7/30/2019 CS017Ben Steel_pH in Electrolytic Galvanising

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Metal/iron & steel industryDigital pH-sensor saves Salzgitter Flachstahla six-figure sum

Memosens turns the pH-electrode intoa digital sensor with integrated datastorage

pH-measurement with Liquisys M transmitter ... and digital electrode withMemosens connection

The breakthrough came with Memo-sens

New, modern and innovative. Threeattributes which admittedly are oftensomewhat overworked. This is not thecase with Endress+Hausers digital Me-mosens technology: it defies humidity,dirt, strong electric fields, does withoutfield calibration, increases plant availa-bility and what is more is unbelievablycost-effective to acquire and to operate.The pH-sensor has underlined the factthat it can cope with everything, evenunder the harshest operating condi-tions, in its six months of application inelectrolytic galvanization in the surfacefinishing department of SalzgitterFlachstahl.

You dont mess with sulfuric acid. GerdReimann, operations engineer in the surfacefinishing department of Salzgitter Flach-stahl and Henning Borchers, manager ofinstrumentation and control technology inSZST Salzgitter Service und Technik, theinternal services company, are both wellaware of this. After all, in its concentratedform, the colorless, oily liquid will easilyeat through textiles and many metals, notto mention human skin. Even when it isheavily diluted, as when used in electrolyticgalvanizing at Salzgitter Flachstahl, nothingis done without tight safety goggles andrubber gloves. The only things that must

perform their duty day-in day-out practical-ly without protection are the measuring in-struments. These are permanently exposedto the aggressive environmental conditionsand are thus very susceptible to attack. This

was at least always true for pH measuringpoints in the past. They are of decisiveimportance for the quality of products and,in the past, were a heavy burden on theelectrolytic galvanizing department withtheir high costs of acquisition, maintenanceand servicing. We have been looking foralternatives for a long time now, and havereally tried everything in the last 20 years.But there is nothing. The breakthroughdidnt come until we tried Memosens byEndress+Hauser, said Reimann.

Demanding driversThe surface treatment process takes therolled and annealed cold strip and finishesit into high quality steel sheet in eitherhot-dip galvanizing or in electrolyticgalvanizing. The majority of the 3 to 6 ft

wide coils, which may be up to 19,700 ftlong and weigh some 44,100 to 66,140lbs, produced by Salzgitter Flachstahl areused in the automotive industry. Becauseof the very different requirements in carbuilding, this demands a broad spectrum ofdifferent steel grades and qualities. Thus,for instance, a side rail, which is required toprevent the worst in the event of a crash,needs to have quite different material pro-perties than the thin outer skin, for which

the surface finish is most important.Demands on the surface finish have growneven more challenging since the automotiveindustry has begun working with water-based paints. This is why the company hasrecently bought a surface inspection system,known by its German abbreviation of OIS(Surface inspection system), which willfind even the smallest defect. But beforeit gets that far, the base material passesthrough the pickling line. The acid bathcleans the surface before galvanizing, at thesame time preventing oxidation. We adjustthe pickling line to a pH value between 1.4and 1.8 so that the zinc coating adherescorrectly and the quality of the finishedsheet meets requirements. We use 96 %sulfuric acid, which makes the process a bittricky according to Reimann.

How things used to beThe old pH measurement system consistsof a container with a comparison andreference electrode, a diaphragm, and isfilled with a potassium chloride solution.On top of the container there is an amplifier

with four contacts which oxidize quicklyand can cause problems. In addition, thesystem incorporates an internal temperaturesensor. A source of endless errors, groansReimann. If there was any doubt we, orat least Mr Borchers team, which wasresponsible for the measuring points, hadto swap out the complete container. Andunfortunately, that was quite a common

7/30/2019 CS017Ben Steel_pH in Electrolytic Galvanising

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CS 017B/11/en/10.0671032782Straub/INDD CS2

