Welding Tips and Tricks

I am in an argument that I need help with. I have been told by a friend who was a nuke tech that in some very critical apllications that a piece may be weled and bolted or riveted as a precaution such as the verticle stabilizer on an aircraft. I agree with this bit I have a guy who says that bolting and/or riveting a welded piece actually weakens the piece. I have no experience to draw on in this aspect.

The vertical stabilizer on an aircraft may well contain welded, bolted, and riveted components, but none are redundancies for the others. Each to it's application.

Steve S

So is bolting or otherwise ever used as a redundancy for a weldment that is absolutely critical or is one or the other only used? In all my years of building scaffold in refineries and power plants I cannot recall seeing anything that would be a backup. Is there such a thing?

exnailpounder wrote:So is bolting or otherwise ever used as a redundancy for a weldment that is absolutely critical or is one or the other only used? In all my years of building scaffold in refineries and power plants I cannot recall seeing anything that would be a backup. Is there such a thing?

On occasion I've been known to purposely design something so that gravity keeps pieces together and the welds just keep stuff from moving.

In other words, designed so a weld is in compression instead of tension when there is a choice.

Or, a piece may be held in containment by other pieces in the case of a failure.

Or, if the bolted connections for an assembly can serve double duty to reinforce, or backup, a welded area, I'll set it up like that.

I know, it's a little paranoid - but what happens after a failure is the kind of stuff that keeps me awake at night.

Some questions:.
Loads : dynamic ,static or a mix, frequency, chemical, temperature, repetitive
You might weaken the piece by drilling for fastener but depending on attachment do you weaken the application.
Bolting could generate some stress concentration not left by welding.
Welding might affect base metal properties
What allowance for factor of safety, inspection, cost
Failure consequences, responsibility
Geometry, fit, material, maintenance, life expectancy of part/assembly
sensitivity to uncertainty
Knowing any or all of these items doesn't prove an answer.

I don't know enough to understand and I don't understand all I know about it.

Gene

There is alot of questions about this subject. I am of the belief that drilling something for anchoring removes metal and possibly weakens the piece but welding can and does affect (HAZ) metals properties. The whole discussion came about when discussing a bridge collapse and it just got me wondering if I have ever seen a redundant fixture.

I don't know anything about airplane construction but in the world of structural steel we will use two or more bolts to temporarily hold pieces until the entire joint can be welded and if the bolts aren't in the way of anything they're not always removed.