The contribution is focused to the aspects of prevention untimely damage of exterior steel constructions at variable climatic conditions. The aspects for assurance of continual service of strategic steel constructions (bridges, pipelines, pylons, pressure vessels, containers, frameworks, cranes, chimneys, towers, etc.) is by action of severe climatic conditions in our climatic zones deteriorative. The service safety of construction mentioned is decreasing and could cause preterm damages. To avoid preterm damage there are two ways. First is to create conditions excluding the damage and second is proposal of construction safety also after expected limit state. During the lifetime is needed to assure failure free service of external steel constructions stressed by variable loading. At the same time is needed to calculate with action of aggressiveness of external environment as well as worsen atmospheric conditions. From load and conditions analysis could be calculated the residual life of external steel constructions

Polak, Peter

English

Materials Engineering - Materiálové inžinierstvo (MEMI - E-Journal)

P. Polák, M. Kasenčák, V. Piussi: Residual life of external steel constructions 
Materials Engineering - Materiálové inžinierstvo 25 (2018) 1-6 
1 
RESIDUAL LIFE OF EXTERNAL STEEL 
CONSTRUCTIONS 
Peter Polák1, Martin Kasenčák1, Vladimír Piussi1 
 
1 First Welding Company, Inc., Kopčianska 14, 85101 Bratislava 5, Slovak Republic 
 
 
Resume 
The contribution is focused to the aspects of prevention untimely damage of 
exterior steel constructions at variable climatic conditions. The aspects for 
assurance of continual service of strategic steel constructions (bridges, pipelines, 
pylons, pressure vessels, containers, frameworks, cranes, chimneys, towers, etc.) 
is by action of severe climatic conditions in our climatic zones deteriorative. The 
service safety of construction mentioned is decreasing and could cause preterm 
damages. To avoid preterm damage there are two ways. First is to create conditions 
excluding the damage and second is proposal of construction safety also after 
expected limit state. During the lifetime is needed to assure failure free service of 
external steel constructions stressed by variable loading. At the same time is 
needed to calculate with action of aggressiveness of external environment as well 
as worsen atmospheric conditions. From load and conditions analysis could be 
calculated the residual life of external steel constructions. 
 
 
 
Article info 
Article history: 
Received 10 August 2018 
Accepted 15 October 2018 
Online 15 October 2018 
 
Keywords: 
Steel construction; 
Corrosion; 
Ageing; 
Residual life. 
 
 
 
 
 
ISSN 1338-6174 (online version) 
 
1. Introduction 
Determining criteria of operation of steel 
constructions is their reliability what in praxis 
means that it is needed to provide required 
function for defined period. Generally we speak 
about robust investment units as bridges, pylons, 
reservoirs, pressure and pipeline systems, 
frameworks of buildings etc. Operator is fixed to 
pay attention to keep reliability of own 
investments. Nowadays is calculated about 
utilizing of diagnostic methods and monitoring 
of exposed nodal points together with 
mathematics modeling of ageing. It enables to 
define the residual life of particular components 
using on line system. The residual life is relevant 
to plan maintenance and repair which guarantee 
safety and failure free operation of modern steel 
constructions. 
 
2. Analysis of operational stress 
Decisive part of external steel 
constructions are in service loaded by dynamic 
loading simultaneously with activity of climatic 
conditions. Dynamical loading causes a response 
in the critical locality of structure by 
accumulation of damage. In beginning phases 
this is an event without visible signs on material 
surface, when the incubation phase of fatigue 
failure on the level of structure and substructure 
takes place, mainly by growth in density of 
dislocations. This stage of development of 
fatigue cracks is usually affected by the stress 
concentration from notches and also by residual 
stresses, mainly in the zone of welded joints. 
After incubation stage of fatigue process, the 
stage of fatigue crack growth follows. The 
damage process terminates by rupture of the 
remaining cross section. In case of existence of 
surface defects (crack, lack of fusion, cold lap, 
etc.) the incubation phase is abandoned and the 
entire process of fatigue consists only in the 
fatigue crack growth. 
The resistance of material against 
formation of brittle fracture depends from ability 
of plastic deformation. In the root of crack is the 
stress theoretically extremely high. In real life is 
formed in this place the plastic zone. The size of 
plastic zone depends on limit of elasticity Re of 
P. Polák, M. Kasenčák, V. Piussi: Residual life of external steel constructions 
Materials Engineering - Materiálové inžinierstvo 25 (2018) 1-6 
2 
material, Fig. 1. Steels with higher limit of 
elasticity create smaller plastic zone. The risk of 
brittle fracture is therefore higher by using high 
strength steels, where the radius of plastic zone 
rp is already very small. Increasing of the risk is 
caused in the region of welded joints and in using 
of high thickness of material, where plane strain 
is dominant [1].  
 
