Brake Pipes

[wally]

Daveg, I still can't follow how you have done this

Quoted from your post
"I have now taken more measurements and have an average outside diameter of 4.74mm"

"therefore the Mean diameter of the internal pipe based on this method is 2.50mm"

"the result concludes that the wall thickness is indeed as measured 1.18mm"

Now, if I take a cross section of a pipe as in your diagram and remove the top 49.9% and then remove the bottom 49.9%
I would be left with two lines with a gap between them, eg - - (but larger).

The length of the two lines and the gap betwen them will without doubt equate to the wall thickness, the internal dia, and the other wall thickness. The total from left to right being the outside diameter. If the outside dia is 4.74 as you measured, and the inside dia is 2.50 as you measured, then the two remaining figures must be 1.12 each.

eg 1.12+2.50+1.12 = 4.74

But, using your calculated figures the lines and gap would be 1.18+2.5+1.18 which equals 4.86 not the 4.74 you measured.

Something does not quite add up (pun intended)

Wally

[drivewasher]

how does a verneer caliper record average dia? Did you take 20 readings then add them all up and then divide by 20?

Personally I think its a brake pipe, Its probably been coiled in a bag so its probably out of round. And it's all pretty irellivant as we can't cut a pipe to asses corrosion.AND the pipes on vehicles that we have to asses corrosion on ARE STEEL thats why they corrode so are probably different dimensions to the copper or kuniffer pipe used to replace them

[Daveg]

Aug 19, 2012 17:32:19 GMT wally said:

Daveg, I still can't follow how you have done this Quoted from your post "I have now taken more measurements and have an average outside diameter of 4.74mm" "therefore the Mean diameter of the internal pipe based on this method is2.50mm" "the result concludes that the wall thickness is indeed as measured 1.18mm" Now, if I take a cross section of a pipe as in your diagram and remove the top 49.9% and then remove the bottom 49.9% I would be left with two lines with a gap between them, eg - - (but larger). The length of the two lines and the gap betwen them will without doubt equate to the wall thickness, the internal dia, and the other wall thickness. The total from left to right being the outside diameter. If the outside dia is 4.74 as you measured, and the inside dia is2.50 as you measured, then the two remaining figures must be 1.12 each. eg 1.12+2.50+1.12 = 4.74 But, using your calculated figures the lines and gap would be 1.18+2.5+1.18 which equals 4.86 not the 4.74 you measured. Something does not quite add up (pun intended) Wally

I don't want to get too bogged down in all this Wally, but there are different understandings going on here between us. The average outside diameter has been calculated by me by taking different readings along the pipe and then using the average of those readings taken. The pipe is not exactly the same diameter at every increment along its length, whether that be because of engineering tolerances or because the pipe has been coiled and un-coiled a few times I don't know.

It's like resistance in a electrical wire that is a mile long, the resistance will be more in some sections than others, so an average is used.

With regards the internal diameter I said I used a drill bit, which measured 02.37mm. I also said that the diameter of the pipe internally was found to be greater than 02.37mm, as I said that this measurement only was accurate at the entry of the pipe, as I said that the drill bit had a leftwards and rightwards swing of 05mm. The mean of this being 02.50mm.

The maths quite accurately calculated 02.47mm, which if truncated is 02.50mm. The vernier caliper did measure the wall thickness at 01.18mm, the maths have established this to be correct.

I am sorry to read that you are struggling to follow the reasoning and I thank you for trying, but you do remind me of what I used to be like many moons ago when I did'nt understand maths.

By example you appear to believe that a circle has two walls for some reason, where if you refer to my diagram of the circle with the blue section painted in it, this is the area of the material of the brake pipe and it is worked out like this;

Area = pi x d^2 / 4 (OUTSIDE) Diameter
Area = pi x d^2 / 4 (INSIDE) Diameter

Outside = pi x22.47 / 4 = 1765
Inside = pi x 6.25 / 4 = 4.909

Annulus = 1765 - 4.909 = 1760.10 mm^2

This result represents the area between the outer diameter and the inner diameter, i.e. the wall thickness but recorded as the area contained within that space. The area does not have two sides to it and in the perfect sense the area would be exactly the same at every mm around the annulus. When you think about dividing by2, this means that you are just taking an average of a reading, it does not mean there are two walls as in this example of a pipe if you could un-rap it out and lay it flat, there would be one flat sheet of metal, which is not a rectangle

Edited to remove justification to text to make it easier to read and add the follow note from Wally's maths above.

