Stainless pipes & tubes

What is Nominal Pipe Size and Actual Pipe Size

A. Nominal Pipe size: It is the nominal size specified in the standard such ASME B36.10m, ASME B36.19m, the ideal size that users and manufacturers hope to obtain, and the order size specified in the contract.

B. Actual Pipe size: It is the actual size obtained during the production process, which is often larger or smaller than the nominal size. This phenomenon of being larger or smaller than the nominal size is called deviation.

European Standard

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

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

From D1 to D4 class for outer diameter, and T1 to T4 for wall thickness tolerance comply to 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 above table, greater value shall be selected.

EN 10312 has specific values in table series 1 and series 2.

America Standard

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

ASTM A999	ASTM A1016
ASTM A312 / A12M A358 / A358M A376 / A376M A409 / A409M A778 A790 / A790M A813 / A813M A814 / A814M A928 / A928M	A213 / A213M A249 / A249M A268 / A268M A269 A270 A688 / A688M A789 / A789M A803 / A803M

But A511 for seamless stainless steel mechanical tubing and A554 welded stainless steel mechanical tubing not conform to 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 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 with EU standards in 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 specify the OD tolerance is tight, compared to thickness tolerance.

China GB standards and EU standard 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 difference between the maximum and minimum dimensions of outside diameter, is carefully measured the high and low points at any one section of the tube or pipe.

Eccentricity

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

 

 

Concentricity be contained 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,

WTmax – WTmin ≤ ±10% (WTmax + WTmin) / 2

For welded tube,

WTmax – WTmin ≤ 5% (WTmax + WTmin) / 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 between 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

A. Normal length / Random Length (also called non-fixed-length length): Any stainless steel tube whose length is within the length range specified by the standard and has no fixed length requirement is called normal length. For example, the structural stainless steel pipe standard stipulates: hot-rolled (extruded, expanded) steel pipe 3000mm - 12000mm; cold drawn (rolled) steel pipe 2000mm - 10500mm.

B. Fixed Length: The fixed-length should be within the usual length range, which is a certain fixed-length dimension required in the contract. However, it is impossible to cut out the absolute fixed-length length in actual operation, so the standard stipulates the allowable positive deviation value for the fixed-length length.

Take the structural stainless steel pipe standard as:

The yield rate of production of fixed-length pipes is much lower than that of normal-length pipes, and it is reasonable for manufacturers to request price increases. The rate of price increase varies from company to company. Generally, the price increase is about 10% on the basis of the base price.

C. Length of double ruler: The length of the double ruler should be within the usual length. The contract should indicate the length of the single ruler and the multiples of the total length (for example, 3000mm×3, which is 3 multiples of 3000mm, and the total length is 9000mm). In actual operation, the allowable positive deviation of 20mm should be added to the total length, plus a margin for the incision of each single ruler length. Take the structural pipe as an example, the allowance for cutting is stipulated: 5-10mm for outer diameter ≤159mm; 10-15mm for outer diameter >159mm.

If there is no double-length deviation and cutting allowance in the standard, it should be negotiated by the supplier and the buyer and indicated in the contract. The double-length scale is the same as the fixed-length length, which will bring about a substantial reduction in the yield rate of the manufacturer. Therefore, it is reasonable for the manufacturer to raise the price, and the price increase is basically the same as the fixed-length length.

D. Range length: The range length of the stainless steel pipe is within the usual length range. When the user requires a fixed range length, it must be indicated in the contract.

For example: Usually the length is 3000-12000mm, and the range cut-to-length length is 6000-8000mm or 8000-10000mm.

It can be seen that the range length is looser than the fixed-length and double-length length, but it is much stricter than the usual length, which will also reduce the yield of production enterprises. Therefore, it is reasonable for the manufacturer to raise the price, and the price increase is generally about 4% above the base price.

 

Stainless Steel Density

Stainless steel density refers to substance mass per unit volume, it is one of typical property of stainless steel, commonly, density of stainless steel range from 7600 kg/m3 to 8000 kg/m3.

