ASTM A999-23 Permissible Variation in Outside Diameter 1

[SimonRuda]

We have here a discussion about the interpretation of ASTM A99-23 for the permissible Variation in Outside Diameter
We have a welded pipe with NPS of 812,8 mm and a wallthickness of 6 mm
The measurement of the OD (cross-section) is 815 / 810 mm and 814 / 811 mm

According to Table 3 of the active ASTM A999-23 Outside Diameter is 4,0mm for Over and 0.8 mm for under. It is a bit confusing why this might be allowed for a thin wall pipe that the OD is still within tolerance. Can someone give a hint or feedback if the tolerance for this pipe-example is okay. Many thanks for your support.

 

[r6155]

How was the outer diameter measured?
Do not confuse outer diameter with ovality.

Regards

 

[LittleInch]

Sorry, but what does 815/810 and 814/811 actually mean? OD/ ID, variance at different angles?

Does the wall thickness vary?

Pipe spec for OD variance rarely changes with wall thickness

 

[SimonRuda]

Dear Sir,
Measurements were taken at both ends of the pipe, in each case in a crosswise fashion. The diameter was measured as 810 mm in one case and 814 mm in the other. Since this pipe has a relatively thin wall, the question is whether the product is outside the tolerance.
We interpret the standard as meaning that the deviation of the outer diameter may only be -0.8 mm.
The measurements also show that the tube is oval, i.e. no longer perfectly round.

 

[SimonRuda]

Sorry, but what does 815/810 and 814/811 actually mean? OD/ ID, variance at different angles?

Does the wall thickness vary?

Pipe spec for OD variance rarely changes with wall thickness

Cross-Section measurement like a compass. From North to South it is 815 mm OD and from East to West it is 810 mm. NPS is 812,8 mm

 

[r6155]

How was the outer diameter measured?
Do not confuse outer diameter with ovality.

 

[GBTorpenhow]

Need to find the extremes (smallest and largest diameter) in a cross section, not just check 12-6 and 3-9 o'clock. The math is straightforward.

From A999-16:

12. Permissible Variation in Outside Diameter
12.1 Variations in outside diameter, unless otherwise agreed upon, shall not exceed the limits given in Table 1. The tolerances for outside diameter include ovality, except as provided for in 12.2 and 12.2.1. (See Note 2.)
12.2 For thin-wall pipe, defined as pipe having a wall thickness of 3% or less of the specified outside diameter, the diameter tolerance of Table 1 is applicable only to the mean of the extreme (maximum and minimum) outside diameter readings in any one cross-section.
12.2.1 For thin-wall pipe, the difference in extreme outside readings (ovality) in any one cross-section shall not exceed 1.5% of the specified outside diameter.
NOTE 2—Thin-wall pipe usually develops significant ovality (out-of-roundness) during final annealing, straightening, or both. The diameter tolerances given in Table 1 are usually not sufficient to provide for additional ovality expected in thin-wall pipe.

 

[r6155]

OD= take a measurement of the external perimeter and divide by PI.

 

[LittleInch]

Need to find the extremes (smallest and largest diameter) in a cross section, not just check 12-6 and 3-9 o'clock. The math is straightforward.

From A999-16:

that's great information. So 6mm wt is <1% of the OD. Pretty thin alright.

Sounds to me more like you're lucky to get it anywhere near straight and kind of round.

 

[GD2]

that's great information. So 6mm wt is <1% of the OD. Pretty thin alright.

Sounds to me more like you're lucky to get it anywhere near straight and kind of round.

That's correct. It looks OP never opened the Standard A999 and looked into Para 12. GBT had provided all info except Table 1, which is the variance table for OD.
To get it started in a right note, NPS 812,8 mm is not correct. NPS is a unitless number and most likely he means NPS 32. (DN 800 ).