This paper examines leakage and damages of steam and provides an overview of NDT testing in order to determine the cause of steam lines failure in power plants and heating plants. This approach may be applied to similar structures and its application in preventive maintenance would help extend the life of steam pipes

Ljubica Milovic

Srdjan Bulatovic

Vujadin Aleksic

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                                                                   S. Bulatovic et alii, Frattura ed Integrità Strutturale, 26 (2013) 41-48; DOI: 10.3221/IGF-ESIS.26.05  41        Failure of steam line causes determined by NDT testing  in power and heating plants   Srdjan Bulatovic  Yugoslav River Shipping, Belgrade, Serbia srdjan.bulatovic@yahoo.com  Vujadin Aleksic Institute for testing materials-IMS Institute, Bulevar voijvode Mišića 43, Belgrade, Serbia  Ljubica Milovic  Faculty of Technology and Metallurgy, Belgrade, Serbia   ABSTRACT. This paper examines leakage and damages of steam and provides an overview of NDT testing in order to determine the cause of steam lines failure in power plants and heating plants. This approach may be applied to similar structures and its application in preventive maintenance would help extend the life of steam pipes.   KEYWORDS. Steam line; Failure; NDT testing.    INTRODUCTION  team lines and high pressure pipelines are vital parts of the thermal power plant system. In fact, they are the connection between the boiler and turbines in power plants or boilers in power stations and customers in heating plants. They are critical components in power plants and heating plants and have a significant impact on the reliability and availability of power plants and heating plants. Continuous exploitation in very hard working conditions can lead to relatively frequent system steamline failure. Damages on steam line elements may appear well before it is expected, and not just as a result of internal pressure and temperature, but also as a consequence of the loads that occur due to poor design and inadequate maintenance. Also, damage of steam line elements may appear because of numerous on-off switching of the boiler as well as misuse of start diagram. Failures of steam lines, other than direct material damage, could jeopardize the safety of personnel and equipment. Among the causes of these failures inadequate operation and maintenance takes a high rank. Leaking of steam lines caused by material creep is expected if number of hours spent in operation is higher than design number of hours. Fig. 1 shows part of steam line of heated vapor in block 1 on TPP "Kolubara A" - Veliki Crljeni (near Belgrade). The RA, RB and RC line thermal units 1 to 5 span lenghts of 200-300 m and capacities of 300-500 t/h. During its operation there were relatively frequent delays caused by defects of supporting structure [1, 2], and in extreme case even failure or steam line leakage, which is usually explained by gaps in technology development and mishandling.  S  S. Bulatovic et alii, Frattura ed Integrità Strutturale, 26 (2013) 41-48; DOI: 10.3221/IGF-ESIS.26.05                                                                      42     Figure 1: Part of the steam line during NDT.   TECHNICAL DIAGNOSTICS  uring the operation period, fatigue of steam line components may occur. Degradation of material properties and deformation of elements can be accelerated due to the exploitation and repair errors, that's why periodic or continuous diagnostic measurements, conducting periodic tests and data collection programs defined by [1, 2] are needed. In this way, processes that could lead to the creation of system damage are under systematic control, what is also the legal obligation imposed by the regulations, directives and harmonized standards [3 - 5]. Properly conducted technical diagnostics protects parts of the steam line from accident, and also ensures safer conditions for employees as well as rational techno-economic exploitation and maintenance. Technical diagnostic of steam lines must be based on three basic principles:   volume of tests and measurements shall be in accordance with the program of research [1] and an expert knowledge of steam line structure and working conditions;   tests and measurements must be performed in accordance with special procedures, using appropriate equipment and qualified personnel;   test results should be presented in such way that the conclusions include steam line operating conditions, the availability of the test team and staff with appropriate experience and knowledge in the field of design, construction, installation, operation, maintenance, reliability, fracture mechanics and others.   NDT TO DETERMINE CAUSE OF STEAM LINE FAILURE  or purpose of determining the causes of failure it is necessary to make steam line 100% visual inspection, magnetic, penetrant, ultrasonic, hardness and method of replica testing.  If necessary, other tests that would give us a reliable and useful results to determine causes of steam line failure could be done. Fig. 2 shows the possibility of evaluating some damage using NDT methods in the life of the steam line.  Visually optical control (VT) VT is used to detect defects that are visible on the surface of the steam line from the outside or inside of the tube. It applies regardless the method to be applied after it, because it is possible to detect errors, such as in our case, and avoid the use of other, more costly methods of NDT. It is often used for the selection of critical areas of the facility for the application of other NDT testing methods. At the same objects it may be performed multiple times (eg, before and after cleaning, or before and after the execution of corrosion protection, etc.). Control of the inside of the tube (endoscopy) allows optical access to the interior of steam lines. It is performed using an endoscope, and as a result we get control of video or photograph controlled inner surface, Fig. 3.   D F                                                                    S. Bulatovic et alii, Frattura ed Integrità Strutturale, 26 (2013) 41-48; DOI: 10.3221/IGF-ESIS.26.05  43    Figure 2: Application of NDT methods in detecting defects in the life of the steam line [6].    Figure 3: Photo of interior surfaces steamline.  Magnetic particle testing (MT) The method is based on emphasizing the stray magnetic flux caused by the presence of surface or subsurface defects like cracks, notches, inclusions and other types of sharp or planar defects. Advantage of the method is that it requires a moderate cost, and if done correctly, you get a very good sensitivity for the detection of surface defects. The disadvantages of this method is that it could only be appllied to ferromagnetic materials as well as the potential need for degaussing after completing the testing. The method is commonly used for the detection of cracks and other defects in weld joints, castings and forgings.  Ultrasonic testing (UT) The method is based on detecting changes in acoustic resistance due to the presence of cracks, voids, inclusions, and general physical separation in the material. The advantage of the method is that is also applicable to the thicker material, it is excellent for detecting and locating cracks and other defects, and it is suitable for automation. The biggest disadvantages are the need for a medium on the surface to be tested (or complete immersion of testing item in contact medium), as well as the request that surface on which the probe is moving is relatively smooth (ie cleaning needs, grinding the metallic shine). The most common application is to detect and precisely determine the position of defects in plate, welded joints (and butt and fillet) steel castings and forgings (if their geometric configuration allows). Application of this method for testing materials with high attenuation of ultrasound energy (for example, high alloyed austenitic steels, cast bronze ...) is difficult and can be done only under special circumstances.  Hardness testing (HT) For evaluation of properly applied heat treatment after welding, hardness testing of the base metal, HAZ and weld materials are performed. At the same time, hardness and hardness differences must be within the limits of applied materials. In Tab. 1. the recommended values of hardness [7] of materials that are commonly used to produce steam line are shown.  S. Bulatovic et alii, Frattura ed Integrità Strutturale, 26 (2013) 41-48; DOI: 10.3221/IGF-ESIS.26.05                                                                      44   Materials Hardness [HV]Base materials2 Weldjoint Heat Affected Zone (HAZ) 1.5415 15 Mo3  140-190  260  320 1.7335 13CrMo44  135-185  270  320 1.7380 10CrMo910  140-190  280  320 1.7715 14MoV63  145-190  280  320 1.7745 15CrMoV510  140-215  280  320 1.4922 X20CrMoV12-1  215-265  300  3501 1 Hardness value of 350 HV must not be exceeded in the HAZ 2 For cold-rolled sections such as tube bends in the base material greater hardness for HV 60 are allowed. HB  0.95HV; M  1/3HB  Table 1  Method of replica testing (REP) Metallographic examination, Fig. 4, the surface layer of material of pipe bends, weld joints and pipes on the old steam pipe RA 10 block A1, is conducted by the method of nondestructive testing of materials, using metallographic replica, according to [8].   Figure 4: Overview of possible damage to the established method of replica [9].  In order to detect the microstructure of materials, adequate preparation is made  of tested surfaces, and that included cleaning and a range of fine sanding operations. After the final polishing and cleaning, the test surfaces were eroded with appropriate reagent, ie. 4% nital.   