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PubMed2002

Evaluation of occupational exposure to toxic metals released in the process of aluminum welding.

The objective of this study was to evaluate occupational exposure to welding fumes and its elements on aluminum welders in Polish industry. The study included 52 MIG/Al fume samples and 18 TIG/Al samples in 3 plants. Air samples were collected in the breathing zone of welders (total and respirable dust). Dust concentration was determined gravimetrically, and the elements in the collected dust were determined by AAS. Mean time-weighted average (TWA) concentrations of the welding dusts/fumes and their components in the breathing zone obtained for different welding processes were, in mg/m3: MIG/Al fumes mean 6.0 (0.8-17.8), Al 2.1 (0.1-7.7), Mg 0.2 (< 0.1-0.9), Mn 0.014 (0.002-0.049), Cu 0.011 (0.002-0.092), Zn 0.016 (0.002-0.14), Pb 0.009 (0.005-0.025), Cr 0.003 (0.002-0.007), and TIG/Al fumes 0.7 (0.3-1.4), Al 0.17 (0.07-0.50). A correlation has been found between the concentration of the main components and the fume/dust concentrations in MIG/Al and TIG/Al fumes. Mean percentages of the individual components in MIG/Al fumes/dusts were Al: 30 (9-56) percent; Mg: 3 (1-5.6) percent; Mn: 0.2 (0.1-0.3) percent; Cu: 0.2 (< 0.1-1.8) percent; Zn: 0.2 (< 0.1-0.8) percent; Pb: 0.2 (< 0.1-1) percent; Cr: < 0.1 percent. The proportion of the respirable fraction in the fumes and their constituents varied between 10 percent and 100 percent. The results showed that MIG/Al fumes concentration was 1.2 times higher than the American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value (TLV), and the index of the combined exposure to the determined agents was 2.3 (0.4-8.0), mostly because of high Al2O3 contribution. The background concentrations of the components (ca. 5-10 times lower than those in the breathing zone of the welders) did not exceed the Polish MAC value. The elemental composition of total and respirable fume/dust may differ considerably depending on welding methods, the nature of welding-related operations, and work environment conditions.

Air Pollutants↗

PubMed2005

Manganese exposures during shielded metal arc welding (SMAW) in an enclosed space.

The work reported here evaluates the effectiveness of various rates of dilution ventilation in controlling welder exposures to manganese in shielded metal arc welding (SMAW) fume when working in enclosed or restricted spaces. Personal and area monitoring using total and respirable sampling techniques, along with multiple analytical techniques, was conducted during the welding operations. With 2000 cubic feet per minute (CFM) (56.63 m3/min) dilution ventilation, personal breathing zone concentrations for the welder using 1/8 inches (3.18 mm) E6010 and E7018 mild steel electrodes were within 75% of the existing threshold limit value (TLV of 0.2 mg/m3 for total manganese and were five times greater than the 2001-2003 proposed respirable manganese TLV of 0.03 mg/m3. Manganese concentrations using high manganese content electrodes were five times greater than those for E6010 and E7018 electrodes. Area samples upstream and downstream of the welder using E6010 and E7018 electrodes exceeded 0.2 mg/m3 manganese. Concentrations inside and outside the welding helmet do not indicate diversion of welding fume by the welding helmet from the welder's breathing zone. There was close agreement between respirable manganese and total manganese fume concentrations. Total fume concentrations measured by gravimetric analysis of matched-weight, mixed cellulose ester filters were comparable to those measured via preweighed PVC filter media. This study indicates that 2000 CFM general dilution ventilation per 29 CFR 1910.252 (c)(2) may not be a sufficient means of controlling respirable manganese exposures for either welders or their helpers in restricted or enclosed spaces. In the absence of site-specific monitoring data indicating otherwise, it is prudent to employ respiratory protection or source capture ventilation for SMAW with E6010, E7018, and high manganese content electrodes rather than depending solely on 2000 CFM general dilution ventilation in enclosed spaces.

Confined Spaces↗

PubMed2002

Control of occupational exposure to hexavalent chromium and ozone in tubular wire arc-welding processes by replacement of potassium by lithium or by addition of zinc.

