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Anonymous Poster #1

# Effect of Thickness on Auto Welding

11/21/2017 1:55 AM

Hello everyone,

I am a fresh graduate mechanical engineer and right now I am working at a fabrication company where we do welding and beveling for large pipes. these days we are working with a chines Company SEPCO to fabricate some pipes for them and for the sake of productivity calculation, they said our productivity must be 150" diameter, and they gave us a formula to calculate the actual diameter for pipes with a thickness larger than 8mm.

the formula as follows:

Spool size *(1+(thickness in mm - 8/2)*0.1)

let me give an example: let's say that we have a 56" spool with a thickness of 25.4 mm, according to their equation the actual diameter will be:

56"*(1+(25.4-8/2)*0.1) = 104.72

104.72 is the actual di and it is the one that we will use to calculate productivity.

I tried to ask them about it but they are refusing to give an answer. so I was wondering if could help.

**the beveling degree is 37.5 (it is Auto Welding)

thank you

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#1

### Re: effect of thickness on Auto welding

11/21/2017 3:00 AM
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#2

### Re: effect of thickness on Auto welding

11/21/2017 5:03 AM

I'm not at all sure what you are trying to calculate here. If it is the weld length, just find the circumference of the ellipse --- formula is ∏*√2*((long axis/2)² +(short axis/2)²).

Short axis is pipe outside diameter and you can easily get the long axis from a scaled side elevation of the cut, and in the example given would be about 201 inches if 56"is OD or 209 inches if it's the ID.

You mention a 56" spool. Is that the diameter or the length? - and why would that relate to the diameter? The diameter is normally made to match the other piping or spool pieces, and the length is as needed to fit the available space. I'm not aware of any formula to correlate the two.

As for that formula, I have no idea what it is supposed to do but by my calculation the correct answer using your figures would be 175.84 not 104.72.

Interestingly the circumference of a 56" outside diameter pipe would be 175.93" which is pretty close to what that formula produces.

I may be way off base with my assumptions here so disregard my comments as desired.

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#6

### Re: effect of thickness on Auto welding

11/21/2017 10:26 AM

<...the correct answer...would be 175.84 not 104.72...the circumference of a 56" outside diameter pipe would be 175.93" which is pretty close to what that formula produces...>

So, the formula predicts the length of the weld bead given the circumference of the pipe, which makes sense here. Such information would be of value to a piping fabricator for estimating the time and materials taken to carry out each weld, perhaps?

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#8

### Re: effect of thickness on Auto welding

11/21/2017 10:32 AM

Agree with your figures - but where does the material thickness come into it?

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#11

### Re: effect of thickness on Auto welding

11/21/2017 10:48 AM

That's unclear here, as there is very little welding experience to call upon.

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#26

### Re: effect of thickness on Auto welding

11/22/2017 9:32 AM

Material thickness would define how many weld passes to make the joint, depending entirely, or course on the weld method used (MIG, FCAW, SAW or other) and the size of the electrode used.

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#20

### Re: effect of thickness on Auto welding

11/21/2017 3:35 PM

Except in this instance the weld is not just around the circumference of the pipe at 90° but at an angle to it, hence needing to calculate the circumference of the ellipse at the prescribed angle of 37.5°.

If you just want the circumference of the pipe then ∏D is a much simpler, and more accurate formula - D being outside diameter.

As for JohnDG's query " but where does the material thickness come into it?" Many pipe sizes are specified as inside diameter, but the weld will be on the outside, so 2 x wall thickness must be added to the ID to be able to calculate the weld length, I still don't see that formula doing that.

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#21

### Re: effect of thickness on Auto welding

11/21/2017 3:41 PM

I don't think that is right, the pipe is square ended, but a welding bevel is cut from outside diameter to inside diameter, to allow for metal deposition during weld-up.

This type and size may require several passes, not including any tack-up.

Root pass, filler pass, and cap pass as a minimum, but with this pipe thickness as stated, about 1" thick, I expect multiple filler passes, and the cap pass is a complicated weave.

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#22

### Re: effect of thickness on Auto welding

11/22/2017 3:55 AM

Wrong. Nothing has been said that makes this a miter of the pipe (as for an angular joint) versus an edge bevel for welding joint prep on collinear pipes.

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#23

### Re: effect of thickness on Auto welding

11/22/2017 5:23 AM

Have just reworked the sums, and you get 104.72 by adding some brackets:

Original: 56*(1+(25.4-8/2)*0.1)

Modified: 56*(1+((25.4-8)/2)*0.1)

=56*(1+(17.4/2)*.1)

=56*(1+8.7*0.1)

=56*(1.87) = 104.72

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#24

### Re: effect of thickness on Auto welding

11/22/2017 7:35 AM

Seems like the government on its unemployment numbers... keep fudging the equation until the administration in charge gets reelected.

