Tensile Testing of Ductile Iron Gravity Sewer Pipe to ASTM A746
Acceptance tensile testing of ductile iron pipe to ASTM A746 requires machined round specimens with shouldered ends — commonly referred to as dumbbell, dogbone, or button-end specimens. These shouldered ends are used for gripping the specimen securely during the tensile test.
Modern ASTM A746 testing must be performed at specific stress rates under servo control, and requires an extensometer for accurate calculation of 0.2% offset yield strength and ultimate tensile strength. Older testing techniques such as manual pacing or drop-of-beam observation are no longer suitable for meeting contemporary accuracy and traceability requirements — particularly given that ductile iron pipe products are destined for underground installation where failure has serious consequences.
Testing System
For tensile testing of standard 0.505-inch and 0.750-inch diameter shouldered-end specimens, as well as the smaller specimen sizes specified in ASTM A746, the maximum load requirement is approximately 30,000 lbf (133 kN). Instron recommends the 5980 Series floor model universal testing system for this application. Built for precision and durability, the 5980 Series is an electromechanical testing system with force capacity up to 600 kN — providing ample capacity for all ASTM A746 specimen sizes. Load measurement accuracy to ±0.5% of reading down to 1/1000 of load cell capacity ensures the precise stress rate control required by the standard.
The large test space of the 5980 Series floor model makes specimen installation straightforward for operators, reducing setup time and improving workflow efficiency.
Gripping and Alignment
Split insert tensile grips and holders designed specifically for ductile iron shouldered-end specimens are used in conjunction with the 5980 Series frame. These grips offer two important safety and productivity advantages:
- Quick specimen changeover — the split sleeve design allows specimens to be loaded and removed rapidly between tests
- Specimen containment at failure — the holders contain the ends of the broken specimen at the point of failure, providing an additional level of operator safety during high-energy fracture events
Universal Spherical Tension Adapters (USTA) connect the tensile grips to the load frame and provide the specimen self-alignment needed during loading. This ensures the testing system easily meets the alignment requirements of ASTM E8, which governs tensile testing of metallic materials.
Software
Bluehill® Universal provides the control parameters and calculation algorithms required to satisfy both ASTM E8 and ASTM A746. The software manages servo-controlled stress rate testing, automatically calculates 0.2% offset yield strength and ultimate tensile strength, and provides a straightforward test setup process to support efficient, repeatable testing operations.
Talk to an Instron Expert
Whether you are setting up a new ductile iron pipe testing program or modernizing an existing one, Instron has the systems, grips, and software to meet the requirements of ASTM A746 and ASTM E8.
Contact Sales to discuss your ductile iron testing requirements with our team.