Tolerance of Stainless Steel Tube & Pipe

Outside diameter (OD), wall thickness and length are three basic parameters in the process of manufacture and distribution for stainless steel tube & pipe, and these parameters have been standardized.

The outer diameter and wall thickness are particularly important, they are not only the basic support for meeting the design requirements of various types of applications such as strength, stiffness and fluid delivery but also have a decisive influence on the subsequent processing, therefore, standards for stainless steel tube & pipe diameter and wall thickness of the manufacturing accuracy (tolerance) should be standardized.

European Standard

European stainless steel tube & pipe standards specify 4 classes outer diameter and wall thickness in percentage or absolute value based on nominal dimension.

Generally, larger diameter or heavy wall thickness stainless steel pipe use percentage, and small diameter or thin wall thickness stainless steel tube use absolute value.

Standard	Manufacturing Process & Type	Outer Diameter Tolerance		Wall Thickness Tolerance	Others
		OD (Mm)	Class
EN10216-5	Hot Finished Seamless Tube	219.1～610	D1	+22.5%T，-15%T	T/D≤0.05
				T1	T/D≤0.09
				T2	T/D>0.09
		30～219.1	D2	T1
				T2
	Cold Finished Seamless Tubes	≤219.1	D3	T3
			D4	T4	Agreement
EN10297-2	Hot Finished Seamless Tube		D1	T1
			D2	T2	Agreement
	Cold Finished Seamless Tubes		D3	T3
			D4	T4	Agreement
EN10217-7	Welded Tubes	>168.3	D2	T3
		≤168.3	D3	T3
			D4	T3	Agreement
EN10296-2	Welded Tubes	>168.3	D2	T3
		≤168.3	D3	T3
		≤114.3	D4	T3	Agreement
EN10312	Welded Tubes	Series 1	D4	T3	T=0.6～2 Mm
		Series 2	D3 – D4	T3 – T4	T=1～3 Mm

From D1 to D4 class for outer diameter, and T1 to T4 for wall thickness tolerance comply with DIN EN ISO 1127 standard, stainless steel tubes – Dimensions, tolerances and conventional masses per unit length.

Outside Diameter		Wall Thickness
Class	Tolerance	Class	Tolerance
D1	±1.5%, Or ±0.75 Mm Min.	T1	±15%, Or ±0.6 Mm Min.
D2	±1.0%, Or ±0.5 Mm Min.	T2	±12.5%, Or ±0.4 Mm Min.
D3	±0.75%, Or. ±0.3 Mm Min.	T3	±10%, Or ±0.2 Mm Min.
D4	±0.50%, Or ±0.1 Mm Min.	T4	±7.5%, Or ±0.15 Mm Min.
		T5	+/- 5.0 %, Or +/- 0.10 Mm Min.

The tolerances on outside diameter and thickness from the above table, greater value shall be selected.

EN 10312 has specific values in Table Series 1 and Series 2.

America Standard

American standard has two standard rules to specify outside diameter and thickness, ASTM A999 / A999M and A1016 / A1016M.

ASTM A999	ASTM A1016
ASTM A312 / A312M ASTM A376 / A376M ASTM A409 / A409M ASTM A778 ASTM A790 / A790M ASTM A813 / A813M ASTM A814 / A814M ASTM A928 / A928M	ASTM A213 / A213M ASTM A249 / A249M ASTM A268 / A268M ASTM A269 ASTM A270 ASTM A688 / A688M ASTM A789 / A789M ASTM A803 / A803M

But A511 for seamless stainless steel mechanical tubing and A554 welded stainless steel mechanical tubing do not conform to the above standards, they have separate outside diameter and thickness tolerances.