 
 
 
 
 
 
 
 
 
 
 
 
Fig. 1. Size of radius of plastic zone for different 
steels. 
(full colour version available online) 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Fig. 2. Setting of strain greatness for constructional 
steel 
(full colour version available online) 
 
The steel constructions loading is 
composed of external dynamic loading, 
corrosion, and internal influences as residual 
stresses and stress concentration factors. Final 
loading is superposition of all internal and 
external loadings on critical cross section of steel 
construction. Critical point is regularly on the 
surface of the body. Here is anticipated also 
initiation of eventual fatigue crack. The 
evaluation of total stress σ, that subject limit state 
of construction is depends on stress intensity 
factor KI, and critical defect size 2a in regarded 
cross section [1], [2], Fig. 2. 
 
3. The integrity of steel constructions and 
residual life 
During the operation of external steel 
constructions comes to degradation of their 
utility properties. Therefore there is need to 
estimate residual life continuously. For 
minimizing of the risk of failure is needed to 
realize the maintenance of construction in 
defined intervals of inspection. The structures 
dynamically loaded in service may be loaded 
either by high-cycle fatigue, low- cycle fatigue, 
or by irregular fatigue loading. Theoretical 
background for determining the growth rate of 
fatigue cracks is sufficiently mastered at present. 
For crack growth rate at high cycle fatigue, the 
Paris - Erdogan's (1936) relationship is used, 
whereas for the strain fatigue the Manson - 
Coffin's (1954) relationship is applied and at 
irregular fatigue, the cumulative hypotheses are 
employed, whereas the most widely used seems 
to be the Palmgren - Miner's (1945) criterion in 
conjunction with Wohler's (1860) curve [3]. 
Present direction in the field of design, 
manufacture, service, repairs and liquidation of 
structures is governed by the approaches making 
use of the theoretical and practical knowledge of 
the „Fitness For Service - FFS" approach. (This 
method was conceived and developed within IIW 
- International Institute of Welding, in 
Commission XV - „Design, analysis and 
fabrication of welded structures "(1990). 
Following proceedings at present became the 
contents of Commission X - Structural 
Performances of Welded Joints - Fracture 
Avoidance. The „Fitness For Service" theory 
P. Polák, M. Kasenčák, V. Piussi: Residual life of external steel constructions 
Materials Engineering - Materiálové inžinierstvo 25 (2018) 1-6 
3 
may be used actually in all fields of fabrication 
and service of metallic but also non-metallic 
(plastics, composites, ceramics, concrete etc.) 
structures and products. Documents from this 
field are accessible on the web site: 
www.eurofitnet.org. 
The limit state may occur from several 
reasons, for example from the material loss of the 
bulk structure, caused by surface corrosion or by 
gap corrosion. Material degradation may occur 
due to ageing, distortion of crossbars and due to 
defect growth by fatigue process, most often by 
loading caused by the sharp atmospheric 
influences. Optimum solution of maintenance 
and repairs supposes determination of suitable 
inspection intervals. Their determination follows 
from the analysis of damage risks (Risk Based 
Inspection - RBI) [4], as shown in Fig. 3. The 
structure must be capable to tolerate the failures 
formed between the two inspection intervals. 
Thus, in spite of existence and growth of damage 
caused by corrosion and/or dynamic loading, the 
structure must be safe and functional up to the 
next planned inspection. Determination of 
interval of diagnostic inspections directly 
depends on the admissible probability of failure. 
The system of diagnostics measurement 
is destined for an objective determination of 
factual state of steel construction material 
from the viewpoint of its damage during the 
service. Modern non-destructive and 
destructive diagnostic methods used for 
determination of factual stage of steel 
construction damage allow obtain a complex 
picture about the internal and external defects 
in the critical cross sections, as well as the 
measure of material damage due to ageing. 
The damage process of steel structure 
progresses in the course of life separately in 
its individual components (corrosion, ageing, 
defect growth, distortions of crossbars etc.) 
but the resultant effect of damage is 
represented summarily. The degradation 
process is governed by actual physical and 
chemical laws, which allow to predict their 
expected further development and to predict 
residual life.  
Residual life generally depends on the 
state in structure damage, on acceptable 
damage size and on the supposed service 
conditions in the course of time form 
diagnostics performance till the end of safe 
life. Four significant modes of damage may 
occur on steel structures which alter during the 
course of life and affect the residual life of 
construction: material ageing, corrosion, 
fatigue crack growth and distortion of 
crossbars. 
Determination of supposed residual life 
is an engineering problem, which solution 
consists in unimpeachable estimation of time 
during which construction may be utilised and 
met requirements for service safety. Residual 
life of construction is thus considered till 
termination of a safe service and not up to 
reaching the emergency (limit) state. Each of 
the mentioned damage modes may separately 
cause the termination of service period, due to 
exceeding the critical damage size (CDS). The 
time courses of assessment properties can be 
obtained on the basis of long-term monitoring 
of individual damage modes. This allows to    
achieve the life function of studied property. 
At individual damage modes, attention should 
be mainly paid to the two issues. First is course 
of the life function at individual damage 
modes, and second is critical degree of 
degradation (CDS) of an actual damage. 
Regarding the fact that the development of 
individual damage modes, as well as the 
admissible degree of degradation mutually 
differ, since they are of different physical or 
chemical essence, it is necessary to approach 
to individual damage modes separately.  
 
