SEP 1921 (1984) — Ultrasonic Testing Standard for Steel

German Iron and Steel Association — Steel Committee | December 1984

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Table of Contents

1. Purpose and Nature of the Testing Standard
2. Scope
3. Classification
4. Preparation of Forgings to be Tested
5. Testing System
   • 5.1 Testing Instrument
   • 5.2 Probes
   • 5.3 Verification of the Testing System
   • 5.4 Couplant
6. Execution of Testing
   • 6.1 When to Conduct Testing
   • 6.2 Scope of Testing
   • 6.3 Testing Procedure
   • 6.4 Signals
   • 6.5 Acceptance Levels
   • 6.6 Recording Level
7. Testing Report
8. Information Regarding Evaluation
9. Tables
10. Download Original PDF

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1. Purpose and Nature of the Testing Standard

This standard covers the specification for ultrasonic testing of forgings and steel bar stock for general use (hereinafter referred to as “forgings”). Its primary purpose is to detect internal defects using the pulse-echo (flaw detection) method. Ultrasonic testing provides information regarding the location, size, magnitude, and frequency of reflectors. This standard provides guidance for determining the scope of testing and acceptance levels for forgings (see Section 6.2). It describes testing methods applicable to various testing systems, required testing conditions, the condition of workpieces to be tested, and the classification of test results.

2. Scope

This standard applies to ultrasonic testing of alloy and non-alloy steel forgings of suitable geometry, in the machined or unmachined, untreated or heat-treated condition (see Section 6.1).

For forgings subject to more stringent requirements, the SEP 0000 standard shall be applied.

If this testing method is applied to forgings made from non-transforming steels, sound attenuation and other factors may limit the applicability of the method. In such cases, the achievable recording and acceptance levels must be specified to assess the feasibility of testing. If testing is not feasible, consultation with the purchaser or their representative is required to agree on the next steps.

3. Classification

Forging testing is divided into four test groups based on the scope of testing (see Section 6.2), and five size classes based on the allowable signal magnitude and length (see Sections 6.4 and 6.5, Table 1). Similarly, the allowable signal frequency is further subdivided into five frequency classes (see Section 6.4.3).

4. Preparation of Forgings to be Tested

The forging to be tested shall be supplied as a rough forging with a simple or rotationally symmetric shape (see DIN 54126 Part 1, Chapter 6). The surface used for reflector detection and other surfaces must have a profile and roughness that allows proper coupling of the probe to the forging.

A smooth surface without scale is suitable for testing, provided adequate probe coupling is achieved. Turned surfaces must be machined such that the average roughness index Ra does not exceed 20 μm, in accordance with DIN 4762.

For steels that have not been heat-treated, it must be ensured that the sound attenuation of the workpiece is such that the agreed acceptance level (or recording level) can be detected during testing. Where the steel permits phase transformation, the forging may be heat-treated first to reduce sound attenuation.

5. Testing System

5.1 Testing Instrument

The ultrasonic testing instrument must utilize the pulse-echo flaw detection method and must be capable of measuring echo-peak ratios with an accuracy of ±2 dB using a gain control calibrated in decibels (dB). The amplifier must not exhibit any gain knee or saturation within the sensitivity range of the instrument in use. The adjustment range must be settable such that the maximum permissible deviation from linearity is 25%.

5.2 Probes

The nominal frequency of the probe must be appropriate for the size of the circular reflector being detected, the sound path length, and the sound attenuation of the workpiece. In general, frequencies between 1 and 4 MHz are used for testing. Other frequencies may also be employed provided that the acceptance limit values (as specified in Section 6.5) can be determined.

5.3 Verification of the Testing System

Based on DIN 54126 Part 1, reference block 1 as specified in DIN 54120 must be available for instrument calibration and for monitoring instrument function and probe performance. Reference block 2 as specified in DIN 54122, or other suitable reference blocks with defined reflectors, may also be used.

5.4 Couplant

The working surface must be completely wetted with a couplant. Water (preferably with a thickening agent), machine oil, or gel may be used. The same type of couplant must be used both for establishing the testing system and for all subsequent testing operations. If finished forgings are being tested, the probe must not cause corrosive damage.