Standard	Manufacturing & Delivery Condition	Outside Diameter OD / Mm	OD Tolerance Mm	Thickness T / Mm	T Tolerance Mm
					Minimum	Average
ASTM A1016 A1016M	Hot Drawn Seamless Tubes	<=100	+0.4, -0.8	<=2.4	+0.4t, 0
		100 – 200	+0.4, -1.2	2.4 – 3.8	+0.35t, 0
		200 – 225	+0.4, -1.6	3.8 – 4.6	+0.33t, 0
				>=4.6	+0.28t, 0
	Cold Drawn Seamless Tubes	<25	+0.1, -0.11		+0.20t, 0	+/-0.10t
		25 – 40
		40 – 50	+/-0.2		+0.22t, 0	+/-0.10t
		50 – 65	+/-0.25
		65 – 75	+/-0.3
		75 – 100	+/-0.38
		100 – 200	+/-0.38, -0.04
		200 – 250	+/-0.38, -1.14
	Welded Tubes	40 – 50	+/-0.2		+0.18t, 0	+/-0.10t
		50 – 65	+/-0.25
		65 – 75	+/-0.3
		75 – 100	+/-0.38
		100 – 200	+/-0.38, -0.04
		200 – 250	+/-0.38, -1.14
ASTM A999 / M	Seamless Tubes And Welded Tubes	<48.3	+0.4, -0.8			-0.125t
ASTM A312 / M	Seamless Tubes And Welded Tubes	48.3-114.3	+/-0.8	OD=10.3-73		+0.20 T, -125t
		168.3-219.1	+1.6, -0.8	T/OD<=5% OD=88.9-457.2		+0.225 T, -125t
		219.1-457.2	+2.4, -0.8	T/OD>5% OD=88.9-457.2		+0.15 T, -125t
	Welded Tubes	508-660	+3.2, -0.8	OD>=508		+0.175 T，-0.125 T
		711-864	+4.0, -0.8	T/OD<=5%, OD>=508		+0.225 T，-0.125 T
	Seamless Tubes	914-1209	+4.8, -0.8	T/OD>5%, OD>=508		+0.15 T, -125t
ASTM A409 / M	Welded Tubes		+/-0.2%	T<4.8
			+/-0.4%	T>=4.8
ASTM A358 / M	Welded Tubes		+/-0.50%
ASTM A511	Seamless Tubing	<=12.7	+/-0.1			+/-0.15t
		12.7-38.1	+/-0.2			+/-0.10t
		38.1-88.9	+/-0.3
		88.9-139.7	+/-0.4
		139.7-203.1	+/-0.8
		203.1-220	+/-1.1
		220-325	+/-1.6

American standard outside diameter tolerance is mainly used to represent the absolute value, over and below tolerances are often asymmetric, SS tube and pipe in American standard average tolerance can reach even higher than D4 class in EN ISO 1127 standard.

Wall thickness tolerance should be +/-10%t or better, and average thickness tolerance should be ( +/-20 – 22%t, 0 ), pipeline pipe has a larger tolerance, hot finished seamless pipe largest.

China Standards

China has more quantity standards compared to European standards, but less than American standards,
SS tube and pipe standards are similar to EU standards in the system and absorb favorable experience in USA specifications.

Specification	Manufacturing	O.D(Mm)	O.D Tolerance	W.T(Mm)	W.T Tolerance
GB13296	Cold Rolled Seamless Pipe	6~30	±0.15/-0.2	1~3	+20%	-0%
		＞30~50	±0.3	＞3	+22%	-0%
		＞50	±0.75%	Also Average Wall
GB/T14976	Cold Rolled Seamless Tube	6~10	±0.15	1~3	+12.5%	-12.5%
		10~30	±0.2	＞3	+12.5%	-10%
		30~50	±0.3	Average Wall, +22%
		＞50	±0.8%

Standard Comparison

Stainless steel tube & pipe wall thickness tolerance are the same as the general accuracy of American ASTM / ASME and EU standards, but slightly lower than the high requirements of the EU standards.

Stainless steel tube & pipe outer diameter tolerances are mostly lower than American standards, and approaching the EU standards. it is more reasonable that the American standard specifies the OD tolerance is tight, compared to thickness tolerance.

China GB standards and EU standards have no weight tolerance specified, seamless tube & pipe in GB standard delivery goods as actual weight or theoretical weight, welded tube & pipe as theoretical weight or actual weight.

Out Of Roundness

Out of roundness, sometimes referred to as ovality is tube or pipe on the same cross-section of the outer diameter, roundness or ovality is the difference between the maximum and minimum dimensions of the outside diameter, and is carefully measured by the high and low points at any one section of the tube or pipe.

Out-of-roundness tolerance should not exceed OD tolerance, that specified in EU standard seamless tube & pipe, OD <=406.4MM welded tube & pipe and t/OD>3% American standard seamless tube, especially for thin thickness tube & pipe.

Eccentricity

Concentricity or eccentricity refers to tube & pipe wall thickness variations, if need a high precision in tube tolerance, or fit into other tubes or parts, which need good concentricity.

Concentricity contains wall thickness tolerance specified in EU standard and just specified in ASTM A1016/M OD≥50 mm and t≥5.6 mm thick wall stainless steel tube the same cross-section thickness varieties.

For seamless tube,

WT_max – WT_min ≤ ±10% (WT_max + WT_min) / 2

For welded tube,

WT_max – WT_min ≤ 5% (WT_max + WT_min) / 2

Straightness

Standard pipes and tubes are supplied straightened to the eye: for special applications, the permissible deviation from the straight line may be agreed upon between the purchaser and tube manufacturer; the maximum permissible deviation from the straight line related to the length of measurement L is to be indicated, e.g. 1mm/1000mm.

For example:

OD Mm ≤	OD Inches ≤	Wall	Straightness Commercial	FT Achievable Mm
15.9	0.625	All Sizes	1 In 600	1 In 2000
25.4	1.00	2% Of OD Or Heavier	1 In 600	1 In 1500
25.4	1.00	Less Than 2% Of OD	1 In 400	1 In 1000