ASTM A418/A418M-24
Standard Practice for Ultrasonic Examination of Turbine and Generator Steel Rotor Forgings
Standard Practice for Ultrasonic Examination of Turbine and Generator Steel Rotor Forgings
- Статус документа:
- Действующий
- Формат:
- Электронный (PDF)
- Количество страниц:
- 8
- Дата публикации:
- 1 мая 2024 г.
- Издание:
- A418/A418M
- ICS:
- 77.040.20
SIGNIFICANCE AND USE 4.1 This practice shall be used when ultrasonic inspection is required by the order or specification for inspection purposes where the acceptance of the forging is based on limitations of the number, amplitude, or location of discontinuities, or a combination thereof, which give rise to ultrasonic indications. 4.2 The acceptance criteria shall be clearly stated as order requirements. SCOPE 1.1 This practice for ultrasonic examination covers turbine and generator steel rotor forgings covered by Specifications A469/A469M, A470/A470M, A768/A768M, and A940/A940M. This practice shall be used for contact testing only. 1.2 This practice describes a basic procedure of ultrasonically inspecting turbine and generator rotor forgings. It does not restrict the use of other ultrasonic methods such as reference block calibrations when required by the applicable procurement documents nor is it intended to restrict the use of new and improved ultrasonic test equipment and methods as they are developed. 1.3 This practice is intended to provide a means of inspecting cylindrical forgings so that the inspection sensitivity at the forging center line or bore surface is constant, independent of the forging or bore diameter. To this end, inspection sensitivity multiplication factors have been computed from theoretical analysis, with experimental verification. These are plotted in Fig. 1 (bored rotors) and Fig. 2 (solid rotors), for a true inspection frequency of 2.25 MHz, and an acoustic velocity of 2.30 in./s × 105 in./s [5.85 cm/s × 105 cm/s]. Means of converting to other sensitivity levels are provided in Fig. 3. (Sensitivity multiplication factors for other frequencies may be derived in accordance with X1.1 and X1.2 of Appendix X1.) FIG. 1 Bored Forgings Note 1: Sensitivity multiplication factor such that a 10 % indication at the forging bore surface will be equivalent to a 1/8 in. [3 mm] diameter flat bottom hole. Inspection frequency: 2.0 MHz or 2.25 MHz. Material velocity: 2.30 in./s × 105 in./s [5.85 cm/s × 105 cm/s]. FIG. 2 Solid Forgings Note 1: Sensitivity multiplication factor such that a 10 % indication at the forging centerline surface will be equivalent to a 1/8 in. [3 mm] diameter flat bottom hole. Inspection frequency: 2.0 MHz or 2.25 MHz. Material velocity: 2.30 in./s × 105 in./s [5.85 cm/s × 105 cm/s]. FIG. 3 Conversion Factors to Be Used in Conjunction with Fig. 1 and Fig. 2 if a Change in the Reference Reflector Diameter is Required 1.4 Considerable verification data for this method have been generated which indicate that even under controlled conditions very significant uncertainties may exist in estimating natural discontinuities in terms of minimum equivalent size flat-bottom holes. The possibility exists that the estimated minimum areas of natural discontinuities in terms of minimum areas of the comparison flat-bottom holes may differ by 20 dB (factor of 10) in terms of actual areas of natural discontinuities. This magnitude of inaccuracy does not apply to all results but should be recognized as a possibility. Rigid control of the actual frequency used, the coil bandpass width if tuned instruments are used, and so forth, tend to reduce the overall inaccuracy which is apt to develop. 1.5 This practice for inspection applies to solid cylindrical forgings having outer diameters of not less than 2.5 in. [64 mm] nor greater than 100 in. [2540 mm]. It also applies to cylindrical forgings with concentric cylindrical bores having wall thicknesses of 2.5 [64 mm] in. or greater, within the same outer diameter limits as for solid cylinders. For solid sections less than 15 in. [380 mm] in diameter and for bored cylinders of less than 7.5 in. [190 mm] wall thickness the transducer used for the inspection will be different than the transducer used for larger sections. 1.6 Supplementary requirements of an optional nature are provided for use at the option of the...
