Use of Cleaning Pre-Film Agent; Inspection of Cleaning Pre-Film Agent

Use of cleaning pre-film agent; inspection of cleaning pre-film agent

Regardless of whether it is the first use of a new system or the re-use of an old system after maintenance cleaning is required before startup. After cleaning, pre-passivation should be performed immediately, and the system can be put into formal use only after pre-passivation. That is a layer of chemical film or adsorption film is covered on the metal surface, which can effectively prevent chemical reactions between the metal and impurities in the water, reduce system corrosion, also reduce the amount of corrosion inhibitor. Pre-passivation treatment before the new and old circulating cooling water systems are put into normal use is an economical and efficient method of corrosion.Selection of pre-passivation agent:According to the "GB/T50050-2007 Industrial Circulating Cooling Water Design Specification", the following two agents can be used: A, 7-8 times the amount of scale inhibitor and corrosion inhibitor; B, 160/L of sodium hexametaphosphate and 40mg/L of zinc sulfate monohydrate.Selection of pre-passivation time:The pre-passivation time for agent A is 120 hours; the pre-passivation time for agent B is 48 hours.Selection of prepassivation pH value:Agent A is pre-passivated under the condition of pH 5.5-6.5; agent B is pre-passivated under condition of pH 6.0-7.0.Agent B is a widely used pre-passivation agent at present. The advantage of pre-passivation with B is that the pre-passivation time is short and the effect is good, but the disadvantage is that the pre-passivation conditions are relatively harsh, the amount of prepassivation agent is large and it is easy to cause environmental pollution; the pre-passivation operation and management of agent A is relatively simple, the pre-passivation effect is acceptable, but the pre-passivation time is long, generally it needs 5-15 days, which is more suitable for circulating cooling water systems with serious scaling tendency. to the problem of pre-passivation time, it is less used on site.Since agent B is used more on site due to the pre-passivation time and-passivation effect, it needs to be closely monitored during the pre-passivation process. Generally speaking, the following indicators need to be monitored during the pre-passivation processAnalysis itemAnalysis frequencypHEvery half an hour when unstable; once every 1-2h when stableTotal phosphorusAs the case may beurbidityOnce every 12hCa2 Once every 12hTotal ironOnce every 12hThe inspection of the-passivation effect on site is generally carried out by using standard monitoring hang pieces. Generally, the color halo is observed with the naked eye or the copper sulfate test film solution in "HG/T 3778-2005 Chemical Cleaning and Pre-passivation Technology Treatment Rules for Cooling Water Systems" is used for inspection. copper sulfate test film solution is prepared by dissolving 15.0g of sodium chloride and 5.0g of copper sulfate pentahydrate in100ml of distilled water. The film reacts with the copper sulfate test film solution, and the time difference of color change is not less than 10s, is pre-passivation. Success.