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#25

### Re: effect of thickness on Auto welding

11/22/2017 9:19 AM

the equation as written did not contain the extra brackets parenthetical or not.

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#27

### Re: effect of thickness on Auto welding

11/22/2017 9:50 AM

Just been messing about: 1+ (25.4 - 8/2)*0.1 = 1+(25.4-4)*0.1 = 1+2.14=3.14

But the formula only gives ≈Π for a wall thickness of 25.4mm !

Looks like a crock of unsavoury stuff to me!

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#31

### Re: effect of thickness on Auto welding

11/22/2017 11:42 AM

yeap!

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#3

### Re: effect of thickness on Auto welding

11/21/2017 7:06 AM

The formula mixes inches and mm.

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#4

### Re: effect of thickness on Auto welding

11/21/2017 8:20 AM

They maybe going off of their WPS (Weld Procedure Specification).

Try asking them if this is their WPS requirement.

56"*(1+(25.4-8/2)*0.1) = 104.72.

while I get 175.84

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#7

### Re: effect of thickness on Auto welding

11/21/2017 10:28 AM

Same here. So, could it be that it's the words in the original posting that are off?

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#9

### Re: effect of thickness on Auto welding

11/21/2017 10:38 AM

Its hard to extrapolate... but this comment;

right now I am working at a fabrication company where we do welding and beveling for large pipes.

It just may be info that was gather through the company's existence. Similar to intellectual property.

just toying with this... but this formula and ignoring the results...

56"*(1+(25.4-8/2)*0.1) = 104.72

Maybe this should have been a constant 25.4-8/2 instead use 6.35 as a constant. But it seems to be a futile task.

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#10

### Re: effect of thickness on Auto welding

11/21/2017 10:47 AM

Good suggestion.

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#5

### Re: effect of thickness on Auto welding

11/21/2017 9:04 AM

Neither the terminology nor the formula nor the process description makes any sense.

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#12

### Re: effect of thickness on Auto welding

11/21/2017 10:50 AM

Give it time. Some of the best brains on the planet are working on it. See #2⇑.

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#33

### Re: effect of thickness on Auto welding

11/22/2017 12:50 PM

That's OK. It's still likely to turn soon and crash land on Mars.

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#13

### Re: Effect of Thickness on Auto Welding

11/21/2017 12:06 PM

It is very obvious to the Chinese, that know how to carry out arithmetic using the order of operations as taught in school, the answer is not 104.72, but it is in fact 175.84"

which is the same as 56" diameter x pi, where pi= 3.14

if you use the true value of pi against 56.000" diameter, you end up with: 175.929"

This is where the 56" represents the outside diameter of the pipe. To figure the volume of metal deposited, is a complicated business, as you must allow for any penetration into I.D. (that might not be allowed??). You also have to know the profile of bead above surface. You may calculate the cone from the 37 degree bevel, according to a formula in your WPS. It is simply done in estimate by assuming the bead is more or less radial section of a circle, and calculation of the area of a 74 degree segment, then integrating it over the circumference. Good luck.

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#14

### Re: Effect of Thickness on Auto Welding

11/21/2017 1:17 PM

Unless you oversold yourself during the interview process, and made claims about your knowledge/experience that were not true, surely there is a person in your organization who can give you advice.

That advice may even come from the production floor itself since someone is responsible for set-up and operation of the welders.

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#15

### Re: Effect of Thickness on Auto Welding

11/21/2017 1:29 PM

The law of linearity in engineering integrity and character, well formulated.

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#16

### Re: Effect of Thickness on Auto Welding

11/21/2017 1:46 PM

had a fresh out of college engineer a friend of owners nephew that he hired.

I was talking to one of the lead fabricators down on the shop floor about an issue... and this green horn butted in. about the tolerances... nothing to do with the issue just a arrogant college grad.

Any ways the lead fabricator said he can take care of it with the Stanley tool... (Tape Measure).

So I picked up on what he was laying down and asked "How's that?"

He said he could split the lines and come to within 0.030" (1/32")

I caught on,... and added "Excellent idea... and if your split your split again, your come to 0.015". He added one more time you'd be down to 0.007"

I glance at the engineer and he was lost... "So I ask, do you know what we're doing here..."

He looked so confused, but he said "yes".

I corrected him and said, "I don't think you do. We're pulling your leg". when he walked away, the lead fabricator told me some of the things this greenhorn of a engineer said to him that was just plain ridicules.

Both of us shook our heads,, and at the same time we said "Kids"... and that was pretty funny.

It took him a while to adjust, but he did end up being a pretty decent engineer, once he got over himself.

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#17

### Re: Effect of Thickness on Auto Welding

11/21/2017 2:15 PM

Stanley has saved a great deal more than just Livingstone. Livingstone, actually never found the head waters of the Nile, but he was onto it. He did far more for that equality of mankind than for geography. He did more to promote abolition of slavery world-wide than any man, far more than Abraham Lincoln, although I do admire Lincoln a great deal, more than Disraeli, although I should dare not heed his words:

" Like all great travellers, I have seen more than I remember, and remember more than I have seen.

