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Dissimilar metal weld failure of steam piping in a hydrogen unit of petroleum refinery
Abstract
Steam generation from hot reformer effluent in a hydrogen unit of a petroleum refinery increases the refinery margin. Upstream and downstream piping in hydrogen plant were constructed by SA335 P22 (AS) and type SS304L (SS) materials, respectively. This paper reports
failure of dissimilar pipe weld after six months of high pressure steam service. Visual inspection indicates several ratchet marks initiated from outer wall surface at heat affected zone (HAZ) of AS pipe accompanied with brittle fracture. Further, failed samples were examined for chemical analysis, micro-hardness, fractography & elemental analysis and microstructural analysis. Fractographic
results indicated that the dissimilar weld was failed due to thermal fatigue. Moreover, microstructural analysis revealed the presence of martensite in AS HAZ region with higher micro-hardness. In-spite of fixed operating temperature at 600 °C, there was a difference in thermal expansion that induced large strain gradient at interface and result in low cycle thermal fatigue failure. Type 308L filler metal was directly employed for dissimilar welding without buttering at interface layer was the main cause of failure. The principal factors that were responsible for Dissimilar Metal Weld (DMW) failure are discussed with respect to Schaeffler diagram and correct welding procedure for failure prevention is proposed. It is further recommended to employ 309/309L filler metal at interface layer according to ASME codes & standards to avoid DMW failure.
... Selected process like hydro cracking can crack intermediate crude oil products using hydrogen at higher pressure and temperature. Therefore, hydrogen is essential in refining process and it will be produced within refinery complex in hydrogen unit [6,7]. Continuous operation of hydrogen unit is essentially required for production of intermediate and finished hydrocarbon products [8]. ...
... This latent or sensible heat will be in form of thermal energy must attribute to temperature difference (ΔT). The design of heat exchanger was aimed for high heat transfer with low fouling rate [6]. There were wide variety of heat exchangers used in oil refinery, boiler plants, chemical units and nuclear plants [9][10][11]. ...
The reformer effluent is serially cooled down to produce hydrogen in the hydrogen unit of an oil refinery. The process heat from effluent is effectively utilized for low pressure steam generation using heat exchanger. This exchanger shell and tube side fluids were boiler feed water and process gas, respectively. Several tubes of this heat exchanger were failed especially within tube sheet after 4 years of useful service. Therefore, failed exchanger tube was subjected to engineering failure analysis to determine the cause of failure. Initially visual inspection was conducted using videoscopy in heat exchanger dry condition and evidenced circumferential crack. Subsequently, all failed tubes were separated from U tube bundle. Selected tube was subjected to visual inspection, dye penetrant and dimensional measurement. No evidence of visual deformation and thickness loss observed in the failed tube. Further investigated tube was subjected to chemical analysis and confirmed the required metallurgy as per design specification. The fracture surface was subjected to elemental analysis, fractographic, metallographic and hardness investigations. The micro hardness of an exchanger tube at failure location was higher than specified hardness value. Investigation also revealed that exchanger tubes were expanded from tube inner surface to establish tube to tube sheet joint according to specified design drawing. Tube expansion was done prior to start of service and attributed to residual stress within tube material. The results revealed that presence of chloride in the accumulated deposits within tube to tube sheet joint favored conducive environment for chloride stress corrosion cracking. Recommendations were suggested for failure prevention. Achievement in this paper may supplement the similar heat exchanger tube failure database and mitigation of failure will be possible by good engineering practices.
... The boilers are generally designed for 30 years of useful service; however, premature failures can occur in any section leading to the boiler outage. In boilers, several metallurgical and corrosion failures were reported such as creep [1], sulfidation [2], stress corrosion cracking SCC [3], fouling [2], graphitization [4], thermal fatigue [5], water hammer-induced vibration fatigue [6], sigma phase formation [7], carburization, decarburization [8], hightemperature oxidation [9], departure nucleate boiling DNB [10], high-temperature hydrogen attack (HTHA) [11], dew point corrosion [12], oxygen corrosion [13] and hightemperature oxidation [14]. Most failures evidenced in high-temperature boiler section, especially in super heater banks, which were much complex as well as damages were synergistic in real-time boiler operating conditions. ...
The high-pressure and high-temperature super heater tubes are critical in circulating fluidized bed combustion coal-fired boilers. The intention of this paper is to avoid the failure of platen super heater tubes by careful boiler operation and inspection, thereby improving the reliability of boiler equipments.
... However, the experimental result (figure 7(a)), which was the absence of martensite, was related to slow cooling rate and fusion zone composition. In a study by Subramanian [30], referring to the Schaeffler diagram for fusion boundary phase prediction, it was found that using type 309/309L filler wire was considered, assuming 30% dilution, it resulted in austenite and ferrite with no present martensite in the Schaeffler diagram prediction. Therefore, the result used in this study (10% dilution of 70A and 12% dilution of 100A using the ER309L filler 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 Hence, the dilution percentage would be shown on a smaller scale than the dilution percentage of the 100A-ER308L specimen. ...
