Crevice corrosion, increased bending loads due to longer bolt lengths, the greater impacts to strength that welding issues have on a fillet weld over a full penetration granular orientation to load are among the issues.
In this thread I recognize that there were questions left unanswered and I wish we could go back and answer them but that takes time I never seem to have. The most dangerous thing about life are the things we do not know or refuse to understand. Asking questions is the best way to combat this.
Please ask questions as it is a great way to gain knowledge. Please be patient with the answers as the sources may not be the best at explaining there understanding of the subject. Also come with a critical mind so you can work your way thru the fog that is sometimes created either intentionally or unetentually.
Work is busy repairing Nevada St Rt 233. So I it may take me a few days to repond
Robby Peartree

So my question is what do you mean when you write "full penetration granular orientation " in the context of your last post?

Thank you, CCdW

Dear CCDW
The post shows the dangers of posting when you are tired.
I was trying to bring up the potential issues of crystalline structures within a weld. The following links discusses the issues that can occur within a weld in localized zones, within the structure that have different characteristics that can be found in a weld.

http://ispatguru.com/weldability-of-steels/

http://fgg-web.fgg.uni-lj.si/~/pmoze/es ... /l0100.htm

One issue for fillet welds is failure due to loading of the weld in sheer which occurs with staybolts. This is compounded by grain orientation created by the welding process. Atomic stackings take loads better in certain directions than others. The different orientations within each grain structure causes a metal to have similar properties in all directions.

Dear PMC

Good engineering needs to understand the advantages and issues to each way of accomplishing a task. It is equally important for those also involved in the construction process to not change a parameter because of a lack of skill.

On the fillet welded bolts in the thread entitled technical questions I wrote the following in a post on page two;

When looking at the loading one must ask just how thick will the weld be? The Czechoslovak State Railways application for 4-8-2 wheel arrangement locomotive boiler called for a 6 mm (thick weld (app 15/64”) over the 1 mm (1/32”) gap between the edge of the stay bolt and the sheet. That means if your side sheets are 3/8” thick you loose 37% of your cross sectional area of the sheet at the point where the “crevice” is bridged. Each crevice has an approximate area of 0.050 sq. in. If you have 3000 staybolts you are looking at a sum of 150 sq. in. of area that is effectively 15/64 of an inch in thickness before corrosion or other factors begin to affect the joint. After a few years of service you will be looking at repairing staybolts due to the metal thinning at the joint. If this does not happen the line of failure will not be a bolt breaking across its diameter but thru the weld between the sheet and the staybolt.

The link to the thread is here

viewtopic.php?f=1&t=22217

It is important to realize that fillet welded stay bolts were typically used in communist countries where geopolitical pressures of each person having a job and creating work were important. I understand Fillet welding in China was renewed every five years.

Robby Peartree

I read this three times - are you proposing that the section of the side sheet which is included in the weld area somehow disappears? Sheer? Do you mean "shear?" I'm finding this discussion hard to follow........ It's late and I'll take another look in the morning.

Dave,

The way I read Robby's post, the specifications for his Czechoslovak State Railways example included 1mm (.039") of clearance in the holes for the stays, with the fillet weld bridging the gap, so the sheet was essentially never there. The weld bead specified was less than the thickness of the sheet. Don't know if this would be a common clearance or not.

I went back and looked over this thread again as the technical aspects are outside of my knowledge base. But my question is: why is option A Mr Austin listed above (12 thread per inch - USF) not the preferred option? Welding always necessarily damages the metal to a certain extent, why wouldn't you want to avoid this problem entirely? What option was used prior to the existence of arc welders?

I must assume that this is strictly an academic discussion. I have never seen a note on a welded structure blue print that says orient grain in this direction when welding. I would also think that in new construction the orientation wouldn't be an issue to the inspector and the consumer, especially where the boiler was to go to final heat treat and follow a prescribed temperature cycle. That also holds true for a welded repair.