Instruments International

Endress+Hauser GmbH+Co. KGInstruments InternationalP.O. Box 222279574 Weil am RheinGermanyTel. +49 7621 975 02Fax +49 7621 975 345http://www.endress.cominfo@ii.endress.com

occurrence. Because the system used didnot close properly tight, aggressive liquids

which dripped onto the housing, slowlyand silently destroyed the connections,cables and electrodes. Although the metal

was gold-plated, that eventually becamedamaged and grew a green crust. Then thecontact is lost and at 5 mV and poor contactresistance you are lost, Reimann says. Be-cause of the complex structure of the elec-trodes, Salzgitter Service und Techniksengineers often found that troubleshootingbecame a real test of patience.In addition to the ad hoc repairs, regularmaintenance work was required. As thediaphragm is in direct contact with thefluid, it is easily soiled by the ferrous oxideoccurring in the process. The electrodedegenerates with time. To ensure correctmeasuring, someone on site has to removethe electrode, clean it, immerse it in abuffer solution and calibrate the amplifier,Borchers explains. The same procedure isthen repeated with buffer solution numbertwo. In the past this has taken up to onehour. Or: two men were occupied twice a

week taking eight pH measurements. Thisdoes not only tie up people, but also costsmoney.

Beyond any doubtThe old version has not developed inthe last two decades. I was most impres-sed with the encapsulated electrode inEndress+Hausers Memosens. You can pouracid over the plastic housing without acare, says Reimann cheerfully. But ini-tially he had his doubts whether the digitaltechnology would meet his high require-ments. The basic precondition for their use:high electromagnetic compatibility. This isbecause the galvanizing station followingthe pickling station has 34 rectifiers eachrated at 25,000 amps. For this reason,the managers at Salzgitter Flachstahl,Salzgitter Service und Technik andthe Endress+Hauser contact for the steel

industry, Stefan Weiss, from the HannoverTechnical Office, initially decided on atwo-week test run. If the electrode hadnot displayed reasonable measured valuesbecause of the high electric fields, all theother benefits of a digital pH-sensor wouldhave been of no use to me, Reimannexplains drily. However, there was stillone question to resolve. Would the changebe at all worthwhile? This is easy to say.

Although relatively high costs are incurredin the initial steps for the modificationsrequired to the pipe work, these are rapidlybalanced out by the savings made. Onthe one hand, the Endress+Hauser systemis already substantially cheaper to buy. Onthe other hand, the old pH measurementscosted us up to 5,000 $ a week includingmaterials and work force costs. That addsup to 100,000 $ a year, according toReimann. No wonder, therefore, that inthe last two years Salzgitter Flachstahl hassuccessively re-equipped the plant withMemosens. The old stock is being used upon the last remaining measuring point forthe old style of sensor.There are a few left in the stores. The storesalways carried 12 spare electrodes becauseof the familiar high rate of wear. Sometimesthe operation could not cope with the orde-ring. Reimann today keeps just three of thenew sensors as spare part inventory. Justbeing able to keep three instead of 12 elec-trodes in the stores as dead capital makesa difference.As a secondary effect,

Memosens increases plant availabilitywith its operational reliability and thisminimizes the work of the internalservice provider in surface treatment.But Borchers is not sad about this: Eventhough we are an independent servicecompany, we still benefit from the fact thathere at this location good, inexpensive steelis produced. We welcome any technicaldevelopment that helps us in our work andour advice and support to the companiesreflect this.

Unbreakable technologyReimann sees a further decisive benefitof Memosens in the fact that the elec-trode does not have to be calibrated tothe measuring transmitter on which itis used: We can now calibrate centrally.This means that no-one has to go to thesite, which means a clear saving in timeand money. Furthermore, all operations thatcan take place outside the plant enhancesafety at work, Reimann notes. This is whySalzgitter Flachstahl has purchased a slim-med-down measuring transmitter especiallyfor the laboratory on which a laboratorytechnician can calibrate the electrodesalong the way. This takes just 20 minutesper electrode. No comparison with the past,

when two staff took two days to do it. Theelectrodes are then stored on a rack for ca-librated electrodes. When someone needs anew one, he can just take it from the rack,swap it over and put the used sensor in tothe rack for non calibrated sensors.

Positive secondary effect: the electrodeglass swells up in the process over timeand suffers a toxic reaction. Immersingthe electrode in a solution of potassiumchloride or water over night returnsthe glass to its original condition.Because the old electrodes were put backin the process directly after calibration, theypractically never had time to completelyregenerate. Salzgitter Flachstahl sees thisprecautionary maintenance which it is nowable to perform itself as an indispensablequality assurance measure significantly ex-tending the service life of the pH measuringstations.

And how do Memosens operating timesshape up by comparison with the earliermeasuring systems? Up to now, I am onlyable to say that in the last half year since wehave been using the electrodes in our pick-ling line, we are yet to need to fetch a newone from the stores, grinned Reimann.