Welding of B7 bolts 1

[starfarooq]

During a recent activity on one of our equipment, one of its head bolt M100 X 4 broke in the middle. The bolt one side is in the tapped hole of the channel head , whereas nut is applied on the other side. We had a spare bolt, so cut the spare bolt from the length where the bolt stuck in the channel heads broken,made a V-joint and welded with 8018 B2 electrode. Please note that the equipment has total 26 bolts. Proper PWHT was done after welding (applicable to P11 material, as the B7 composition is nearest to it). Is it safe procedure?

 

[MikeHalloran]

Safe for what?

At least provide a drawing.


Mike Halloran
Pembroke Pines, FL, USA

 

[btrueblood]

Bit late to ask that question now, isn't it? I'd say it's not likely a safe procedure, as you have no real idea of the material condition of the original bolt (strain history, heat treatment history), and whether the welding and subsequent HT caused any loss of strength. Put it this way, I have two bolts to sell you, one with a weld in the middle, and one without - which would you prefer?

 

[Screwman1]

My first question would be why the first bolt broke? You need to eliminate that problem or the same thing is going to happen with this cobbled together repair that you have attempted. I would never sanction welding a broken bolt as a repair method, there are way to many variables that are not controlled.

 

[SnTMan]

If you are welding the two to remove the broken stud, hey, great.

If not, no.

Regards,

Mike

 

[miningman]

Methinks that some of these responses are a bit harsh. Certainly if the usage is say hi presure steam lines, perhaps there is a significant risk but this reminds me of an occurrence earlier in my career. The main shaft of a dodge reduction gear box sheared in half , and took out the oil seals. This was at a remote site, a replacement box was at least 10 days away. I asked my mechanics to weld up the shaft and fill the box with grease rather than oil. They all predicted that this was a waste of time, wouldn't last, was a really foolish endevour etc etc. They should have been correct but six months later the replacement was box was gatherring dust on the warehouse shelf while we waited for the box to fail so we would have an excuse to take the machine out of service for half a day.


Dont be too quick to criticize "on the spot repairs" if you dont know all the circumstances.

 

[starfarooq]

Sorry for not posting the sketch of t he bolt along with my question. Here it is attached. I look forward to the valuable comments.

 

[MikeHalloran]

Well, now I understand why you couldn't phone Grainger for a replacement stud.
... but you had one on hand. I guess you couldn't remove the damaged one?

It's an odd assembly, in that the female thread of the housing or whatever is not very deep, so maybe the working pressure is not super high. ... but you haven't given us a clue about that.

The flange closure plate (retained by all those studs) is also a bit odd, in that one edge, adjacent what might be a gasket face, is chamfered so far that the stud shanks are exposed. ... which may be why the stud threads were damaged, e.g. by corrosion or by impact of something falling on the flange.

Whether it's safe for continued operation, well that's not what we do here, and even if it were, nobody here has enough information to answer a question like that.


Mike Halloran
Pembroke Pines, FL, USA

 

[desertfox]

Hi starfarooq

Well I don't think its a good idea, but as someone calculated the strength of the weld in tension?
Once the stud is loaded via the nut, the weld needs to transfer the tensile load to the female threads and in addition are the studs subject to cyclic loading?
What caused the stud to fail in the first place?

desertfox

 

[SnTMan]

Let me back up a bit...

If you are assured of the weld properties and quality, and they then meet the required strength, you should be OK.

If not, no. Welding B7 (or any high-strength fastener material) is generally a bad idea.

Regards,

Mike

 

[Guest102023]

As a welding engineer - I don't like it.
As a failure analyst, including numerous fractured fasteners - I especially don't like it.
How straight is that 'new' bolt?

 

[starfarooq]

The straighness was ensured by making a pin on upper piece of bolt and hole in the lower (both at exactly the centerline of the bolt) The pin was inserted in the hole. With the help of straight edge the alignment was checked before welding and found perfect. This is illustrated in figure

 

[Guest102023]

Warning - my AVG detected a problem when opening that last file.
The picture did not illuminate anything for me.

 

[starfarooq]

I have changed format from png to jpg . Hope AVG will not show any problem this time

 

[metengr]

Hope you have enough design margin to accommodate a weld region. If so, and you followed all necessary precautions it will probably hold.

By the way, why ask such an obvious question? You did what you needed to do. Except if I was the client I would make you jump through so many hoops - weld mock-up and demonstration test for procedure qualification and NDT is required.