Dissimilar metal welding is a popular process in very large coal and gold, power generation, and pulp and paper factories. It has mainly been applied to produce large boilers in sugar factories. The aim of the present study was to examine the characteristics of dissimilar metal welded joints made from carbon steel and 3CR12 ferritic stainless steel. The welding specimen was made from filler wires of ER308L and ER309L, and a gas tungsten arc welding process was employed for the V-shaped butt weld joints. The effects of the process parameters, such as the microstructural characteristics and mechanical properties, were investigated. The results from the welding parameters with filler wire of ER308L applied at 70A of welding current showed the microstructure of delta ferrite and austenite. In comparison, 100A of welding current presents delta ferrite, austenite, and martensite. Furthermore, carbide formation was not observed in the fusion zones of any of the experiments. When the ER308L filler wire was used, the amount of delta ferrite was higher than that of the ER309L filler wire, and the amount of delta ferrite increased with increasing hardness. In addition, the results of the filler wire of ER308L could replace the ER309L filler wire, which effectively reduces the material cost.
... The shell-and-tube heat exchanger's versatility has made it the standard in the industry [2]. Heat exchangers were utilized for effective heat exchange between two fluids by evaporation, condensation, and occasionally without phase changes [3]. Various heat exchangers were employed in nuclear power plants, boiler plants, chemical factories, and oil refineries [4][5][6][7]. ...
Shell and tube heat exchangers are widely used in the oil and gas, petrochemical and nuclear power sectors. The most important aspect of the turnaround is the routine testing and inspection of the in-service heat exchanger. Heat exchangers in use are the primary cause of tube flaws such as pitting, corrosion, erosion, fretting corrosion, crevice corrosion, stress corrosion cracking, wear, galvanic corrosion, fatigue cracking, microbiologically influenced corrosion, and so forth. For research, a seamless nickel–iron–chromium alloy-tubed SB 163 (UNS 8810) heat exchanger was taken. The total number of tubes that need to be inspected is 286 tubes with a specification of 19.05 mm OD × 2.11 mm thickness × 5000 mm length. From the different advanced NDT techniques, the eddy current testing (ECT) was chosen for inspection since it has become one of the most popular NDT methods for locating discontinuities in heat exchanger tubes. A standard calibration tube was used to calibrate the system's response and set the sensitivity. During the inspection, the ECT probe was inserted from the below side up to the other end and collected while pulling the probe from the tube. Inspection data were recorded for the length of each tube. All indications were assessed, and defects were categorized as different extents of wall thickness loss after inspection. The inspection report shows how many tubes were found defective and need to be plugged or removed (retubing). From the inspection data (the result of statistics), defects like corrosion, pitting, wall loss, wear, etc., that resulted in notable material loss were identified. Inspection data also summarized where the defects were located (like between the first baffle and the second baffle) and are helpful for further research. After analysis using ECT reports, the defective tubes were categorized according to their defect percentage and location, which helps to do retubing effectively by avoiding the 100% retubing concept.
... The crack occurred on the surface of high hardness location of much localized region below 82 • C which is a favorable condition for SSC cracking. In case of carbon and low alloy steels, high hardness could be evidenced on cover pass or last pass of weld that are usually not subjected to tempering or softening by subsequent passes [59]. Therefore post weld heat treatment (PWHT) is essentially required on carbon or low alloy steels to reduce the residual stress. ...
The light hydrocarbon containment leakage in a petroleum industry overhead piping have caused severe fire explosion.
This paper reports Sulfide Stress Cracking (SSC) in an overhead piping of splitter unit which separates out lighter components from heavier hydrocarbon. The failed overhead piping has been analyzed to determine the root cause of fire incident. The piping metallurgy was SS316L and chemistry of failed fitting components & its weld have been complied with NACE specification. Initially fittings were evaluated for intergranular corrosion to determine as-received material condition and confirmed defect free material. However, metallographic evaluation clearly evidenced transgranular brittle mode of cracking while hardness was higher than NACE specification (22HRC). Furthermore, virgin pipe joint was compared with damaged pipe joint for microstructural assessment. Moreover, actual service conditions were evaluated to obtain pH and H2S concentration in overhead condensed
boot water. Microstructural factors have been discussed in detail as well. The results revealed that cold deformed austenitic structure attributed to SSC and undesired manufacturing steps were employed. Further, the root cause of an accident investigation also revealed failed components were not according to NACE specified metallurgy for sour service conditions.
... Sa335-P22 steel pipes [1][2][3][4][5] consist of 2.25Cr-1Mo low alloy steel, as this material exhibits good weldability and persistent plasticity, and is mainly used in the pressure bearing system of main-steam pipelines in thermal power plants. A comprehensive inspection of a powerplant (Location: Nanjing, Jiangsu Province) in 2015 found that the metallographic structure of a section of SA335-P22 pipeline was moderately spheroidized. ...
In this study, the comprehensive properties of a P22 high-temperature steam pipeline with moderate spheroidization were evaluated after more than 11,700 h of operation through a series of physico-chemical properties testing, especially for a creep test. The remaining life of the P22 high-temperature steam pipeline was analyzed and predicted by the θ parameter method, to guide the normal operation of the P22 high-temperature steam pipeline.
