to AsTM standard practices were rigorously followed. Subsequent investigation and analysis of the indications revealed no growth of the laps in service. Nevertheless, the corrective action defined that all forgings showing laps be removed from service. Preventive measures involved critical review and revision of the forging process(so that future lots would be properly forged) and revisions to the nondestructive evaluation (NDE) procedures at the forging supplier Building an application-life diagram around this case(Fig. 20)(Ref 29), one can explore the impact of material defects of various sizes on service life. In one possible scenario, the lower curve in Fig. 20 could describe the observed lap, being detectable by nDe and of a size sufficient to sustain growth under the anticipated service conditions at some time in the future. However, at the time of the inspection, the defect was smaller than that required for crack growth, since the date of the inspection is relatively early in the intended service life of the component. The risk of crack growth and premature failure at some time in the future (as shown by the"X"in Fig. 20) prompted the removal from service of all forgings showing NDE indications Flaw smaller than NDE detectability (required) efect smaller than size required for growth Anticipated severty I Defect larger than size required for growth Increasing service life Inspection date Intended life Fig 20 Application -life diagram showing effects of different sized material discontinuities on service life Manufacturing/Installation Defects Manufacture refers to the process of creating a product from technical documentation and raw materials, generally performed at a factory. Installation can be considered manufacturing in-place, such as at a construction site or a new plant. Products can be designed properly using sound materials of construction, yet be defective as delivered from the manufacturer, due to rejectable imperfections (i.e, defects)introduced during the manufacturing process or due to errors in the installation of a system at a site. A wide variety of manufacturing- caused defects exist; each and every manufacturing/installation process has many variables that, when allowed to drift toward or to exceed control limits, can result in a defective product(Ref 34) Some examples of such manufacturing/installation anomalies are listed below(Ref 35, 36). Failures associated with metalworking, welding, and heat treating operations are also discussed in more detail in other articles in this Volume, and example 4 also illustrates the effects of manufacturing anomalies on the life of a component Metal removal processes Cracks due to abusive machining Chatter or checking due to speeds and feeds Thefileisdownloadedfromwww.bzfxw.com
to ASTM standard practices were rigorously followed. Subsequent investigation and analysis of the indications revealed no growth of the laps in service. Nevertheless, the corrective action defined that all forgings showing laps be removed from service. Preventive measures involved critical review and revision of the forging process (so that future lots would be properly forged) and revisions to the nondestructive evaluation (NDE) procedures at the forging supplier. Building an application-life diagram around this case (Fig. 20) (Ref 29), one can explore the impact of material defects of various sizes on service life. In one possible scenario, the lower curve in Fig. 20 could describe the observed lap, being detectable by NDE and of a size sufficient to sustain growth under the anticipated service conditions at some time in the future. However, at the time of the inspection, the defect was smaller than that required for crack growth, since the date of the inspection is relatively early in the intended service life of the component. The risk of crack growth and premature failure at some time in the future (as shown by the “X” in Fig. 20) prompted the removal from service of all forgings showing NDE indications. Fig. 20 Application-life diagram showing effects of different sized material discontinuities on service life Manufacturing/Installation Defects Manufacture refers to the process of creating a product from technical documentation and raw materials, generally performed at a factory. Installation can be considered manufacturing in-place, such as at a construction site or a new plant. Products can be designed properly using sound materials of construction, yet be defective as delivered from the manufacturer, due to rejectable imperfections (i.e., defects) introduced during the manufacturing process or due to errors in the installation of a system at a site. A wide variety of manufacturing-caused defects exist; each and every manufacturing/installation process has many variables that, when allowed to drift toward or to exceed control limits, can result in a defective product (Ref 34). Some examples of such manufacturing/installation anomalies are listed below (Ref 35, 36). Failures associated with metalworking, welding, and heat treating operations are also discussed in more detail in other articles in this Volume, and example 4 also illustrates the effects of manufacturing anomalies on the life of a component. Metal Removal Processes · Cracks due to abusive machining · Chatter or checking due to speeds and feeds The file is downloaded from www.bzfxw.com