There are three kinds of lies: lies, damned lies, and statistics.

The secret of success in life is for a man to be ready for his opportunity when it comes."

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#18

### Re: Effect of Thickness on Auto Welding

11/21/2017 2:39 PM

I didn't know Disraeli made welders. And I didn't know he said this.

The source for this view is the autobiography of Mark Twain, where he makes that attribution. Nevertheless, no version of this quotation has been found in any of Disraeli's published works or letters. An early reference to the expression, which may explain Twain's assertion is found in a speech made by Leonard H. Courtney, (1832-1918), later Lord Courtney, in New York in 1895:

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#19

### Re: Effect of Thickness on Auto Welding

11/21/2017 3:31 PM

I should not dare to eschew his words, that is what I should have said.

Still, we have liars, damned liars, and statisticians.

While the source of that seems more convoluted than a photo-finish at a snake race, the truth seems harder to press out of the pages even than that.

To distill one ounce of truth is better than to supply one's friends with barrels of hogwash!

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#28

### Re: Effect of Thickness on Auto Welding

11/22/2017 9:56 AM

Building on posts #3, 4, 23 and 26...this is a productivity formula, effectively "empirical" so don't get hung up on units. It is about total weld length noting that heavier wall pipe requires more fill passes and capping passes.

What concerns me is the impression that the company imposes an 8mm standard pass, as if one pass will produce 8mm of weld thickness, which depending upon not only the welding process itself but many of the other essential parameters of the WPS is not realistic and could lead to flaws (for example the land prep on the lower bevel for a root pass is only 3mm)...but then again in that region I've come to understand that the corporate philosophy is chase money not quality and use fictitious performance targets to jack your suppliers out of a buck. In any case I am sure that someone with more welding "knowledge" than the OP signed the contract for this work and agreed such rates...

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#29

### Re: Effect of Thickness on Auto Welding

11/22/2017 10:05 AM

What concerns me is the impression that the company imposes an 8mm standard pass, as if one pass will produce 8mm of weld thickness,

if that's the case...I agree. at 8mm that could be at the range that there may be too much weld re-enforcement on the weld that it should/would get rejected by QA. But like the theme of this thread... a lot of members is 'massaging' the posts and formulas to make things work or at the very least trying to understand.

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#34

### Re: Effect of Thickness on Auto Welding

11/22/2017 1:29 PM

Could you please take a look at the picture attached to the following link:

https://ibb.co/ksJYL6

Thank you

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#36

### Re: Effect of Thickness on Auto Welding

11/25/2017 2:48 AM

I think you may have left out a left parenthesis in the OP versus the pictured formula.

The comments involving 3.14 are a special coincidence based on the particular thickness of 25.4 mm. That has been a distraction.

For a V-groove weld (whatever angle of bevel), the amount of weld material required is proportional to the square of pipe thickness (give or take root and crown particulars). The given formula is related instead to pipe thickness only.

That will make it harder for you to achieve quota as the thickness becomes greater. That would be less of a problem if you can do J-groove preparation.

Di or di usually means pipe inside diameter. The diameter-inch unit used here is an invention. Not necessarily bad, but probably not the best, either.

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#37

### Re: Effect of Thickness on Auto Welding

11/27/2017 4:59 PM

I know this is a bit off topic but typically you don't mix metric and SAE dimensions unless you are making a part that requires SAE construction with possibly one or two metric call-outs. however this is a formula where you have to convert in the equation but it doesn't tell you to do that. It assumes you've read the full specification. I actually have to do this on a regular basis as I'm sending in parts to an SAE machine shop but the critical dimensions are called out in metric so they know where to hit the tolerance. Like a call-out for 8 mm equals .314961 inches, when I want 8 mm it's just so much easier and the machinist knows where to concentrate and not on the 9/16" holes that could be plus/minus 1/16". Some of the other posts hit it on the head. This was translated from a language that was not translated well. though I have seen much, much worse on cheap chinese product manuals!

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#30

### Re: Effect of Thickness on Auto Welding

11/22/2017 10:07 AM

To quote the Boss in Cool Hand Luke, "What we (may) have, is failure to communicate!"

You've got a Chinese spec, translated into some other language (guessing it's a country with cheaper labor costs) that is then offered to an English speaking forum by someone whose English may not be the best.

Maybe something is getting lost in the translations?

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#32

### Re: Effect of Thickness on Auto Welding

11/22/2017 12:08 PM

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#35

### Re: Effect of Thickness on Auto Welding

11/22/2017 8:52 PM

A pipe that diameter would probably require a weld on the inside of the pipe as in oil pipelines.

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