Dissimilar metal welded (DMW) joint plays a crucial role in constructing and maintaining ultra-supercritical (USC) nuclear power plants while presenting noteworthy environmental implications. This research examines different welding techniques utilized in DMWJ, specifically emphasizing materials such as P91. The study investigates the mechanical properties of these materials, the impact of alloying elements, the notable difficulties encountered with industrial materials, and the concept of buttering. The USC nuclear power plants necessitate welding procedures appropriate for the fusion of diverse metal alloys. Frequently employed methodologies encompass shielded metal arc welding (SMAW), gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), and flux-cored arc welding (FCAW). Every individual process possesses distinct advantages and limitations, and the choice of process is contingent upon various factors, including joint configuration, material properties, and the desired weld quality. The steel alloy known as P91, which possesses high strength and resistance to creep, is extensively employed in advanced ultra-supercritical (AUSC) power plants. P91 demonstrates exceptional mechanical characteristics, encompassing elevated-temperature strength, commendable thermal conductivity, and notable resistance against corrosion and oxidation. The presence of alloying elements, namely chromium, molybdenum, and vanadium, in P91, is responsible for its improved characteristics and appropriateness for utilization in (AUSC) power plant applications. Nevertheless, the utilization of industrial materials in DMW joint is accompanied by many noteworthy concerns, such as the propensity for stress corrosion cracking (SCC), hydrogen embrittlement, and creep deformation under high temperatures. The challenges mentioned above require meticulous material selection, process optimization, and rigorous quality control measures to guarantee the dependability and sustained effectiveness of DMW joint. To tackle these concerns, a commonly utilized approach referred to as buttering is frequently employed. When forming DMW joint in nuclear facilities, it is customary to place a buttering coating on ferritic steel. This facilitates the connection between pressure vessel components of ferritic steel and pipes of austenitic stainless steel. The primary difficulty in DMW joint manufacturing is in mitigating the significant disparity in material characteristics resulting from carbon migration and metallurgical alterations along the fusion interface between ferritic steel and austenitic stainless steel. The process of buttering entails the application of a compatible filler material onto the base metal before the deposition of the desired weld metal. The intermediate layer serves as a mediator, enhancing the metallurgical compatibility, diminishing the probability of fracture, and enhancing the overall integrity of the joint. Buttering is still a new research area with a wide scenario of scope in terms of development, which could revolutionize developing high-temperature. These long-term sustainable joints could serve under critical conditions like AUSC power plants and reduce CO2 emissions by increasing the overall efficiencies of the systems.
This paper reports the oxygen corrosion of heat exchanger tubes serviced in dilute steam generation system. The floating head heat exchanger employed in a petrochemical industry underwent remnant corrosion failures particularly at lower passes of tube bundle. Initially remote field eddy current inspection technique was employed for tube bundle conditional assessment and further, root cause of degradation of tube had been analyzed. Comprehensive experimental techniques including visual examination, tube chemistry analysis, external tube surface morphological analysis, elemental mapping, scanning electron microscopy, light microscopy and x-ray dif-fraction studies were employed. The tube surface at the degraded position with its cross sectional examination was rigorously evaluated as well. Moreover, actual steam parameters such as pH, conductivity and iron & chloride concentration have been monitored in the petrochemical facility. The detailed analysis concluded that dissolved oxygen in boiler feed water (BFW) was the root cause for corrosion failure. Several other foreign elements were detected and source of each element was discussed in the context of actual heat exchanger operating conditions. Simulated conditions of BFW service have electrochemically been evaluated in two different dissolved oxygen concentrations at 7.5 ppm and 12.7 ppm, respectively. Even small increase of dissolved oxygen in BFW could lead to promotion of oxygen reduction reaction. Theoretically SA179 tubes operated at pH of 9.75 could lead to formation of bicarbonate and it could protect the tube in absence of dissolved oxygen as evaluated by Molecular Dynamics simulation. However , according to obtained results, tube has been degraded due to presence of dissolved oxygen in BFW. Various contributing factors such as external paint/coat removal, absence of de-aerator system in BFW treatment and improper corrosion inhibitor programme were discussed. Several practical countermeasures have been suggested to mitigate oxygen corrosion failure in petrochemical refineries.
In this study, using flux cored wire, S235JR and S460MC structural steels with a thickness of 16 mm were joined by MAG welding method. Welding processes were carried out to join the same (S235JR-S235JR, S460MC-S460MC) and different types of materials (S235JR-S460MC). In the microstructure examinations, grain coarsening occurred in all conditions, from the base material to the weld metal. From the tensile test results, in all combinations, fracture occurred on the S235JR side. Since fractures are not from the weld zone (weld nugget and HAZ), the weld zone strengths are clearly understood to be higher than the main material tensile strengths. On microhardness tests, the highest microhardness was obtained from the welded metal in all combinations, followed by HAZ and base material. Also, the highest microhardness measured on dissimilar joints of S235JR-S460MC on weld metal was 269 HV (Vickers). The welded specimens were also subjected to fatigue tests; the failure occurred on the base material in all three joints. S460MC-S460MC joint had the highest fatigue strength at the most elevated stress, 625 MPa; however, S235JR-S235JR joint had the lowest fatigue strength at the lowest priority, 300 MPa. Although the fatigue strength results of the same and different combinations and the tensile test results have parallelism, the highest microhardness is seen in S460MC-S235JR dissimilar joints, and its fatigue strength is lower than S460MC-S460MC joints.