Hexavalent chromium [Cr(VI)] and ozone are produced in many arc-welding processes. Cr(VI) is formed when welding with chromium-containing alloys and is a suspected carcinogen. Ozone is formed by the action of ultraviolet light from the arc on oxygen and can cause severe irritation to the eyes and mucous membranes. Previous work has demonstrated that reduction of sodium and potassium in manual metal arc-welding electrodes leads to substantial reductions in Cr(VI) concentrations in the fume as well as a reduction in the fume formation rate. In this paper replacement of potassium by lithium in a tubular wire welding electrode (self-shielding flux-cored) is shown to give reductions in Cr(VI) concentrations and fume formation rates. Previous work has also demonstrated that use of a tubular wire (metal cored) containing 1% zinc can, under certain conditions, result in a reduction in Cr(VI) formation rate and in ozone concentration near the arc but with a rise in the total fume formation rate. The effects of different shield gases and different levels of zinc are examined. An experimental chromium-containing tubular wire with 1% zinc was used with the following shield gases: argon, Argoshield 5, Argoshield 20, Helishield 101, Ar + 2% CO2, Ar + 5% CO2, Ar + 1% O2 and Ar + 2% O2. The wire gave > 98% reduction in Cr(VI) formation rate compared to the control wire provided the shield gas contained no oxygen. When the shield gas did contain oxygen, 1% zinc enhanced Cr(VI) formation rate, resulting in more than double the rates measured when welding with the control wire. Experiments with zinc concentrations, from 0.018 to 0.9% using Helishield 101, gave results indicating that there is an optimum zinc concentration from the point of view of Cr(VI) reduction. Implications of the use of lithium or zinc on the overall exposure risk are discussed.

Chromium↗

PubMed2003

Fume generation and content of total chromium and hexavalent chromium in flux-cored arc welding.

This study was performed to investigate the fume generation rates (FGRs) and the concentrations of total chromium and hexavalent chromium when stainless steel was welded using flux-cored arc welding (FCAW) with CO2 gas. FGRs and concentrations of total chromium and hexavalent chromium were quantified using a method recommended by the American Welding Society, inductively coupled plasma-atomic emission spectroscopy (NIOSH Method 7300) and ion chromatography (modified NIOSH Method 7604), respectively. The amount of total fume generated was significantly related to the level of input power. The ranges of FGR were 189-344, 389-698 and 682-1157 mg/min at low, optimal and high input power, respectively. It was found that the FGRs increased with input power by an exponent of 1.19, and increased with current by an exponent of 1.75. The ranges of total chromium fume generation rate (FGRCr) were 3.83-8.27, 12.75-37.25 and 38.79-76.46 mg/min at low, optimal and high input power, respectively. The ranges of hexavalent chromium fume generation rate (FGRCr6+) were 0.46-2.89, 0.76-6.28 and 1.70-11.21 mg/min at low, optimal and high input power, respectively. Thus, hexavalent chromium, which is known to be a carcinogen, generated 1.9 (1.0-2.7) times and 3.7 (2.4-5.0) times as the input power increased from low to optimal and low to high, respectively. As a function of input power, the concentration of total chromium in the fume increased from 1.57-2.65 to 5.45-8.13% while the concentration of hexavalent chromium ranged from 0.15 to 1.08%. The soluble fraction of hexavalent chromium produced by FCAW was approximately 80-90% of total hexavalent chromium. The concentration of total chromium and the solubility of hexavalent chromium were similar to those reported from other studies of shielded metal arc welding fumes, and the concentration of hexavalent chromium was similar to that obtained for metal inert gas-welding fumes.

Air Pollutants, Occupational↗

PubMed2006

In vitro toxicity evaluation of silver soldering, electrical resistance, and laser welding of orthodontic wires.

The long-term effects of orthodontic appliances in the oral environment and the subsequent leaching of metals are relatively unknown. A method for determining the effects of various types of soldering and welding, both of which in turn could lead to leaching of metal ions, on the growth of osteoblasts, fibroblasts, and oral keratinocytes in vitro, is proposed. The effects of cell behaviour of metal wires on osteoblast differentiation, expressed by alkaline phosphatase (ALP) activity; on fibroblast proliferation, assayed by the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulphophenil)-2H-tetrazolium-phenazine ethosulphate method; and on keratinocyte viability and migration on the wires, observed by scanning electron microscopy (SEM), were tested. Two types of commercially available wires normally used for orthodontic appliances, with a similar chemical composition (iron, carbon, silicon, chromium, molybdenum, phosphorus, sulphur, vanadium, and nitrogen) but differing in nickel and manganese content, were examined, as well as the joints obtained by electrical resistance welding, traditional soldering, and laser welding. Nickel and chromium, known as possible toxic metals, were also examined using pure nickel- and chromium-plated titanium wires. Segments of each wire, cut into different lengths, were added to each well in which the cells were grown to confluence. The high nickel and chromium content of orthodontic wires damaged both osteoblasts and fibroblasts, but did not affect keratinocytes. Chromium strongly affected fibroblast growth. The joint produced by electrical resistance welding was well tolerated by both osteoblasts and fibroblasts, whereas traditional soldering caused a significant (P < 0.05) decrease in both osteoblast ALP activity and fibroblast viability, and prevented the growth of keratinocytes in vitro. Laser welding was the only joining process well tolerated by all tested cells.

