Ultrasonic XLERPLATE® Testing Confirms Plate Compliance

Ultrasonic testing is the most common non-destructive group of tests conducted at BHP Steel, and yet it remains more widely used than it is understood, often requested to meet a required standard rather than with a clear idea of its purpose.

For critical applications, ultrasonic testing remains vital to performance. As a practical and effective method of ensuring the structural integrity of the plate for use in critical applications, it continues to be in high demand despite advances in steelmaking technology. In recent years, the introduction of technologies such as continuous casting and improved ladle treatment have reduced the need for ultrasonic testing in less critical applications. Such technologies have led to dramatic improvements in plate quality, in particular the steel "cleanness" which is a measure of the level of inclusions (or impurities) found in the steel.

Continuous casting of slabs, which are rolled into plate, has also virtually eliminated the occurrence of internal lamination type defects in steel plate from BHP Steel. Consequently, the use of ultrasonic testing is largely confined to product required in the fabrication of critical structures, such as some pressure vessels, bridges and plates subjected to through thickness loads.

Ultrasonic testing is typically requested where designers, welding engineers or fabricators require assurance that the internal soundness of plates meets certain prescribed quality levels. In addition to critical structural or pressure vessel applications, this may apply where plates will be used for general engineering work covered by a particular code, standard or in-house requirement.

AS 1710 - 1986

The standard for ultrasonic testing of plate in Australia is AS 1710 - 1986, which applies to plates from 5 mm to 180 mm thick and is closely aligned to the British Standard BS 5996 - 1980. Within the AS 1710 standard there are three levels of testing - Levels 1, 2 and 3 - which apply solely to the body of the plate (as opposed to the edges). The different levels in the Australian Standard AS 1710 relate to the size of inclusions or "internal laminations" in the steel. For Level 1 the allowable size of inclusions is smaller than that for Level 2 and so on.

Levels 1 and 2 are only applicable to plate produced from fully killed steel, and are used for more critical structural and engineering applications. Level 1 requires exacting standards in internal cleanness, and is specified for plates required in the fabrication of the most critical structures.

Level 3, the least stringent level, applies to plate produced from fully killed or semi-killed steel. It is traditionally used in more general structural and engineering applications where some measure of assurance with regard to steel quality is required by the specifier. In practice this level is rarely specified today for BHP Steel plate, due to the range of quality assurance measures in place during the production of plate at BHP Steel.

Where additional assurance is required with respect to the structural integrity of the plate edges, an extra quality level, referred to as "E", may be specified. Testing for Level E involves scanning a band 25mm wide, measured from the trimmed edge, around the entire perimeter of the plate. Customers can optimise savings by ordering specific scans - body scanned only, edge scanned only, or combinations of body plus edge scan to suit their particular requirements.

Details of the discontinuities allowed within the various test standards are shown in the following tables.

The Process

Ultrasonic testing is conducted by sweeping a probe across the surface of the plate. The probe emits ultrasonic waves which reflect off any inclusions (or internal lamination) that may be present in the steel. Reflected waves are captured by the probe, to provide a measure of the size and distribution of inclusions.

The standard specifies the scanning pattern that is to be used for the various levels of testing. All scanning is carried out in the transverse direction (across the plate) at specified intervals. The narrowest intervals are specified for Level 1 testing, with wider spacings for Levels 2 and 3 respectively.

Where ordered, ultrasonic testing is conducted on the plate after the rolling process. In this situation the type and level of ultrasonic testing must be specified at the time of ordering. Orders should include reference to AS 1710 in addition to the quality classification. For example, AS 3678-250 XLERPLATE®/AS 1710-2 (Body scan to level 2 only), or AS3678-250 XLERPLATE®/AS1710-1E (body scan to level 1 plus edge scan). Also, wherever edge testing is required, orders must specify plates in the trimmed edge condition.

Compliance with the specified ultrasonic test standard is indicated by an appropriate endorsement on the material test certificate provided by BHP Steel. Where plates comply with the test standard, but show significant discontinuities, a plan showing the location and classification of the discontinuities in individual plates will be attached to the certificate. In addition, plates are stencilled to show the steel grade and the ultrasonic testing standard, such as "AS3678- 250 XLERPLATE®/AS1710-2E".

Field Testing

Ultrasonic testing can also be conducted in the field where required, as can other forms of non-destructive testing. In particular, ultrasonic testing is commonly used in the fabrication industry to ensure there are no significant disconti-nuities in the weld structure.

BHP Steel employs a team of specialists to carry out non-destructive testing at the Port Kembla steelworks and where required across Australia. The team can offer ultrasonic testing in accordance with a range of overseas test standards. BHP Steel's Non-Destructive Test Laboratories are approved by the National Association for Testing Authorities (NATA), and the service is part of the BHP Steel commitment to providing a quality product to the Australian and New Zealand fabrication and engineering industries. For advice on ultrasonic testing, and the full range of testing services available, Contact Us. 

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