Oil and gas industrial assets process hydrocarbons, which include several light and
heavier components. The hydro-cracking process involves the cracking of gas oil to produce diesel and other marketable products. The containment leakage in an oil refinery can not only lead to unit shutdown but also have a significant impact on the safety of the operators involved. According to the author’s previous experience, poor operating and maintenance practices often result in pressure vessel and piping failures
Cold cracking is one of the major issues during welding High Strength Low Alloy (HSLA) 950A steel. The aim of the present research work is to optimize preheating temperature, the addition of oxide particles, and heat input using the Taguchi design of experiments for bead on plate, especially on the improved impact strength of weld metal. The experiments are carried out at three levels of mentioned parameters and Charpy impact strength is considered as a response. L27 orthogonal array is selected for experimentation in the present investigation using three parameters. An addition of vanadium oxide (V2O5) has acted as a nucleation site for acicular ferrite and enhanced the cold cracking resistance of investigated steel. The experimental results suggested that the impact strength of weldment is strongly influenced by pre-heating temperature (74.5%) and less influenced by oxide particle concentration (12.7%), and heat input (12.2%). Microstructure at HAZ revealed
the presence of a small proportion of acicular ferrite of Widmanstatten morphology and upper bainite near weldment causes the reason for enhancement in cold cracking resistance. Fractographic examination revealed the presence of both ductile and brittle fracture modes, which attributed to higher and lower impact strength of weld joint respectively
This paper reports failure of elbow from side cut piping after three years of refinery gasoil service and piping metallurgy was SS316L austenitic stainless steel. Systematic investigations including visual inspection coupled with laboratory studies were carried out to determine the cause of failure. The samples from failure location were examined for chemical analysis, hardness, fractography, elemental analysis and metallographic evaluation. Further, crude feedstock was evaluated as well. Various characterization studies concluded that presence of material defect encapsulated in elbow prior to start of initial distillation column (side cut piping) operation was the root cause of failure. Localized stresses induced from internal pressure act on remaining wall thickness have lead to brittle fracture and resulted in gasoil leakage. The existence of material defect in failed elbow prior to initial operation had revealed poor pre-commissioning inspection practice. The origination of detected material defect was discussed and similar leakages shall be avoided by defect free piping components provided with proper support system at critical piping locations. The results in this article intended for petroleum refinery piping/energy pipeline operators for use of qualified piping components at critical locations especially during plant/piping commissioning stage.
The aim of the present work is to monitor dew point corrosion of crude and vacuum distillation column overhead section in a petroleum refinery. The material of construction of overhead line pipe was carbon steel. The state of art of crude unit process was introduced. The corrosion and associated hydrolyzing mechanisms were briefly described. The crude processing in a petroleum refinery was extremely dynamic and thus field monitoring attempts were made, which provides some useful information on structural integrity of column downstream equipments. The demulsifier, neutralizer, and corrosion inhibitor were mixed in crude unit at specific locations for corrosion prevention. Field monitoring includes evaluation of pH and chloride content of desalter extracted water and overhead condensed water, Base Sediment & Water (BS&W) and chloride content of as‐received & desalted crude, and iron content of overhead condensed water. Furthermore, corrosion coupon was installed in overhead section to obtain the actual corrosion rate. All the field study was conducted for a specified period. The acidity, chloride concentration, and iron loss of condensed water confirmed that acidic corrosion was under control. The corrosion rate of the installed coupons confirmed that corrosion rate was within the specified limit. The results revealed in this paper intended for refinery operators and corrosion engineers involved in understanding of actual process parameters in prevention of overhead acidic corrosion.
In this work, macroscopic and microscopic examinations on the failure specimen were conducted on T91/HR3C dissimilar steel welded joints for the high temperature reheater in a 3033t/h USC boiler. The cracking is along the circumferential direction of tube, initiated in the CGHAZ (course grain HAZ) and terminated at the FGHAZ (fine grain HAZ) of the outer wall. The high hardness and unstability microstructure in the HAZ are responsible for the cracking failure. Post welding heat treatment (PWHT) is suggested for improving the ductility and reducing the residual stress for the welded joints. The delta ferrite with lower hardness was observed near the fusion line of T91 side. However, it was not related to the failure.
Dissimilar Metal Weld (DMW) joint between alloyed steel (AS) and stainless steel (SS) failed at one of intermediate temperature superheater (ITSH) tube in steam/power generation plant boiler. The premature failure was detected after a relatively short time of operation (8 years) where the crack propagated circumferentially from AS side through the ITSH tube. Apart from physical examination, microstructural studies based on optical microscopy, SEM and EDX analysis were performed. The results of the investigation point out the limitation of Carbides precipitation at the alloyed steel/welding interface. This is synonym of creep stage I involvement in the failure of ITSH. Improper post-welding operation and bending moment are considered as root causes of the premature failure.
A number of weld joints between carbon steel (CS) pipe and type 304 stainless steel (SS) elbows constituting a gas piping system of a petrochemical unit developed cracks after a relatively short period of usage, resulting in leakage. The gas flowing through the pipe, was hydrogen rich at a temperature of 45 °C and a pressure of 16 kg/cm2. Light optical metallography and scanning electron microscopy, combined with energy dispersive X-ray spectroscopy, inductively coupled plasma and microhardness testing were used to determine the most probable cause of failure. Analysis showed that the cracks originated at the interface between the CS pipe and the SS root weld. A narrow band between the CS pipe and SS weld exhibited a hardness of Rockwell C 60 suggesting the formation of martensite due to C segregation at welding temperature and subsequent quenching during cooling. The ferritic region of CS adjacent to the weld was decarburized and was devoid of pearlite; corroborating C diffusion. The weld region was diluted comprising mainly of Fe with small amounts of Cr and Ni. Cracking is thought to have initiated at the hardened region. However, the failure might have been aided by hydrogen rich medium and soft C-depleted ferrite region.
