Aplication Of Phosphates In Corrosion Control Of Water Distribution System

Corrosion control is a big issue for the performance of drinking water distribution systems.Ductile iron pipe sectionswith different cement coatings were used to study thewater qualityimprovementin the resultsof chemicalstability and mitigation oferosioneffects on the inner wallofthe pipe networkby differentphosphate.Combined phosphateinhibitorformulationsinthe experiment includethose inhibitorsinvolved with different concentrations ofsodiumhexametaphosphatewith calcium and magnesium ions,differentconcentrationsofsodiumphosphatewithcalciumandmagnesium ions,combined sodiumhexametaphosphateandsodiumphosphateinhibitor.For theinhibition effectproduced bytheseinhibitors,interms ofchemicalstability,mainly LSI,IR,LRandAI in the influent and effluent were considered.The inhibition effect indicators mainly include waterturbidity,pH,andtotal hardnessandtotal iron and total phosphorus.The results show that,water qualityindicators for chemical stability such as LSI,LR in the effluent from water works using ShanghaiHuangpu Riveras raw waterpresentedcorrosion tendency and would causeerosion inthe pipe.Addition of phosphateinhibitor slowed the erosionin the pipeline and curbedtherate of substanceon the wall released into thewater.The results showed that the inhibition effect of phosphate inhibitor increased with the concentration of inhibitors.In the case of equal concentrations of phosphorus,sodium hexametaphosphate combined with calcium and magnesium ions in wate rare better thanthe effect of sodium phosphate combined with calcium and magnesium ionsin water.For the combination of sodium phosphateand sodium hexametaphosphate,the inhibition effect will be better than the sodium phosphate combined with calcium and magnesium ions and inferior tosodium hexametaphosphate combined with calcium and magnesium ions.In the water distribution system,cement coating can give a positive protection to pipe corrosion.Addition of 5mg/L and 10mg/Lsodium hexametaphosphate can greatly improve the water chemical stability and the water stability indexes were mainly influenced by the dosage of inhibators.It was because of the discontinuous protective film formed on the surface of cement lining which lead to inhibition effect by the complexation of calciumhexametaphosphate with oxidized iron and oxidized alumina and Fe,Ca and Al were sealedto improvewater quality.Corrosion inhibitionby orthophosphateinthe pipelineis due tothe formationofCaHPO₄inhibiting the growth ofcalcitecrystals,as well as the formation of FePO4andCa3?PO4?₂reducing therelease of Fe,Cato the water body.In summary,additionof3mg/Lsodium hexametaphosphate into thepipe networkhas bettertechnologyand economy benefits.