Ultrasonic Examination of Steel Forgings for Fittings and Flanges

Ultrasonic examination of steel forgings is a key volumetric NDT method for detecting internal discontinuities that could compromise forged flanges, fittings, and other pressure-containing components. For EPC engineers and procurement managers, understanding the applicable ASTM practices is essential for specifying the right inspection and avoiding costly misinterpretations.

Why Ultrasonic Examination Matters for Forgings

Forgings can contain internal voids, inclusions, cracks, or lamination-like defects that are not visible on the surface. Ultrasonic examination uses high-frequency sound waves to detect and locate these discontinuities. For critical service components, a volumetric examination is often required by the purchase specification.

The two most referenced ASTM documents in this area are ASTM A388/A388M, Standard Practice for Ultrasonic Examination of Steel Forgings, and ASTM E114, Standard Practice for Ultrasonic Pulse-Echo Straight-Beam Contact Testing. They are complementary: A388/A388M is the product-level practice for steel forgings, while E114 provides the general methodology for straight-beam contact testing.

What ASTM A388/A388M Covers

A388/A388M describes contact, pulse-echo ultrasonic examination of heavy steel forgings using straight-beam and angle-beam techniques. The practice is invoked whenever the inquiry, contract, order, or specification states that forgings are to be examined in accordance with A388/A388M.

The standard requires the ultrasonic instrument to be a pulsed reflection type with linear presentation for at least 75% of the screen height. The apparatus must include an attenuator, search units, transducers, couplants, reference blocks, and DGS scales.

The forging must be prepared to allow the examination:

• Round forgings must be machined to provide cylindrical surfaces for radial examination.
• The ends must be machined perpendicular to the axis for axial examination.
• Disk and rectangular forgings must have faces machined flat and parallel to one another.

These machining requirements directly affect the buyer's RFQ: you cannot simply send a rough forging for ultrasonic testing without confirming that the supplier has machined the appropriate surfaces.

Acceptance Levels Must Be Stated in the Order

A common misconception is that A388/A388M contains a universal acceptance level for all forgings. It does not. The practice states that the ultrasonic quality level shall be clearly stated as order requirements. Acceptance is based on limitations of the number, amplitude, or location of discontinuities that give rise to ultrasonic indications.

This means the buyer or the product specification must define the acceptance criteria. If your purchase order only says "ultrasonic examination per A388/A388M", the supplier has no basis to accept or reject a forging. The RFQ should reference the applicable material specification or an agreed quality level, such as a specific class or severity level defined by the project specification.

Straight-Beam and Angle-Beam Techniques

A388/A388M covers both straight-beam and angle-beam methods. Straight-beam examination uses normal-incident longitudinal waves, as described in ASTM E114. Angle-beam examination is used for rings and hollow forgings to detect discontinuities at other orientations.

The choice of technique depends on the forging geometry and the discontinuities of concern. EPC engineers should specify which technique is required, or require the supplier to demonstrate that the selected technique provides adequate coverage for the part geometry.

Calibration Methods Under A388/A388M

Sensitivity for straight-beam examination is established by one of three methods:

• Reflection technique
• Reference-block technique
• DGS (distance gain-size) method

DGS is described in Appendix X3 of A388/A388M. The calibration method must be defined in the written procedure. Buyers should ask which method will be used, especially when comparing acceptance results across suppliers.

What E114 Adds to Your Procedure

ASTM E114 is the foundational practice for pulse-echo straight-beam contact testing. It uses normal-incident longitudinal waves introduced by direct contact of the search unit with the material. Although not all requirements of E114 can be applied universally to every inspection situation, it provides the basis for establishing contractual criteria between suppliers and purchasers.

E114 identifies the types of information obtainable:

• Apparent discontinuity size by comparing signal amplitudes from the test piece to reference standards
• Depth location of discontinuities by calibrating the horizontal scale of the A-scan display
• Material properties as indicated by relative sound attenuation or velocity changes
• Extent of bond and unbond between two ultrasonic conducting materials

The note that discontinuity size is "apparent" is important. True size depends on orientation, composition, geometry, and equipment limitations. E114 therefore does not give acceptance criteria; it is a procedural basis for developing a detailed procedure.

Procurement Checks and RFQ Inputs

When preparing an RFQ for forged fittings or flanges requiring ultrasonic examination, include:

1. Invoke A388/A388M explicitly if it is required by your project specification.
2. Define the acceptance level in the purchase order. Refer to the material specification or project-specific class.
3. State whether supplementary requirements in A388/A388M apply.
4. Specify the examination stage—for example, after heat treatment and machining.
5. Ask the supplier for a written examination procedure that references A388/A388M and/or E114.
6. Confirm the calibration method (reflection, reference block, or DGS) and how sensitivity is set.
7. Verify the forging surface condition. Rough surfaces or insufficient machining may prevent a valid examination.
8. Clarify whether angle-beam examination is required for rings and hollow forgings.

For a full range of forged flanges and fittings, browse our products at /en/products. To send a detailed RFQ with your inspection requirements, use our inquiry page at /en/inquiry.

Inspection and Documentation Points

During inspection, verify that:

• The instrument meets the linearity requirement: at least 75% of screen height is linear.
• The attenuator, search units, transducers, couplants, reference blocks, and DGS scales are available and correctly used.
• The forging has been machined according to the requirements for radial, axial, or flat/parallel surfaces.
• The written procedure is being followed, including the calibration technique.
• The acceptance criteria in the purchase order are being applied correctly.

Ask for the ultrasonic examination report, including instrument settings, calibration blocks, scan coverage, and indication data. If a third-party inspector is involved, confirm they have the A388/A388M and E114 standards and know which acceptance level applies.

Common Risks and How to Avoid Them

• Missing acceptance criteria: The most frequent problem. Without a defined ultrasonic quality level, the examination is meaningless. Always state the acceptance level in the purchase order.
• Incorrect surface preparation: If the forging is not machined to the required geometry, results may be unreliable or impossible. Confirm surface condition before examination.
• Using only E114 for acceptance: E114 is a procedure practice, not an acceptance standard. Reference the product specification and state acceptance limits.
• Assuming all forgings can be examined the same way: Scanning requirements depend on geometry, heat treatment, and discontinuities. A written procedure must be agreed upon.

Sources

• https://store.astm.org/a0388_a0388m-26.html
• https://store.astm.org/e0114-20.html