Two dissimilar metal butt-welded joints between P92 steel and SUS304 stainless steel were fabricated with different groove shape, namely single V-groove and X-groove, by gas tungsten arc welding process. Based on Sysweld software, three-dimensional thermal-metallurgical-mechanical coupled finite element analyses were performed to investigate the welding-induced residual stresses in P92/SUS304 dissimilar metal butt-welded joints. Meanwhile, the hole-drilling strain gauge method was used to measure the distributions of residual stresses on the top and bottom surfaces of the two butt-welded joints. The results obtained indicate that the predicted welding residual stresses achieve good levels of agreement with the measurements. In the numerical model, the solid-state phase transformation in P92 steel, the strain hardening and annealing effect in SUS304 stainless steel, and the discrepancy in thermal expansion coefficients between dissimilar metals were carefully considered. The simulated results show that these three factors have significant influence on the formation of longitudinal residual stresses in P92/SUS304 butt-welded joints. In addition, the distribution of welding residual stresses in the butt-welded joint with X-groove was compared with that in the joint with single V-groove. The results suggest that the butt-welded joint with X-groove may be superior to that with single V-groove in reducing the region of high tensile residual stress.
The bellow is a flexible component which compensates an expansion allowance imposed by axial strain during high temperature service. The bellow failure during turbine operation of boiler unit has been systematically investigated. The metallurgy of bellow was AISI 316L stainless steel. The comprehensive laboratory investigation includes visual inspection, chemical analysis, mechanical tests, metallographic and fractographic studies. Visual inspection in the field revealed multiple cracks in the bellow and failed debris were collected for laboratory investigation. The mechanical tests of the expansion bellow confirmed to material property specification. The microstructure revealed austenitic structure and fracture surface revealed striation marks. The striation marks attributed to fatigue failure. Finite element analysis revealed that maximum stress induced in the trough region and stress could be higher as compared to ASME VIII Div 1 design equations. It can be concluded that actual operating pressure range could resulted in sufficient stress cycles to initiate fatigue cracks from surface of the bellow. The large number of stress cycles owing to actual varied pressure range attributed to fatigue failure. It is recommended to reduce many intermittent operating conditions by good operational practice and installation of strain gauges at critical locations of the bellow. It is further proposed to increase the existing ply thickness and install reinforced expansion bellow & sandwich/layered plies for prevention of fatigue failure.
After welding or servicing at high temperature, carbon migration will occur in dissimilar welded joint. Correspondingly, the carburized layer with high carbon content and decarburized layer with low carbon content are formed near weld fusion line. Carbon migration has a great influence on the properties of the joint and leads to premature failure. However, due to the small size of carburized layer and decarburized layer, it is difficult to use the traditional uniaxial tensile test method to study their mechanical properties. In this work, the elastoplastic properties of base metal (BM), carburized zone (CZ), decarburized zone (DZ) and weld metal (WM) in A302/ Cr5Mo dissimilar weld joint were investigated by nanoindentation tests. nanoindentation tests results indicate that the decarburized zone is the weakest position in the weld joint. Metallographic and carbon content distribution analysis were also carried out and found that the width of CZ is related to the width of fusion zone (FZ) and the CZ does not exceed the boundary of FZ.
As temperature cycling drives fatigue failure of solder joints in electronic modules, characterisation of the thermal fatigue response of different solder alloy formulations in BGA solder joints functioning in mission-critical systems has become crucial. Four different lead-free and one eutectic lead-based solder alloys in BGA solder joints are characterised against their thermal fatigue lives (TFLs) to predict their mean-time-to-failure for preventive maintenance advice. Five finite elements (FE) models of the assemblies of the BGAs with the different solder alloy compositions are created with SolidWorks. The models are subjected to standard IEC 60749-25 temperature cycling in ANSYS mechanical package environment. Plastic strain, shear strain, plastic shear strain and accumulated creep energy density responses of the solder joints are obtained and inputted into established life prediction models – Coffin Manson, Engelmaier, Solomon and Syed – to determine the lives of the models. SAC405 joints have the highest predicted TFL of circa 13.2 years while SAC387 joints have the least life of circa 1.4 years. The predicted lives are inversely proportional to the magnitude of the areas of stress-strain hysteresis loops of the BGA solder joints. The prediction models are significantly not consistent in predicted magnitudes of TFLs across the solder joints. With circa 838% variation in the magnitudes of TFL predicted for Sn63Pb37, the damage parameters used in the models played a critical role and justifies that a combination of several failure modes drives solder joints damage. This research provides a technique of determining preventive maintenance time of BGA components in mission-critical systems. It proposes developing a new life prediction model based on a combination of the damage parameters for improved prediction.
The aim of this investigation is to examine the premature failure of a low-pressure steam superheater tube used in a vacuum distillation unit of a petrochemical industry. Failure of the heater tube occurred in the form of leakages of fluid during the hydrostatic test. Visual observation of the failed tube revealed several fine cracks on the outer surface of the tube and localized corrosion pits/cavities on the inner surface of the tube. Chemical composition, hardness and tensile properties of the failed tube conform to the designated standard of ASTM A335 P11 grade of steel. The microstructure of the tube comprises ferrite–pearlite structure without any remarkable microstructural degradation. SEM micrographs of the leaked surface revealed the presence of fatigue cracks generated because of fluctuating thermal stresses experienced due to frequent shutdowns during plant operation. Fatigue cracks were found to originate from the pits/cavities on the inner surface of the tube. Pits/cavities were formed because of localized corrosion due to the presence of excess dissolved oxygen in the water along with S and Cl.