Cells, Cultured↗

PubMed2003

Thorium exposure during tungsten inert gas welding with thoriated tungsten electrodes.

The exposure to 232Th from TIG welding with thoriated electrodes has been determined at five different workshops. Welding with both alternating and direct current was investigated. The exposure levels of 232Th were generally below 10 mBq m(-3) in the breathing zone of the welders. Two samples from AC welding showed significant higher exposure levels, probably due to maladjustment of the TIG welding power source. Samples of the respirable fraction of 232Th from grinding thoriated electrodes were also collected showing exposure levels of 5 mBq m(-3) or lower. A dose estimate has been made for two scenarios, one realistic and one with conservative assumptions, showing that the annual committed effective dose from inhalation of 232Th, 230Th, 228Th and 228Ra, for a full-time TIG welder, in the realistic case is below 0.3 mSv and with conservative assumptions around 1 mSv or lower. The contribution from grinding electrodes was lower, 10 microSv or lower in the realistic case and 63 microSv or lower based on conservative assumptions. The study does not exclude occurrence of higher exposure levels under welding conditions different from those prevailing in this study.

Air Pollutants, Occupational↗

PubMed2001

Lung fibrosis in Sprague-Dawley rats, induced by exposure to manual metal arc-stainless steel welding fumes.

To investigate the disease process of pneumoconiosis induced by welding-fume exposure, a lung fibrosis model was established by building a stainless steel arc welding fume generation system and exposing male Sprague-Dawley rats for 90 days. The rats were exposed to welding fumes with concentrations of 57-67 mg/m3 (low dose) and 105-118 mg/m3 (high dose) total suspended particulates for 2 h per day in an inhalation chamber for 90 days. The concentrations of the main metals, Fe, Mn, Cr, and Ni, were measured in the welding fumes, plus the gaseous compounds, including nitrous gases and ozone, were monitored. During the exposure period, the animals were sacrificed after the initial 2-h exposure and after 15, 30, 60, and 90 days. Histopathological examinations were conducted on the animals' upper respiratory tract, including the nasal pathway and conducting airway, plus the gas exchange region, including the alveolar ducts, alveolar sacs, and alveoli. When compared to the control group, the lung weights did not increase significantly in the low-dose group, yet in the high-dose group there was a significant increase from day 15 to day 90. The histopathological examination combined with fibrosis-specific staining (Masson's trichrome) indicated that the lungs in the low-dose group did not exhibit any progressive fibrotic changes. Whereas, the lungs in the high-dose group exhibited early delicate fibrosis from day 15, which progressed into the perivascular and peribronchiolar regions by day 30. Interstitial fibrosis appeared at day 60 and became prominent by day 90, along with the additional appearance of pleural fibrosis. Accordingly, it would appear that a significant dose of welding-fume exposure was required to induce lung fibrosis.

Administration, Inhalation↗

PubMed2003

Effects of welding fumes of differing composition and solubility on free radical production and acute lung injury and inflammation in rats.

The goals of this study were to examine acute lung damage and inflammation, as well as free radical production, caused by welding fumes of different chemical compositions and solubilities. The fumes were from a gas metal arc welding using a mild-steel (GMA-MS) or stainless-steel electrode (GMA-SS) and a manual metal arc welding using a stainless-steel electrode (MMA-SS), which was further separated into soluble and insoluble fractions. The MMA-SS was the only fume to contain soluble chromium. Free radical production was observed only in suspensions of MMA-SS fume under various conditions. Male Sprague-Dawley rats were intratracheally instilled with either a welding fume suspension at 2 mg/rat or a saline vehicle, and various parameters of inflammation and damage were measured at 3 h and days 1, 3, and 6. Only the MMA-SS treatment caused a continued increase in lung weight until day 6 and elevated lipid peroxidation at day 3. All of the fumes caused increases in macrophages and neutrophils obtained by lavage, but the increased cellularity was extended through day 6 following the MMA-SS treatment only. Only the MMA-SS treatment led to an increased recovery of eosinophils and damage to the alveolar-capillary barrier. While all of the fumes produced increases in cytotoxicity, the MMA-SS treatment caused the maximal response at day 3. These findings indicate that different welding fumes caused varied responses in the lungs of rats, correlated to their metal composition and ability to produce free radicals. Additionally, both the soluble and insoluble fractions of the MMA-SS fume were required to produce most effects, indicating that the responses are not dependent exclusively on the soluble metals.

