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ASTM A791 / ASME SA791 / Welded Unannealde Ferritic Stainless Steel Tubing supplier & distributor in India

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ASTM A 791-88 / ASME SA 791 

WELDED UNANNEALED FERRITIC STAINLESS STEEL TUBING
1 

This standard is issued under the fixed designation A 791; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript epsilon ( ε) indicates an editorial change since the last revision or reapproval.

1. Scope

1.1 This specification covers welded, unannealed, ferritic stainless steel tubing intended for high-temperature and corrosive serice where post-weld heat treatment is not necessary for corrosion resistance. These grades are com-monly known as the "straight-chromium" types and are characterized by being ferromagnetic. The high-chromium, ferritic alloys are sensitive to notch-brittleness on slow cooling to ordinary temperatures. These features should be recognized in the use of thest materials.The user requiring additional testing or examination is referred to the Supple-mentary Requirements or Ordering Information Section, or both. Users requiring a tubular product with post-weld heat treatment are referred to Specification A 2668 /A 268M.

1.2 The values stated in either inch-pound units or SI units are to be regarded separately as standard. Within the text, the SI units are shown in brackets. The values stated in each system are not exact equivalents; theerfore, each system must be used independently of the other. Combining values from the two systems may result in nonconformance with the specification. The inch-pound units shall apply unless the "M" designation of this specification is specified in the order.

NOTE 1-For tubing smaller than 1/2 in. [12.7 mm] in outside diameter, the elongation values given for strip specimens in Table 1 shall apply. Mechanical property requirements do not apply to tubing smaller than 1/8 in. [3.2 mm]in outside diameter or with walls thinner than 0.015 in.[0.4mm].




Chemical composition

Grade Mfg. Process Chemical composition(%)
C Si Mn P S Ni Cr Mo Others
TP409 E, W 0.08Max 1.00Max 1.0Max 0.045Max 0.045Max 0.50Max 10.50~11.75 - Ti 6C~0.75
TP439 E, W 0.07Max 1.00Max 1.00Max 0.040Max 0.030Max 0.50Max 17.00~19.00 N 0.04Max Al 0.15Max Ti 0.20+ 4(C+N)~1.10
TPXM-27 E, W 0.01Max 0.40Max 0.40Max 0.02Max 0.02Max 0.50Max 25.0~27.0 0.75~1.50 Cu 0.2Max N 0.015Max
TPXM-33 E, W 0.06Max 0.75Max 0.75Max 0.040Max 0.020Max 0.50Max 25.0~27.0 Mo 0.75~1.50 Ti 7(C+N) 0.20Min 1.00Max Cu 0.20Max N 0.040Max
25-4-4 E, W 0.025Max 0.75Max 0.75Max 0.040Max 0.030Max 3.5~4.5 24.5~26.0 3.5~4.2 N 0.035Max Ti+Cb 0.2+4(C+N)~0.080
26-3-3 E, W 0.030Max 1.00Max 1.00Max 0.040Max 0.030Max 1.0~3.50 25.0~28.0 3.0~3.50 N 0.040Max Ti+Cb=6(C+N) 0.20Min 1.00Max
29-4 E, W 0.010Max 0.20Max 0.30Max 0.025Max 0.15Max 28.0~30.0 3.5~4.2 - Cu 0.15Max N 0.020Max
29-4-2 E, W 0.010Max 0.20Max 0.30Max 0.025Max 0.20Max 2.0~2.5 28.0~30.0 3.5~4.2 Cu 0.15Max N 0.020Max
18-2 E, W 0.030Max 1.00Max 1.00Max 0.040Max 1.00Max 1.00Max 28.0~30.0 3.60~4.20 N 0.045Max (Ti+Cb)=6(C+N) 0.20Min 1.00Max
29-4C E, W 1.00Max 1.00Max 1.00Max 0.040Max 1.00Max 1.00Max 17.5~2.50 1.75~2.50 N 0.035Max (Ti+Cb)=6(C+N) 0.20Min 1.00Max




Mechanical Properties 


Grade   Tensile Test MPa or N/mm2 Remaks (Similar to JIS) Possibility Temperature
Min Yield point Tensile Strength
TP409 205 380 for High Temperature Service -
TP439 205 415 -
TPXM-27 275 450 -
TPXM-33 310 415 -
25-4-4 515 620 -
26-3-3 450 585 -
29-4 415 550 -
29-4-2 415 550 -
18-2 240 415 -
29-4C 415 515 -



2. Referenced Documents 

2.1 ASTM Standards : A 268/A 268M Specification for Seamless and Welded Ferritic and Martensitic Stainless Steel Tubing for General Service2

A 450/A 450M Specification for General Requirements for Carbon, Ferritic Alloy, and Austenitic Alloy Steel Tubes2
A 700 Practices for Packaging, Marking, and Loading Methods for Steel Products for Domestic Shipment3
A 763 Practices for Detecting Susceptibility to Intergranular Attack in Ferritic Stainless Steels4 

--------------------------------------

1This specification is under the jurisiction of ASTM Committee A-1 on Steel, Stainless Steel, and Prlated Alloys and is the direct responsibility of Subcommittee A01.10 on Pipe. Current edition approved July 15, 1991, Published September 1991. 