Abstract
Overview
ASTM A418/A418M-24, Standard Practice for Ultrasonic Examination of Turbine and Generator Steel Rotor Forgings, defines the recommended procedures for ultrasonic testing of steel rotor forgings used in power generation. Developed by ASTM, this standard ensures reliability and quality in critical components by detecting internal discontinuities using ultrasonic methods. Applicable to steel forgings covered by standards A469/A469M, A470/A470M, A768/A768M, and A940/A940M, this practice outlines the use of contact ultrasonic testing for both solid and bored cylindrical rotor forgings.
This standard is intended for use when the acceptance of a forging is dependent on limits concerning the number, amplitude, or location of discontinuities that generate ultrasonic indications. Clear acceptance criteria must be established in the procurement documents. The practice supports consistent examination sensitivity regardless of forging or bore diameter and provides procedures for adjusting inspection techniques and sensitivity as technology advances.
Key Topics
- Scope of Examination: Covers ultrasonic inspection of generator and turbine steel rotor forgings using contact testing only, applying to both solid and bored cylinders with defined dimensional limits.
- Inspection Procedures: Describes step-by-step processes for ultrasonic scanning, including radial and axial testing, transducer selection, scanning speeds, and data recording.
- Sensitivity Calibration: Specifies the use of sensitivity multiplication factors to maintain constant centerline or bore surface inspection sensitivity, detailed for true inspection frequencies of 2.0 MHz and 2.25 MHz, and material acoustic velocities common in steel forgings.
- Equipment and Calibration:
- Requirements for pulse-echo instruments, appropriate frequencies, and qualified and calibrated transducers.
- Mandates regular equipment checks and detailed instrument calibration to ensure repeatable, accurate ultrasonic measurements.
- Reporting: Establishes guidelines for documentation, including mapping and characterizing all significant ultrasonic indications as per defined criteria.
- Personnel Qualifications: Examinations must be performed by personnel qualified and certified per recognized training and certification programs, such as ASNT’s SNT-TC-1A.
- Supplementary Requirements: Optional enhancement of inspection protocols, such as detailed coverage, use of dual element transducers for specific regions, and stricter surface finish requirements, may be invoked by agreement.
Applications
The ASTM A418/A418M-24 standard is essential for:
- Power Generation: Ensuring safety and reliability in steam and gas turbine generators by verifying the integrity of forged steel rotors.
- Steel Manufacturing: Supporting nondestructive quality assurance during production of large cylindrical forgings.
- Procurement and Quality Control: Providing a standardized acceptance practice for suppliers and purchasers in specifying and verifying ultrasonic inspections for rotors.
- Maintenance and Life Assessment: Serving as a reference practice during in-service inspections or evaluations for reuse and refurbishment of turbine or generator rotors.
By applying this standard, organizations can prevent undetected flaws that could lead to catastrophic failures, maintain regulatory compliance, and ensure confidence in the materials used for high-stress rotating machinery.
Related Standards
- ASTM A469/A469M - Vacuum-Treated Steel Forgings for Generator Rotors
- ASTM A470/A470M - Vacuum-Treated Carbon and Alloy Steel Forgings for Turbine Rotors and Shafts
- ASTM A768/A768M - Vacuum-Treated 12% Chromium Alloy Forgings (withdrawn)
- ASTM A940/A940M - Differentially Heat Treated Alloy Forgings (withdrawn)
- ASTM E317 - Evaluating Performance Characteristics of Ultrasonic Testing Instruments
- ASTM E1065/E1065M - Evaluating Characteristics of Ultrasonic Search Units
- ASTM E1316 - Terminology for Nondestructive Examinations
- ASNT SNT-TC-1A - Personnel Qualification and Certification in Nondestructive Testing
Adhering to ASTM A418/A418M-24 ensures best practices in ultrasonic inspection of high-value turbine and generator steel rotor forgings, directly supporting operational safety and product performance in power generation sectors.
Технические детали
- Технический комитет
- A01 - Steel, Stainless Steel and Related Alloys
- SKU
- ASTM A418/A418M-24
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