In this review article, microstructure and mechanical behavior of the dissimilar welded joint (DWJ) between ferritic-martensitic steel and austenitic grade steel along with its application have been summarized in Ultra Super Critical (USC) power plant. Creep-strength enhanced ferritic-martensitic (CSEF/M) P91 steel was developed to sustain at extreme operating conditions of ultra-supercritical (USC) power plants, and later, P92 was developed to achieve better mechanical properties, higher creep-rupture strength and high operating temperature with the reduction in wall thickness as compared to P91 steel. The most common application of P91/P92 material in power plants includes high pressure and high-temperature steam piping, headers, super-heater tubing, and water-wall tubing. The other most commonly used material in the power plants is austenitic stainless steel, i.e., SS 304 L. The austenitic grade stainless steel offers high resistance to corrosion due to the high wt. % chromium and nickel content (18–20 and 8–12, respectively). Due to the low carbon content, the SS 304 L is less sensitive to the sensitization problem and offers excellent weldability. The joining of these dissimilar materials is frequently required in the power generation industry. The current review focuses on the main difficulty associated with dissimilar welding of martensitic P91/P92 and austenitic grade stainless steel. The different chemical composition, mechanical, physical and metallurgical properties of the martensitic P91/P92 and austenitic grade stainless steel leads to the problems such as hot cracking and carbon migration. The other weldability issues are the formation of a brittle intermetallic compound, the formation of soft transaction heat affected zone along with martensitic steel, δ ferrite formation in fusion zone, diffusion related problem, and residual stresses, which necessitates thorough study and qualification of welds. The effect of coarsening of various precipitates such as M23C6 carbides, MX carbonitrides, and effect of laves phase, z-phase, and sigma phase on mechanical property, and creep-rupture strength of DWJ are also discussed in detail. Based on the literature reviewed, it has been found that some of the above-stated problems can be solved by using nickel-based filler wire due to its intermediate physical and mechanical properties. The selection of the proper filler metal is another vital issue in dissimilar welds joint that is also covered in this review article. The reason behind the formation of the unmixed zone, filler deficient region, peninsula, island, beach, migrated grain boundaries, solidified grain boundaries, and solidified subgrain boundaries during DWJ of martensitic P91/P92 and austenitic grade stainless steel is also discussed. The heat treatment is required to eliminate the heterogeneous microstructure during the dissimilar welding. The effect of post-weld heat treatment (PWHT) on the microstructure and mechanical behavior of the DWJ also reviewed. The residual stress developed during the DWJ may cause the premature failure of the components under service, has also been discussed in detail. The effect associated with the residual stress deformation has been reviewed in the different conditions of the DWJ.
Steam generation from intermediate petroleum products of different hydrocarbon processes ensures zero waste in oil and gas industries. The generated steam is again used for production of refinery final products. Although, zero waste increases refinery margin, there is downside associated with tube failure in utility boiler. Fire side corrosion occurred on economizer tube and failure was systematically analysed. A series of characterization techniques were conducted to find out root cause of failure. Visual inspection, mechanical characterization, plant data collection, morphology investigation of scales using SEM, elemental analysis using EDX, and microstructural analysis were employed. Sulfur content was precisely determined on fire side scale deposits. Steam side feed water and steam products were analysed as well. Characterization of fire side deposits revealed iron oxide scales with severe sulfur concentration as well. The results revealed that failure was primarily owing to acid dew point corrosion and sulfur came from intermediate fuel oil (IFO). The failure mechanisms were discussed and good engineering practices were put forward to combat and mitigate acid dew point corrosion.
Thick stainless steel clad plate is used widely in the petroleum and petrochemical industries because of its low cost and good corrosion resistance. It is generally welded by the multilayer and multipass welding process with stainless steel filler metal matched with the clad layer. In this research, the base metal of stainless steel clad plates was filled with carbon steel filler metal, and the microstructures and mechanical properties of joints with diverse filler metals were analysed and compared. The results indicate that a local hardening zone (LHZ) forms in the weld filled with the filler metals of stainless steel and carbon steel because of the formation of martensite phase in the first layer of weld with filler metal of carbon steel. The microhardness value in LHZ reaches up to 425 HV1, which is significantly higher than that of the base metal. However, the tensile strength value of joints filled with carbon steel filler metal is equivalent to that of the joints with stainless steel filler metal. The results of the side bending test indicate that the LHZ protrudes from the weld, and the crack occurs near the LHZ if the area of the LHZ on the cross section of joint is larger than 17% of that of the whole cross section of the joint. The studied results show that it is feasible to use carbon steel filler metal to fill the base metal of carbon steel in welding of stainless steel clad plate.
Thermomechanical fatigue (TMF) experiment with dwell times on a nickel-based superalloy turbine blade was conducted. The strain field and temperature field of the test section were simulated well through adjusting gripping fixture and induction coil. In addition to the loading, heating, cooling and control subsystems, high temperature strain measurement subsystem was introduced into the experiment to ensure the accuracy of the simulation results of service condition for the test section. In the whole experiment, the service condition of the test section was reproduced. The experiment result showed that TMF crack initiated at the trailing edge of the test section and propagated along the leading edge direction. Using the scanning electron microscope (SEM), multiple crack sources at the surface of turbine blade were observed and the crack surface was oxidized seriously. In addition, based on the fractographic and metallographic observation, the mixed features of intergranular fracture and transgranular fracture were found. The interaction of oxidation, creep damage and fatigue damage is an important reason for the TMF failure of the turbine blade.
