STEEL IMAGE Inc. Metallurgical Analysis Included in the Inspection Toolbox Shane Turcott, M.A.Sc Fail, Learn, Succeed NDT in Canda 2014
STEEL IMAGE INC. S. Turcott, B.Eng, M.A.Sc 10 years experience (Dofasco, Bodycote, Liburdi Turbine Services) Expert in Failure Analysis and In-Situ Metallography Company founded in 2007. Located in Hamilton, Ontario Failure Analysis & On-Site / In-Situ Examination Supporting engineering, reliability and inspection. Steel, nickel, copper based alloys. Metallographic Laboratory Facility Supporting a broad spectrum of industries including oil, manufacturing, mining and energy. Such as Suncor, Imperial Oil, Nova Chemical, Vale, Hitachi, OPG, Boart Longyear, Magna, ArcelorMittal, HATCH, etc.
TOOLS FOR INSPECTION 1 In-Situ Metallography (on-site examination, non-destructive) Inspect metal condition, evaluating for service degradation. Non-destructively examine indications found by NDT inspection. 2 Metallurgical Failure Analysis (how & why it failed, destructive) Lab-based analysis to explain causes of damage/cracking found by NDT inspection. Assess material quality/conditions. 3 Additional Lab Support General material testing. Metallurgical expertise.
IN-SITU METALLOGRAPHY (on-site) boiler tube microstructure In-situ metallography allows for on-site, non-destructive examination of the steel structure. Can examine the steel s microstructure, assessing for: Thermal / service degradation. Identify material flaws and welding defects. Assess for proper heat treating at manufacture.
IN-SITU METALLOGRAPHY (on-site) boiler tube microstructure Preparation of ~3/4 x 1 inch location includes: Grind/polish to a 1µm polish (hot work permit required). Chemical etch. Direct examination at low magnifications, 100-200x (if PPE permits) Replicate, creating a copy for in-lab examination. Thorough examination of replications under a high-powered microscope. Either near off-site or back in laboratory. Takes about 45-60min per location. Approx 8-12 per 12hr shift
REPLICATION Direct Examination (steel directly under microscope) From On-Site Replication (field copy of structure) Ferrite & Pearlite 1000x 1000x Replications can accurately copy the microstructure up to resolutions needed for 1000x magnification. Allows for reliable examination of the microstructure.
IN-SITU SUPPORTING INSPECTION In-situ metallography useful tool to support inspection and reliability efforts. Three areas of application include: 1 2 3 Shutdown Inspection Damage Survey after Failure Examination of NDT Indications
SHUTDOWN INSPECTION
SHUTDOWN INSPECTION Generally used to evaluate for elevated temperature damage including: Long term overheating Short term overheating (excursions) Hydrogen damage Sensitization / sigma phase formation (stainless steel) Provides information regarding the material condition and operating history. Parent Metal Heat Affected Zone Weld
LONG TERM OVERHEATING New Condition Lamellar Pearlite Beginning of Degradation Beginning to spheroidize Significant Long- Term Damage Ferrite & Pearlite Bainite Advanced spheroidization Long-term overheating from temperatures just above the rating of the material type (<1340ºF for carbon steel). Results in thermal degradation of the pearlite, causing spheriodization, weakening the material. Creep damage occurs simultaneously from (a) higher operating temperature and (b) weakened material.
INSPECTION EXAMPLE #1 Furnace Manifold Long-Term Overheating (significant degradation) During shutdown inspection, furnace manifold found to exhibit significant thermal degradation from long-term overheating. Material Type - ASTM A213 P11 (1¼% Cr, ½% Mo). Owner did quick fitness-for-service analysis. Able to monitor remaining life by dimensional measurements, assessing creep. Safe for short-term continued use.
INSPECTION EXAMPLE #2 Inlet (as-manufactured condition) Other locations (changed, excursion >1600 F) Ferrite & Pearlite Bainite Process heater tubes exhibited short-term overheating (process excursion). Tubes had changed from as-manufactured structure to bainite. Tubes had reached temperatures >1600 F (>871 C), then quenched. Damage from a gas flow interruption event
OTHER FORMS OF DAMAGE Creep Voids (KHR 35 high temp alloy) SS Sensitization Significant Long- (304 stainless Term steel) Damage Creep Voids Sigma Phase Formation (Duplex stainless steel) Sigma Phase (black phase) Carbide formation along grain boundaries Various other degradation modes distinguishable by in-situ metallography Some specific to material types.
SHUTDOWN INSPECTION 1) Assess the material condition. SUMMARY 2) Detect material degradation which may require further consideration and risk future reliability. 3) Identify operating conditions contributing to degradation. Added value if results provided during the shutdown. Parent Metal Heat Affected Zone Weld
EXAM OF NDT INDICATIONS
EXAM OF NDT INDICATIONS Same in-situ metallography techniques can be used to evaluate NDT indications. Not as thorough as sending sample to lab. Yet useful when destructive testing is not possible. Stretch goal to determine cause of cracking. Can usually narrow down: If service degradation or as-manufactured flaw Family of cracking / indication
EXAM OF NDT INDICATIONS Inspection of a 50yr old ammonia tank found cracks in SAW welds at CF Industries. Unsure the cracking mechanism. Cases of corrosion cracking known to occur to ammonia tanks. Had in-situ metallography completed to better understand cracking.