Wally wrote;

eg 1.12+2.50+1.12 = 4.74 But, using your calculated figures the lines and gap would be 1.18+2.5+1.18 which equals 4.86 not the 4.74 you measured.

You would have been better to use my measured figures shown here from previously;

OD = 4.74, id = 2.37, wall thickness = 1.18

Not the correct way to do it but in this example it works;

1.185 + 2.37 + 1.185 = 4.74mm

Daveg

[Stealth]

Nothing new occurring here then !!

[wally]

"By example you appear to believe that a circle has two walls for some reason, where if you refer to my diagram of the circle with the blue section painted in it, this is the area of the material of the brake pipe" (which is the wall of the pipe )

No I believe a pipe has two walls and what we are talking about here is the thickness of the walls not the area of it. I was quoting your diagram and was refering to the blue at either side of the id circle. If you had drawn a line through the center from one side to the other, that line would go through the blue wall on the left then through the id circle and then though the other blue wall on the right.

I really would like you to stop changing all the figures Dave.
Every time I ask you to justify the calcs you change the numbers or include averages etc.
First you said. Pipe OD = 4.80, Pipe id = 2.28, wall= 1.18 but these do not add up.
Then you said Pipe OD = 4.74, Pipe id = 2.37 wall = 1.18 mm, now these do add up but they are not the pipe od or id we were talking about and you blaim it on using averages.


Please bear with me here, Just for clarity.

I have a perfect pipe here, no averages needed at all, as it is perfect, measured with lazers.
T
he outside Dia is 4.80, the inside dia is 2,28 hence the walls (the blue sections on the left and right of your diagram) are 1.26.

I know this for certain, gauranteed, 100% correct, without doubt, and I think most folk on this forum will know this beacause

(Od - id) /2 = 1.26

(Wall x 2) + Id = 4.80

Od - (2 x wall) = 2.28

Od radius - id radius = 1.26

1.26 + id radius = od radius

etc etc


Which ever way you work this out it always comes to the right figure.

All I want you to do now is use your formula to prove these same figures and explain to me how to do it. As i can not get the same results.

It is a bit like me saying I am 5ft 8in because that is what I measure from head to foot, but you saying my height is the same as the distance between the center of earth to the centre of the moon less the earths radius less the moons radius less the distance from my head to the moon, but you have to take an average because the moons orbit is not constant.

To me it all appears so complicated and results in an answer that is not as precise, so for something as simple as a brake pipe I can not understand why you even think about using the formulas that you do.

Wally

[Daveg]

Aug 19, 2012 22:14:32 GMT wally said:

"By example you appear to believe that a circle has two walls for some reason, where if you refer to my diagram of the circle with the blue section painted in it, this is the area of the material of the brake pipe" (which is the wall of the pipe ) No I believe a pipe has two walls and what we are talking about here is the thickness of the walls not the area of it. I was quoting your diagram and was refering to the blue at either side of the id circle. If you had drawn a line through the center from one side to the other, that line would go through the blue wall on the left then through the id circle and then though the other blue wall on the right. I really would like you to stop changing all the figures Dave. Every time I ask you to justify the calcs you change the numbers or include averages etc. First you said. Pipe OD = 4.80, Pipe id =2.28, wall= 1.18 but these do not add up. Then you said Pipe OD = 4.74, Pipe id =2.37 wall = 1.18 mm, now these do add up but they are not the pipe od or id we were talking about and you blaim it on using averages. Please bear with me here, Just for clarity. I have a perfect pipe here, no averages needed at all, as it is perfect, measured with lazers. T he outside Dia is 4.80, the inside dia is2,28 hence the walls (the blue sections on the left and right of your diagram) are 1.26. I know this for certain, gauranteed, 100% correct, without doubt, and I think most folk on this forum will know this beacause (Od - id) /2 = 1.26 (Wall x2) + Id = 4.80 Od - (2 x wall) =2.28 Od radius - id radius = 1.26 1.26 + id radius = od radius etc etc Which ever way you work this out it always comes to the right figure. All I want you to do now is use your formula to prove these same figures and explain to me how to do it. As i can not get the same results. It is a bit like me saying I am 5ft 8in because that is what I measure from head to foot, but you saying my height is the same as the distance between the center of earth to the centre of the moon less the earths radius less the moons radius less the distance from my head to the moon, but you have to take an average because the moons orbit is not constant. To me it all appears so complicated and results in an answer that is not as precise, so for something as simple as a brake pipe I can not understand why you even think about using the formulas that you do. Wally

