About the new classification NDT methods based on positions of risks and
eguipment life assessment
Professor A.A. Dubov, Dr. V.T. Vlasov
The most important stages of risk and inspection object’s (IO) residual life
assessment process should comprise not only defects detection and determination
of their parameters (flaw detection measurements) but, which is more
detection of local zones of developing damages – stress concentration zones
detection of the most dangerous SCZs, which are the most probable sites of
an object’s failure;
determination of stress-strained (energy) state parameters in the most
determination of actual structural-mechanical characteristics of the
material in SCZs;
evaluation of damage development rate and direction based on the revealed
mechanism of damaging development.
It follows that the main function of non-destructive testing methods is
obtaining of information in the volume required and sufficient for carrying out
life calculations and risks assessment. This implies that a 100% object
inspection is required for guaranteed detection of the most dangerous zones –
SCZs and of developing damages. At present the TC-371 Technical Committee of the
Russian Technical Regulation Body (Rostechregulation) reviews GOST 18353
"Non-destructive testing. Classification of types and methods". Current standard
classification of NDT methods, which was introduced for the field of flaw
detection, has a formal character and distinguishes the entire variety of NDT
methods and means rather by the way of identification of the applied effect than
by the type of physical fields.
Upon classifying of the known NDT and diagnostic methods by the type of
physical fields we obtain the following types:
At the same time such well-known and widely used methods as optic, radiowave,
X-ray, acoustic, holographic, capillary, methods of electrical resistance,
strain gage methods as well as moiré, net, photoelasticity and other methods did
not disappear. They occupied their places within these five types.
It is principally important to classify in the new GOST the NDT methods by: active - with creation in the inspected object’s material of a
"forced" physical field with specified orientation, and passive using proper physical fields reflecting the internal energy of the inspection
The following NDT methods may be referred to passive ones:
acoustic emission method;
metal magnetic memory method (contact and non-invasive);
thermal method (contact and non-invasive).
Active NDT methods include all other methods listed in the draft GOST
Classification of NDT methods by active and passive ones creates the
background for objective classification of detected defects by dangerous
(developing) and not dangerous (not developing) ones. The supposed
classification of NDT methods is virtual for the sake of inspection objects
industrial safety assurance at equipment life assessment, reliability and risks
evaluation at operation of various industrial objects.
"Stress control"must be included in the list of NDT types. Various methods
and means of stresses NDT are widely spread in Russia and abroad nowadays.
"Stress control" is included in the list of inspection types for personnel
training in ISO 9712 (2005). The same NDT type is included in the draft EN-473
In 2005 the RSNDTD President V.V. Kluev approved the "System of voluntary
personnel certification in the file of non-destructive testing and diagnostics"
where "Stress control" is included in the list of NDT methods.
At present the topic of "Stress control" is actual both for machine-building
products quality inspection and in operation at equipment life assessment.
Thus, the necessity of "Stress control" inclusion in the list of NDT methods
has become imminent. At the same time classification of certain stress control
methods by the type of physical fields used will correspond to classification of
flaw detection methods.
GOST R 52330-2005 "Non-destructive testing. Stress-strained state tests on
industrial objects and transport. General requirements" was put into effect in
2005 in Russia.
It is known that stress concentration zones (SCZs), occurring due to
manufacturing process defects, working loads or their combinations, are main
sources of equipment damaging.
SCZs may vary from fractions of microns (product’s micro volume) to sizes
comparable to those of the product itself (macro volume).
A SCZ – stress concentration zone – is a local zone of a product, in which
large strain occurred compared to the average strain across the entire product’s
For new machine-building products SCZs are determined by structural
inhomogeneity and manufacturing technology.
Presence of SCZs both on new and used products sufficiently reduces their
life. Therefore inspection of products’ stress-strained state and SCZ detection
using non-destructive means is an important national economic task.
This Standard specifies general requirements to application of methods and
means of industrial objects’ and transport’s stress-strained state
non-destructive testing at machine-building products, equipment and structures
The Standard covers products and equipment manufactured of steel and alloys,
cast iron and other structural materials without limitations by size and
thickness including welded joints.
Energodiagnostika Co. Ltd. specialists first prepared the new National
Standard on the above-indicated theme, and it has no analogues in Russia and
abroad. This Standard was presented by the Russian delegation as a draft ISO
International Standard at the Annual Assembly of the International Institute of
Welding in Quebec (Canada).
At present a large arsenal of methods and means for materials’ SSS
diagnostics has been accumulated in Russia and other countries. However till
date there are no standard specimens, programs and centers for specialists
straining in non-destructive testing of equipment and structures’ SSS for
objective comparison of these methods and means application effectiveness.
Unfortunately, currently the theoretical basis is insufficiently developed as
well for objective comparison of SSS inspection methods effectiveness and
determination of boundary conditions and scope of their application.
A uniform theoretical basis developed based on modern scientific achievements
in the field of fracture mechanics, material engineering, solid-state physics
may become a basis for resolution of contradictions occurring nowadays at
practical implementation of various methods and means of materials’ SSS
Based on many years’ experimental and theoretical investigations, the authors
made an attempt of developing such a uniform theoretical basis for comparison.
The Proceedings of the 4th International Scientific-Technical
Conference"Equipment and Structures Diagnostics Using the Magnetic Memory of
Metal" (February 14-16, 2007, Moscow) contain one fragment of investigations
carried out in the form of an article by Vlasov V.T. and Dubov A.A. "Physical
criteria of structures materials’ and elements’ stress-strained state
A Program for specialists training in "Stress-strained state inspection" was
developed in 2006 on the initiative of the Scientific-Training Center "Quality"
with involvement of DIGAZ Co. Ltd. and STC DIATECH Co. Ltd. specialists.
Energodiagnostika Co. Ltd. experts were actively involved in the discussion and
approval of this Program. Table 1 shows the list of topics, which, to our
opinion, should be included in the Program of specialists training in "SSS
inspection". At present this Program, upon agreement with SIU "RISCOM", was
submitted to Rostechnadzor for consideration.
||Study of the "Provision about the order of technical devices,
equipment and constructions safe operation period prolongation at
hazardous industrial objects" (GD 03-484-02).
||Problems of ageing equipment residual life assessment.
||Analysis of IO state based on technical documentation (operational,
repair, design). Analysis of equipment failures by units and reasons.
||Study of the "Methodical guideline for residual life determination of
potentially dangerous objects under control of Rostechnadzor" (GD
09-102-95). Study of branch GDs on life assessment.
||Study of standards on engineering diagnostics GOST 27.004-85 and
safety GOST 27.002-89.
||Basics of fracture mechanics. Energy criteria.
||GOST R 52330-2005. Non-destructive testing. Stress-strained state
tests on industrial objects and transport. General requirements.
||Methods and instruments for stress-strained state (SSS) inspection.
Theory and practice.
||The procedure of SSS and metal’s mechanical properties inspection
methods and flaw detection methods application at life assessment.
||Drawing up of expert conclusions at equipment life assessment.
||Laboratory classes. Sitting for a practical examination in methods of
SSS inspection, mechanical properties investigation and flaw detection