Originally published as A790-81. Last previous edition A791/A 791M-90 2Annual Book of ASTM Standards, Vol 01.01. 3Annual Book of ASTM Standards, Vol 01.05. 4Annual Book of ASTM Standards, Vol 01.03.





TABLE 1 Tensile Requirements 

Grade UNS
Designation
Tensile
Strength, min,
ksi [MPa]
Yield Strength,
min, ksi [MPa]
ElongationA in
2 in. or 50mm
min, %
TP 409 S40900 55[380] 30[205] 20
TP 439 S40335 60[415] 30[205] 20
TP XM-27 S44627 65[450] 40[275] 18
TP XM-33 S44626 68[410] 45[310] 20
25-4-4 S44635 90[620] 75[515] 12
26-3-3 S44660 85[585] 65[450] 20
29-4 S44700 80[550] 60[415] 20
29-4-2 S44800 80[550] 60[415] 20
18-2 S44400 60[415] 35[240] 20
29-4C S44735 75[515] 60[415] 12



AFor longitudinal strip tests, a deduction of 0.60% for 29-4C, 0.90% for TPXM-27 and 1.00% for all other grades shall be made
from the basic minimum elongation for each 1/32 in. [0.8mm] decrease in wall thickness below 5/18 in.[8mm]. The following 
table gives the computed minimum values : 

Wall Thickness in. mm Elongation in 2 in. or 50mm, min, %
29-4C TP XM-27 All other Grades
5/16[0.312] 8 12 18 20
9/32[0.281] 7.2 11 17 19
1/4[0.250] 6.4 11 16 18
7/32[0.219] 5.6 10 15 17
3/16[0.188] 4.8 10 14 16
5/32[0.156] 4 9 13 15
1/8[0.125] 3.2 8 13 14
3/32[0.332] 2.4 8 12 13
1/16[0.062] 1.6 7 11 12
0.062 to 0.035, excl 1.6 to 0.9 7 10 12
0.035 to 0.222, excl 0.9 to 0.6 7 10 11
0.022 to 0.015, excl 0.6 to 0.4 6 10 11




NOTE - The above taaable gives the computed minimum elongation values for each 1/32 in.[0.8mm] decrease in 
wall thickness. Where the wall thickness lies between two values shown above, the minimum elongation value 
shall be determined by the following equation : B Grade 29-4C E = 19.2t +6.00 [E = 0.75t + 6.00]
Grade TP XM-27 E = 28.8t + 9.00 [E = 1.13t + 9.00]

All Other Grades E = 32t + 10.00 [E = 12.5t +10.00] where : E = elongation in 2 in. or 50mm, %, and
t = actual thickness of specimens, in.[mm].
BCalculated elongation requirements shall be rounded to the nearest whole number. 



TABLE 2 Chemical Requirements
 

UNSS
Grade
S40900
TP 409
S40335
TP 439
S44627
TP XM-327
S44626
TP XM-33
S44635
25-4-4
S44660
26-3-3
S44700
29-4
S44800
29-4-2
S44735
29-4C
S44500
18-2
Composition, %
Carbon, max 0.08 0.07 0.01C 0.06 0.025 0.030 0.010 0.010 0.030 0.025
Manganese,max 1.0 1.00 0.40 0.75 1.00 1.00 0.30 0.30 1.00 1.00
Phosphours,max 0.045 0.040 0.02 0.040 0.040 0.040 0.025 0.025 0.040 0.040
Sulfur,max 0.045 0.030 0.020.40 0.020 0.030 0.030 0.020 0.020 0.030 0.030
Siicon,max 1.00 1.00 0.5Dmax 0.75 0.75 1.00 0.20 0.20 1.00 1.00
Nickel 0.50max 0.50max 25.0-27.5 0.50max 3.5-4.5 1.0-3.50 2.0-2.5 2.0-2.5 1.00max 1.00max
Chromium 10.50-11.75 17.00-19.00 0.75-1.50 25.0-27.0 24.5-26.0 25.0-28.0 28.0-30.0 28.0-30.0 28.00-30.00 17.5-19.5
Molybdenum ... ... ... 0.75-1.00 3.5-4.5 3.0-4.0 3.5-4.2 3.5-4.2 3.60-4.20 1.75-2.50
Aluminum ... 0.15max 0.2max ... ... ... ... ... ... ...
Copper ... ... 0.015max 0.20max ... ... 0.15max 0.15max ... ...
Nitrogen ... 0.04max ... 0.040max 0.035max 0.040max 0.020maxB 0.020maxc 0.045max 0.035max
Titanium 6 x C min;
0.75
max
0.20+4(C+N) min;
1.10max
7X(C+N)
but no
less than
0.20min
1.00max
(Ti+Cb)=
0.20+4
(C+N)
min;0.80
max
(Ti+Cb)=
6 X(C+N)
but no
less than
0.20min
1.00max
(Ti+Cb)=
6 X(C+N)
but no
less than
0.20min
1.00max
(Ti+Cb)=
0.20+4
(C+N)
min;0.80
max
Columbium ... ... 0.05-0.20 ... ... ... ... ... ... ...