P. Polák, M. Kasenčák, V. Piussi: Residual life of external steel constructions 
Materials Engineering - Materiálové inžinierstvo 25 (2018) 1-6 
4 
 
Fig. 3. Intervals of structure inspection by the Risk Base Inspection theory. 
(full colour version available online) 
 
 
 
4. Controlled ageing of steel constructions 
Integrity of steel constructions must be 
ensured continually. The quality systems have 
introduced the principle of responsibility of 
manufacturer and operator for the safety of 
products during the entire period of their 
technical life. This requirement can be ensured 
by the method of controlled ageing of 
constructions. Principle of controlled ageing 
consists in the fact that a complex diagnostics 
with subsequent maintenance (eventually also 
repairs) of all defective points is performed in the 
intervals defined in advance. After such action 
the structure gets to its „initial" state. However, 
the material degradation caused by ageing will 
remain a permanent change that cannot be 
removed. These intervals are determined by the 
RBI (risk based inspection) method. Controlled 
ageing has a direct effect upon two most 
important performance criteria, namely the 
service reliability and Life Cycle Cost (LCC) [5]. 
However, also time of safe service is prolonged. 
On the side of expenditures, the costs for 
diagnostics, maintenance and repairs are 
involved, whereas on the side of savings a 
prolonged time of safe life of constructions is 
obtained. Practice have shown, that the cost for 
controlled ageing are considerable lower, than 
the savings obtained by prolonged time of safe 
service with postponing of new investment. 
In design of steel constructions was 
supposed that theoretical development of 
degradation will be linear and finish by limit 
state. Research indicates that theoretical trend of 
degradation of steel construction is in real 
conditions modified above all by effect of 
damage accumulation and local disorders as 
corrosion or wearing. Development of the life 
cycle of steel constructions with three times 
inspection and repair is plotted in Fig. 4. 
Assessing of risk probability index for lack 
integrity of construction is in Tab. 1. 
Realisation intervals for inspection tests 
and consistent repairs or maintenance are defined 
to keep the probability of damage under 30%. 
Parallel the propagation of damage is in zone of 
very low risk of fail. Heavy line represented 
development of lifetime of real steel construction 
with three inspections and three repairs (1, 2 and 
3). After repairs is not possible to come to 
original degradation because of ageing process of 
material. This advance makes possible to ensure 
that 76% of lifetime will the construction work 
in low risk of damage. 
P. Polák, M. Kasenčák, V. Piussi: Residual life of external steel constructions 
Materials Engineering - Materiálové inžinierstvo 25 (2018) 1-6 
5 
In the case of next inspection and repair 
the lifetime will be prolonged. The operator 
could make a decision either to repair the 
construction or make a new investment. 
Consecutive degradation of steel 
constructions causes also changes of original 
mechanical properties of material. The damage 
accumulation is decisive especially on critical 
nodal points of construction. In this places are 
peaks of loading from notches mainly in welded 
joints [6]. The factors of damage collection are 
loading, surroundings, changing temperature and 
ageing process. For avoiding of limit state of 
construction is needed to fulfill three conditions, 
namely proper material, precise dimensioning, 
and quality of production and inspection. 
Table 1 
Setting of index of probability of risk lack integrity of construction. 
Risk index Probability of damage Probability of outcome Probability of risk 
1 any any right low 
2 little improbable low 
3 average eventual average 
4 significant probable big 
5 serious much probable emergency 
 
