| Gaskets and packings take an important role in modern industry. Productive continuity is influenced by the failures caused by seals. whether seal is good or not has something to do with productive security directly. The development of gaskets and packings is increasingly paid much more attention. However, generally speaking, gaskets and packings used in domestic and overseas contain leachable chloride during production process or raw materials, from which the leachable chloride dissociates. It is very likely that those leachable chlorides can cause corrosion to seal faces, pump shafts and valve-spindles, which leads to accelerate leakage rates and even destroys the seals. So it is necessary to study the test methods and means to the leachable chloride content in gaskets and packings and to discuss the influence the leachable chloride concentration has on corrosion effects to the seal faces, pump shafts and valve-spindles. So far, there are a few related test methods of chloride content about flexible graphite blanders by using corresponding criterion JB/T 6622-93, namely burning-mercuric rhodanate spectrophotometry. But there is no corresponding criterion about methods to test the chloride content of gaskets made by other materials.The related experiments were done to study the leaching of dissociative chloride ions in gaskets and packings. By ion-selective electrode technique, the method to test quickly the dissociative chloride ions in gaskets and packings was established in this paper. And then, corrosive experiments about gaskets and packings were designed reasonably. The results studied mainly contents the following points:1. Through the dissociative experiment to test leachable chloride in gaskets and packings, the leachable optimum parameters were obtained. That is, extracted temperature is controlled at 90℃; sodium hydroxide concentration in the liquor of gaskets and packings is 0.01mol/L; extraction time is 4 hours. And then, the granularity of gaskets andpackings is analyzed as well as the results of extraction times so as to optimize extraction conditions.2. Chloride ion-selective electrode technique and spectrophotometry were respectively adopted to test the leachable chloride content in gaskets and packings and then the experiment results were compared. The experiment showed that the average relative deviation (ARD) obtained by above two test methods is 7%. Therefore, it is feasible that chloride ion-selective electrode technique is adopted to test the leachable chloride in gaskets and packings and the results are reliable.3. The interference caused by the liquor of gaskets and packings was analyzed one by one and the interfere these ions cause were eliminated. The experiment result showed that S2- and Fe3+ have a great influence on ion-selective electrode. So, the interference was eliminated or sheltered respectively by hydrogen peroxide liquor and potassium sodium tartrate in this paper. As a result, the interference was eliminated well.4. Each influential factor about plotting work curves was studied through experiment. By every influential factor confirmed, the work curves are linear within the range from 1×10-1mol/L to 5 ×10-5mol/L and the related coefficient R=0. 99705.5. The corrosion experiments about gaskets, which have different chloride ion content, were done to confirm the upper limit of chloride ion content in gaskets or packings through corrosion depth on stainless steel surfaces which contact with gaskets. From the above experiments, it proved that stainless steel didn't encounter corrosion when chloride ion content is below 36μg/g and there are corrosion phenomena on stainless steel surfaces when chloride ion content exceeds 50μg/g.The traits to test chloride ion content by ion-selective electrode lie in its convenient, sensitive and less interfere factors. The disadvantage that reagent-mercury salt originally used in spectrophotometry is toxic heavily can be avoided. In the corrosion experiments, the upper limit of chloride ioncontent was obtained, which can properly supply a selective standard for industry that products and selects gaskets and packings. |
