[标准解读]ASTM A388大型锻件超声检测标准操作方法

问题2：使用底面反射法时候，如何进行检测灵敏度设定及验收标准参考？

答：该标准是美标体系中碳钢锻件的检测方法核心标准，包括了直射波、斜射波技术。该标准对锻件的直射波检测灵敏度、验收标准没有详细说明，看完了标准也不知道怎么检测。实际上该标准必须和A788，S20一起使用，除非设计或者合同有详细的要求。

S20. Ultrasonic Examination

S20.1 Ultrasonic examination of forgings shall be carried

out in accordance with Practice A 388/A 388M.

S20.2 Unless otherwise agreed upon between the manufac￾turer and the purchaser, acceptance levels BR or DA shall be

specified for the longitudinal wave examination and level S for

shear wave examination.

S20.2.1 The back reflection method of tuning shall be used

in accordance with Practice A 388/A 388M.

S20.2.2 In addition to the reportable conditions of the

Recording Section of Practice A 388/A 388M, indications

exceeding the resultant back reflection shall be recorded.

S20.2.3 The following conditions are subject to rejection, or

repair if applicable.

S20.2.3.1 Complete loss of back reflection accompanied by

an indication of a discontinuity. For this purpose, a back

reflection less than 5 % of full screen height shall be consid￾ered complete loss of back reflection.

S20.2.3.2 An indication equal in amplitude to that of the

back reflection established in an indication-free portion of the

forging.

S20.2.4 Reference blocks of acoustically similar metal shall

be used for calibration. Blocks shall meet one of the following

requirements:

S20.2.4.1 A comparison of the back reflections between

equivalent thicknesses of the reference block material and the

actual forging to be tested, without change in instrument

setting shall not show a variation in excess of 25 %.

S20.2.4.2 The reference blocks shall be manufactured from

steel that is similar in chemistry and processing history to the

production forging being tested. The reference blocks shall be

fabricated in accordance with the procedures of Practice E 428.

S20.2.4.3 For test sections up to and including 12 in. (300

nm) thick, the reference blocks shall contain a 1⁄4 in. (6.5 mm)

diameter flat-bottom hole; for over 12 in. (300 mm) up to and

including 18 in. (300 to 455 mm), the hole diameter shall be 3⁄8

in. (9.5 mm); and for over 18 in. (455 mm), it shall be 1⁄2 in.

(13 mm).

S20.2.4.4 A distance-amplitude correction curve shall be

established for the proper grade of steel and specified hole size.

S20.2.4.5 A forging containing one or more indications

equal in amplitude to that of the applicable reference hole,

when properly corrected for distance, is subject to rejection, or

repair if applicable.

S20.2.5 Calibration notches, calibration reference, and

method of scanning shall be in accordance with Practice

A 388/A 388M. Unless otherwise agreed upon, a 60° V-notch

shall be used.

S20.2.6 A forging containing a discontinuity which results

in an indication exceeding the amplitude of the reference line

is subject to rejection.

S20.2.7 The report of the ultrasonic examination shall be in

compliance with Practice A 388/A 388M.

S20.2.8 Additional nondestructive examination or trepanning may be employed to resolve questions of interpretation of

ultrasonic indications. The manufacturer shall accept responsibility for injurious conditions which will not be removed in

final machining.

S21.1 When subcritical heat treatment, applied to a completed forging during subsequent fabrication, may affect the

mechanical properties of the forging, then coupons for the

mechanical testing required by the product specification shall

be given a laboratory heat treatment which simulates the

anticipated subcritical heat treatment.

S21.2 The purchaser shall specify the required heat treatment temperature range, minimum time at temperature, and the

rates of heating and cooling.

S21.3 The required number of test coupons shall be taken

from the forging location described in the product specification.

S21.4 The test specimens shall meet the minimum mechanical test requirements of the product specification, as well as

those of any additional tests agreed upon between producer and

purchaser, after completion of the test coupon heat treatment.

S21.5 The forgings supplied in accordance with this supplementary requirement shall be marked in accordance with

17.1.7.

S21.6 The material test reports shall include the heat treatment of the as delivered material and the results of the

mechanical tests from the test coupons subjected to the

purchaser specified heat treatments which represent fabrication.

S22.1 Bored cylindrical forgings shall be examined from the

bored surface in accordance with Test Method A 939. The

acceptance criteria shall be agreed upon between the purchaser

and the producer.