DETERMINING DAMAGES  tructures of the steam line is exposed to the low cycle fatigue loads. This load caused a fatigue damage of pipes and leakage of steam lines on observed object, Fig. 5, which was confirmed by visual inspection. After that, NDT methods are used for testing the steam pipeline section and supporting structure before and after damage. Fig. 6 and 7 show the measurement of control and testing methods, NDT, and in Tab. 2 and 3 the results of measurements of diameter and wall thickness of the damaged part of the steam line are listed.  S                                                                    S. Bulatovic et alii, Frattura ed Integrità Strutturale, 26 (2013) 41-48; DOI: 10.3221/IGF-ESIS.26.05  45     Figure 5: Determination of damage by visual inspection.    Figure 6: Scheme of measurement tests (dimensional inspection of the damaged steam line part).    Figure 7: Scheme of measuring and making replicas of the damaged steam line part RA-10.   S. Bulatovic et alii, Frattura ed Integrità Strutturale, 26 (2013) 41-48; DOI: 10.3221/IGF-ESIS.26.05                                                                      46   Part of the tube  Diameters (mm) Plane measurements  A  B  C  D  E Axis measurements 0º-180º  288.9 276.8 285.0 285.9 283.1 Axis measurements 90º-270º  282.4 284.0 285.1 284.3 283.4  Table 2   Part of the tube  Wall thickness (mm) Plane measurements  A  B C D E Remark Designation of measuring point 0º  21.2  20.1 (R3)  22.4 22.4 22.9  23.2 (A-R1) 90º  24.3 24.7 25.6 25.8 25.5  24.7 (A-R2) 180º 27.0 27.3 27.0 27.9 27.1 / 270º 24.2 23.3 23.1 23.9 23.7 / R - place where replicas are taken  Table 3  Assessment of the microstructure of the materials that are used for tube bends and welded joints and creep damage level are made according to the recommendations for the assessment of the microstructure [10]. The degree of quality degradation of the microstructure of the old pipe was determined according to the recommendations of the European Commission for assess the remaining life of the microstructure [11]. Fig. 8 and 9 show the typical microstructure of the surface layer of the old pipe taken from a replica in accordance with the drawing in Fig. 7.      Figure 8: Replica RA10-R1. Assessment of the microstructure [11]: Level B / Level C: Initial spheroidization and carbide precipitation per grain boundary in places with the presence of globular pearlite. 4% nital. Figure 9: Replica RA10-R3. Macro cracks. Assessment of the microstructure [10]: 5; Assessment of the microstructure [11]: Level B / Level C: Initial spheroidization and carbide precipitation per grain boundary in places with the presence of globular pearlite. 4% nital. In microstructure of tested replica taken from the surface of the material of the old pipe, a certain degree of quality degradation was observed wich is caused by initial spheroidization and carbide precipitation per grain boundary in places with the presence of globular pearlite- the level of quality degradation of microstructure B / C, according to [11]. Products of corrosion and corrosion damage in spots are present in the microstructure of tested replica.                                                                     S. Bulatovic et alii, Frattura ed Integrità Strutturale, 26 (2013) 41-48; DOI: 10.3221/IGF-ESIS.26.05  47   ANALYSIS OF DAMAGE  he damaged parts of steam line were analyzed, to determine the cause of the problem, which is a process that requires a systematic approach. Test results of NDT methods contribute to the knowledge of damage formation and allow us to determine the cause of steam line failure. Based on the research of failure and causes of failure of certain components of steam line using method FMEA and reliability parameters obtained from the analysis of the data collected in real operating conditions, a system of continuous diagnosis could be established. Stress analysis [12,13,14], damage and fractures [15,16] of welded joints of steam line elements provide important directives for the development of design methods and construction elements of the steam line to improve the properties of existing materials and their processing technologies. Also, by analyzing fractures, the development of new technical solutions and methods of testing is enabled [17] in the prototype stage. It is necessary to take into account the risk analysis and structural integrity [18,19], as a new approach to the assessment of structural integrity.   THE DATABASE INFORMATION  oad data, the characteristics of the base material and its welded joints, technology development, technical and physical characteristics reported fractures data and preventive measures provided for damage and destruction are obtained from the databases. Database of implemented testing [2] and research [20] on the appropriate structures allows us to analyze the behavior of supporting elements of steam line in order to determine changes in mechanical properties of materials. Load data, as well as the characteristics of the base material and its welded joints, technology development, technical and physical characteristics of the recorded fracture and destruction are inserted into the appropriate database. Reliable assessment of the integrity of the observed elements, could be made only after creation of adequate database and the basis for the development of computer programs [21]. Supporting software packages would allow more efficient use of the database, the analysis of some influencing factors, and the search of alternative solutions in all phases of design and development of construction.   CONCLUSION  nly by examining the construction of steam line operating conditions it is possible to assess their condition completely. During examination period the necessary data are obtained to determine the quality and structural integrity assessment and evaluation of the impact of the elements on the capacity and is given the necessary data to establish the joint work of devices and structure of steam line. The results presented in this paper and conducted research projects allow us to analyze the behavior of supporting elements of steam line in order to determine changes in mechanical properties of materials.   ACKNOWLEDGEMENTS  he paper was done within the project TR 35011, "The integrity of the pressure equipment with the simultaneous action of fatigue load and temperature," founded by the Ministry of Education, Science and Technological Development of the Republic of Serbia.   REFERENCES  [1]  KLBA-M9-013: The test program of the technological metal machine part, TEK A, Jun, 2001. [2]  Reports on NDT testing methods of steam line at the Kolubara A, Institute IMS, 2000-2012. [3]  Regulation on the technical requirements for the design, development and conformity assessment of pressure equipment (Sluzbeni glasnik RS no. 87/2011). [4]  Regulation on pressure equipment inspections during the operation (Sluzbeni glasnik RS no. 87/2011). [5]  Pressure Equipment Directive (PED 97/23/EC). T L O T  S. Bulatovic et alii, Frattura ed Integrità Strutturale, 26 (2013) 41-48; DOI: 10.3221/IGF-ESIS.26.05                                                                      48  [6]  Sposito, G., et al.: A review of non-destructive techniques for the detection of creep damage in power plant steels, NDT&E International, 43 (2010) 555. [7]  VGB-R 508 L : Richtlinie für die Herstellung und Bauüberwachung von Rohrleitungsanlagen in Wärmekraftwerken. [8]  SRPS ISO 3057/2011: Non-destructive testing -- Metallographic replica techniques of surface examination (identical with ISO 3057/1998). [9]  SPRINT SP 492. [10] VGB - TW 507 e: Guideline for the Assessment of Microstructure and Damage Development of Creep Exposed Materials for  Pipes and Boiler Components (1992). [11] ECCC Recommendations - Volume 6: Residual life assessment and microstructure, 1. [12] Jakovljević, A., Numerical stress analysis of high pressure steam lines in power plants, Structural integrity and life, UDK 620.169.1:621.643.023-988, 7 (1) (2007) 13-20. [13] Petronić, S., Comparative Analysis of the Design Stress According to Different Regulations on Pressure Equipment, Structural integrity and life, UDK 66-988(083.133), 12(2) (2012) 143-148. [14] Petronić, S., Grujić, B., Balać, M., Test Pressures and Stresses for Pressure Vessels According to New Regulation 87/11, Structural integrity and life, , UDK 620.1:66-988, 12(3) (2012) 209-213. [15] Milović, L., Significance of cracks in the heat-affected-zone of steels for elevated temperature application, Structural integrity and life, UDK 621.791.051:669.14, 8(1) (2008) 55-64. [16] Milović, L., Vuherer, T., Radaković, Z., Petrovski, B., Janković, M., Zrilić, M., Daničić, D., Determination of Fatigue Crack Growth Parameters in Welded Joint of HSLA Steel, Structural integrity and life, UDK 620.172.24: 669.15, 620.172.24:66-988-112.81, 621.791.05:539.4.013, 11 (3) (2011) 183-187. [17] Gubeljak, N., Application of Stereometric Measurement on Structural, Structural integrity and life, UDK 620.169.1, 6(1-2) (2006) 65-74. [18] Đorđević, P., Kirin, S., Sedmak, A., Džindo, E., Risk Analysis in Structural Integrity, Structural integrity and life, UDK 65.012.32, 11(2) (2011) 135-138. [19] Kirin, S., Jovanović, A., Stanojević, P., Sedmak, A., Džindo, E., Risk Analysis in Structural Integrity – Application to a Large Company, Structural integrity and life, UDK 65.012.32, 11(3) (2011) 209-212. [20] Sedmak, S., Radaković, Z., Milović, L., Svetel, I., Significance and Applicability of Structural Integrity Assessment, Structural integrity and life, UDK 620.172.24, 620.169.1, 539.42, 12(1) (2012) 3-30. [21] Popović, A., Marković, M., Panić, B., Nikolić, M., Data Acquisition and Processing, Structural integrity and life, UDK 620.17.05:004, 6 (1-2) (2006) 53-64.    

