tensile breaking machine for test welds

To be honest the welder's tests that I have actually seen done were at the job site and what was done was the welded tags were clamped in a vice and bent - hammered - into a "U". If the weld broke they failed. On pipe, the only tests we did - only a couple of times - was Xrayed the test samples as we had an xray crew on the site any way.

I've never worked a welding job in the U.S. but overseas the customer or his insurance company had to be satisfied and that was it.

Thanks John

I'm in the UK, BTW. World of ISO's and EN's. More like what a University graduate would produce, rather than the mixed experience and practicality of North American specs. Hence admiration of API1104.

You've reminded me how you go finding weld defects or proving the absence of... I forgot about the side-bend tests. There's also the nick break tests of both fillet welds and butt welds, where the point is to expose if there are defects in a long test-length of weld.

Where the machine needed to do this is a regular general-purpose hydraulic press, applying compression. Planar plattens (no grips needed) and a few rectangular bars for putting samples in 3-point bend using the compression of the press. Plus the press has many other uses on a fabrication site too :-)

My ulterior motive is different. Investigating the real performance of welds. See for myself what the strength is and which welds perform best. Hydraulic pressure would give a sufficiently good estimate of force for this type of test.

The "tensile breaking machine" - in email discussions, agreement is - need for grips means this isn't a device which can be fab'ed out of a pile of plate offcuts in a fab-shop. Need machining and need hardened alloy steel grip jaws.

Regards, Rich Smith

I've never seen the machine but I was in a shop where the lathe operator was turning the tensile test pieces to test steel bar strength. It was simply a round bar with a section turned to a smaller diameter with rounded, radius, shoulders. The butts were full size, maybe two inches, or so and obviously were held in some sort of jaws and probably pulled apart with, as you say, hydraulic pressure.

By the way, we did strength test steel cable slings at Edwards AFB directly. I didn't actually see it but was told that the sling being tested was connected to a large steel plate and lifted by a crane with a large scale attached to the sling and the crane hook. They piled weight on the steel plate to the test weight for the sling.

I got involved when the eye bolt attachments on the corners of the steel plate broke under load. They said it was sort of like being under fire from a machine gun with bits and pieces flying all over :-)

Some sort of dead weight tester could be built. The test piece would probably have to be cut to a very precise width and thickness and then just hoist away :-)

You can hack a cheap, portable, uncalibrated 20,000 Lb pull tester from auto repair equipment and a pressure gauge, and use it to experiment with on-site sample preparation methods such as cutting slices of test welds with a portable bandsaw.

I proof test my home projects with this:

That looks like a nice economical tester with a simple design someone with a good home shop could make. On the other end of the spectrum are the test lab tensile machines such as:

The Instron testers I have seen stretch the precisely machined samples with a pair of large screws which raise or lower the upper crossarm at a controlled rate for tensile or compression, in either case force (from a load cell) versus deflection (from witness marks on the narrow section of the sample) is recorded, as well as reduction in area of the neck of the stretching sample in some cases.

This sort of tester provides more accurate measurements of yield strength, elongation, and ultimate strength than a bend test, but are generally too expensive for use outside R & D or qualifying critical weld materials and processes in high pressure power plant piping and the like.

Hi John

Re your lifting accessories experience

I think you have to be careful of these because, compared to general structural load-to-break tests because

• wire rope has a very high strength and energy stored goes up as a square of the stress reached (??)

• the lifting accessories have a very uniform compliance so local break = general break which could have happened anywhere - so the entire lifting accessory is at high stress - more huge amount of energy and vast amounts of elastic recoil

• the bits are light, so high energy + long length of elastic recoil + light weight = you'd better be under cover.

If you made say a welded frame and overloaded to break there would probably be a dull thump as it suffered a local overload in a stress hotspot, with much of the energy used up tearing the metal anyway.

Videos of wire rope tensile testing to destruction indicate how violent breaks are.

Even with fibre rope, which I am familiar with and it breaking on overload, you need to keep out of line of where it could recoil. It can kill - as you will know... What you describe is way way up the scale.

Anyway - thanks for sharing. Nice start to my morning sharing these thoughts.

Regards, Rich Smith

That is definitely a useful piece of kit for real weld testing and everyone knowing the goal shall be 100% achieved on this job. As it seems to me...

As I see it

These machines test the materials characteristics of a sample of a homogenous uniform single-material.

With a test weld, it's an engineering outcome you are measuring, not a material property. A weld isn't uniform, so a full-thickness and some-length sample is needed to give a representive result. A single part can't tell the whole story.

Force - several times bigger for the full thickness plate.

This machine would be a monster, and I am rightly pointed-out to why such a "mythical" machine remains mythical - because for testing on the pipeline spread, you'd use side-bend and nick-break for weld quality. Both with general-purpose compression hydraulic machines. (OK, that side-bend tester is one-purpose, but that specificness makes it light and carryable, lowering the barrier to doing many quality-control tests)

Rich Smith