I did in previous posts make it clear that the internal diameter was not accurate, and that later I used a drill bit for better accuracy, but even with that method I advised that the mean of the pipe id was 2.50mm. I also said that I took more measurements along the OD and found that the pipe was not accurate, hence variations and I averaged a reading, 4.74mm.

A pipe no matter how you explain it if drilled correctly will have a hole in the centre and the wall is that part of the pipe at the outer circumference of the inner hole all round it, i.e. 360 degrees. A washer is the same idea, it has a hole in the centre and a wall all round it, one wall and not two walls, or four walls if you start drawing perpendiculars.

The way you would like to conclude the results of the maths in this thread Wally can't work, the measurements I took originally were flawed and not accurate enough, I can't be more honest than that, and further more the results you want to conclude with a wall thickness can't be right in my example because I practically measured the pipe wall thickness and put the picture on the thread, posted again here, clearly showing a thickness of 1.18mm and not 1.26mm as you want to believe.

I believe in an imperfect example I have done the best possible, being honest and using and explaining my methods to work out as near as can be the results of a experimental assessment of a pipe.

In conclusion the accuracy of the measurements are not that exact and open to error, so by the most reliable reading I got, the wall thickness and some average readings I did the best possible, which at best is just a guide.

Daveg

[spotty]

How does the wall thickness of the pipe that was measured (it looks like replacement brake pipe to me), compare to the manufacturers steel brake pipe that we all too often have to assess for corrosion?

[excessive]

My initial point was that it is impossible for us to measure if a brake pipe is corroded by more than a 1/3 - We do not have that ability within the constraints of an mot test.

Yet, the manual clearly states that it has to be corroded by more than a 1/3 before we can fail it.

Think about that for a moment.

I'm the same as you guys, I go with my experience when assessing a brake pipe, but to take the manual on its wording, I do wonder how we would defend ourselves if we had to show how we measured for a 1/3rd of deterioration due to corrosion.

The answer is, we can't.

[David]

Aug 18, 2012 21:20:42 GMT phaetonott said:

You know what? I just look at them and decide pass, P&A or fail.

I tend to be a little harsh (in my opinion) so if they look pretty bad I fail them, The only people who have ever argued are traders, and one of those broke a rear brake pipe on a Fiesta while he was "proving" to me that it was only surface rust.

The responsible customer would rather replace a pipe than kill his family, and if they want to protest to VOSA I'll explain my reasons to them and rely on their common sense.

well said, if it looks bad (excessively corroded) fail it, we all know what a brake pipe in good condition looks like so base your decision on what you see and put the gauges away

[Daveg]

Aug 20, 2012 10:26:33 GMT David said:

Aug 18, 2012 21:20:42 GMT phaetonott said:

You know what? I just look at them and decide pass, P&A or fail.

I tend to be a little harsh (in my opinion) so if they look pretty bad I fail them, The only people who have ever argued are traders, and one of those broke a rear brake pipe on a Fiesta while he was "proving" to me that it was only surface rust.

The responsible customer would rather replace a pipe than kill his family, and if they want to protest to VOSA I'll explain my reasons to them and rely on their common sense.

well said, if it looks bad (excessively corroded) fail it, we all know what a brake pipe in good condition looks like so base your decision on what you see and put the gauges away

David in my opinion that is not a good answer, yes we can't get involved in complicated maths and measurements ;D, but if I failed every brake pipe that looked corroded then my fail rate would be high

Now I know you don't fail every vehicle you test with corroded brake pipes becasue your PR report figures are too low for the average age of vehicles you test, so you like me are passing and or passing and advising, but you are not failing them all ;D

Tomorrow is a new day , I'll get the manufacturer OEM pipe out and do some calc's on it to establish proper conclusions and probably prove that after market pipe is not a good, which I think we already know that ;D

Daveg

[David]

Aug 21, 2012 20:16:14 GMT Daveg said:

Aug 20, 2012 10:26:33 GMT David said:

well said, if it looks bad (excessively corroded) fail it, we all know what a brake pipe in good condition looks like so base your decision on what you see and put the gauges away

David in my opinion that is not a good answer, yes we can't get involved in complicated maths and measurements ;D, but if I failed every brake pipe that looked corroded then my fail rate would be high

Now I know you don't fail every vehicle you test with corroded brake pipes becasue your PR report figures are too low for the average age of vehicles you test, so you like me are passing and or passing and advising, but you are not failing them all ;D

Tomorrow is a new day , I'll get the manufacturer OEM pipe out and do some calc's on it to establish proper conclusions and probably prove that after market pipe is not a good, which I think we already know that ;D

Daveg

I said excessively corroded, not corroded daveg

[Daveg]

Aug 22, 2012 8:07:35 GMT David said:

Aug 21, 2012 20:16:14 GMT Daveg said:

David in my opinion that is not a good answer, yes we can't get involved in complicated maths and measurements ;D, but if I failed every brake pipe that looked corroded then my fail rate would be high

Now I know you don't fail every vehicle you test with corroded brake pipes becasue your PR report figures are too low for the average age of vehicles you test, so you like me are passing and or passing and advising, but you are not failing them all ;D

Tomorrow is a new day , I'll get the manufacturer OEM pipe out and do some calc's on it to establish proper conclusions and probably prove that after market pipe is not a good, which I think we already know that ;D

Daveg

I said excessively corroded, not corroded daveg

I knew what I meant David, which is if every time a brake pipe had what looked like penetrated corrosion into the pipe surface then PR figures would be high for failing them all. I have and no doubt you will have seen many brake pipes that have failed at other garages and then thought in my and your opinion that surface corrosion is a pass and advise, say like in "excessive's" post on here, you would'nt normally fail that pipe would you, but now it has leaked you would say it is excessively corroded.

1mm of surface corrosion on a pipe surface is not excessive corrosion, but 1mm of corrosion that has caused the pipe to leak is now excessive corrosion, if you see my point.

Anyway did a bit of research with a manufacturer OEM brake pipe today. It was a pipe that had been removed from a van being scrapped so was good for the experiment.

The outside diameter of the pipe was measured at 4.70mm, which is a steel pipe with the protective coating removed so allowing an accurate measurement to be taken.

I used a drill bit to measure the internal diameter, the closest fit drill bit I could get in was 3.0mm. Then I tried to move the drill bit laterally I did get very slight movement indicating that the internal diameter of the pipe was slightly more than 3.0mm, but I do mean very slightly, you would never have got a next size drill bit in the pipe.

So I have done some simple maths and accepted that the area of the pipe wall will not reflect a perfect circle.

OD - id = 1.70mm This is based on the measurements taken.

Using maths

17.35 - 7.0686 = 10.28

Sq rt = 3.21mm

So the internal diameter of the brake pipe is 3.21mm mathematically, which based on the diameter of the drill bit of 3.0mm, and slight lateral movement, the mathematical results are in the right order of magnitude.

4.70 - 3.21 = 1.49

1/3 of 1.49 = 0.49

1.49 - 0.49 = 1.0mm

So the OEM pipe is much better than the after market pipe we fit in garages, the original wall thickness is 0.31mm thicker before wear and corrosion occurs, and the OEM pipe is almost as thick as the after market pipe even when it is considered to be excessively corroded, although the after market pipe has the advantage that it does not corrode.

Daveg

[Tom]

Confused.

Outside diameter = 4.70mm
Inside diameter = 3.21mm

Outside - Inside = 4.70 - 3.12
= 1.49mm

This is total thickness of the brake pipe walls across the diameter.
So the wall thickness on each side will be:
1.49 / 2
=0.745mm

This matches the 0.70mm mm thicknesses that others have mentioned early in the thread.

Q How is 0.745mm "Much better than the aftermarket pipe we fit" ?

Seems the same to me.


Me thinks someone is confusing himself & others in the process.


If a brake pipe wall of 0.745mm is corroded by 1/3rd, then it will be around 0.5mm. FAIL.