Frattura ed Integrità Strutturale

Failure of steam line causes determined by NDT testing  in power and heating plants

This paper examines leakage and damages of steam and provides an overview of NDT testing inorder to determine the cause of steam lines failure in power plants and heating plants. This approach may beapplied to similar structures and its application in preventive maintenance would help extend the life of steampipes

Bulatovic, Srdjan

Aleksic, Vujadin

Milovic, Ljubica

Gruppo Italiano Frattura (IGF)

                                                                   S. Bulatovic et alii, Frattura ed Integrità Strutturale, 26 (2013) 41-48; DOI: 10.3221/IGF-ESIS.26.05 
 
41 
 
 
 
 
 
  
Failure of steam line causes determined by NDT testing  
in power and heating plants 
 
 
Srdjan Bulatovic  
Yugoslav River Shipping, Belgrade, Serbia 
srdjan.bulatovic@yahoo.com 
 
Vujadin Aleksic 
Institute for testing materials-IMS Institute, Bulevar voijvode Mišića 43, Belgrade, Serbia 
 
Ljubica Milovic  
Faculty of Technology and Metallurgy, Belgrade, Serbia 
 
 
ABSTRACT. This paper examines leakage and damages of steam and provides an overview of NDT testing in 
order to determine the cause of steam lines failure in power plants and heating plants. This approach may be 
applied to similar structures and its application in preventive maintenance would help extend the life of steam 
pipes. 
  
KEYWORDS. Steam line; Failure; NDT testing. 
 
 
 
INTRODUCTION 
 
team lines and high pressure pipelines are vital parts of the thermal power plant system. In fact, they are the 
connection between the boiler and turbines in power plants or boilers in power stations and customers in heating 
plants. They are critical components in power plants and heating plants and have a significant impact on the 
reliability and availability of power plants and heating plants. Continuous exploitation in very hard working conditions can 
lead to relatively frequent system steamline failure. Damages on steam line elements may appear well before it is expected, 
and not just as a result of internal pressure and temperature, but also as a consequence of the loads that occur due to poor 
design and inadequate maintenance. Also, damage of steam line elements may appear because of numerous on-off 
switching of the boiler as well as misuse of start diagram. Failures of steam lines, other than direct material damage, could 
jeopardize the safety of personnel and equipment. Among the causes of these failures inadequate operation and 
maintenance takes a high rank. Leaking of steam lines caused by material creep is expected if number of hours spent in 
operation is higher than design number of hours. Fig. 1 shows part of steam line of heated vapor in block 1 on TPP 
"Kolubara A" - Veliki Crljeni (near Belgrade). The RA, RB and RC line thermal units 1 to 5 span lenghts of 200-300 m 
and capacities of 300-500 t/h. During its operation there were relatively frequent delays caused by defects of supporting 
structure [1, 2], and in extreme case even failure or steam line leakage, which is usually explained by gaps in technology 
development and mishandling. 
 