Stainless steel is a wide used material, containing at least 10.5% of Chromium, and other elements added to form stainless steel structure, these elements have Carbon, Silicon, Manganese, Phosphorus, Sulfur, Nickel, Molybdenum, Titanium and Copper, it is noted as high strength and excellent corrosion resistance.

Densities change depending on these alloy elements changing, different alloy content have different density value, even it is the same grade, it is difficult to calculate accurate density values, theoretic density value is given below for reference.

The following is the comparison of several commonly used stainless steel density, data may not be completely accurate, only for reference.

• Material 201, 202, 301, 302, 304, 304L, 305, 321
• Density 7.93 7.93 7.93 7.93 7.93 7.93 7.93 7.93

Stainless Steel Density Table Chart

Grade	Density ( G / Cm3 )	Density ( Kg / M3 )
201 202 301 302 303 304 304L 304LN 305 321	7.93	7930
309S 310S 316 316L 316Ti 316LN 317 317L 347	7.98	7980
904L	7.98	7980
2205 S31803	7.80	7800
S32750	7.85	7850
403 410 410S 416 431	7.75	7750
440A	7.74	7740
440C	7.62	7620
420	7.73	7730
439 430 430F	7.70	7700
434	7.74	7740
444	7.75	7750
405	7.72	7720

*These densities given at standard conditions for temperature and pressure condition.

304 And 316 Stainless Steel Densities

304 and 316 are the most used stainless steel grades, their densities are not the same, this decide by chemical composition and content, stainless steel 304 density is 7930 kg / m3, 316 density is 7980 kg / m3, so when calculating stainless steel weight, it is different between 304 and 316 stainless steel.

Stainless Steel Density Conversion, Kg/M3, G/Cm3 And Lbs/In3
Density of stainless steel calculated by dividing the mass by the volume, usually measured in g/cm3, kg/m3, and lbs/in3, each unit can be converted to other units.

Conversion: 1 kg/m3 = 0.001 g/cm3 = 1000 g/m3 = 0.000036127292 lbs/in3.

Density Relations With Temperature And Pressure

Densities of stainless steel vary by changing either the temperature or the pressure, in general, increasing the temperature decreases the density, increasing the pressure always increases the density.

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Difference Between Seamless And Welded Tube & Pipe

Seamless and welded are mainly two types stainless steel tube & stainless steel pipe, there is a debate whether seamless is better than welded for a long time.

Although with improved metallurgy and welding processes in welded tubes, the arguments typically focus on structural integrity and corrosion resistance in weld area.

Obviously, seamless and welded tubes & pipes difference is manufacturing process.

There are some cases where paying extra for a different, higher-performing alloy is necessary.

Welded Tube Manufacturing Process

Depending on the outer dimension, wall thickness and final application, there are different ways of manufacturing welded tubes and pipes, and different manufacturing method.

Strip Welded Tubes & Pipes

Welded tube start from stainless steel strip and coil that is passed through grooved rollers till the shape is formed and the free edges are properly shaped for welding, cold forming is performed step by step from flat strip into a round profile, the edges are welded together as they approach the welding rolls.

Typical welding method for strip welded tubes is traditionally autogenous tungsten inert gas (TIG), TIG welding method have some advantages that can effectively protect weld seam.

After welding outside and inside grinding of the weld seam, solution annealing or stress relieving may be necessary by application requirements.

Today, most of the modern welding lines are equipped with inline induction annealing, then straitening and calibration to control dimension of tube & pipe, cut to standard or special lengths, de-burred, NPD & DT testing and inspection should be carried out as standard or requirement.

Heavy Wall Tubes & Pipes

When large outside diameter or heavy wall or both welded tubes & pipes required, there is a different welding method and process, for large diameter and heavy wall pipes, EFW, ERW and other welding methods can be used.

Starting from stainless steel plate or sheet, the forming is done in a roller bending machine or in a hydraulic press, then some steps are same with strip welded tubes.

For testing and inspection, large diameter sizes, radiography test (RT) and hydrostatic test (HT) are often required.

For large diameter welded pipes, double welding method can be accepted.

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Seamless Tube Manufacturing Process

Seamless tubes are generally made in complex steps starting with the drilled hollows from billets, by cold drawing and cold rolling manufacturing process with cold drawing & cold rolling machines.