Marcio I Haraguchi. Mahmod Samman. Ediberto B. Tinoco Fábio C. Marangone Hezio R. Silva Gustavo C. Barcelos

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1 Marcio I Haraguchi TRICOM TECNOLOGIA Mahmod Samman HOUSTON ENGINEERING SOLUTIONS Ediberto B. Tinoco Fábio C. Marangone Hezio R. Silva Gustavo C. Barcelos PETROBRAS S.A.

2 COMMON SHELL FAILURES Bulging Cracking Tilting (banana effect) Clad separation Coke drum shell bulging in early 1960s

3 WHY DO DRUMS BULGE? Very high transient stresses Axial and hoop stresses in the drum may exceed yield during operation Flow patterns inside drums Uneven heating and cooling Fabrication Imperfections Material / thickness mismatch Can-to-can and plate-to-weld

4 WHY BULGING AND CRACKING? Coke drums are typically designed as pressure vessels per ASME Section VIII Division 1 using rated pressure and Temperature RVI photo - Bulge at internal weld Not designed for transient stresses or cyclic operation Plastic deformation and fatigue damage RVI photo - Crack at internal overlay

5 DIFFICULTY OF BULGING ASSESSMENT Bulging failure is complex Combination of excessive plastic strain and fatigue Magnitude of bulging is false indicator Large uniform growth is less severe than small non-uniform growth Linear stress analysis inadequate for plasticity Must simulate bulging process in order to be valid No applicable standard Bulge assessment rules for non-cyclic service in API-579 of 2001 were withdrawn.

6 WHERE TO EXPECT CRACKS? Inside of bulge peaks Outside of bulge valleys Heat-Affected-Zone of circumferential welds especially at the thinner side of thickness changes

7 LOW PERSONEL RISK HIGH REPAIR COMPLEXITY Risks: Through-wall cracks Leaks Fires (sometimes) Repairing: Complex Extensive operation interruption

8 BULGING STATISTICS (1996 API Coke Drum Survey, Final Report, 2003) Bulging was reported by 57% Of the drums that bulged, 87% also experienced cracks Circumferential cracking was found 97% of the time Cracking without bulging was reported only by 6% 23% reported that they had experienced a fire as a consequence of cracks

9 EXPERIENCE Country Customer # Reators Analisys Year Argentina YPF Lujan de Cuyo YPF La plata Shell La Boca SCF SCF SCF 2007, Brasil Petrobras RPBC Petrobras REFAP Petrobras REGAP SCF e PSI SCF SCF e PSI 2010, Venezuela PDVSA Petromonagas PDVSA Sincor PDVSA Petropiar SCF SCF SCF Total: 31 coke drums

10 3D LASER SCANNING State of the art Laser Scanner Faster and accurate Scan 100 % of internal area Easy setup High density cloud points 100 ~ 200x10 6 points per drum Good statistics! Internal surface 100% of internal surface No data interpolation Specific Software Data handling Statistical treatment 3D View od coke drum cloud data points

11 NEW 3D CLOUD POINTS OLD Partial scanning

12 Elevação [m] CONTOUR MAP NEW OLD Incomplete and interpolated Map Azimute [graus]

13 NEW DATA MATRIX OLD Low density cloud points Good statistics Poor statistics

14 Altura (pulg) Esfuerzo (psi) NEW ANALISYS QUALITY OLD Noise Incomplete data Azimut (grados) High density cloud points Low density data

15 IS BULGING MAGNITUDE AN INDICATION OF SEVERITY?

16 STRESS CONCENTRATION FACTOR (SCF) Developed in 1995 Linear elastic finite element analysis Uniform internal pressure loading Failure expected at stress concentration of 6 (some use 5) Advantages: Simple analysis Some basis in mechanics Disadvantages: Grossly simplified loading Use of linear elastic model does not account for plastic damage or residual stresses Only sensitive to large bulges w/ high aspect ratios No compliance with industry standards Poor correlation with failures Oval drum with high SCF

17 PLASTIC STRAIN INDEX (PSI) PSI (%) = Developed in 2011 Plastic strain analysis Compares plastic strain to the local failure limits of API 579/ ASME FFS versions 2000 and 2007 Includes nonlinear mechanical properties of material in calculations Advantages: Excellent correlation with failures Basis in mechanics Not limited to coke drums Based on a recognized industry standard (API 579/ ASME FFS) Disadvantages: Relatively new Effective plastic strain Failure limit

18 PSI PSI VERSUS SCF SCF False indication PSI Outside axial SCF

19 PSI PSI VERSUS SCF SCF False indication Coke patch Coke patch PSI Inside Axial SCF

20 OTHER BULGED DRUMS Oval Many bulges

21 Classificação PSI PSI : EXCELLENT CORRELATION WITH FAILURES PSI magnitude Severity Grade Likelihood of Bulging- Related Cracks Recommended Frequency of Laser Scanning 80 to 100% Failure Likely 6 months to 1 year 60 to 80% Danger Probable 1 year 40 to 60% Concern Possible 1 to 2 years 0 to 40% Design Unlikely 2 to 3 years RVI photo RVI photo PSI 81% Failure PSI 62% Danger

22 SUMMARY High-density laser: full internal surface scans are needed for precise and high-quality characterization of bulging in coke drums. Stress analysis techniques such as SCF have too many technical limitations to be effective for bulging assessment. The strain analysis technique PSI correlates well with available data of bulging failures. Since PSI is based on the local failure criterion of API 579/ ASME FFS Standard, its results are expected to have more standing with regulatory agencies than stress analysis techniques.

23 THANK YOU!