I can see the images and read them just fine.

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It's curious that no one has addressed "Hammer-Testing" of staybolts.

Well, we could start here:

https://www.ecfr.gov/current/title-49/subtitle-B/chapter-II/part-230/subpart-B/subject-group-ECFR015bf96f39f0d2e/section-230.40

Here's a Bruce Babcock article on some of the things being tested for, and showing how the hammers are applied:

https://www.farmcollector.com/steam-traction/testing-staybolts/

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Thanks Guys.

After hours and days of being "Taught" by some very knowledgeable gents the "Art of Hammer Testing", I've witnessed "Bad" staybolts cut out and replaced for no reason; have seen "good" flexible bolt "Nuts" fall out on the floor when the cap was removed!

My opinion (worth what you paid for it):

Hammer testing of staybolts is obsolete. It is questionable, and may have been the best easy method "back in the day", but we now have better testing equipment.

A simple UT machine (Ultrasound Thickness Tester) which is commonly used to check boiler plate thickness can be used to check for staybolt cracks.

UT is used to check for axle cracks. The same thinking can be done for staybolts. Prepare the end of the staybolt to accept the transducer and see if the length of the reading corresponds with the known length of the bolt.

If the reading is shorter, or questionable, then the bolt is probably cracked or broken.

A long-time boiler maker once told me that the best hammer to use for rivet and stay testing was one made from beryllium. It gives a good, clear ring. I have one, but have never used it for testing. There are still a couple of boiler inspectors around who will don their overalls when they arrive on site, and proceed to hammer test and do a thorough visual before anything else.
Until recently, and perhaps this is still so, there were jurisdictions in North America for whom the primary boiler testing procedure was a hydrostatic test. Although a hydro test, or even a hammer test, can tell you plenty about a boiler at the moment that you inspect it, they only tell a fraction of the story.
There are plenty of modern procedures that do a far better shop that can ensure a clearer and long range understanding of the boiler's condition -- ultrasound, magnetic particle, even nuclear isotope testing. Basic ultrasound machines have come down in price where they are affordable to the average person. Perhaps your personal machine might not be acceptable to the licensing body, but it can certainly give you peace of mind to know the true thicknesses of the boiler.
A good, thorough, hands-on visual still has great value. Some local inspectors have supplied themselves with borescopes to be able to peer into the darkest recesses. For stays, a good internal visual is important to help identify stay necking and other issues.
Oh? How much, or what percentage of wastage (necking) is allowed by existing codes?

This boiler was signed off by an insurance inspector 6 weeks before I crawled in. It helps if you know what your looking at...





If you have to ask yourself "is it ok?" then the answer is "NO".
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A hydro only tells you if it leaks. It does not tell you IF IT IS SAFE!!!

This boiler passed a hydro test and had a valid California certificate. Then I crawled in...

The boiler at Mentor would likely have 'passed a hydro test' -- despite part of the plate being wasted to a measure 1/16".

My opinion of hydros is that they're useful in finding existing leaks -- NOT for proving boiler structure is solid.

I apologize for causing this thread to drift away from stay bolts and into hydro testing. That was my point, however, that that sort of testing only gives you the "value" of the boiler at the moment it is tested. Likewise, a traditional boiler inspection using those simpler methods only guarantees that the boiler was safe at that moment.
Back to the earlier post, I am truly interested if there are any codes or guidelines related to stay necking?
One project I helped with a few years back was a traction engine boiler swap. The "new" boiler was excellent, but the local inspector wanted a few crown stays replaced because of necking. He was within his rights to demand they be changed, because it would be his name on the certificate. We changed about 12, as I recall. The necked stays looked worse than they actually were, once observed after removal. There was still plenty of solid metal, so wastage might have been around 5 percent, 10 percent with the very worst one.
In the end, it was a good project, we felt pleased with the results, and the inspector was delighted when we put the final squeeze on the boiler for him, and everything was dry that was supposed to be dry. We saved the removed stays for him to view.
Oh, we removed the old stays by drilling out, then upsized the holes, and used new threaded stays. The threads were cut on a lathe. The stay ends were butted over and sealed using an air tool.

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Thank you Mr. Anderson. That is very educational.