Acute Disease↗

PubMed2004

Recovery from welding-fume-exposure-induced lung fibrosis and pulmonary function changes in sprague dawley rats.

Welder's pneumoconiosis has generally been determined as benign based on the absence of pulmonary function abnormalities in welders with marked radiographic abnormalities. Yet, there have also been several reports on welders with respiratory symptoms, indicating lung function impairment, X-ray abnormalities, and extensive fibrosis. Accordingly, this study attempted to investigate the inflammatory responses and pulmonary function changes in rats during a 60-day welding-fume-inhalation exposure period to elucidate the process of fibrosis. The rats were exposed to manual metal-arc stainless-steel welding fumes (MMA-SS) with total suspended particulate concentrations of 64.8 +/- 0.9 (low dose) and 107.8 +/- 2.6 mg/m3 (high dose) for 2 h per day in an inhalation chamber for 60 days. Animals were sacrificed after the initial 2-h exposure and after 15, 30, and 60 days, and the pulmonary function was also measured every week after the daily exposure. Elevated cellular differential counts were also measured in the acellular bronchoalveolar lavage fluid of the rats exposed to the MMA-SS fumes for 60 days. Among the pulmonary function test parameters, only the tidal volume showed a statistically significant and dose-dependent decrease after 35 to 60 days of MMA-SS welding-fume exposure. When the rats exposed to the welding fumes were left for 60 days to recover their lung function and cellular differentiation, recovery was observed in both the high and low-dose rats exposed up to 30 days, resulting in the disappearance of inflammatory cells and restoration of the tidal volume. The rats exposed for 60 days at the low dose also recovered from the inflammation and tidal volume loss, yet the rats exposed for 60 days at the high dose did not fully recover even after a 60-day recovery period. Therefore, when taken together, the results of the current study suggest that a decrease in the tidal volume could be used as an early indicator of pulmonary fibrosis induced by welding-fume exposure in Sprague Dawley rats, and fibrosis would seem to be preventable if the exposure is short-term and moderate.

Animals↗

PubMed2003

Lung function in Pakistani welding workers.

Our objective was to study the effects of welding fumes and their duration of exposure on lung function. This was a matched case-control cross-sectional study of spirometry in 50 nonsmoking manual metal arc welders who work without the benefit of welding fume control ventilation or respiratory protective devices. Welding workers, with exposures longer than 9 years, showed a significant reduction in spirometry (forced expiratory volume in one second [FEV1], FEV1/forced vital capacity [FVC%], and peak expiratory flow [PEF]) relative to controls. Lung function in nonsmoking welding workers is impaired and stratification of results shows a dose-effect of years of welding on lung function. This effect primarily shows an obstructive pattern of airways disease. Preventive measures in developing countries have to be adopted to avert long-term lung damage in welders.

Adult↗

PubMed2005

Microstructural characterization of autogenous laser welds on 316L stainless steel using EBSD and EDS.

This research is concerned with autogenous welding of 316L stainless steel and the microstructure generated by such a process. Autogenous welding does not require a filler material and in this case relies on an initial shallow melt phase to maintain a conduction limited weld. Essentially, a high power laser beam traverses the substrate, with the beam shaped by conventional optics, which produces a Gaussian irradiance distribution; or with a diffractive optical element, used to produce a uniform irradiance distribution. Initial results have shown that due to the nature of the heating cycle, complex microstructures are developed. These fine, complicated microstructures cannot be satisfactorily resolved and quantified using standard optical microscopy techniques. Electron backscatter diffraction (EBSD) and energy dispersive spectroscopy (EDS) have been carried out on a number of different microstructures prepared using a range of welding parameters. It is demonstrated that the simultaneous determination of the chemistry and crystallography is a very useful tool for rapid identification of the different phases formed on solidification as a consequence of varying welding procedures.