S 
 S. Bulatovic et alii, Frattura ed Integrità Strutturale, 26 (2013) 41-48; DOI: 10.3221/IGF-ESIS.26.05                                                                    
 
42 
 
 
 
 
Figure 1: Part of the steam line during NDT. 
 
 
TECHNICAL DIAGNOSTICS 
 
uring the operation period, fatigue of steam line components may occur. Degradation of material properties and 
deformation of elements can be accelerated due to the exploitation and repair errors, that's why periodic or 
continuous diagnostic measurements, conducting periodic tests and data collection programs defined by [1, 2] 
are needed. In this way, processes that could lead to the creation of system damage are under systematic control, what is 
also the legal obligation imposed by the regulations, directives and harmonized standards [3 - 5]. 
Properly conducted technical diagnostics protects parts of the steam line from accident, and also ensures safer conditions 
for employees as well as rational techno-economic exploitation and maintenance. 
Technical diagnostic of steam lines must be based on three basic principles: 
 volume of tests and measurements shall be in accordance with the program of research [1] and an expert knowledge 
of steam line structure and working conditions; 
 tests and measurements must be performed in accordance with special procedures, using appropriate equipment and 
qualified personnel; 
 test results should be presented in such way that the conclusions include steam line operating conditions, the 
availability of the test team and staff with appropriate experience and knowledge in the field of design, construction, 
installation, operation, maintenance, reliability, fracture mechanics and others. 
 
 
NDT TO DETERMINE CAUSE OF STEAM LINE FAILURE 
 
or purpose of determining the causes of failure it is necessary to make steam line 100% visual inspection, magnetic, 
penetrant, ultrasonic, hardness and method of replica testing.  
If necessary, other tests that would give us a reliable and useful results to determine causes of steam line failure 
could be done. Fig. 2 shows the possibility of evaluating some damage using NDT methods in the life of the steam line. 
 
Visually optical control (VT) 
VT is used to detect defects that are visible on the surface of the steam line from the outside or inside of the tube. It 
applies regardless the method to be applied after it, because it is possible to detect errors, such as in our case, and avoid 
the use of other, more costly methods of NDT. It is often used for the selection of critical areas of the facility for the 
application of other NDT testing methods. 
At the same objects it may be performed multiple times (eg, before and after cleaning, or before and after the execution of 
corrosion protection, etc.). 
Control of the inside of the tube (endoscopy) allows optical access to the interior of steam lines. It is performed using an 
endoscope, and as a result we get control of video or photograph controlled inner surface, Fig. 3. 
 
 
D 
F 
                                                                   S. Bulatovic et alii, Frattura ed Integrità Strutturale, 26 (2013) 41-48; DOI: 10.3221/IGF-ESIS.26.05 
 
43 
 
  
Figure 2: Application of NDT methods in detecting defects in the life of the steam line [6]. 
 
 
 
Figure 3: Photo of interior surfaces steamline. 
 
Magnetic particle testing (MT) 
The method is based on emphasizing the stray magnetic flux caused by the presence of surface or subsurface defects like 
cracks, notches, inclusions and other types of sharp or planar defects. Advantage of the method is that it requires a 
moderate cost, and if done correctly, you get a very good sensitivity for the detection of surface defects. The 
disadvantages of this method is that it could only be appllied to ferromagnetic materials as well as the potential need for 
degaussing after completing the testing. The method is commonly used for the detection of cracks and other defects in 
weld joints, castings and forgings. 
 
Ultrasonic testing (UT) 
The method is based on detecting changes in acoustic resistance due to the presence of cracks, voids, inclusions, and 
general physical separation in the material. The advantage of the method is that is also applicable to the thicker material, it 
is excellent for detecting and locating cracks and other defects, and it is suitable for automation. The biggest disadvantages 
are the need for a medium on the surface to be tested (or complete immersion of testing item in contact medium), as well 
as the request that surface on which the probe is moving is relatively smooth (ie cleaning needs, grinding the metallic 
shine). The most common application is to detect and precisely determine the position of defects in plate, welded joints 
(and butt and fillet) steel castings and forgings (if their geometric configuration allows). Application of this method for 
testing materials with high attenuation of ultrasound energy (for example, high alloyed austenitic steels, cast bronze ...) is 
difficult and can be done only under special circumstances. 
 
Hardness testing (HT) 
For evaluation of properly applied heat treatment after welding, hardness testing of the base metal, HAZ and weld 
materials are performed. At the same time, hardness and hardness differences must be within the limits of applied 
materials. In Tab. 1. the recommended values of hardness [7] of materials that are commonly used to produce steam line 
are shown. 
 S. Bulatovic et alii, Frattura ed Integrità Strutturale, 26 (2013) 41-48; DOI: 10.3221/IGF-ESIS.26.05                                                                    
 
44 
 
 
Materials 
Hardness [HV]
Base 
materials2 
Weld
joint 
Heat 
Affected 
Zone 
(HAZ) 
1.5415 
15 Mo3 140-190 260 320 
1.7335 
13CrMo44 135-185 270 320 
1.7380 
10CrMo910 140-190 280 320 
1.7715 
14MoV63 145-190 280 320 
1.7745 
15CrMoV510 140-215 280 320 
1.4922 
X20CrMoV12-1 215-265 300 3501 
1 Hardness value of 350 HV must not be exceeded in the HAZ 
2 For cold-rolled sections such as tube bends in the base material greater 
hardness for HV 60 are allowed. 
HB  0.95HV; M  1/3HB 
 
Table 1 
 
Method of replica testing (REP) 
Metallographic examination, Fig. 4, the surface layer of material of pipe bends, weld joints and pipes on the old steam pipe 
RA 10 block A1, is conducted by the method of nondestructive testing of materials, using metallographic replica, 
according to [8]. 
 
 
Figure 4: Overview of possible damage to the established method of replica [9]. 
 
In order to detect the microstructure of materials, adequate preparation is made  of tested surfaces, and that included 
cleaning and a range of fine sanding operations. After the final polishing and cleaning, the test surfaces were eroded with 
appropriate reagent, ie. 4% nital. 
 
