What is the staybolt stress?

M Austin · **Joined:** Sat Feb 05, 2005 1:05 am **Posts:** 488

Click on Attachment for Large Print Edition

staybolt1.jpg [ 62.7 KiB | Viewed 14392 times ]

The calculations are provided. Those who have correctly filled out an FRA Form 4 should immediately know the correct answer. The blueprint shows the first three rows as flexible staybolts. For the purpose of this poll, the roof threaded staybolt ends are shown.
Poll will run for 7 days to give the weekend for those may want time to verify calculations.

Longitudinal Pitch = 3-15/16 inches = 3.9375"

Roof Transverse Pitch = 4-9/16 inches = 4.5625"

Crown Transverse Pitch = 4-9/32 inches = 4.2813"

Staybolt Material is 1.00" Diameter
Roof Sheet End is upset to 1-1/4" Diameter
Crown Sheet End is upset to 1-1/2" Diameter
Thread Profile is Whitworth Pitch = 12 TPI (p=0.0833 in.) (d=p x 0.64033)
Staybolt Shaft Diameter = 1.00" Area = 0.7854 sq. in.
Roof Stay Threads Root Diameter = 1.143" Area = 1.027 sq. in.
Roof Stay Threads Diameter = 1-1/4" Area = 1.227 sq. in.
Crown Stay Threads Root Diameter = 1.393" Area = 1.525 sq. in.
Crown Stay Threads Diameter = 1-1/2" Area = 1.767 sq. in.

You may vote in the poll here
No registration required.

Atkinson_Railroad · **Posted:** Wed Aug 26, 2015 7:11 am

A couple of unknowns immediately stood out to me among the list.

The "Material" is listed as a dimension of 1 inch.
What would typically be the material used in making the component?
Some sort of steel of course. (Grade, and type of material.)

It's unlikely the ends are "rolled" to produce the threads... yet the way
the threads are cut would effect the strength of the part.

Perhaps this info is denoted in FRA specifications?

John

TimReynolds · **Joined:** Sat Aug 31, 2013 4:11 pm **Posts:** 287

This will expose my obvious lack of any experience in boiler making. But how is the nut installed on the water side of the staybolt at the crown sheet?

J.David · **Posted:** Wed Aug 26, 2015 2:19 pm

Administrator or whoever:
I keep getting an "invalid form" message...
JDC

dinwitty · **Joined:** Wed Oct 22, 2008 8:18 pm **Posts:** 2226

TimReynolds wrote:

This will expose my obvious lack of any experience in boiler making. But how is the nut installed on the water side of the staybolt at the crown sheet?

aha..no water in boiler, steam dome opened up, probably no tubes in the boiler. You probably have 3 people helping install them, holding and nut turning, one inside the boiler, one outside, one in the firebox inserting the bolt.

I recall Joe Karol on 765 banging on them with a hammer, if they had a good bell ringing like sound, they may be in good shape, a thuddish sound may be a problem.

they might be installed during boiler construction in the Lima Shops before the boiler segments are placed together.

TimReynolds · **Joined:** Sat Aug 31, 2013 4:11 pm **Posts:** 287

dinwitty wrote:

they might be installed during boiler construction in the Lima Shops before the boiler segments are placed together.

If you are installing a new crown or whole fire box I imagine you work your way from the cab end towards the front sequentially. But dang if under inspection you find a bum bolt in the field of crown stays it seems that you'd have to remove good ones around it to be able to install that nut.

CCDW · **Joined:** Wed Jan 28, 2009 4:30 pm **Posts:** 211

I am in accord with J.David. I am unable to enter my vote.

M Austin · **Joined:** Sat Feb 05, 2005 1:05 am **Posts:** 488

The fix

Atkinson_Railroad · **Posted:** Thu Aug 27, 2015 6:51 pm

Understanding the technical glitch in the forum poll.

Still... no clarification about the actual component!

A very nice drawing, and mathematical data is presented for the poll,
yet the root (very necessary) data on the actual stay-bolt is still missing.

What is the staybolt made out of, and what manufacturing process was
used in its fabrication?

Does the FRA Form 4 specify any of the above information?
Perhaps the FRA Form 4 should compliment the post?

Reference the below thread from over a decade ago from right here at RYPN:

viewtopic.php?f=1&t=7514

Is there a polite way of articulating the poll seems somewhat erroneous and meaningless until further clarification?

Sorry, "...20 questions", I know.

Always enjoying the forum though ; )
John

M Austin · **Joined:** Sat Feb 05, 2005 1:05 am **Posts:** 488

Stress is a function of geometry only.
Once the stress is determined, then the stress value and application environment determines the material selection.

Sully · **Joined:** Thu Dec 01, 2005 2:24 pm **Posts:** 76

M Austin wrote:

Stress is a function of geometry only.
Once the stress is determined, then the stress value and application environment determines the material selection.

or determines the re-design and engineering of the component(s) when no suitable material is available, economical, or certified to meet the load as designed. Copper or titanium anyone? Lol. Skunkworks and space stuff, if you will.

Still, the vector dynamics of load need to be calculated and?or the component destructively tested for safety. I do not know the answer to the question, but my guess would be highest load in the most fatigue prone area.

https://www.nde-ed.org/EducationResourc ... Strain.htm

Dave · **Posted:** Fri Aug 28, 2015 12:08 am

[quote="Atkinson_Railroad"]
What is the staybolt made out of, and what manufacturing process was
used in its fabrication?

It doesn't friggin matter. The question is about the amount of stress on the bolt, not whether a theoretical bolt made of any particular alloy or material can withstand it. The cross section of the weakest part of the bolt, or of the weakest attachment if that's less strong than the smallest cross section, provides you with the amount of material X that has to withstand the stress - PSI times the quantity of square inches of plate that particular bolt is handling - it's share, in other words...... so whatever material it is, it needs to withstand so many pounds of force per square inch for the amount of cross section that is weakest. We know what the pitch areas are, and what the dimensions of the bolt are - might need to apply a little trigonometry to work the angles....... which if I wasn't an English major I might be able to do.

CCDW · **Joined:** Wed Jan 28, 2009 4:30 pm **Posts:** 211

So I will go out on the limb. The question is “What is the staybolt stress for the FRA Form 4?” I will assume that the math is correct. So the answer is 5359. The FRA is not a complex organization that spends a lot of time getting all philosophical. They want to know that the values are within parameters and was it accurately determined. So, state the highest stress calculated and have done with it. Material isn’t the issue, design and construction are not the issue, and pressure isn’t the issue. Unit stress is the issue. Material, design, construction, and pressure come into play elsewhere.

CCdW

M Austin · **Joined:** Sat Feb 05, 2005 1:05 am **Posts:** 488

If its broken, fix it -- or build a new one. You may vote in the poll here

M Austin · **Joined:** Sat Feb 05, 2005 1:05 am **Posts:** 488

Dave wrote:

might need to apply a little trigonometry to work the angles

Actually, no. The wonders of the Belpaire firebox is the crownstays are radial and perpendicular to the roof and crown sheets. No fancy calcs required.