35.3.1 Visualinspection
Visualinspection is still probably the most widelyusedinspectiontechnique for
assessing the impactof fouling and cleaningand in particularconfirmingthat
the cleaning results are satisfactory.While a visually cleansurfacewillnot
guarantee a microbiologicallyacceptableproduct,failure to achieve at least
visualcleanliness willmean that furthercleaningis essential,otherwisethe
subsequent production process may be compromised. The main practical
problemwithvisual inspection,particularlywithclosedplant, is accessto the
product contact surfaces. Ideally, visualinspectionshouldbe carried out in areas
wherethe heaviestfoulingand hencegreatest challengeto the cleaning system
occurs.In the caseof heat exchangers,the geometry will definethe practicality
of visualinspection. Sometubularheat exchangergeometries,suchas multiple
tubein tubeand monotubedesigns,can in principle be inspectedby removing
the product inletand outletconnections and exposingthe internalsurfaces.
Otherdesignssuchas the concentrictripletube(tubein tubein tube)cannotbe
inspected in this way. Plateheatexchangerscan in principlebe dismantled for
inspection but, in practice,this couldonly be considered on an infrequent basis
due to the timethat wouldbe required. Sucha visual inspectionshould,
however, forma key part of the commissioningand acceptanceprotocolfor a
heatexchange system.
Table35.3 Measurementof materialconcentrationwithinsystem
Technique Measurement Classifi- Key issues
principle cation
Chemicalassay Determines Retro- Relativelysimple,can be
concentrationof spective carriedout by trained
detergents/biocides Localised operators
Non-
invasive
Turbidity Attenuationof incidentRealtime Assumesthat steadystate
(Gallot-Lavalleeet al. lightas a measureof Localised conditionsmeanscleaning
1981) soil in cleaning Invasive has beencompleted,
solution althoughsystemmaystill
containsoil
Liquidelectrical Liquidconductivity, Realtime Reliabilityof measurement,
properties(capacitance,e.g. detergents/ Localised measuresmaterialin liquid
conductivity, biocides Invasive not on surface
amperometric)
Rinsewateranalysis Detectionof organic Realtime Assumesthat steadystate
(ATP) matterin circulating Indirect conditionsmeanscleaning
rinsewater Non- has beencompleted,
invasive althoughsystemmaystill
containsoil
Monitoringof fouling, cleaning and disinfection in closedprocessplant 577