6. Execution of Testing

6.1 When to Conduct Testing

Preliminary testing must be conducted as early as possible to determine whether the forging is testable and suitable. Testing should be performed, wherever possible, in the unmachined state of the forging but after heat treatment, since this has a critical influence on material properties.

6.2 Scope of Testing

Depending on the requirements for the forging, testing can be divided into four test groups:

Test Group 1

Using a straight-beam probe, test on the outer surface over the full length, one or more scan paths of width not exceeding 50 mm on the cross-sectional center area.

Test Group 2

For discs with gridded surfaces, using a straight-beam probe on the full surface length or entire periphery, test two or more scan paths of width not exceeding 50 mm. The scan coverage includes the cross-sectional center area and a portion outside the center volume.

Test Group 3

On the accessible outer surface of the forging that covers the maximum volume, test from mutually perpendicular directions using a straight-beam probe. Other types of probes may be used for signal evaluation.

Test Group 4

If special testing requirements exist, test the entire accessible volume. The scope of testing, the types of probes to be used, and the testing and beam directions are usually already agreed between the manufacturer and purchaser or specified by the customer as special requirements.

6.3 Testing Procedure

Testing must comply with DIN 54126 Part 2. The surface of the forging to be tested must be scanned in a manner corresponding to its test group. All instrument systems must first be set up and tested at typical locations to confirm that the forging’s structure can be tested at the selected nominal frequency.

6.4 Signals

6.4.1 Non-Elongated Signals: A non-elongated signal is a reflected echo received when a probe uniformly scans a test area, exhibiting attenuation of the same amplitude in all directions. Its size is expressed by the acceptable circular reflector diameter listed in Table 1.

6.4.2 Elongated Signals: An elongated signal does not exhibit uniform amplitude attenuation in all directions. The elongated length is determined by the half-value method and exceeds the diameter of the acceptable circular reflector.

6.4.3 Signal Frequency: Signal frequency is the number of signals above the recording level within the forging volume or from an agreed zone (see Section 6.5). Table 2 divides the frequency classes into categories a through d.

6.4.4 Back-Wall Echo Attenuation: If an assessable back-wall echo exists (back-wall echo amplitude decreases until it reaches the recording level), the relevant zone must be examined at an alternative testing frequency and with a different beam direction.

6.5 Acceptance Levels

The limit values for signal acceptability must be agreed between the manufacturer and the purchaser, in accordance with the size classes listed in Table 1 and the frequency classes listed in Table 2.

6.6 Recording Level

Unless otherwise agreed, the recording level shall be equal to the corresponding acceptance level (see Table 1). In such cases, the relevant acceptance/recording level must be at least 6 dB. The noise margin for the recording level must also be at least 6 dB.

7. Testing Report

The testing report must include the following information:

• a) Characteristic data of the test piece;
• b) Reference to the testing standard used;
• c) Type of testing instrument and type of probe;
• d) Condition of the test zones;
• e) Couplant used;
• f) Scope of testing for each test group;
• g) Recording limit values and acceptance limit values;
• h) Test results.

Ultrasonic signals exceeding the agreed recording limit values must be described in terms of location, size, extent, and frequency, or illustrated with a scaled diagram of the forging or its cross-section.

8. Information Regarding Evaluation

For testing orders based on this testing standard, agreement must be reached regarding the test group and size class. Where appropriate, the agreement should also include the allowable frequency, recording level, surface condition, and required heat treatment condition.

Tables

Table 1: Size Classes for Acceptable Signal Limit Values

Size Class	Non-Elongated Signal (mm, CR*)	Elongated Signal (mm, CR*)	Max. Elongated Length (mm)
A	14	10	80
B	10	7	60
C	7	5	40
D	5	3	30
E	3	2	30

* CR = Circular Reflector. Size class grading is based on amplitude differences of approximately 6 dB.

Table 2: Frequency Classes

Frequency Class	Non-Elongated Signals	Elongated Signals
a	32	16
b	16	8
c	8	4
d	4	2

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📄 Download Original PDF

Download Original PDF (Chinese Version)

Reference: SEP 1921 (1984) — Ultrasonic Testing of Forgings and Steel Bar Stock. German Iron and Steel Association — Steel Committee.

This page presents an English translation of the original Chinese version for reference purposes. The original German standard remains the authoritative reference.