Operating Manual

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Status of CR standards
For CR, standard EN 14784 has been issued with EN 444, EN 584-1 and EN 462-5 in mind
to achieve conformity with film radiography. Part 1 of EN 14784 describes classification of
systems and part 2 describes principles and applications (not including welds). Although a
working group for the compilation of an EN standard for welds exists, the issue of such a
standard would still take several years.
Status of DR standards
Application standards for DR do not exist at all, which hampers the strong potentials of this
method to be used. A first document (ASTM E 2597-07) related to DR hardware has been
issued. It is intended for use by manufacturers of digital detector arrays to quantify the per-
formance of such devices. This is also of importance for those involved in the selection/pur-
chase of systems. This ASTM document includes paragraphs describing the terminology for
specification of the condition of pixels (e.g. dead, noisy, over- or under responding, bad
clusters, etc.), as well as figures on noise, contrast sensitivity, etc.
Impact of standards
Despite the lack of a full range of supporting documents CR and DR are in use for lots of appli-
cations that do not require international standards. Example are e.g. in manufacturing plants
(castings), corrosion detection (profile or on-stream radiography, which is a fast growing
market) and a limited amount of weld inspections based on the ASME or DNV standards
that allow CR and DR. Certainly CR and DR would already have found more applications if
standards would have been available. Regardless of the availability of such documents, if there
is a choice, economics will determine which method is selected for a particular application.
In addition to codes, standards, norms etc. (which permit a certain NDT-technique), plant
owners often compile specifications, which complement codes and standards with their
own requirements. NDT service providers often compile so-called application processes
which describe how to apply a technique in a defined application. Such procedures are often
part of the formal contract between parties and are essential to achieve uniformity. To speed
up the instruction of a new NDT method or technique industry sometimes takes initiatives
through JIP’s (Joint Industry Projects) to develop procedures or recommended practices, in
order to obtain the quality and uniformity of results industry requires. For example HOIS
(an international working group with members active in the offshore industry), is working
on an improved procedure for the application of CR. Such documents indicate the require-
ments for NDT-education (level), CR application training and image interpretation.
The results of such efforts are often (partly or in their entirety) implemented in documents
issued by international standards-issuing organisations.
Standards for weld inspection
No EN standards exist (2008) for weld inspection. However, other standards are formulated
in such a manner that digital radiography can be an alternative.
For example ISO 3183-2007 permits other means as formulated below:
E.4.2.1 The homogeneity of weld seams examined by radiographic methods shall be determined by
means of X-rays directed through the weld material in order to create a suitable image on a radiogra-
phic film or ano
ther X-ray imaging system, provided that the required sensitivity is demonstrated.
Also API 1104 20th edition permits X-ray imaging with other means:
11.1.2.3 Other Imaging Media
As a minimum, the procedure f
or radiography using imaging media other than film shall
include the following details: (....)
A similar formulation is included in DNV OS F101:
Radioscopic testing:
Specific requirements to radiography of installation of girth welds.
213 R
adioscopic testing techniques in accordance with 13068 may be used provided the
equipment has been demonstrated, in accordance with Subsection F, to give sensitivity and
detection equivalent to conventional X-ray according to ISO 12096.
Last but not least ASME V (2007) supports the use of the CR technique for weld inspection
as well. Although no EN-standard for welds exists until yet, an international working group
is involved in its compilation. It is the intention to split existing EN 1435 covering weld
inspection into three parts; respectively for film, CR and DR.
For CR, already many years on the market, not even an (EN) “working document” for weld
inspection exists, so it will take several more years for it to appear.
Data exchange and tamper proof standard
Similar to the medical world, where digital radiography has been in use long before its
introduction in the NDT industry, standards for data recording have been developed. For
industry a standard practice exists (ASTM E 2339-04) to facilitate interoperability (between
systems and third parties) of digital NDT data acquisition and imaging.
This document harmonises image file formats. ASTM E 1475-02 regards DICONDE file
formats. DICONDE is the acronym for D
igital Imaging and COmmunication in Non
D
estructive Evaluation. This document includes a tamper proof file protocol to eliminate
potential concerns. In any case data is recorded in unprocessed format.
16.10 Selection of CR- and DR methods
In radiography, as in other areas of NDT, no one method or technique will serve all situa-
tions of need. There are a number of factors to be considered when evaluating a radiogra-
phic imaging system beginning with the size, shape and the flexibility of the sensor.
Contrast sensitivity or grey scale range (e.g. 8 bit versus 12 bit), and resolution (pixel size)
are major factors in determining the imaging performance and scan rate. All these factors
must be traded off against size, mobility and cost.
In storage on phosphor based imaging plates for computed radiography, the conversion of
radiation into an image is a two-step process. The DR technique, however, immediately
(during exposure or within seconds following exposure) produces an image on the screen of
the workstation (see figure 33-16). This makes DR extremely useful in automated, robotic,
production processes. Although DR, with the correct exposure parameters, offers a higher
relative image quality than CR, flat panel detectors are less suitable for field use and for appli-
cations with difficult access requirements due to their physical size (thickness) and inflexibi-
lity/rigidness. Contrary to DR, CR plates are thin and can be bent to conform with to curva-
ture of the component which sometimes is a condition for certain exposures. Moreover flat
panel detectors require a considerably higher capital investment than the CR method.