What Is Tensile Testing?
Tensile testing pulls a standardized specimen to failure in a universal testing machine, measuring the material\u0027s yield strength, ultimate tensile strength (UTS), elongation, and reduction of area. These mechanical properties determine whether a pipe, fitting, flange, or weld meets the requirements of ASTM, API, or EN material specifications.
Tensile testing is performed at the mill on every heat/lot and on weld procedure qualification specimens per ASME Section IX. The results are reported on mill test certificates and are the primary evidence that the delivered material meets its specification.
What Tensile Testing Measures
| Property | Symbol | Definition | Unit |
|---|---|---|---|
| Yield strength | Ys (Rp0.2 or Rt0.5) | Stress at which permanent deformation begins (0.2% offset or 0.5% total extension) | MPa / ksi |
| Ultimate tensile strength | UTS (Rm) | Maximum stress before necking begins | MPa / ksi |
| Elongation | El (A) | Percentage increase in gauge length at fracture | % |
| Reduction of area | RA (Z) | Percentage decrease in cross-sectional area at fracture | % |
Yield strength governs allowable stress calculations in ASME B31.3 and ASME Section VIII. UTS is the primary acceptance criterion on mill test certificates. Elongation and reduction of area indicate ductility.
Specimen Types
| Specimen | Standard | Shape | Application |
|---|---|---|---|
| Round bar (standard) | ASTM E8, 12.5 mm dia, 50 mm gauge | Cylindrical, machined from pipe wall | Mill testing of pipe, plate, forging |
| Round bar (sub-size) | ASTM E8, 6.25 mm or 8.75 mm dia | Cylindrical, for thin-wall products | Thin-wall tubes, small fittings |
| Flat (strip) | ASTM E8, rectangular cross-section | Flat strip cut from pipe/plate | Welded pipe (transverse to weld), sheet |
| Full-section | ASTM E8, full pipe cross-section | Entire pipe wall as specimen | Small-diameter pipe (NPS 1 and below) |
| Transverse weld | ASME IX QW-150 | Specimen across the weld | WPS qualification: weld must exceed base metal UTS |
Tensile Requirements for Common Piping Materials
| Material | Specification | Min Yield (MPa) | Min UTS (MPa) | Min Elongation (%) |
|---|---|---|---|---|
| CS seamless pipe | ASTM A106 Gr. B | 240 | 415 | 30 (longitudinal) |
| CS welded pipe | ASTM A53 Gr. B | 240 | 415 | 30 |
| CS plate | ASTM A516 Gr. 70 | 260 | 485 | 17 (transverse) |
| CS forging | ASTM A105 | 250 | 485 | 22 |
| LT pipe | ASTM A333 Gr. 6 | 240 | 415 | 30 |
| SS pipe | ASTM A312 TP316L | 170 | 485 | 35 |
| Duplex pipe | ASTM A790 S31803 | 450 | 620 | 25 |
| API line pipe | API 5L Gr. X65 PSL2 | 450 | 535 | 18 (transverse) |
| Alloy pipe | ASTM A335 P11 | 205 | 415 | 30 |
Test Temperature
Standard tensile tests are performed at room temperature (10-35 degrees C per ASTM E8). Elevated-temperature tensile tests per ASTM E21 are required for design above ~370 degrees C or when the code specifies allowable stresses at operating temperature. The purchase order or pipe class must specify if elevated-temperature testing is needed.
Weld Tensile Testing (ASME IX)
For welding procedure qualification (WPS/PQR), transverse tensile specimens are tested per ASME Section IX QW-150:
| Requirement | Criterion |
|---|---|
| Number of specimens | 2 (one from each side for pipe) |
| Failure location | Must break in base metal or weld at a stress equal to or greater than the minimum specified UTS of the base material |
| Acceptance | UTS of specimen >= minimum UTS of the weaker base metal |
| Weld reinforcement | May be removed flush or left in place (per QW-150) |
If the specimen breaks in the weld below the base metal UTS, the procedure fails qualification and the WPS parameters must be revised.
Tensile test results are documented on material certificates (EN 10204 3.1/3.2) and weld procedure qualification records reviewed during pipe inspections.
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