Corrosion effects on structural integrity and life of oil rig drill pipes/Efekti korozije na integritet konstrukcije i zivotni vek cevi za busenje izvora nafte

Corrosion effects on structural integrity and life of oil rig welded pipes are analysed by experimental, analytical, and numerical methods. Experiments were performed using standard tensile specimens and CT specimens for static loading, Charpy specimens for impact loading, and 3 Point Bending specimens for fatigue crack growth with amplitude loading. In each case new and old pipes were used to evaluate corrosion effects. Results indicated negligible corrosion effects in the case of tensile properties and impact toughness, and strong effects in the case of fracture toughness and especially fatigue crack growth rates, increasing the risk of static failure and reducing significantly structural life. Analytical expressions are used for oil rig pipe structural integrity and life assessment to quantify these effects. Recently introduced risk-based approach is applied to analyse oil rig drill pipe with a corrosion defect treated as a surface crack. Keywords: risk-based assessment; failure analysis diagram; fatigue; risk matrix. Available on-line at the Journal web address: (Naucni rad) Uticaj korozije na integritet i vek naftnih busecih cevi je analiziran eksperimentalnim, analitickim i numerickim metodama. Eksperimenti su radeni na standardnim zateznim i "CT" epruvetama, ispitinim statickim opterecenjem, Sarpi epruvetama ispitanim na udarno opterecenje i epruvtama na savijanje u 3 tacke, ispitanim na amplitudno opterecenje. U svakom slucaju je ispitan novi i korisceni materijala da bi se odredio uticaj korozije. Rezultati su ukazali na mali uticaj korozije u slucaju zateznih svojstava i zilavosti, a relativno veliku uticaj u slucaju zilavosti loma I brzine rasta zamorne prsline, sto znacajno povecava rizik od loma i smanjuje preostali vek cevi. Kvantifikacija ovog uticaja je odredena pomocu analitickih izraza za factor integriteta napona. Nedavno uvedeni pristup analizi rizika je primenjen da se odredio nivo rizika u novim i koricenim cevima, pri proracunskom i ispitnom pritisku. Kljucne reci: procena rizika; dijagram analize loma; zamor; matrica rizika