ANew designation established in accordance with ASTM E 527 and SAE J1086, Practice for Numbering Metals and 
Alloys (UNS). BCarbon plus nitrogen = 0.025max. CFor small diameter or thin walls, or both, tubing, where many 
drawing passes are required, a carbon maximum of 0.015% is necessary. Small outside diameter tubes are defined 
as those less than 0.500 in. [12.7mm] in outside diameter and light wall tubes as those less than 0.049 in.[1.2mm] 
in everage wall thickness (0.040 in. [1mm]. DNickel plus copper. 


TABLE 3 Hardness Requirements

Grade Brinell Hardness, max Rockwell Hardness,
B Scale, max
TP 409 207 95
TP 439 207 95
TP XM-27 241 100
TP XM-33 241 100
25-4-4 ... 30
26-3-3 265 25A
29-4 241 100
29-4-2 241 100
18-2 217 95
29-4C ... 25A



ARockwell hardness, C scale. NOTE 2 - For product analysis and flange requirements, the term lot applies to all tubes, 
prior to cutting, of the same nominal size and wall thickness that are produced from the same heat of steel. 
The number of tubes of the same size and from the same heat in a lot shall be determined from the size of the tubes as
prescribed in Table 4. NOTE 3 - For tensile and hardness test requirements, the term lot applies to all tubes,
prior to cutting, of the saaa8.1 The material shal conform to the tensile properties prescribed in Table 2.   



TABLE4 Number of Tubes in a Lot

Size of Tube Size of Lot
2 in.[50.8mm] and over in outside diameter and 0.200 in. [5.1mm] and over in wall thickness not more than 50 tubes
Less than 2 in. [50.8mm] but over 1 in.[25.4mm] in outside diameter and under 0.200 in.
[5.1mm] in wall thickness
not more than 75 tubes
1 in.[25.4mm] or less in outside diameters not more than 125 tubes



10.2 The permissible variatioins in outside diameter given in Table 5 are not sufficient to provide for ovality in thin-walled tubes,
as defined in the Table. In such tubes, the maximum and minimum diameters at any cross section shall deviate from the 
nominal diameter by no more than twice the permissible variation in outside diameter given in Table 5; however, the mean 
diameter at that cross section must still be within the given permissible variation.   



TABLE 5 Permissible Variations in Dimensions
 

Group Size, Outside 
Dianmeter,
in. [mm]
Permissible Variations
in Outside Diameter,
in.[mm]
Permissible
Variations
in Wall
Thickness, %
Permissible Variations
in Cut Lneght, 
in.[mm]A
Thin Walled TubesC
1 Up to 1/2[12.7], excl ±0.0055 [0.13] ±15 1/8 [3] 0 ...
2 1/2 to 1 1/2[12.7 to 38.1], excl ±0.0005 [0.13] ±10 1/8 [3] 0 less than 0.065 in.
[1.6mm] nominal
3 1 1/2 to 3 1/2[38.1 to 88.9], excl ±0.0010 [0.25] ±10 3/16 [5] 0 less than 0.095in.
[2.4mm] nominal
4 3 1/2 to 5 1/2[88.9 to 139.7], excl ±0.0015 [0.38] ±10? 3/16 [5] 0 less than 0.150 in.
[3.8mm] nominal
5 5 1/2 to 8[139.7 to 203.2], incl ±0.0030 [0.76] ±10 3/16 [5] 0 less than 0.150 in.
[3.8mm] nominal



AThese tolerances apply to cut lengths up to and including 24 ft [7.3m]. For lengths over 24 ft [7.3m] andn additional over 
tolerance of 1/8 in.[3mm] for each 10 ft [3.0m] or fraction thereof shall be permissible up to a maximum of 1/2 in.[3mm]. 

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