 
DETERMINING DAMAGES 
 
tructures of the steam line is exposed to the low cycle fatigue loads. This load caused a fatigue damage of pipes and 
leakage of steam lines on observed object, Fig. 5, which was confirmed by visual inspection. 
After that, NDT methods are used for testing the steam pipeline section and supporting structure before and after 
damage. Fig. 6 and 7 show the measurement of control and testing methods, NDT, and in Tab. 2 and 3 the results of 
measurements of diameter and wall thickness of the damaged part of the steam line are listed. 
S 
                                                                   S. Bulatovic et alii, Frattura ed Integrità Strutturale, 26 (2013) 41-48; DOI: 10.3221/IGF-ESIS.26.05 
 
45 
 
 
 
 
Figure 5: Determination of damage by visual inspection. 
 
 
 
Figure 6: Scheme of measurement tests (dimensional inspection of the damaged steam line part). 
 
 
 
Figure 7: Scheme of measuring and making replicas of the damaged steam line part RA-10. 
 
 S. Bulatovic et alii, Frattura ed Integrità Strutturale, 26 (2013) 41-48; DOI: 10.3221/IGF-ESIS.26.05                                                                    
 
46 
 
 
Part of the tube Diameters (mm) 
Plane measurements A B C D E 
Axis measurements 
0º-180º 288.9 276.8 285.0 285.9 283.1 
Axis measurements 
90º-270º 282.4 284.0 285.1 284.3 283.4 
 
Table 2 
 
 
Part of the tube Wall thickness (mm) 
Plane measurements A B C D E Remark 
D
esi
gn
ati
on
 of
 
me
as
ur
in
g p
oin
t 0º 21.2 20.1 (R3) 22.4 22.4 22.9 
23.2 
(A-R1) 
90º 24.3 24.7 25.6 25.8 25.5 24.7 (A-R2) 
180º 27.0 27.3 27.0 27.9 27.1 / 
270º 24.2 23.3 23.1 23.9 23.7 / 
R - place where replicas are taken 
 
Table 3 
 
Assessment of the microstructure of the materials that are used for tube bends and welded joints and creep damage level 
are made according to the recommendations for the assessment of the microstructure [10]. 
The degree of quality degradation of the microstructure of the old pipe was determined according to the 
recommendations of the European Commission for assess the remaining life of the microstructure [11]. 
Fig. 8 and 9 show the typical microstructure of the surface layer of the old pipe taken from a replica in accordance with 
the drawing in Fig. 7. 
 
  
 
Figure 8: Replica RA10-R1. Assessment of the microstructure 
[11]: Level B / Level C: Initial spheroidization and carbide 
precipitation per grain boundary in places with the presence of 
globular pearlite. 4% nital. 
Figure 9: Replica RA10-R3. Macro cracks. Assessment of the 
microstructure [10]: 5; Assessment of the microstructure [11]: 
Level B / Level C: Initial spheroidization and carbide 
precipitation per grain boundary in places with the presence of 
globular pearlite. 4% nital.
 
In microstructure of tested replica taken from the surface of the material of the old pipe, a certain degree of quality 
degradation was observed wich is caused by initial spheroidization and carbide precipitation per grain boundary in places 
with the presence of globular pearlite- the level of quality degradation of microstructure B / C, according to [11]. Products 
of corrosion and corrosion damage in spots are present in the microstructure of tested replica. 
 
                                                                   S. Bulatovic et alii, Frattura ed Integrità Strutturale, 26 (2013) 41-48; DOI: 10.3221/IGF-ESIS.26.05 
 
47 
 
 
ANALYSIS OF DAMAGE 
 
he damaged parts of steam line were analyzed, to determine the cause of the problem, which is a process that 
requires a systematic approach. Test results of NDT methods contribute to the knowledge of damage formation 
and allow us to determine the cause of steam line failure. Based on the research of failure and causes of failure of 
certain components of steam line using method FMEA and reliability parameters obtained from the analysis of the data 
collected in real operating conditions, a system of continuous diagnosis could be established. 
Stress analysis [12,13,14], damage and fractures [15,16] of welded joints of steam line elements provide important 
directives for the development of design methods and construction elements of the steam line to improve the properties 
of existing materials and their processing technologies. Also, by analyzing fractures, the development of new technical 
solutions and methods of testing is enabled [17] in the prototype stage. It is necessary to take into account the risk analysis 
and structural integrity [18,19], as a new approach to the assessment of structural integrity. 
 
 
THE DATABASE INFORMATION 
 
oad data, the characteristics of the base material and its welded joints, technology development, technical and 
physical characteristics reported fractures data and preventive measures provided for damage and destruction are 
obtained from the databases. Database of implemented testing [2] and research [20] on the appropriate structures 
allows us to analyze the behavior of supporting elements of steam line in order to determine changes in mechanical 
properties of materials. Load data, as well as the characteristics of the base material and its welded joints, technology 
development, technical and physical characteristics of the recorded fracture and destruction are inserted into the 
appropriate database. Reliable assessment of the integrity of the observed elements, could be made only after creation of 
adequate database and the basis for the development of computer programs [21]. Supporting software packages would 
allow more efficient use of the database, the analysis of some influencing factors, and the search of alternative solutions in 
all phases of design and development of construction. 
 
 
CONCLUSION 
 
nly by examining the construction of steam line operating conditions it is possible to assess their condition 
completely. During examination period the necessary data are obtained to determine the quality and structural 
integrity assessment and evaluation of the impact of the elements on the capacity and is given the necessary data 
to establish the joint work of devices and structure of steam line. 
The results presented in this paper and conducted research projects allow us to analyze the behavior of supporting 
elements of steam line in order to determine changes in mechanical properties of materials. 
 
 
ACKNOWLEDGEMENTS 
 
he paper was done within the project TR 35011, "The integrity of the pressure equipment with the simultaneous 
action of fatigue load and temperature," founded by the Ministry of Education, Science and Technological 
Development of the Republic of Serbia. 
 
 
REFERENCES 
 
[1] KLBA-M9-013: The test program of the technological metal machine part, TEK A, Jun, 2001. 
[2] Reports on NDT testing methods of steam line at the Kolubara A, Institute IMS, 2000-2012. 
[3] Regulation on the technical requirements for the design, development and conformity assessment of pressure 
equipment (Sluzbeni glasnik RS no. 87/2011). 
[4] Regulation on pressure equipment inspections during the operation (Sluzbeni glasnik RS no. 87/2011). 
[5] Pressure Equipment Directive (PED 97/23/EC). 
T 
L 
O 
T 
 S. Bulatovic et alii, Frattura ed Integrità Strutturale, 26 (2013) 41-48; DOI: 10.3221/IGF-ESIS.26.05                                                                    
 