In this present paper, failure analysis is conducted for a pipe used in fire water applications. In petroleum industries many failures were observed in API 5 L grade steel pipes. The past inspection history records were observed, which reveals that failed pipeline is poorly maintained since construction. Visual inspection, macroscopic and microscopic examinations were conducted for the failed pipe. The microscopic analysis reveals that the pitting corrosion is a root cause of failure which perforates the wall thickness at 6′o′ clock pipe position. The mechanism of pitting corrosion is correlated with ferrite matrix dissolution. The Cu, Co & Zn ions were detected in scale deposits reveals that the fire water is severely contaminated by various makeup water sources which results in under deposit corrosion. The various sources of foreign elements are discussed in detail. The copper deposits identified at suspected location attributed to galvanic corrosion. Moreover, the severity of pitting is aggravated by grain boundary attack which acts as an anode during corrosion process. Based on various experimental evidences, the conclusions were drawn and further recommendations are discussed to mitigate the corrosion failure.
Boiler tubing is subjected to alternate cycles of heating and cooling during operation initiating alternate thermal expansion and contraction. Alternate cycles of differential expansion and contraction causes thermal fatigue of the component. Thermal fatigue causes tube failures, significantly reducing the working life of the tubular components. Boilers have matured into super critical design using T91 grade materials thereby increasing the operating efficiency. The studies involving thermal fatigue of tubes of T91 grades for boiler components in operating conditions are thus an important area. A simple experimental set up has been developed to simulate thermal fatigue conditions in the internal diameter (ID) side of the tube. The work involves both experimental and numerical investigations of the thermal fatigue behaviour by creating a simulated environment and a Finite Element Model (FEM). FEM analyses are carried out based on the decoupled thermal and inelastic stress analyses to compute the total plastic strain range experienced by the boiler tubes. The cyclic spray cooling causes thermal fatigue cracks in the T91 tube. The number of cycles to crack initiation has been obtained from the experimentation and number cycles to failure has been calculated using modified Coffin-Manson relation. The study thus presents a reliable fatigue failure analysis of 9Cr 1Mo steel tubes used in boiler industry.
In petroleum refining, the equipment are subjected to both high-temperature and corrosion damages. The most common high-temperature attack is related to sulphidation attack both in absence and presence of hydrogen in the processing media. The attack in the presence of hydrogen is much higher than its absence and, therefore, material of construction also varies in two cases. High-temperature attack also occurs if there is presence of naphthenic acid in the crude requiring different considerations in selection of material. The other high-temperature damages like bulging, low cycle fatigue and temper embrittlement are also experienced. Low-temperature corrosion due to presence of HCl and H2S in the overhead system and sulphide stress corrosion cracking are also of major concern for which specific mechanical and corrosion control measures are to be implemented. The chapter presents problems experienced in different units and steps taken in material selection and implementation of suitable corrosion control and monitoring systems.
In this study failure of AISI 347 stabilized stainless steel pipe after 60000 hour of working in a petrochemical plant was investigated. Result showed that the main cause of failure was thermal stress fatigue. Fatigue cracks were formed at the outer surface of the investigated pipe, and were grown towards the inner surface at the fusion line of welded area. The formation of chromium-rich phases together with thermal fatigue stresses were found to be main causes of failure.
The failure analysis of a dissimilar weld in a heat exchanger has been conducted. Within hours of being placed in service, the circumferential weld joining the carbon steel shell to the duplex stainless steel tubesheet experienced partial cracking as H2S was being introduced into the exchanger. The cracking of the weld was determined to be associated with sulfide-stress corrosion cracking facilitated by high weld hardness levels and local dilution of chemistry in the weld.
This paper deals with a fracture mechanics analysis of a narrow-gap Dissimilar Metal Weld in the brittle fracture domain. The considered case is a Ni base alloy weld joint between a ferritic component and an austenitic pipe and the aim of the present study is to show that in the same loading conditions, the weld joint is less sensitive to the brittle fracture than the nearby ferritic part of the component: two positions of a postulated crack are compared, showing that the benefit in terms of fracture resistance for a crack in the ferritic Heat Affected Zone is mainly due to the loss of constraint induced by the plasticity in the Nickel
base alloy weld metal.
Computational models of austenite decomposition are widely used to predict external shape and internal microstructural changes as functions of time and temperature. One modeling approach involves converting the measured transformation strain to phase fractions using the lattice parameters of parent and product phases, because the transformation strain is caused by crystal structural change and an enrichment/depletion of the solute atoms in solid solution. A conversional model of transformation strains occurring during austenite decomposition to phase fractions was developed using an optimal set of lattice parameters and thermal expansion coefficients of each phase associated with low alloy steels. The model is composed of four different transformation strain formulae for ferrite, pearlite, bainite and martensite transformations, respectively, and can be applied to continuous cooling transformations as well as isothermal ones. The conversional model demonstrated a good match between calculated and measured phase fractions of industrial low alloy steels cooled at the different rates after austenitization.
One important part of the integrity demonstration of large
ferritic components is based on the demonstration that they
could never undergo brittle fracture. Connections between a
ferritic component and an austenitic piping (Dissimilar Metal
Weld - DMW) have to respect these rules, in particular the Heat
Affected Zone (HAZ) created by the welding process and
which encounters a brittle-to-ductile transition.
Within that frame, the case considered in this article is a
Ni base alloy narrow gap weld joint between a ferritic pipe
(A533 steel) and an austenitic pipe (316L stainless steel). The
aim of the present study is to show that in the same loading
conditions, the weld joint is less sensitive to the brittle fracture
than the surrounding ferritic part of the component. That is to
say that the demonstration should be focused on the ferritic
base metal which is the weakest material.
The bases of this study rely on a stress-based criterion
developed by Chapuliot et al., using a threshold stress (σth)
below which the cleavage cannot occur. This threshold stress
can be used to define the brittle crack occurrence probability,
which means it is possible to determine the highest loading
conditions without any brittle fracture risk.
