IFMASS10

163

PRACTICAL ASPECTS OF PRESSURE VESSELS INTEGRITY

Miodrag Arsić

Institute for materials testing - IMS, Belgrade. Serbia

1. INTRODUCTION

Designing and manufacturing of pressure equipment (PE), according to Directive

97/23/EC – PED /1/, is carried in correspondence with technical and legal regulations,

implementing harmonized standards for equipment manufacturers is optional. Directive

(PED 97/23/EC) refers only to designing, manufacturing and compatibility assessment of

pressure equipment and assembles designed for maximal pressure greater than 0.5 bar.

Pressure equipment must be designed, manufactured, tested, equipped and installed in

such way that ensures safety during service, and it should be handled following manufac-

turer’s instructions, in accordance with defined working conditions. Nondestructive

testing of welded joints must be performed by qualified personnel. For the examination of

the pressure equipment of higher categories, personnel must be authorized by the inde-

pendent organization. Final inspection may be applied during manufacturing to any part

of the equipment, internally and externally, if it is necessary from the safety aspect.

Structural integrity is new approach, which comprises state analysis and diagnosis of

behaviour, life assessment and structure revitalization. Except common situation regar-

ding life assessment after the imperfection has been detected by nondestructive testing,

this approach includes stress state analysis. Precise and detailed distribution of strains and

stresses, obtained in this way, enable to determine "weak" spots of the structure. This

approach is important for highly loaded structures, such as pressure equipment.

This lecture gives an overview of new approach to standardization and technical

harmonization for pressure equipment, which refers to structural integrity, i.e. on the

fundamental safety requirements, calculations, design, strength testing and nondestructive

testing (NDT). Methodological approach to modelling and strength calculation of

pressure vessel structure by using the finite element method (FEM), calculation of

fracture mechanics parameters for surface crack and state assessment by application of

nondestructive testing methods, are also presented.

When pressure equipment is used in energy structures it may be classified in different

directives. For example, compressor unit (Fig. 1), can be classified to PED 97/23/EC, but

also to Simple Pressure Vessels Directive 87/404/EEC, Machinery Directive 98/37/EEC

and Low Voltage Directive 2006/95/EC, because some parts of the unit (compressor,

cooler, measuring devices, control devices, valves, electromotor and other components)

they fall into corresponding directive. Directive 99/36/EC (TPED) is applied to

Transportable Pressure Equipment. Manufacturer’s and distributor’s responsibility is that

all parts of the unit comply with the requirements of relative directive /2/.

2. STRUCTURE AND CONTENT OF PRESSURE EQUIPMENT DIRECTIVE

The PED 97/23/EC was introduced into Serbian legislation by the Regulation of

technical requirements for pressure equipment /3/. This regulation prescribes the requi-