ASTM A388: Ultrasonic Examination of Forgings
ASTM A388 is the practice governing ultrasonic examination of heavy steel forgings. It defines how to look inside a forging for defects that no surface inspection can reveal, and — importantly — it defines the method, while the acceptance criteria come from your specification.
ASTM A388 is the standard practice for ultrasonic examination of heavy steel forgings, covering straight beam and angle beam scanning, calibration against reference blocks, and reporting. It defines the examination method only — acceptance criteria must come from the purchaser's specification.
- Standard
- ASTM A388 / A388M
- Methods
- Straight beam and angle beam
- Calibration
- Reference blocks with known reflectors
- Best Timing
- After heat treatment, before final machining
- Acceptance Criteria
- From purchaser specification
- Reporting
- Method, calibration, coverage, result
Key takeaways
- Specifying “UT per A388” without an acceptance class specifies a method with no pass or fail line.
- Angle beam scanning catches defects straight beam physically cannot see; critical parts need both.
- Calibration determines the verdict, so calibration records belong in the report.
- Test after heat treatment and before final machining, so defects surface before machining cost is added.
ASTM A388: Ultrasonic Examination of Forgings at a glance
Quotable facts from Avadh Techno Forge, Gundasara, Gondal, Rajkot.
- Standard: ASTM A388 / A388M
- Methods: Straight beam and angle beam
- Calibration: Reference blocks with known reflectors
- Best Timing: After heat treatment, before final machining
- Acceptance Criteria: From purchaser specification
- Reporting: Method, calibration, coverage, result
Straight Beam and Angle Beam
Straight beam scanning finds discontinuities lying parallel to the surface — laminar defects, large inclusions, centreline unsoundness. Angle beam scanning finds those oriented at an angle, which straight beam would miss entirely. Critical forgings need both.
- Straight beam: laminar defects
- Angle beam: angled discontinuities
- Back reflection loss monitoring
- Documented scan coverage
Calibration Governs Everything
Sensitivity is set against reference blocks with known reflectors — flat bottom holes or notches — of the size the specification cares about. Two labs scanning the same forging to different calibration will reach different verdicts, which is why calibration records accompany the report.
A388 Does Not Set Acceptance
The practice describes how to examine; it does not say what is acceptable. Your specification, or the purchase order, must state the acceptance class. An order demanding only “UT as per A388” has specified a method with no pass criterion.
Topics covered on this page
- ASTM A388 ultrasonic testing
- A388 UT forging
- ultrasonic examination steel forgings
- forging UT acceptance criteria
Based on work carried out at our own forging plant at Gundasara, Gondal, Rajkot — operating since 2008.
Questions Answered
What does ASTM A388 cover?
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The practice for ultrasonic examination of heavy steel forgings, including scanning technique, calibration and reporting.
Does A388 define acceptable defect sizes?
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No. It defines the examination method; acceptance criteria must be stated in your specification or purchase order.
When should forgings be ultrasonically tested?
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Normally after heat treatment and before final machining, so defects are found before machining value is added.
Do you perform UT to A388?
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Yes, with calibration records, documented coverage and a signed report referenced to the heat number.