IN THE ENCLOSED AND POORLY VENTILATED SECTION IN MARINE STRUCTURES POLLUTING ORGANIC SUBSTANCES CAN CAUSE PUTREFACTION PHENOMENA TO OCCUR WITH THE FORMATION OF SULPHURETTED HYDROGEN AS WELL AS LOCALIZED CORROSION WITH THE FORMATION OF FREE ACIDS. THIS CAN GIVE RISE TO THE CONDITIONS FOR THE OCCURRENCE OF TWO TYPE OF DAMAGE IN WHICH HYDROGEN APPEARS TO PLAY A FUNDAMENTAL PART AND WHICH COULD RESULT IN TIME IN CATASTROPHIC FAILURE : HSCC (STRESS CORROSION) IN THE PRESENCE OF INTERNAL OR EXTERNAL STRESSES AND HIC (HYDROGEN EMBRITTLEMENT CRACKS) IN THE ABSENCE OF SUCH STRESSES).
A PRECISE KNOWLEDGE OF THE OCCURRENCE OF SUCH PHENOMENA, OF THE MECHANISMS BY WHICH THEY ARISE AND THE RELATIONSHIPS BETWEEN THEM IS OF ENORMOUS PRACTICAL IMPORTANCE TO THE SAFETY, STABILITY AND RELIABILITY OF SUCH STRUCTURES. INDEED, WHILE HYDROGEN PLAYS A FUNDAMENTAL BUT UNQUANTIFIABLE ROLE IN SUCH PHENOMENA AND IN PARTICULAR IN HSCC BOTH THE CATHODIC PROTECTION OF THE STRUCTURE AND THE DESIGN CRITERIA IMPOSED ON THE USE OF THE CRITICAL STRESS VALUES (K ISCC) WILL BE QUESTIONED. THE AIM OF THE PROJECT IS TO STUDY THE MECHANISMS OF THE HSCC AND HIC PHENOMENA AND ANY INTERRELATION THEY MAY HAVE IN WELDED JOINTS OF STEELS FOR MARINE APPLICATIONS WITH PARTICULAR REFERENCE TO THE METALLURGICAL PROPERTIES AND HARDNESS OF THE HAZ BY INVESTIGATING THE PART PLAYED BY THE ACIDITY OF SEAWATER, THE PRESENCE OF SULPHURETTED HYDROGEN AND EFFECT OF CATHODIC PROTECTION.