Microstructural damage due to dull tool Grinding burn Electrochemical machining intergranular attack Electrical discharge machining recast layer cracki Residual stress cracking due to overheating Metalworking Processes Cracking, tears, or necking due to forming/deep drawing Laps due to thread rolling/spinning Tool marks and scratches from forming Surface tears due to poor surface preparation prior to working Residual stress cracking due to flowforming Luders lines due to forming strain rate Microstructural damage due to shearing, blanking, piercing Overheating damage during spring winding Laps and cracks due to shot penin Stress-corrosion cracking due to use of improper die lubricants Heat Treatment Grain growth Incomplete phase transformation Quench crack Decarburization Untempered martensite Temper embrittlement and similar embrittlement conditions nadequate precipitation Sensitized microstructure Inhomogeneities in microstructure Loss of properties due to overheating during post-plating bake Welding Lack of fusion Brittle cracking in heat-affected zone(HAz) Sensitized haz Residual stress cracking Slag inclusions Cratering of fusion zone at endpoint Filler metal contour out of specification · Hot cracking Cracking at low exposure temperatures Hydrogen embrittlement due to moisture contamination Liquid metal embrittlement from plating contamination Cleaning/ Finishing Corrosion due to inadequate cleaning prior to painting Intergranular attack or hydrogen embrittlement due to acid cleaning Hydrogen embrittlement due to plating Stress corrosion from caustic autoclave core leaching of castings Assembly at Factory/nstallation at Site Misalignment ong parts
· Microstructural damage due to dull tool · Grinding burn · Electrical discharge machining recast layer cracking · Electrochemical machining intergranular attack · Residual stress cracking due to overheating Metalworking Processes · Cracking, tears, or necking due to forming/deep drawing · Laps due to thread rolling/spinning · Tool marks and scratches from forming · Surface tears due to poor surface preparation prior to working · Residual stress cracking due to flowforming · Lüders lines due to forming strain rate · Microstructural damage due to shearing, blanking, piercing · Overheating damage during spring winding · Laps and cracks due to shot peening · Stress-corrosion cracking due to use of improper die lubricants Heat Treatment · Grain growth · Incomplete phase transformation · Quench cracks · Decarburization · Untempered martensite · Temper embrittlement and similar embrittlement conditions · Inadequate precipitation · Sensitized microstructure · Inhomogeneities in microstructure · Loss of properties due to overheating during post-plating bake Welding · Lack of fusion · Brittle cracking in heat-affected zone (HAZ) · Sensitized HAZ · Residual stress cracking · Slag inclusions · Cratering of fusion zone at endpoint · Filler metal contour out of specification · Hot cracking · Cracking at low exposure temperatures · Hydrogen embrittlement due to moisture contamination · Liquid metal embrittlement from plating contamination Cleaning/Finishing · Corrosion due to inadequate cleaning prior to painting · Intergranular attack or hydrogen embrittlement due to acid cleaning · Hydrogen embrittlement due to plating · Stress corrosion from caustic autoclave core leaching of castings Assembly at Factory/Installation at Site · Misalignment · Missing/wrong parts
Inappropriate fastening system, improper torque Improper tools Inappropriate modification Inadequate surface preparatio Inspection Techniques Arc burn due to magnetic particle inspection Intergranular attack or embrittlement due to macroetch Fatigue or quench crack from steel stamp mark xample 4: Forming Process Anomalies in Diesel Fuel Injection Control Sleeve(Ref 28 ). A user complained of a diesel engine that failed to start in cold weather. Troubleshooting isolated the problem to the diesel fuel control assembly, which was changed out, fixing the problem. Teardown of the fuel control assembly by the manufacturer revealed that a small subcomponent known as the cold start advance solenoid sleeve(Fig. 21) was leaking through the wall. The sleeve operates under relatively high pressure cycles in service. This component is a tubular product with a"bulb section at one end and threads on the other The manufacturing method used to create the bulb shape was hydroforming, using a 300 series stainless steel tube in the full-hard condition Fig. 21 Cold start advance solenoid sleeve. 0.85x The leak was attributed to a crack in the sleeve(Fig. 22), in the radius between the bulb area and the cylindrical portion of the sleeve. Scanning electron microscope examination of the broken-open crack revealed fatigue cracks initiated at multiple sites near the outside diameter(oD)of the sleeve(Fig. 23). The crack origins were determined to be extending from shallow(0.013 mm, or 0.0005 in. ) zones exhibiting ductile shear(see area between arrows in Fig. 23). Viewing the OD surface of the sleeve adjacent to the fracture plane revealed an extensive network of microcracks on the od in the radius between the bulb and cylindrical portions(Fig. 24 ). A cross section through one of the fatigue crack origins revealed slip bands emanating from the microcracks(Fig. 25) Thefileisdownloadedfromwww.bzfxw.com