Crystallography↗

PubMed2005

Effect of heat treatment on joint properties of laser-welded Ag-Au-Cu-Pd and Co-Cr alloys.

PURPOSE: This study investigated the effect of heat treatment on the strengths of laser-welded cast Ag-Au-Cu-Pd and Co-Cr alloys. MATERIALS AND METHODS: Cast plates of Ag-Au-Cu-Pd (Ag) and Co-Cr (Co) alloys were prepared. After polishing the surfaces to be welded, the plates were matched and butted Ag to Ag (Ag/Ag), Co to Co (Co/Co), and Ag to Co (Ag/Co) and welded using Nd:YAG laser at a pulse duration of 10 ms, spot diameter of 1 mm, and voltage of 200 V. Five specimens were prepared for each experimental condition by bilaterally welding them with five spots. The Ag/Ag, Ag/Co, and control Ag underwent two heat treatments-softening (ST) and hardening (AH). A group of as-cast specimens serving as controls was not given either heat treatment. The failure load and percent elongation were measured at a crosshead speed of 1.0 mm/min. RESULTS: The fracture resistance of Co/Co was similar to that of the control Co, while the fracture resistance of Co/Ag was significantly lower than that of both like alloy pairings for all heat-treating conditions. The control Ag had greater fracture resistance after AH and lower fracture resistance after ST. The AH treatment increased the fracture resistance, and the ST treatment decreased the fracture resistance of both Ag/Ag and Co/Ag, although not significantly. The percentage of elongation appeared to positively correlate with the fracture resistance results. CONCLUSIONS: The results obtained in this study indicated that the age-hardening heat treatment increased the weld strength between the paired Au-Ag-Cu-Pd alloys and between the Au-Ag-Cu-Pd and Co-Cr alloys.

Chromium Alloys↗

PubMed1980

The mammalian spot test and its use for the testing of potential carcinogenicity of welding fume particles and hexavalent chromium.

Welding fume particles, potassium chromate and cyclophosphamide are tested in the mammalian spot test. Female mice C57BL/6J/BOM9 weeks old have been mated to T-stock male mice and treated with welding fume particles 100 mg/kg, potassium chromate 20 or 10 mg/kg, or cyclophosphamide 10 or 2.5 mg/kg intraperitoneally at day 8, 9 and 10 of pregnancy. The fur of the offspring was checked week 2 through week 5 after birth for coloured spots. The characterisation of the different types of spots are discussed. Welding fume particles 100 mg/kg and potassium chromate 10 mg/kg induce approximately to the same extent as cyclophosphamde 2.5 mg/kg, grayish or brownish spots in tvo screening test for mutagenic and carcinogenic potential of chemicals. The positive results for potassium chromate and cyclophosphamide are in agreement with previous in vitro experiments and confirm the sensitivity of the test. The effect of welding fume particles in this in vivo system suggests a potential risk for humans directly exposed to welding fumes.

Animals↗

PubMed1996

Welder identity, weld date, and the risk of outlet strut fracture in Björk-Shiley convexo-concave valves: the Dutch cohort study.

OBJECTIVE: To establish whether there is an association between subsequent fracture of the outlet strut and welder identity and the weld date of Björk-Shiley convexo-concave (BScc) valves. DESIGN: Cohort study. PATIENTS: All Dutch BScc valve recipients (n = 2266). MEAN OUTCOME MEASURES: Documented outlet strut fracture during follow up. RESULTS: Weld dates were known for 97.0% of all BScc valves (n = 2534) implanted in Dutch patients (n = 2266) and welder identity was known for 52.2%. During a mean follow up of 9.4 years, 46 fractures were documented. For 60 degrees valves welded from 1981 to 1984 the fracture rate (0.22 per 100 person-years (95% CI 0.13 to 0.34)) was higher than that for valves welded before 1981 (0.04 (95% CI 0.01-0.10)). When all fracture related risk factors were taken into account, fracture rates per welder did not show any statistically significant differences. CONCLUSIONS: Welder identity does not contribute to the risk of strut fracture. Other factors in the production of BScc valves may explain the increased risk for valves welded from 1981 to 1984.

Cohort Studies↗

PubMed2001

Effects of heat treatments on mechanical strength of laser-welded equi-atomic AuCu-6at%Ga alloy.

