Who can explain about Thin-wall pipe as per ASTM standard 1

[MujtabaQA]

Can anyone help to explain the following paragraph quoted from ASTM A530 (with example please)?

"Thin-wall pipe usually develops significant ovality

(out-of-roundness) during final annealing, straightening, or

both. The diameter tolerances of Table 2 are not sufficient to

provide for additional ovality expected in thin-wall pipe and

are applicable only to the mean of the extreme (maximum and

minimum) outside diameter readings in any one cross-section.

However, for thin-wall pipe the difference in extreme outside

diameter readings (ovality) in any one cross-section shall not

exceed 1.5 % of the specified outside diameter"?

 

[SWComposites]

Seems pretty clear. What is your specific question?

 

[EdStainless]

There is a similar comment in A1016 (the general spec for SS tube).
That one actually says what they consider thin wall.
These are general specifications, it is possible for product specs to take precedent over these.

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P.E. Metallurgy, consulting work welcomed

 

[MujtabaQA]

It is a bit confusing to me

can you please give one example for a thin wall pipe and calculate the maximum and minimum outer diameter as well as the maximum ovality permitted. So the picture will be clear to me.

 

[Gr8blu]

Mujitaba : Thin wall pipe is just that - the thickness of the material is such that - at larger diameters - it does not have enough strength to support the weight of the cylinder and becomes oval: narrow from top-to-bottom, and wider at the horizontal. This is not just restricted to thin wall pipe by the way - lots of cylindrical objects will show this same result if there is not enough material to maintain the "hoop".

Below are some random numbers - I don't have access to the actual Table in ASTM A530 at the moment. But you should be able to see how things are determined.

The "standard" pipe dimensions if the pipe were truly round, including tolerances.
PIPE OUTSIDE DIA = 100 +0/-2 mm
PIPE INSIDE DIA = 95 +1/-0 mm
MAX WALL THICK = (100+0 - 95-0) = 5 mm
MIN WALL THICKNESS = (100-2 - 95+1) = 2 mm

Now look at actual dimensions for an oval pipe.
PIPE OD (vertical) = 98 mm
PIPE OD (horizontal) = 103 mm
PIPE ID (vertical) = 94 mm
PIPE ID (horizontal) = 97 mm
Ovality for OD = difference between measured actual dims in the two planes, compared to the specified value
Ovality (horiz) = ABS|103 - 100| = 3 mm Ovality (vert) = ABS |98 - 100| = 2 mm
Since one or both of these Outside diameters is more than 1.5% of nominal (i.e., ovality > 1.5, since nominal is 100), then the pipe is out of tolerance according to the standard.

Converting energy to motion for more than half a century

 

[MujtabaQA]

Thank you Dear Gr8blu for your detail answer, it was really good example and helpful.

 

[EdStainless]

Slight correction/clarification
In Gr8blu's example the wall thickness is 2.5mm
The wall tol in this spec is +22.5%/-12.5% (for sizes over 75mm with wall <5% of OD).
So the wall could vary from 2.19-3.06mm.
But a wall of 2.5% is thin enough for this to apply.
The 1.5% allowed in this clause is roughly twice the standard ovality allowance.
The issue isn't 'sag' because of gravity it is just lack of stiffness.
In manufacturing you have to balance straightness and roundness.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed