What Is Impact Testing?

Quick Answer

Impact testing measures a material\u0027s resistance to sudden fracture under a high-strain-rate load at a specified temperature. The Charpy V-notch (CVN) test is the standard method for piping materials. A notched specimen is struck by a pendulum hammer, and the energy absorbed during fracture is measured in joules (J) or foot-pounds (ft-lbs). Materials that absorb high energy are “tough” (ductile fracture); materials that absorb low energy are “brittle” (cleavage fracture). Impact testing is mandatory for piping operating below the material\u0027s minimum design metal temperature (MDMT) threshold and for sour service per NACE MR0175/ISO 15156.

Charpy V-Notch Test Setup

Parameter	Standard Value
Specimen size	10 x 10 x 55 mm (full size)
Notch type	V-notch, 2 mm deep, 45-degree angle, 0.25 mm root radius
Pendulum energy	300 J (typical machine capacity)
Strike velocity	5.0-5.5 m/s
Temperature	Specified by code or project (e.g., -46 degrees C, -29 degrees C, 0 degrees C)
Number of specimens	3 per test set (average + individual minimums apply)
Standard	ASTM E23 / EN ISO 148-1

Sub-size specimens (7.5 x 10, 5 x 10, or 2.5 x 10 mm) are used when material thickness is insufficient for full-size samples. Acceptance values are reduced proportionally.

Impact Test Requirements by Code

Code/Standard	When Required	Test Temperature	Minimum Energy
ASME B31.3	MDMT below exempt curve (Fig. 323.2.2A) or thickness >25 mm	MDMT or colder	20 J avg / 14 J individual (full size, carbon steel)
ASME Section VIII, Div. 1 (UCS-66)	Based on MDMT exemption curves and thickness	MDMT or colder	Per UG-84: 20 J avg / 14 J individual
ASTM A333 Gr. 6	All heats (mandatory)	-46 degrees C	18 J minimum (single value, full size)
ASTM A350 LF2	All heats (mandatory)	-46 degrees C	20 J avg / 14 J individual
EN 10216-1/2	When specified in order	As specified	Per EN 10216 Table; typically 27 J avg at test temp
NACE MR0175	Sour service materials	Per ASME code	Per ASME code (additional to NACE hardness)

Impact Test Results Interpretation

A typical test report for three Charpy specimens:

Specimen	Absorbed Energy (J)	Lateral Expansion (mm)	Shear Area (%)	Result
1	45	0.89	85	Pass
2	38	0.76	70	Pass
3	42	0.82	80	Pass
Average	41.7	0.82	78	Pass

Acceptance requires both: (1) the average of three specimens meets the minimum, and (2) no single specimen falls below the individual minimum. If one specimen fails, ASME codes allow retesting per defined rules (test three additional specimens; each must exceed the required average).

Common Piping Materials and Impact Properties

Material	Grade	Typical CVN at -46 degrees C	Standard
Carbon steel pipe	ASTM A333 Gr. 6	30-80 J (normalized)	ASTM A333
Carbon steel forging	ASTM A350 LF2	40-100 J (normalized)	ASTM A350
Low-alloy pipe	ASTM A335 P11	30-60 J (at room temp)	ASTM A335
Stainless steel pipe	ASTM A312 TP304L	>100 J (at -196 degrees C)	Exempt from testing per ASME
Duplex stainless	ASTM A790 S31803	45-120 J (at -46 degrees C)	ASTM A790

Austenitic stainless steels (304, 316, 321, 347) are exempt from impact testing under ASME B31.3 and Section VIII because they retain ductility at cryogenic temperatures. Ferritic, martensitic, and duplex grades require testing.

Common Mistake

Ordering ASTM A106 Gr. B pipe for low-temperature service (-29 degrees C or below) without specifying supplementary impact testing. A106 does not mandate CVN testing; the mill will ship material that may be brittle at your design temperature. Specify ASTM A333 Gr. 6 instead—it requires mandatory impact testing at -46 degrees C and is normalized for guaranteed toughness.

Impact test results are reported on mill test certificates (EN 10204 3.1/3.2) and verified during pipe inspections at the manufacturing facility.

Read the full guide to non-destructive testing