What's a "Flexible" Staybolt?

To add to what Rich posted, flexible stay bolts also have a 3/16" hole formed/drilled through the length of the bolt up to just under the forged head of the bolt. Thus, it the bolt breaks, steam blows out of that tell-tail hole into the firebox, which is readily visible by a crew member or inspector. The FRA has specific rules about how many broken staybolts are allowed within the firebox, and no two broken bolts next to each other are allowed.  

Thanks!

Practical/silly question, who manufactures staybolts these days? Doesn't seem like they would be a high demand item.

Thanks in advance.

Custom makers?

@PLCProf posted:

Practical/silly question, who manufactures staybolts these days?

The problem is obtaining the correct extremely low carbon steel rods, in the diameter needed (1", 1 1/16", 1 1/8", 1 1/4", etc.). Then finding somebody with a "gun drill" machine to drill the hole into the bolt, the forge/up-set the head of the bolt. Some flexible staybolts, such as those that support the crown sheet (crown bolts), are over 30" long. 

Doesn't seem like they would be a high demand item.

You would be surprised!

Thanks in advance.

WOW, I didn't think they'd be that long, that's a precision drilling operation to drill that far and not stray from your line!

Thank you, Hot Water, for the reply.

I would have expected the manufacture of staybolts to be subject various legal certifications and standards, due to the safety-related nature of the product.

@PLCProf posted:

Thank you, Hot Water, for the reply.

I would have expected the manufacture of staybolts to be subject various legal certifications and standards, due to the safety-related nature of the product.

There are indeed material specifications for every type of steel used in steam locomotive boilers, plus ANY type of steam boiler.

@gunrunnerjohn posted:

WOW, I didn't think they'd be that long, that's a precision drilling operation to drill that far and not stray from your line!

That's why a "gun barrel drilling machine", which uses a hollow drill bit (for cutting fluid circulation through the drill bit), is so VERY important for producing flexible staybolts!

One of the changes that came about when CFR 230 was changed (the Federal regs for steam locomotives) was a requirement that every piece of steel used in the boiler had to be traceable back to the heat of steel used to make the sheet, bolt or whatever. The paperwork required can be an admin nightmare.

Gad Rich, sounds like airplanes!   We used to joke that the design wasn't finished until the paperwork outweighed the airplane!

At least with locomotive parts we don’t need FRA approval for anything, unlike aircraft parts that have to be approved by the FAA, AAA, PMA, EAA and even the PTA. The steel just has to meet the specs laid out in the rule.

@PLCProf posted:

Practical/silly question, who manufactures staybolts these days? Doesn't seem like they would be a high demand item.

Thanks in advance.

Still quite a number of coal fired electric plants.  Found this old document on staybolts some may like to browse.            j

http://www.athra.asn.au/library/staybolt_catalogx.pdf

How was the spacing around staybolts, one bolt next to the other, determined? Were there calculations? Trial and error until a formula was determined? It would seem the sheet metal might be a determining factor.
Steve

@RideTheRails posted:

How was the spacing around staybolts, one bolt next to the other, determined?

Mathematical formulas based on the boiler pressure. 

Were there calculations?

Yes. In the "modern era", based on a safety factor of 4.

Trial and error until a formula was determined?

Continuous improvement/development of the decades. 

It would seem the sheet metal might be a determining factor.

The thickness of the steel sheets was also determined by the designed boiler pressure.

Steve

Flexible staybolt  a true oxymoron

@LLKJR posted:

Flexible staybolt  a true oxymoron

I get where you're going with that but there are multiple definitions for the term "stay." In this case it means something that lends support.  Old corsets and braziers has "stays" in them.  In that case it didn't mean something that remained in one place.

@LLKJR posted:

Flexible staybolt  a true oxymoron

Not at all. It provides restraint (ie acts as a “stay”) in one direction, whilst allowing a degree of movement in other directions. 

@LLKJR posted:

Flexible staybolt  a true oxymoron

Well, there are ridged staybolts throughout the firebox also. What is your opinion of THOSE?