EXAM OF NDT INDICATIONS High Temp Oxide Abnormal Precipitates - Contamination In-situ metallography found high temperature oxide in weld cracks (ie. cracks formed during welding). Abnormal microstructure weld contamination.
EXAM OF NDT INDICATIONS Copper Contamination High levels of copper contamination found at one weld location. Tip blow-out during SAW welding contaminated weld, causing weld cracks. No crack growth had occurred during service (benign). Cracks as-welded. Not service degradation.
EXAM OF NDT INDICATIONS Provides information about the nature of NDT indications. Can usually narrow down: If service degradation or as-manufactured flaw Family of cracking / indication Applied when destructive testing not a viable option. Maximized value if metallurgist conducts the on-site evaluation.
LAB SUPPORT Metallurgical Failure Analysis & Lab Support
LAB SUPPORT METALLURICAL FAILURE ANALYSIS provides information as to why a component cracked. Inspection finds it, failure analysis explains it. Uses lab-based equipment to analyze components, providing information regarding causes of failure not visibly recognizable. Analysis is typically destructive.
WHAT IS FAILURE ANALYSIS? Failure Analysis analogous to the show CSI Investigate the failure to understand HOW and WHY it failed You (Inspector) On-site detective. Failure Analysis lab support to assist your investigation. Use lab-based equipment to study components. Provides evidence and eliminates guesswork. Only method to definitively determine cause of failure for some failure scenarios.
FULL METALLURGICAL LAB Failure Analysis uses a full arsenal of laboratory equipment. Provides information not visibly recognizable.
EXAMPLE #1 HEAT EXCHANGER LPI inspection found cracks within tubes on a heat exchanger. Heat exchanger ~15 years old, bundle replaced 6 months ago. Tubes 1803 Duplex Steel (SA-789). Five other heat exchangers re-tubed around the same period using the same tube supplier.
EXAMPLE #1 HEAT EXCHANGER Chlorine found Cracking was stress corrosion cracking (SCC) initiating on the tube OD. Chlorine found. Corrosion agent causing SCC. Water was spike-chlorine treated.
EXAMPLE #1 HEAT EXCHANGER Composition (wt%) C Mn Si S P Ni Cr Mo N 0.013 1.30 0.38 <0.005 0.03 5.42 22.4 3.09 0.174 Typical microstructure (no quality issues observed) Tube chemistry, hardness and microstructure were typical. Nothing wrong with the tube material. Failure was due to an operational issue, not poor material. Either (a) increased levels of chlorine and/or (b) increased operating temperatures. Either could be excursions.
CONCLUSIONS CONCLUSIONS Heat exchanger tubes failed by stress corrosion cracking due to operational issues. Either (a) increased levels of chlorine and/or (b) increased operating temperatures. Either could be excursions. Material was fine. Failure not due to a tube quality issue. RECOMMENDATIONS & OUTCOMES Need to control operational variables to prevent repeat failures. Monitor other five heat exchangers: If chlorine levels were the primary cause of cracking then other exchangers may have been damaged and at risk of failure. If temperature excursions were the primary cause, damage may be isolated to sole heat exchanger.
EXAMPLE #2 SWAGE New equipment failed hydrostatic testing. Using Inspection found a crack/indication at a weld on a swage. Used penetrant inspection to highlight crack/leak. Swage lot had been used at various refineries across Canada.
EXAMPLE #2 SWAGE Optical examination found the swage to have a seam flaw. From original tube manufacture. Deeper than the weld. Created leak path beneath the weld. Extended the full length of the swage (even places where LPI didn t detect it). Seam flaw
CONCLUSIONS CONCLUSIONS Swage contained seam flaw. Present on the original tube material. Deeper than the weld. Created leak path beneath the weld. A portion of other swages made from this lot would also contain seam flaws. LPI did not detect full length of flaw. RECOMMENDATIONS & OUTCOMES Issued company wide quarantine of swage lot. Supplier recalled lot. Those swages already installed were inspected using MPI.
METALLURGICAL FAILURE ANALYSIS Inspection finds it, failure analysis explains it. Failure analysis uses laboratory equipment, extracting additional details regarding the cause(s) of damage/failure. Detailed diagnosis provides information useful to reliability and inspection decisions.
SUMMARY
TOOLS FOR INSPECTION Metallurgical analysis is a useful tool for supporting inspection and reliability efforts. 1 In-Situ Metallography (on-site examination, non-destructive) Inspect metal condition for service degradation Non-destructively examine indications found by NDT inspection 2 Metallurgical Failure Analysis (how & why it failed, destructive) Lab-based analysis to explain causes of damage/cracking found by NDT inspection. Assess material quality/conditions.