48 
 
[6] Sposito, G., et al.: A review of non-destructive techniques for the detection of creep damage in power plant steels, 
NDT&E International, 43 (2010) 555. 
[7] VGB-R 508 L : Richtlinie für die Herstellung und Bauüberwachung von Rohrleitungsanlagen in Wärmekraftwerken. 
[8] SRPS ISO 3057/2011: Non-destructive testing -- Metallographic replica techniques of surface examination (identical 
with ISO 3057/1998). 
[9] SPRINT SP 492. 
[10] VGB - TW 507 e: Guideline for the Assessment of Microstructure and Damage Development of Creep Exposed 
Materials for  Pipes and Boiler Components (1992). 
[11] ECCC Recommendations - Volume 6: Residual life assessment and microstructure, 1. 
[12] Jakovljević, A., Numerical stress analysis of high pressure steam lines in power plants, Structural integrity and life, 
UDK 620.169.1:621.643.023-988, 7 (1) (2007) 13-20. 
[13] Petronić, S., Comparative Analysis of the Design Stress According to Different Regulations on Pressure Equipment, 
Structural integrity and life, UDK 66-988(083.133), 12(2) (2012) 143-148. 
[14] Petronić, S., Grujić, B., Balać, M., Test Pressures and Stresses for Pressure Vessels According to New Regulation 
87/11, Structural integrity and life, , UDK 620.1:66-988, 12(3) (2012) 209-213. 
[15] Milović, L., Significance of cracks in the heat-affected-zone of steels for elevated temperature application, Structural 
integrity and life, UDK 621.791.051:669.14, 8(1) (2008) 55-64. 
[16] Milović, L., Vuherer, T., Radaković, Z., Petrovski, B., Janković, M., Zrilić, M., Daničić, D., Determination of Fatigue 
Crack Growth Parameters in Welded Joint of HSLA Steel, Structural integrity and life, UDK 620.172.24: 669.15, 
620.172.24:66-988-112.81, 621.791.05:539.4.013, 11 (3) (2011) 183-187. 
[17] Gubeljak, N., Application of Stereometric Measurement on Structural, Structural integrity and life, UDK 620.169.1, 
6(1-2) (2006) 65-74. 
[18] Đorđević, P., Kirin, S., Sedmak, A., Džindo, E., Risk Analysis in Structural Integrity, Structural integrity and life, 
UDK 65.012.32, 11(2) (2011) 135-138. 
[19] Kirin, S., Jovanović, A., Stanojević, P., Sedmak, A., Džindo, E., Risk Analysis in Structural Integrity – Application to a 
Large Company, Structural integrity and life, UDK 65.012.32, 11(3) (2011) 209-212. 
[20] Sedmak, S., Radaković, Z., Milović, L., Svetel, I., Significance and Applicability of Structural Integrity Assessment, 
Structural integrity and life, UDK 620.172.24, 620.169.1, 539.42, 12(1) (2012) 3-30. 
[21] Popović, A., Marković, M., Panić, B., Nikolić, M., Data Acquisition and Processing, Structural integrity and life, UDK 
620.17.05:004, 6 (1-2) (2006) 53-64. 
 
 
 


Failure of steam line causes determined by NDT testing in power and heating plants

