IFMASS10

107

THEORETICAL BASIS OF STRUCTURAL INTEGRITYAND LIFE

Dražan Kozak

University of Osijek, Mechanical Engineering Faculty in Slavonski Brod, Croatia

Nenad Gubeljak

University of Maribor, Faculty of Mechanical Engineering, Maribor, Slovenia

1. INTRODUCTION

Any structure, especially a welded structure contains the defects. These defects in wel-

ded structure can appear as a consequence of materials defects (like non-metallic

inclusions) or, more often, as defects in the welded joints (like misalignment, distortion,

root defects, slag, pores, inclusions, cracks). A crack can increase from such an initial

defect to critical crack size. Crack growth frequently takes place in structures subjected to

loads which are lower than nominal design load. The question how to ensure the

structural integrity and reliable work of the structural components through their complete

life, starting with design, through fabrication and exploitation) is continuously open and

is the matter of many investigations. For that it is important to know more details about

structure behaviour regarding when the working conditions are influencing factor of

prime importance. The time interval of crack growth from defect to critical crack size can

be considered as the safe service lifetime. The safe use and full function of a structure is

possible during this time. Total loading capability and the reliable usage of a structure are

the main concern of the investors and the users of a structure.

In this regard key questions are:

- How is the usage of the structure reliable?

- Is it possible to extend service-life-time of the structure?

This article gives the main principles for the safe and reliable use of structures. On the

basis of the proposed principles, it is possible to achieve maximum and efficient use of a

structure. Corresponding procedure is applicable during the stage of design, manufac-

turing and maintenance of a structure. The best effect can be achieved if the testing of

materials and the stress analysis are performed parallel to design and manufacture,

followed by required structure testing. The preparation and manufacturing of specimens

should be taken in account also for next testing during the service lifetime.

The presented procedure principles can be applied for structures in service, although it

is not certain that reliable materials input data are always available, as required /1/.

2. BASIC PRINCIPLES

The procedure for designing against fracture is based on generally accepted standards

for material testing (like ASTM E 1820 /2/, BS 7448 /3/), verified structure design proce-

dures (EN Eurocode 3 /4/) and procedures for structural integrity assessment (like BS

7910 /5/, API 579 /6/, R5 /7/, R6 /8/, SINTAP /9/, ETM /10/).

Some important factors regarding the basic principles like:

- Common experience of structural component producer and of user as well.

- Knowledge about new research results.