Besides short of cutting the boiler apart, etching, and photomicrographing the section how would we know what the orientation is or was?

I think this discussion has lost me. I have no idea how to apply any of this to real life. I shall just faithfully follow ASME code, NBIC code, or my AI's directives in boiler repairs.

CCdW

Absolutely.

Page 14

That's it, huh? Thank you for the very direct answer, that is about as clear as possible.

I'm still curious about welding at all, why not use the 12 thread per inch - USF staybolts you mention above?

Other option is full penetration welded installation. How does that compare?

The bottom line here is that welded stay bolts are easier and cheaper to do than threaded ones. (Fillet welded bolts take the least amount of effort) By that I mean that if you have a welding machine, a semi-competent welder, and the right sized code bar, you can install stay bolts. Threaded bolts require the following –
Expensive custom made taps to thread the sheets.
An air compressor.
An air motor, cutting oil, and two people to thread the sheets.
A machinist to thread the bolts.
One or two people to install the bolts.
One person to cut off the extra length of each bolt. (The extra length required to hold on to the bolt to thread it in)
A welder to “seal weld” each end of the bolt. (If that is part of your installation method)
An air hammer and bucker along with two people to upset each end of the bolt.

I am not a fan of full penetration or fillet welded bolts for several reasons. If the welder has a headache or is in a bad mood, you are likely not going to get a good job. Additionally, when you are welding a bolt adjacent to a corner or flange, you can’t see the other side of the bolt during the process. I have seen very few full pen bolts that are actually full pen. There is almost always a gap where the root pass is supposed to be. The ASME Code says the welds shall be full pen. Both welded installations are difficult to inspect for quality. If you ever need to replace a broken full pen stay bolt, good luck finding the hole. I don’t like the crevice corrosion issue with fillet welded stays. As I understand it, in countries where fillet bolts are/were used, a given percentage of them are changed out at regular intervals as a matter of course.

Traditional threaded stay bolts either thread in properly or they don’t. Quality control is a no-brainer. Our #90 still has many of her original rigid Whitworth threaded bolts still doing the job 93 years later.

I’m not saying welded bolts are bad. I’m only saying I think they are an inferior method compared to threaded bolts. You get what you pay for.

Rick

.

Kelly, where is that picture from, and what part of the boiler does it represent?

Not only do those not appear to be full-penetration welds, the little 'incursions' around the base of the bolt in the foreground look almost like spatter - the metallurgical structure in that area can't be good! -- and from the look of the "fillet" above the crack where that yellow arrow is pointing, that is a circumferential crack in welded metal, not just swelling of an oxide layer on the tube end.

Shouldn't a full-pen weld between the bolt and plate have a default 'fillet' (no matter how small) showing that the metal is fully fused? And should there be no tendency for the fillet so formed to separate from the plate in the manner I think I see?

Looks like radial stays into the crown sheet as viewed from inside the boiler. Overhead welding most likely.

This is why you NEVER get your welding done by the enthusiastic guy who took night courses in auto body work at the local community college, and is ready and anxious with his Harbor Freight wire welder. This is a job for highly skilled and experienced pressure vessel welders, backed up by sound engineering and properly made parts.

People who make their living building or working on pressure vessels in steam power plants, refineries, chemical process plants, etc. don't come cheap, but they also don't use your job as their learning experience. Enthusiasm is no substitute for experience and sound judgement.

People at this level know a great deal about proper fit-up, properly machined parts, fit tolerances, pre-heat, proper rod choice and care, proper materials, and they tend to be fast. They are used to welding in all sorts of odd configurations, be it hanging upside down or whatever is needed to do the job right.

Proper procedures will specify the root pass and all other passes. And there will be pauses to verify the work as it proceeds.

Re: The photo above. If photos could be taken at this stage, they should have been taken as the work was progressing. Had that been the case, this would have been caught and corrected before hundreds of bolts were done, all poorly.