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Life-time extrapolation has often been performed based on a parabolic oxidation law. The new standards, ISO 21608 and ISO 26146, aim at determining the actual oxidation rate constant and exponent in order to describe the oxidation behavior as closely as possible to the observed situation. The present paper extends this approach by the kinetics of subsurface zone depletion of the protective scale-forming alloying element (for example, chromium). Four different types of characteristic depletion kinetics are combined with considerations on the minimum amount of chromium necessary to maintain the protective situation in order to define the extrapolation basis for oxidation-related life-time assessment. This approach is applied to experimental data from exposure in simulated coal combustion environments at temperatures of 550-750 °C and exposure times up to 15 000 h. The materials ranged from low-alloy steel to high-alloy austenitic steels and nickel-base alloys. As a result, it is proposed to use data from metallographic investigations rather than mass change data for life-time assessment together with the respective kinetics approaches. Furthermore, it is recommended to base life-time extrapolation on experimental data from tests of at least 10 000 h duration. The investigated materials were categorized with regard to their potential of oxidation-related life-time assessment. [ABSTRACT FROM AUTHOR]

Fifty consecutive patients with symptomatic endoscopically proven duodenal ulcer were randomized double-blind to Mylanta II or cimetidine treatment schedules. Smoking habits were noted, but patients were not advised to alter these. Healing was determined by reendoscopy at 6 wk. Eighty percent of patients on active cimetidine and 52% on active Mylanta II had healed at 6 wk (not significantly); 85% of nonsmokers healed compared to 44% of smokers (p less than 0.03). In smokers, cimetidine achieved healing in 50%, Mylanta II in 39% (not significantly); while in nonsmokers, cimetidine achieved healing in 100%, Mylanta II in 67% (not significantly). These results indicate a significant and equally adverse effect of smoking on the healing rate of duodenal ulcer achieved by either cimetidine or Mylanta II.

There are conflicting reports on the influence of cigarette smoking on healing in patients with duodenal ulcer; some studies show an adverse effect on healing rate and others no effect. This study reports the influence of smoking on short-term healing and relapse rate in 135 patients with duodenal ulcer who were treated with cimetidine (90), ranitidine (25), and oxmetidine (20), all powerful H2-receptor antagonists. Ulcer healing and relapse were documented endoscopically and all studies were performed in a double-blind manner. In the short term, 95% of nonsmokers healed compared with 63% smokers (p less than 0.01) and there was a positive correlation between failure to heal and number of cigarettes smoked. During a 12-mo follow-up examination after healing and on no treatment, 53% of nonsmokers and 84% of smokers relapsed (p less than 0.01). These results show that smoking adversely affects healing of duodenal ulcer with H2-receptor antagonists and that continued smoking leads to a higher relapse rate.

Information on the relative incidence of Crohn's disease and ulcerative colitis was obtained by a prospective investigation at six Melbourne teaching hospitals. One hundred and eleven patients who presented with chronic inflammatory bowel diseases between 1980-1981 were admitted to the study. Forty (36%) patients were diagnosed as having Crohn's disease and 63 (57%) patients as having ulcerative colitis. The type of chronic inflammatory bowel disease could not be determined in eight (7%) patients. These findings suggest that the relative frequency of Crohn's disease and ulcerative colitis in Melbourne hospitals is within the range that is reported for northern Europe and the United States.

The effect of ranitidine, a new H2-receptor antagonist, on the healing of duodenal ulcer has been assessed in a double-blind study. Fifty patients with endoscopically proven duodenal ulcer were randomly assigned to ranitidine 150 mg twice daily or placebo for 4 weeks. Endoscopic examination at this time showed that 20 of 25 patients (80%) on ranitidine healed compared to 4 of 25 patients (16%) on placebo (P less than 0.01). Smoking adversely affected the incidence of healing: 70% of nonsmokers healed compared to 30% of smokers (P less than 0.03). There were no side effects noted on ranitidine. Review at 6 months after cessation of therapy showed relapse of duodenal ulcer in 10 of 20 patients (50%) healed with ranitidine and 1 of 4 patients (20%) healed with placebo. Thus, ranitidine (300 mg/day) produces similar healing rates to those reported for cimetidine (1000 mg/day); also like cimetidine, the incidence of healing on ranitidine is adversely influenced by smoking and the relapse rate on cessation of therapy is high.