Online concentration analysis system prototype installation at stainless steel strip pickling line

MACO Pilot – Optimisation of the mixed-acid online monitoring and control in stainless steel pickling plants

Initial situation

  • Economic pressure on European steel sector demands high flexible and favourable production
  • Especially the pickling step is of high importance for stainless steel production
  • High process flexibility needs a fast adjustment of defined concentrations in industrial mixed-acid pickling baths for achieving consistently high product qualities and plant productivity.
  • Within the RFCS project FLEXPROMUS an innovative method for continuous HF-HNO3-mixed-acid online analysis was successfully developed
  • First prototype tests at stainless steel strip pickling lines showed very promising results

Project objectives

  • Optimisation of online-measuring-technique for continuous concentration monitoring in HNO3-HF-mixed acids
  • Optimisation of concentration monitoring and control at stainless steel pickling facilities
  • Online-measuring technique prototype test installations at stainless steel strip and wire rod pickling plants and acid regeneration plant
  • Model based optimisation of the pickling process operation at stainless-steel wire rod dip-tank pickling plants

Innovative process approaches

  • Continuous online-concentration monitoring of mixed acid pickling solutions by means of model based measuring technique
  • Development of a „closed loop“-concentration control model for stainless steel strip pickling lines on basis of online-concentration data
  • Development of a pickling programme management model for wire-rod pickling plants
  • Concept development for improvement of existing European mixed acid pickling plants by online monitoring and control

Final results to the end of the project (12/2019)

  • Optimised online-measuring system prototype set-up (increase from TRL5 to TRL7)
  • Successful installation and operation of online measuring systems at a strip pickling line including regenerated acid tank and wire rod dip tank pickling plant in combination with filtration
  • Optimised concentration calculation model for different mixed acid applications, deviations between online analysis and BFI laboratory reference analysis mainly < ± 5 g/L for free HF + total metals and < ± 8 g/L for free HNO3 concentration under optimal measuring conditions
  • Advanced closed-loop and open-loop concentration control models based on high-rate concentration data enable enhanced pickling process stabilization, saving of acids and reduction of emissions as well as saving of costs
  • Reduction of manual mixed acid sample drawing can improve the working conditions and safety
  • An innovative pickling program management model enables more optimised and safe wire rod pickling plant operation


  • Further concentrations calculation model optimisation (soft- and hardware modifications)
  • Finalisation of measuring system set-up from prototype to commercial version


Presentations from the international workshop November 11, 2019


1-BFI Workshop-Presentation- Surface_treatment_by_pickling_(M_ Kozariszczuk)
7-BFI-Workshop-Presentation-Operational_experience_for_the_recycling _of_process water_and_acids_(Steuler)
8-BFI-Workshop-Presentation-Pickling bath particle separation and atline analysis_(Scanacon)



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