Italian Group Fracture (IGF): E-Journals / Gruppo Italiano Frattura

                                                                   S. Bulatovic et alii, Frattura ed Integrità Strutturale, 26 (2013) 41-48; DOI: 10.3221/IGF-ESIS.26.05  41        Failure of steam line causes determined by NDT testing  in power and heating plants   Srdjan Bulatovic  Yugoslav River Shipping, Belgrade, Serbia srdjan.bulatovic@yahoo.com  Vujadin Aleksic Institute for testing materials-IMS Institute, Bulevar voijvode Mišića 43, Belgrade, Serbia  Ljubica Milovic  Faculty of Technology and Metallurgy, Belgrade, Serbia   ABSTRACT. This paper examines leakage and damages of steam and provides an overview of NDT testing in order to determine the cause of steam lines failure in power plants and heating plants. This approach may be applied to similar structures and its application in preventive maintenance would help extend the life of steam pipes.   KEYWORDS. Steam line; Failure; NDT testing.    INTRODUCTION  team lines and high pressure pipelines are vital parts of the thermal power plant system. In fact, they are the connection between the boiler and turbines in power plants or boilers in power stations and customers in heating plants. They are critical components in power plants and heating plants and have a significant impact on the reliability and availability of power plants and heating plants. Continuous exploitation in very hard working conditions can lead to relatively frequent system steamline failure. Damages on steam line elements may appear well before it is expected, and not just as a result of internal pressure and temperature, but also as a consequence of the loads that occur due to poor design and inadequate maintenance. Also, damage of steam line elements may appear because of numerous on-off switching of the boiler as well as misuse of start diagram. Failures of steam lines, other than direct material damage, could jeopardize the safety of personnel and equipment. Among the causes of these failures inadequate operation and maintenance takes a high rank. Leaking of steam lines caused by material creep is expected if number of hours spent in operation is higher than design number of hours. Fig. 1 shows part of steam line of heated vapor in block 1 on TPP "Kolubara A" - Veliki Crljeni (near Belgrade). The RA, RB and RC line thermal units 1 to 5 span lenghts of 200-300 m and capacities of 300-500 t/h. During its operation there were relatively frequent delays caused by defects of supporting structure [1, 2], and in extreme case even failure or steam line leakage, which is usually explained by gaps in technology development and mishandling.  S  S. Bulatovic et alii, Frattura ed Integrità Strutturale, 26 (2013) 41-48; DOI: 10.3221/IGF-ESIS.26.05                                                                     42     Figure 1: Part of the steam line during NDT.   TECHNICAL DIAGNOSTICS  uring the operation period, fatigue of steam line components may occur. Degradation of material properties and deformation of elements can be accelerated due to the exploitation and repair errors, that's why periodic or continuous diagnostic measurements, conducting periodic tests and data collection programs defined by [1, 2] are needed. In this way, processes that could lead to the creation of system damage are under systematic control, what is also the legal obligation imposed by the regulations, directives and harmonized standards [3 - 5]. Properly conducted technical diagnostics protects parts of the steam line from accident, and also ensures safer conditions for employees as well as rational techno-economic exploitation and maintenance. Technical diagnostic of steam lines must be based on three basic principles:  volume of tests and measurements shall be in accordance with the program of research [1] and an expert knowledge of steam line structure and working conditions;  tests and measurements must be performed in accordance with special procedures, using appropriate equipment and qualified personnel;  test results should be presented in such way that the conclusions include steam line operating conditions, the availability of the test team and staff with appropriate experience and knowledge in the field of design, construction, installation, operation, maintenance, reliability, fracture mechanics and others.   NDT TO DETERMINE CAUSE OF STEAM LINE FAILURE  or purpose of determining the causes of failure it is necessary to make steam line 100% visual inspection, magnetic, penetrant, ultrasonic, hardness and method of replica testing.  If necessary, other tests that would give us a reliable and useful results to determine causes of steam line failure could be done. Fig. 2 shows the possibility of evaluating some damage using NDT methods in the life of the steam line.  Visually optical control (VT) VT is used to detect defects that are visible on the surface of the steam line from the outside or inside of the tube. It applies regardless the method to be applied after it, because it is possible to detect errors, such as in our case, and avoid the use of other, more costly methods of NDT. It is often used for the selection of critical areas of the facility for the application of other NDT testing methods. At the same objects it may be performed multiple times (eg, before and after cleaning, or before and after the execution of corrosion protection, etc.). Control of the inside of the tube (endoscopy) allows optical access to the interior of steam lines. It is performed using an endoscope, and as a result we get control of video or photograph controlled inner surface, Fig. 3.   D F                                                                    S. Bulatovic et alii, Frattura ed Integrità Strutturale, 26 (2013) 41-48; DOI: 10.3221/IGF-ESIS.26.05  43    Figure 2: Application of NDT methods in detecting defects in the life of the steam line [6].    Figure 3: Photo of interior surfaces steamline.  Magnetic particle testing (MT) The method is based on emphasizing the stray magnetic flux caused by the presence of surface or subsurface defects like cracks, notches, inclusions and other types of sharp or planar defects. Advantage of the method is that it requires a moderate cost, and if done correctly, you get a very good sensitivity for the detection of surface defects. The disadvantages of this method is that it could only be appllied to ferromagnetic materials as well as the potential need for degaussing after completing the testing. The method is commonly used for the detection of cracks and other defects in weld joints, castings and forgings.  Ultrasonic testing (UT) The method is based on detecting changes in acoustic resistance due to the presence of cracks, voids, inclusions, and general physical separation in the material. The advantage of the method is that is also applicable to the thicker material, it is excellent for detecting and locating cracks and other defects, and it is suitable for automation. The biggest disadvantages are the need for a medium on the surface to be tested (or complete immersion of testing item in contact medium), as well as the request that surface on which the probe is moving is relatively smooth (ie cleaning needs, grinding the metallic shine). The most common application is to detect and precisely determine the position of defects in plate, welded joints (and butt and fillet) steel castings and forgings (if their geometric configuration allows). Application of this method for testing materials with high attenuation of ultrasound energy (for example, high alloyed austenitic steels, cast bronze ...) is difficult and can be done only under special circumstances.  Hardness testing (HT) For evaluation of properly applied heat treatment after welding, hardness testing of the base metal, HAZ and weld materials are performed. At the same time, hardness and hardness differences must be within the limits of applied materials. In Tab. 1. the recommended values of hardness [7] of materials that are commonly used to produce steam line are shown.  S. Bulatovic et alii, Frattura ed Integrità Strutturale, 26 (2013) 41-48; DOI: 10.3221/IGF-ESIS.26.05                                                                     44   Materials Hardness [HV]Base materials2 Weldjoint Heat Affected Zone (HAZ) 1.5415 15 Mo3 140-190 260 320 1.7335 13CrMo44 135-185 270 320 1.7380 10CrMo910 140-190 280 320 1.7715 14MoV63 145-190 280 320 1.7745 15CrMoV510 140-215 280 320 1.4922 X20CrMoV12-1 215-265 300 3501 1 Hardness value of 350 HV must not be exceeded in the HAZ 2 For cold-rolled sections such as tube bends in the base material greater hardness for HV 60 are allowed. HB  0.95HV; M  1/3HB  Table 1  Method of replica testing (REP) Metallographic examination, Fig. 4, the surface layer of material of pipe bends, weld joints and pipes on the old steam pipe RA 10 block A1, is conducted by the method of nondestructive testing of materials, using metallographic replica, according to [8].   Figure 4: Overview of possible damage to the established method of replica [9].  In order to detect the microstructure of materials, adequate preparation is made  of tested surfaces, and that included cleaning and a range of fine sanding operations. After the final polishing and cleaning, the test surfaces were eroded with appropriate reagent, ie. 4% nital.   