[Daveg]

I suppose then Tom that the circular brake pipe, which I accept will not be an exact perfect circle but in yours and others ways of thinking you may think differently, but must also have a "roof" and a "floor" then, if it also has two walls, which would be very interesting to me if you could put a picture on the forum of a brake pipe and please correctly identify the two walls in question

Are we talking about a circle here or a rectangle because somebody is confused

Just for the record, a circle with an outside circumference and an inside diameter, which does not meet the outer circumference in this case because there is indeed an area of material in between, which is called the "annulus" I think makes all the difference between what I am talking about and what a text book would show.

I know somebodies are confused but I am pritty sure it is not me.

Daveg

[Tom]

The mot testers manual will fail a brake pipe if it's WALL thickness is reduced by 1/3rd, approx 0.25mm

[Daveg]

Aug 22, 2012 20:26:00 GMT Daveg said:

I suppose then Tom that the circular brake pipe, which I accept will not be an exact perfect circle but in yours and others ways of thinking you may think differently, but must also have a "roof" and a "floor" then, if it also has two walls, which would be very interesting to me if you could put a picture on the forum of a brake pipe and please correctly identify the two walls in question

Are we talking about a circle here or a rectangle because somebody is confused

Just for the record, a circle with an outside circumference and an inside diameter, which does not meet the outer circumference in this case because there is indeed an area of material in between, which is called the "annulus" I think makes all the difference between what I am talking about and what a text book would show.

I know somebodies are confused but I am pritty sure it is not me.

Edited to add the diagrams for visual reference.

Daveg

Attachments:

[drivewasher]

Aug 22, 2012 20:38:10 GMT Daveg said:

Aug 22, 2012 20:26:00 GMT Daveg said:

I suppose then Tom that the circular brake pipe, which I accept will not be an exact perfect circle but in yours and others ways of thinking you may think differently, but must also have a "roof" and a "floor" then, if it also has two walls, which would be very interesting to me if you could put a picture on the forum of a brake pipe and please correctly identify the two walls in question

Are we talking about a circle here or a rectangle because somebody is confused

Just for the record, a circle with an outside circumference and an inside diameter, which does not meet the outer circumference in this case because there is indeed an area of material in between, which is called the "annulus" I think makes all the difference between what I am talking about and what a text book would show.

I know somebodies are confused but I am pritty sure it is not me.

Edited to add the diagrams for visual reference.

Daveg

Daveg

The two arrows show the outside DIAMETER the "circumference" is the distance all the way around the outer edge. The formula to get the circumference of a circle is Pie x D So a 2" dia circle would have a circumference of Pie x D = 6.2822

[drivewasher]

ALSO IIRC a pack of new copper brake pipe has printed on it's specs Nominal Dia, I take it that means it's not EXACT along all it's lenght.

This rusty brake pipe is begging to BORE me now!

[wally]

Aug 22, 2012 20:26:00 GMT Daveg said:

I suppose then Tom that the circular brake pipe, which I accept will not be an exact perfect circle but in yours and others ways of thinking you may think differently, but must also have a "roof" and a "floor" then, if it also has two walls, which would be very interesting to me if you could put a picture on the forum of a brake pipe and please correctly identify the two walls in question

Are we talking about a circle here or a rectangle because somebody is confused

Just for the record, a circle with an outside circumference and an inside diameter, which does not meet the outer circumference in this case because there is indeed an area of material in between, which is called the "annulus" I think makes all the difference between what I am talking about and what a text book would show.

I know somebodies are confused but I am pritty sure it is not me.

Daveg

God Daveg you are a stubborn character

Quote "So the internal diameter of the brake pipe is 3.21mm mathematically, which based on the diameter of the drill bit of 3.0mm, and slight lateral movement, the mathematical results are in the right order of magnitude.

4.70 - 3.21 = 1.49

1/3 of 1.49 = 0.49

1.49 - 0.49 = 1.0mm

So the OEM pipe is much better than the after market pipe we fit in garages, the original wall thickness is 0.31mm thicker before wear and corrosion occurs, and the OEM pipe is almost as thick as the after market pipe even when it is considered to be excessively corroded."

Please study the diagram. Yes, a pipe only has one wall but it goes all the way around the bleeding hole in the center of the pipe doesn't it?

Yet again it is everybody else that is wrong and forum members like Tom are being confused by the order of magnitude or whatever.

Attachments:

[wally]

Who agrees with my last post ?

Wally

Hope I got it right! It's getting late ;D