Fig. 4. 
Development of life cycle of construction (3 times inspection and repair). 
(full colour version available online) 
 
5. Discussion and Conclusions 
Research in scope of controlled ageing has 
shown the possibilities for optimizing of 
intervals of inspection and maintenance or repair 
of steel constructions to obtain optimal 
operational conditions and safety. In order to 
assure the service reliability as well as the 
optimum economical usage of construction it is 
advisable to elaborate and implement the 
program of controlled ageing of real steel 
construction. This will allow monitoring and 
assess the effect of service and degradation 
processes on individual bearing components of 
steel constructions. Systematic solution and 
attention to service safety of steel constructions 
consist of sophisticated attempt to individual 
segments of cycle of development, production, 
construction, service and clearance of 
investments. The information resource about 
development of damage consists in completion 
of inspection measurements and analysis of 
degradation feedbacks. 
Fundamental effect for long period of 
service is surface shielding of steel construction. 
The quality of surface shielding should be 
monitored regularly and have to be renovated as 
soon as possible during whole life of 
construction [7]. By exploitation of diagnostic 
inspection derived from risk analysis and fracture 
mechanics supported by fitness for service 
P. Polák, M. Kasenčák, V. Piussi: Residual life of external steel constructions 
Materials Engineering - Materiálové inžinierstvo 25 (2018) 1-6 
6 
method is possible to propose maintenance and 
repair processes to assure safe life of 
construction during whole life. This is the basis 
of controlled ageing of steel constructions. The 
assessment of residual life makes possible to 
realize prognosis of safe life and determine either 
new inspection or new investment. The technics 
described enable also to prolong lifetime of steel 
constructions. 
 
 
Acknowledgements 
This contribution was prepared within APVV-
0120-015 project. Authors gratefully 
acknowledge this support. 
 
References 
[1] Vlk, M., Florian, Z.: Limit States and Reliability, 
VUT Brno 2007 (in Czech). 
[2] A.F. Hobbacher: Recommendations for Fatigue 
Design of Welded Joints and Components, 1st 
edition, Springer Int. Publishing, Switzerland 
2009. 
[3] M. Kocak: Welding in the World 51 (5-6) (2009) 
95-105. 
[4] J. Sinay: Risk of technological plants, TU 
Košice 1997. 
[5] D. Daniš: AT&P Journal 10 (55-56) (2005). 
[6] I. Hrivňák: Welding and Weldability of 
Materials, STU Bratislava 2009 (in Slovak). 
[7] P. Polak: Corrosion Cracks Propagation 
Velocity, Welding Research Institute, Bratislava 
1998. 
 


Residual life of external steel constructions

http://www.ojs.mateng.sk/index.php/Mateng/article/download/243/444

Residual life of external steel constructions

Abstract

Similar works

Full text

Available Versions

Materials Engineering - Materiálové inžinierstvo (MEMI - E-Journal)