The transition metal joint (TMJ) between an austenitic stainless steel and a chromium-molybdenum (Cr-Mo) ferritic steel used widely in steam generators of power plants has for a long time presented problems relating to premature failures in service. The direct (bimetallic) TMJ presently in use is designed for a service life of about 200,000 h; but such TMJs with iron-base weld metals have been failing in service within about one-third of their design lifetime, while their counterparts with nickel-base weld metals fail within about one-half of their design lifetime. The causes for such premature service failures of these TMJs are discussed in detail, leading to the development of improved TMJs. One of the improved TMJs with a trimetallic configuration of austenitic stainless steel/Alloy 800/Cr-Mo ferritic steel is discussed in detail, covering its development, characterisation and evaluation. Accelerated performance tests in the laboratory have indicated a four-fold improvement in the service life of the TMJ with this trimetallic configuration compared to the bimetallic configuration. The metallurgical details of these studies are also discussed in this paper.
Cited By (since 1996): 1, Export Date: 8 January 2013, Source: Scopus, CODEN: EFANE, Language of Original Document: English, Correspondence Address: Lee, S.-B.; Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, Science Town, Taejon, 305-701, South Korea
A failure analysis and creep remaining life assessment on hydrogen reformer outlet pigtail tubes in a methanol plant was conducted. The tube material was manufactured to ASME SB-407 (UNS N08810) material specifications. The observed evolution and progression of grain boundary cavity nucleation, coalescence, microcrack formation and eventual cracks were indicative of long-term creep failure, which occurred before the design life of the tubes. The remaining life evaluation was performed based on metallurgical evaluation of the outer diameter (OD), middle of wall thickness, and inner diameter (ID) percentage creep cavities versus tube OD. Very high statistical correlation was achieved by fitting creep data points to the classic creep strain versus time curve by using third order polynomial equations. The onset of tertiary creep was found to occur at 9.3% increase in the strain of the tube OD. This work affirms that using percentage area of creep cavities and the correlation to increase in OD is a robust technique for the reliable and accurate determination of the creep remaining life of superalloy tubes.
Demonstration of large components integrity is based on the demonstration that they could never undergo brittle fracture. In parallel, considering a conventional defect somewhere in the component, failure must prevent ductile crack propagation.
Connections between a ferritic component and an austenitic one have to respect these rules. The considered case is a Ni base alloy weld joint between a ferritic pipe and an austenitic one. For brittle fracture exclusion, the aim of the present study is to show that in the same loading conditions, the weld joint is less sensitive to the brittle fracture than the surrounding ferritic part of the component. That is to say that the demonstration should be focused on the ferritic base metal which is the weakest material.
For that purpose, Chapuliot developed a stress-based criterion model, using a threshold stress (σth) below which the cleavage cannot occur. It can be used to define the brittle crack occurrence probability, which means that it is possible to determine the highest loading conditions without any brittle fracture risk.
For the experimental part of this demonstration, two different mock-ups with DMW are used. The first one is composed of a 16MND5 (A508 cl. 3) steel pipe welded to a 316L stainless steel pipe with Ni base alloy 82. As for the second one, the materials are the 18MND5 (A533) steel, the 316L stainless steel and the Ni base alloy 52. Conventional defects have been considered in the ferritic part, close to the weld joint in the heat affected zone, and far away from the weld joint in the ferritic part. Two hundred specimens have been taken from the mock-ups: special tensile specimens, compact tensile specimens, single edge notch tension specimens, notched tensile specimens, smooth tensile specimens. All the materials have been characterized at −125°C/−130°C and −170°C/−175°C, even the heat affected zones. Finite element calculations have been done to complete the experimental investigations. The first results show that, due to the mismatch of the materials, the brittle fracture risk is much lower in the HAZ. Thus, DMW HAZ could not be a weak part concerning brittle fracture. This paper presents the criterion, the experimental work and the analyses made to evaluate the conservatism of the homogeneous ferritic case compared to the DMW.
In this paper, findings of visual inspections, chemical analysis on deposits, metallurgical examinations and creep analysis on the failed SA210-A1 heat recovery area (HRA) wall side tubes of a boiler unit are presented. The investigations were carried out following two boiler tube failures at heat recovery areas involving the left hand side (LHS) and right hand side (RHS) side wall tubes. Findings from the microscopic examinations are used to support the investigation in determining the failure mechanisms. The first failure at LHS HRA side wall tube is identified due to thermal fatigue while the second failure is as a result of combination of the corrosion fatigue, thermal fatigue and creep damage. Recommendations are made to reduce unavailability of the boiler unit due to the HRA side wall tube failures.
Design and procedure guide for improved welds EPRI report
- R Viswanathan
R. Viswanathan, Dissimilar weld failure analysis and development, Volume 8, Design and procedure guide for improved welds EPRI report (1989).
Section II Part D Properties, subpart 2 Physical Properties Tables
- ASME Boiler and Pressure Vessel Code
Article V, Welding, brazing, and fusing qualifications, ASME Boiler and Pressure Vessel Code
Article V, Welding, brazing, and fusing qualifications, ASME Boiler and Pressure Vessel Code, Section IX (2015) pp: 225-226.
ASME Boiler and Pressure Vessel Code, Section II Part A Ferrous materials specifications
ASME Boiler and Pressure Vessel Code, Section II Part A Ferrous materials specifications, ASME BPV Code (2015) pp: 481-549.