· Improper fit-up · Inappropriate fastening system, improper torque · Improper tools · Inappropriate modification · Inadequate surface preparation Inspection Techniques · Arc burn due to magnetic particle inspection · Intergranular attack or embrittlement due to macroetch · Fatigue or quench crack from steel stamp mark Example 4: Forming Process Anomalies in Diesel Fuel Injection Control Sleeve (Ref 28). A user complained of a diesel engine that failed to start in cold weather. Troubleshooting isolated the problem to the diesel fuel control assembly, which was changed out, fixing the problem. Teardown of the fuel control assembly by the manufacturer revealed that a small subcomponent known as the cold start advance solenoid sleeve (Fig. 21) was leaking through the wall. The sleeve operates under relatively high pressure cycles in service. This component is a tubular product with a “bulb” section at one end and threads on the other. The manufacturing method used to create the bulb shape was hydroforming, using a 300 series stainless steel tube in the full-hard condition. Fig. 21 Cold start advance solenoid sleeve. 0.85× The leak was attributed to a crack in the sleeve (Fig. 22), in the radius between the bulb area and the cylindrical portion of the sleeve. Scanning electron microscope examination of the broken-open crack revealed fatigue cracks initiated at multiple sites near the outside diameter (OD) of the sleeve (Fig. 23). The crack origins were determined to be extending from shallow (0.013 mm, or 0.0005 in.) zones exhibiting ductile shear (see area between arrows in Fig. 23). Viewing the OD surface of the sleeve adjacent to the fracture plane revealed an extensive network of microcracks on the OD in the radius between the bulb and cylindrical portions (Fig. 24). A cross section through one of the fatigue crack origins revealed slip bands emanating from the microcracks (Fig. 25). The file is downloaded from www.bzfxw.com
Fig 22 Crack in sleeve(arrows). 2.5x 个 10 Fig 23 Fatigue cracking from the outside diameter(od) of the sleeve (large arrow) . Area between small arrows shows evidence of ductile shear at od surface 100m
Fig. 22 Crack in sleeve (arrows). 2.5× Fig. 23 Fatigue cracking from the outside diameter (OD) of the sleeve (large arrow). Area between small arrows shows evidence of ductile shear at OD surface
Fig. 24 Network of microcracks(arrows) on the outside diameter surface of the sleeve (lower portion of the micrograph) Fig. 25 Microstructure of cross section through outside diameter surface of sleeve adjacent to fracture. Fracture surface is along top of micrograph. Outside diameter surface is along right side of the micrograph Note slip banding(arrows) emanating from microcrack, 116x analysis revealed that during the hydroforming process, heavy biaxial strains were imparted to the sleeve wall, in the s between the bulb and cylindrical portions of the sleeve. When combined with the heavy strains inherently present in the full-hard 300 series stainless steel, the hydroforming strains in the radius caused the microcracking. The ductile sulting in fatigue cracks initiating and propagating from these flaws through the wall, causing the leak Service stresses, shear areas observed at the origins(see Fig. 23 )are microcracks that served to intensify the cyclic service stresses The physical root cause for this failure is a manufacturing process that omitted an intermediate stress relief or annealing treatment prior to hydroforming to the final shape Some time later, a similar complaint was received at the factory for a nonstart condition in cold weather. The sleeve was again identified to be leaking due to a through-wall crack. Analysis of the broken-open crack(Fig. 26) revealed fatigue cracks initiated on the inside diameter (ID)of the sleeve. This time, the flaw that led to the failure was shallow (approximately 0.005 mm, or 0.0002 in ) intergranular attack on the Id surfaces due to overly aggressive acid cleaning insufficient rinsing after the acid-cleaning operation. Examination of the OD surfaces revealed no microcracking or evidence of localized strain. Thus a second manufacturing defect affecting the same component was identified through failure analysis to have caused the identical complaint from the field Thefileisdownloadedfromwww.bzfxw.com
Fig. 24 Network of microcracks (arrows) on the outside diameter surface of the sleeve (lower portion of the micrograph). Fig. 25 Microstructure of cross section through outside diameter surface of sleeve adjacent to fracture. Fracture surface is along top of micrograph. Outside diameter surface is along right side of the micrograph. Note slip banding (arrows) emanating from microcrack. 116× The analysis revealed that during the hydroforming process, heavy biaxial strains were imparted to the sleeve wall, in the radius between the bulb and cylindrical portions of the sleeve. When combined with the heavy strains inherently present in the full-hard 300 series stainless steel, the hydroforming strains in the radius caused the microcracking. The ductile shear areas observed at the origins (see Fig. 23) are microcracks that served to intensify the cyclic service stresses, resulting in fatigue cracks initiating and propagating from these flaws through the wall, causing the leak. The physical root cause for this failure is a manufacturing process that omitted an intermediate stress relief or annealing treatment prior to hydroforming to the final shape. Some time later, a similar complaint was received at the factory for a nonstart condition in cold weather. The sleeve was again identified to be leaking due to a through-wall crack. Analysis of the broken-open crack (Fig. 26) revealed fatigue cracks initiated on the inside diameter (ID) of the sleeve. This time, the flaw that led to the failure was shallow (approximately 0.005 mm, or 0.0002 in.) intergranular attack on the ID surfaces due to overly aggressive acid cleaning or insufficient rinsing after the acid-cleaning operation. Examination of the OD surfaces revealed no microcracking or evidence of localized strain. Thus a second manufacturing defect affecting the same component was identified through failure analysis to have caused the identical complaint from the field. The file is downloaded from www.bzfxw.com