Subsize Charpy Specimens and Impact Test Records for Fittings

For EPC engineers, procurement managers, and inspectors reviewing Charpy impact test records for pipe fittings, the first question is not simply "what energy value is acceptable?" The more reliable starting point is: which test method was followed, and which document sets the acceptance criteria? This article focuses on subsize Charpy specimens and the records that accompany them, with practical guidance on what to verify before accepting material.

What ASTM E23 and A370 Cover

ASTM E23, Standard Test Methods for Notched Bar Impact Testing of Metallic Materials, describes the Charpy (simple-beam) test and the Izod (cantilever-beam) test. The standard covers test specimens, test procedures, test reports, test machines, verification of Charpy impact machines, optional test specimen configurations, designation of test specimen orientation, and determination of shear fracture appearance.

ASTM A370, Standard Test Methods and Definitions for Mechanical Testing of Steel Products, contains the procedures and definitions used for mechanical testing of steels, stainless steels, and related alloys. It is designed to determine properties required in product specifications and emphasizes that standard testing methods must be followed to obtain reproducible and comparable results.

Neither standard, by itself, provides the pass/fail acceptance limit for a particular fitting. The test method describes how testing is performed; acceptance criteria must come from the applicable product specification, code, or purchase order. This distinction is easy to forget when reviewing a certificate, but it is the most important point in this discussion.

When Subsize Specimens Appear in Fittings Testing

A full-size Charpy specimen may not always be obtainable from a pipe fitting, especially when wall thickness is limited or the fitting geometry prevents machining a standard specimen. In that situation, a subsize specimen may be proposed. ASTM E23 includes optional test specimen configurations for such cases, but it does not declare that a subsize result is acceptable for every product.

The decision to allow subsize testing, the specific specimen dimensions, the test temperature, the specimen orientation, and the minimum absorbed energy are all matters for the applicable product specification, code, or purchase order. If the order does not clearly permit subsize specimens, a manufacturer cannot simply substitute them and still satisfy the contract. The buyer should confirm the requirement in writing before fabrication begins.

Acceptance Criteria Are Not in the Method Standard

ASTM E23 and ASTM A370 are method standards. They describe how to perform tests, what equipment to use, how to verify machines, and how to report results. They do not state how much energy a fitting must absorb. For example, a product specification might call for a certain minimum impact energy at a given temperature, with specific allowance for subsize specimens in thinner walls. Those values live in the product specification, the project code, or the purchase order.

When reviewing an impact test record, check that the stated acceptance criteria match the document that governs your order. If the certificate only lists "ASTM E23" or "ASTM A370" without a product specification, it is incomplete. You should request the governing specification and confirm that the recorded specimen type and test temperature align with that specification.

Procurement Checks for Subsize Charpy Data

Use these checks when evaluating subsize Charpy data for fittings:

• Confirm that the purchase order identifies the product specification, grade, and edition (for example, the applicable ASTM or ASME product standard, including revision).
• Confirm whether impact testing is mandatory, and if so, the required test temperature and acceptance energy.
• Check whether the specification permits subsize specimens for the ordered wall thickness or fitting size, and which specific specimen configuration is allowed.
• Ask the manufacturer to identify the exact specimen dimensions used, the notch orientation, and the location from which the specimen was removed.
• Verify that the test temperature reported on the record is within the tolerance required by the governing specification.
• Compare the reported energy values against the specification's acceptance criteria, not against a value you assume from the test method.

If the certificate does not show the specimen type or configuration, treat the record as incomplete. Request a corrected certificate or a supplementary statement from the manufacturer.

RFQ Inputs That Protect Your Project

The best time to address subsize Charpy issues is during the RFQ stage. When you send an /en/inquiry, include the following details so suppliers can quote and test correctly:

• Exact product specification, material grade, nominal size, and wall thickness.
• Applicable code or project requirement that mandates impact testing.
• Required test temperature and acceptance energy, or a clear reference to the clause in the product specification.
• Statement on whether subsize specimens are permitted and, if so, under what conditions.
• Required documentation, including the Charpy test record, machine verification record, and any third-party inspection requirements.
• Request that the test record identify the edition of ASTM E23 or A370 used and the specimen configuration.

By putting these items in the RFQ, you reduce the risk of receiving a certificate that shows an energy value but lacks the context needed to judge it.

Inspection and Documentation Points

During inspection, pay attention to the documentation as much as to the numeric results. A compliant impact test record should demonstrate the following:

• The test method used, with the standard and edition stated.
• The specimen type and dimensions, including a clear indication that the specimen is subsize if that is the case.
• The test temperature, shown with the appropriate unit and tolerance.
• The absorbed energy for each specimen, and the average if required.
• The percentage of shear fracture area, if the specification requires it.
• The specimen orientation and location, where required by the product specification.
• The Charpy machine verification record, since E23 includes requirements for verifying test machines.

An independent reviewer should compare every field on the record against the purchase order and the governing specification. Do not rely on the manufacturer's summary alone; open the actual test record and check the values yourself.

Common Risks to Avoid

The most significant risk is applying a universal conversion between full-size and subsize specimen energy. The verified guidance is clear: do not invent a conversion. Energy values from different specimen sizes are not directly interchangeable without specification support. If the product specification does not state a subsize acceptance value, ask the manufacturer for the precise source.

Other risks include:

• Treating ASTM E23 or A370 as acceptance standards instead of method standards.
• Assuming that a subsize Charpy result from one fitting geometry can represent another geometry.
• Accepting a test record that omits the specimen configuration or test temperature.
• Overlooking the governing product specification edition, which may have changed impact testing requirements.
• Allowing the manufacturer to substitute subsize specimens when the purchase order calls for full-size specimens without a documented change order.

For fittings that must meet Charpy requirements, clarity in the specification is the buyer's best protection. Review the product specification before ordering, state the requirements in the /en/products enquiry, and verify the records before release.

Sources

• https://store.astm.org/e0023-24.html
• https://store.astm.org/a0370-26.html