DETERMINING DAMAGES  tructures of the steam line is exposed to the low cycle fatigue loads. This load caused a fatigue damage of pipes and leakage of steam lines on observed object, Fig. 5, which was confirmed by visual inspection. After that, NDT methods are used for testing the steam pipeline section and supporting structure before and after damage. Fig. 6 and 7 show the measurement of control and testing methods, NDT, and in Tab. 2 and 3 the results of measurements of diameter and wall thickness of the damaged part of the steam line are listed. S                                                                    S. Bulatovic et alii, Frattura ed Integrità Strutturale, 26 (2013) 41-48; DOI: 10.3221/IGF-ESIS.26.05  45     Figure 5: Determination of damage by visual inspection.    Figure 6: Scheme of measurement tests (dimensional inspection of the damaged steam line part).    Figure 7: Scheme of measuring and making replicas of the damaged steam line part RA-10.   S. Bulatovic et alii, Frattura ed Integrità Strutturale, 26 (2013) 41-48; DOI: 10.3221/IGF-ESIS.26.05                                                                     46   Part of the tube Diameters (mm) Plane measurements A B C D E Axis measurements 0º-180º 288.9 276.8 285.0 285.9 283.1 Axis measurements 90º-270º 282.4 284.0 285.1 284.3 283.4  Table 2   Part of the tube Wall thickness (mm) Plane measurements A B C D E Remark Designation of measuring point 0º 21.2 20.1 (R3) 22.4 22.4 22.9 23.2 (A-R1) 90º 24.3 24.7 25.6 25.8 25.5 24.7 (A-R2) 180º 27.0 27.3 27.0 27.9 27.1 / 270º 24.2 23.3 23.1 23.9 23.7 / R - place where replicas are taken  Table 3  Assessment of the microstructure of the materials that are used for tube bends and welded joints and creep damage level are made according to the recommendations for the assessment of the microstructure [10]. The degree of quality degradation of the microstructure of the old pipe was determined according to the recommendations of the European Commission for assess the remaining life of the microstructure [11]. Fig. 8 and 9 show the typical microstructure of the surface layer of the old pipe taken from a replica in accordance with the drawing in Fig. 7.     Figure 8: Replica RA10-R1. Assessment of the microstructure [11]: Level B / Level C: Initial spheroidization and carbide precipitation per grain boundary in places with the presence of globular pearlite. 4% nital. Figure 9: Replica RA10-R3. Macro cracks. Assessment of the microstructure [10]: 5; Assessment of the microstructure [11]: Level B / Level C: Initial spheroidization and carbide precipitation per grain boundary in places with the presence of globular pearlite. 4% nital. In microstructure of tested replica taken from the surface of the material of the old pipe, a certain degree of quality degradation was observed wich is caused by initial spheroidization and carbide precipitation per grain boundary in places with the presence of globular pearlite- the level of quality degradation of microstructure B / C, according to [11]. Products of corrosion and corrosion damage in spots are present in the microstructure of tested replica.                                                                     S. Bulatovic et alii, Frattura ed Integrità Strutturale, 26 (2013) 41-48; DOI: 10.3221/IGF-ESIS.26.05  47   ANALYSIS OF DAMAGE  he damaged parts of steam line were analyzed, to determine the cause of the problem, which is a process that requires a systematic approach. Test results of NDT methods contribute to the knowledge of damage formation and allow us to determine the cause of steam line failure. Based on the research of failure and causes of failure of certain components of steam line using method FMEA and reliability parameters obtained from the analysis of the data collected in real operating conditions, a system of continuous diagnosis could be established. Stress analysis [12,13,14], damage and fractures [15,16] of welded joints of steam line elements provide important directives for the development of design methods and construction elements of the steam line to improve the properties of existing materials and their processing technologies. Also, by analyzing fractures, the development of new technical solutions and methods of testing is enabled [17] in the prototype stage. It is necessary to take into account the risk analysis and structural integrity [18,19], as a new approach to the assessment of structural integrity.   THE DATABASE INFORMATION  oad data, the characteristics of the base material and its welded joints, technology development, technical and physical characteristics reported fractures data and preventive measures provided for damage and destruction are obtained from the databases. Database of implemented testing [2] and research [20] on the appropriate structures allows us to analyze the behavior of supporting elements of steam line in order to determine changes in mechanical properties of materials. Load data, as well as the characteristics of the base material and its welded joints, technology development, technical and physical characteristics of the recorded fracture and destruction are inserted into the appropriate database. Reliable assessment of the integrity of the observed elements, could be made only after creation of adequate database and the basis for the development of computer programs [21]. Supporting software packages would allow more efficient use of the database, the analysis of some influencing factors, and the search of alternative solutions in all phases of design and development of construction.   CONCLUSION  nly by examining the construction of steam line operating conditions it is possible to assess their condition completely. During examination period the necessary data are obtained to determine the quality and structural integrity assessment and evaluation of the impact of the elements on the capacity and is given the necessary data to establish the joint work of devices and structure of steam line. The results presented in this paper and conducted research projects allow us to analyze the behavior of supporting elements of steam line in order to determine changes in mechanical properties of materials.   ACKNOWLEDGEMENTS  he paper was done within the project TR 35011, "The integrity of the pressure equipment with the simultaneous action of fatigue load and temperature," founded by the Ministry of Education, Science and Technological Development of the Republic of Serbia.   REFERENCES  [1] KLBA-M9-013: The test program of the technological metal machine part, TEK A, Jun, 2001. [2] Reports on NDT testing methods of steam line at the Kolubara A, Institute IMS, 2000-2012. [3] Regulation on the technical requirements for the design, development and conformity assessment of pressure equipment (Sluzbeni glasnik RS no. 87/2011). [4] Regulation on pressure equipment inspections during the operation (Sluzbeni glasnik RS no. 87/2011). [5] Pressure Equipment Directive (PED 97/23/EC). T L O T  S. Bulatovic et alii, Frattura ed Integrità Strutturale, 26 (2013) 41-48; DOI: 10.3221/IGF-ESIS.26.05                                                                     48  [6] Sposito, G., et al.: A review of non-destructive techniques for the detection of creep damage in power plant steels, NDT&E International, 43 (2010) 555. [7] VGB-R 508 L : Richtlinie für die Herstellung und Bauüberwachung von Rohrleitungsanlagen in Wärmekraftwerken. [8] SRPS ISO 3057/2011: Non-destructive testing -- Metallographic replica techniques of surface examination (identical with ISO 3057/1998). [9] SPRINT SP 492. [10] VGB - TW 507 e: Guideline for the Assessment of Microstructure and Damage Development of Creep Exposed Materials for  Pipes and Boiler Components (1992). [11] ECCC Recommendations - Volume 6: Residual life assessment and microstructure, 1. [12] Jakovljević, A., Numerical stress analysis of high pressure steam lines in power plants, Structural integrity and life, UDK 620.169.1:621.643.023-988, 7 (1) (2007) 13-20. [13] Petronić, S., Comparative Analysis of the Design Stress According to Different Regulations on Pressure Equipment, Structural integrity and life, UDK 66-988(083.133), 12(2) (2012) 143-148. [14] Petronić, S., Grujić, B., Balać, M., Test Pressures and Stresses for Pressure Vessels According to New Regulation 87/11, Structural integrity and life, , UDK 620.1:66-988, 12(3) (2012) 209-213. [15] Milović, L., Significance of cracks in the heat-affected-zone of steels for elevated temperature application, Structural integrity and life, UDK 621.791.051:669.14, 8(1) (2008) 55-64. [16] Milović, L., Vuherer, T., Radaković, Z., Petrovski, B., Janković, M., Zrilić, M., Daničić, D., Determination of Fatigue Crack Growth Parameters in Welded Joint of HSLA Steel, Structural integrity and life, UDK 620.172.24: 669.15, 620.172.24:66-988-112.81, 621.791.05:539.4.013, 11 (3) (2011) 183-187. [17] Gubeljak, N., Application of Stereometric Measurement on Structural, Structural integrity and life, UDK 620.169.1, 6(1-2) (2006) 65-74. [18] Đorđević, P., Kirin, S., Sedmak, A., Džindo, E., Risk Analysis in Structural Integrity, Structural integrity and life, UDK 65.012.32, 11(2) (2011) 135-138. [19] Kirin, S., Jovanović, A., Stanojević, P., Sedmak, A., Džindo, E., Risk Analysis in Structural Integrity – Application to a Large Company, Structural integrity and life, UDK 65.012.32, 11(3) (2011) 209-212. [20] Sedmak, S., Radaković, Z., Milović, L., Svetel, I., Significance and Applicability of Structural Integrity Assessment, Structural integrity and life, UDK 620.172.24, 620.169.1, 539.42, 12(1) (2012) 3-30. [21] Popović, A., Marković, M., Panić, B., Nikolić, M., Data Acquisition and Processing, Structural integrity and life, UDK 620.17.05:004, 6 (1-2) (2006) 53-64.    

Failure of steam line causes determined by NDT testing in power and heating plants

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