special chemical use in railcar construction. It adheres fine with the proper surface prep. Make sure to have one of the folks that do a lot of fastener work do the application, it's not the same as a fitting plate.

 

[XL83NL]

We have coated our B8M studs in the past as well with PTFE, partly due to customer requirement, partly since we generally PTFE (i.e. Xylan) coat all or studs and nuts to reduce friction, when design temperatures allow so.

 

[MJCronin]

A little footnote here ..... in favor of fluoro coating fasteners.

When a fastener is coated, the identification etched on the item is typically lost. Having various coating colors available can be an advantage.

(i.e stainless - yellow, low carbon steel - blue, carbon alloy - green..... etc.

In well organized and planned operations, many clients require different colors for stud/nut/bolt material combinations. This help prevent mix-ups and substitutions that can be expensive and dangerous. Inspection and maintenance is made simpler....throughout the life of the plant.

I have been to many plant sites where management does not pay any attention to bolt management and simply gives up and specifies that only the strongest (and most expensive) bolts are used on site. This is an expensive and often lame brained solution

Of course, you can still have uncoated bolts for special cases.

https://www.metcoat.com/assets/files/Fluorokote1Brochure.pdf

MJCronin
Sr. Process Engineer

 

[XL83NL]

Here's a snap of what we have in our bolt spec, to identify colours

 

Screwman1,
I guess I am skeptical because I have only seen such fasteners after the coating has failed and the barrier breached.
I have trouble wrapping my head around the idea that any plastic coating can survive the necessary torqueing.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[XL83NL]

it will not survive repetitive torqueing; a few 'open and closes' will easily take away the coating. But the added cost vs the advantages, even if it were for a single use, is what makes us keep on using the PTFE coating. We usually dont go beyond bolt sizes 1" or larger.

 

[EdStainless]

I personally like fluorocarbon coatings on SS fasteners, it is easier than assuring that the correct anti-seize compound is used every time. And when the coating begins to fail mechanics are willing to use new fasteners.
I have found the cost of coating to less than machining out a seized stud or bolt.

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P.E. Metallurgy, Plymouth Tube

 

[Syahar1975]

XL83NL,

Is there any standard color for florocarbon bolt and nut ?

I look at again the drawings and found the bolt specs is A193B7 with note :florocarbon. The supplier gave us bolt not green color bolts and nuts.

Looking to your snapshot green is A193L7.

Syah

 

[david339933]

No Standard....If you don't specify they will give you anything. The B7's I receive are blue on request.

 

[XL83NL]

The B7's I receive are blue on request.

Same here. Based on that, we made up our own standard and include the colour in our purchase order. L7 doesnt need to be green, it can be anything you want. I just picked the most obvious colours (to visually differentiate from) for the most commonly used grades.