Riboflavin/Wetting Trial for PW/WFI Tanks – Meeting Protocol Expectations Vs Practicality

Praj Hipurity |

Typically almost every alternate interaction with our client friends on clean utilities tankages (Purified Water / Water for Injection) design, usually touches upon spray ball coverage test. Users want to have the spray ball coverage test also called as Riboflavin Test or Wetting Trial mainly because

  • User’s knowledge of CIP for process vessels spilling over to PW /WFI Tank designs
  • Either because it is a query raised by auditors’ in past or

So do PW /WFI Tank really need to undergo Riboflavin / Wetting Trail for clean-ability?

  • PW /WFI Tanks never see product change in their lifetime unlike process vessels
  • PW/WFI tanks don’t see anything but highly purified water with very low conductivity
  • Some PW/WFI Tanks are also designed to undergo SIP at 121 0 C by Pure Steam
  • WFI Tanks are on most occasions maintained at >80 0 C which makes it self-sanitizing
  • Majority of PW Tanks are hot water sanitized at >80 0C on a monthly to quarterly basis

So one can say – PW/WFI tanks are never seeing product change, higher contamination/ impurities and are sanitized intermittently. Do we still need the tanks tested for spray ball coverage test?

Question Remains - Inspite of above points, one can still argue that the top dish still needs wetting to avoid dry patches.

In order to make the tank compliant with wettability/Riboflavin – from design standpoint following process is followed –

In order to meet the minimum flow rate and pressure requirements following challenges are faced –

  • Return Line Flow of PW/WFI loop – the return line flow of PW/WFI is generally set at minimum return line velocity making the return line flow fixed.
    The Challenge: Irrespective of tank size chosen, return line flow always remains pegged at velocity equivalent. The no of spray balls may vary depending on the Tank size.
  • Return Line Pressure : Back Pressure Regulating Valve (most commonly used in the return line) in effect reduces the pressure at spray ball to < 1 bar more often.
    Challenge: Typical spray balls operate in the range upwards of 2 bar.

Though having tank design compliant with wettability /Riboflavin test is desirable, practically during normal operation of PW/WFI loop, the return line flow rate + return line pressure puts limitations on effectiveness of spray ball.

So should the Riboflavin/Wettability Test Requirement be eliminated for PW/WFI Tanks?

Get in touch with Praj Hipurity for the rightful answer!