There is little information available on the mechanical strengthening of laser-welded gold alloys to achieve reliable dental prostheses. This study examined the hypothesis that heat treatments increase the mechanical strength of a laser-welded equi-atomic AuCu-6at%Ga alloy with age "hardenability" at intra-oral temperature. Cut cast gold alloy plates were laser-welded. The specimens were given one of three heat treatments: (1) solution treatment, (2) high-temperature aging after solution treatment, and (3) simulated intra-oral aging after solution treatment. As-cast and uncut specimens were also prepared. Tensile testing was conducted, and the breaking stress and yield strength were recorded. The yield strength values of all the heat-treated specimens nearly reached the values of the corresponding heat-treated control specimens. The results of this study indicated that, for high mechanical strength to be achieved, the laser-welded alloy tested should be aged at a high temperature or be intraorally aged after being laser-welded.

Dental Soldering↗

PubMed1983

Response of bovine alveolar macrophages in vitro to welding fume particles.

Alveolar macrophages (AM) from bovine lungs were exposed in culture to manual metal are (MMA) welding fume particles, chromium (Cr), UICC chrysotile A or anatase for 17-20 hr. All the welding particle samples were more cytotoxic to AM than to anatase. Particles from the welding of mild steel with a rutile-coated electrode were less cytotoxic than those produced with a basic-coated electrode. Particles from the welding of stainless steel were slightly more cytotoxic, and much of this activity was probably due to CrVI. Selective release of N-acetyl-beta-glucosaminidase (beta-NAG) was only detected after exposure of AM to chrysotile. Supplementation of the incubation medium with 10% serum increased the viability of all exposed AM cultures, an effect not produced by serum albumin alone. Incubation of particle samples with dipalmitoyl phosphatidylcholine (DPPC) prior to addition to AM reduced the cytotoxicity of the "rutile" welding particles and of chrysotile.

Acetylglucosaminidase↗

PubMed1990

[Cracking in laser welds of dental Ni-Cr alloys. Effect of alloy composition].

For the purpose of clarifying the effect of alloy compositions on cracking in laser welds of dental Ni-Cr alloys, 12 commercial and 11 experimental Ni-Cr alloys for crown and bridges were subjected to pulsed YAG laser spot welding, and their welds were investigated by optical and scanning electron microscopy, and EDX and thermal analysis methods. Main conclusions are as follows. 1. Cracks in laser welds were solidification cracks at grain boundaries in weld fusion zones. 2. In the case of commercial dental Ni-Cr alloys, a considerable number of eutectics enriched in Si, A1 and/or S were formed. Greater cracking susceptibility was interpreted by considering that these eutectics solidified at solidification temperatures far lower than the nominal solidus. 3. In the case of experimental Ni-Cr alloys with a small amount of eutectics, S and Si enhanced cracking sensitivity, but Mn reduced cracking. 4. The above results suggest that it is beneficial to the prevention or reduction of cracking to decrease harmful elements such as Si and S forming low solidification temperature eutectics or to add some elements such as Mn forming higher solidification temperature eutectics instead of lower ones.

Chromium Alloys↗

PubMed1999

Welding metallurgy's putative influence on Björk-Shiley convexo-concave valve outlet strut failures.

BACKGROUND AND AIM OF THE STUDY: Multiple reports of convexo-concave valve outlet strut fractures have focused on the welds, often implicating putative defects of uncertain character and significance. This study differs from all others in that it systematically assesses a large number (n = 60) of intact and fractured valves and clearly differentiates findings on the critical, tensile-stressed, inflow side of the outlet strut leg from those on the outflow side, which are subject only to compression. METHODS: Each valve was examined by scanning electron microscopy and subjected to multiple metallographic sectioning of each strut-flange interface. All fractures and selected intact valves were further analyzed with X-ray dispersive spectroscopy. RESULTS: Fatigue striations were seen in all fractured valves, and their orientation indicated that every fracture initiated in an area on the inflow side, spreading out progressively towards the outflow side. Data indicated that 22% of the first-to-fail leg separations and 17% of all fractures initiated outside of the weld. Element segregation areas were seen in 40% of welds, significantly more commonly in intact valves, invariably located on the outflow side, and typically (85%) apart from the fracture path. Microporosity was identified in 15% of welds, usually near the outflow side, and in the same proportion of intact and fractured valves. One fracture surface had a 38 microns, inflow-side void that might have been a factor in crack initiation in this valve, which was highly stressed. CONCLUSIONS: With this singular exception, no metallurgical feature of any weld was found that appeared to have contributed, even in a minor way, to the process of outlet fracture.

Biocompatible Materials↗