The main investigation consisted of determining corrosion rates of mild steel
(A lSI 1 020) exposed to de-aerated stagnant solutions of fatty acids in water
at different acid numbers and temperatures, with the aid of mass loss tests.
The temperature range investigated varied from 25°C to 250°C. Results
showed that corrosion rates initially increased with temperature and at
certain elevated temperatures thick multi-laminated corrosion product films
formed on the specimen surfaces which .led to decreases in corrosion rates
with further increases in temperature. Corrosion product films influenced the
control mechanism of the corrosion process and it was seen that the
characteristics of these films were dependent on the temperature as well as
fatty acid type. The acid number range investigated was from 0 to 25 mg
KOH/g solution. Corrosion rates increased with an increase in acid number
irrespective of the control mechanism. Results indicated that the corrosivity
of acid solutions decreased with an increase in chain length of the organic
acid molecule, when no corrosion product films were present. The presence
of corrosion product films rendered complex relationships.
Electrochemical tests were done on specific fatty acid systems at 25 °C.
Corrosion rates evaluated from electrochemical observations correlated well
with mass loss results and it was concluded that the corrosion mechanism
was electrochemical.
Supplementary investigations were conducted on specific fatty acid systems
and included the following:
Turbulence did not influence the corrosion process. This is typical for an
activation-controlled system where no corrosion product films are present
on the specimen surfaces. Mixing of acids showed a corrosion rate of approximately an average of the
two individual corrosion rates of the pure systems.
Monitoring studies showed that results obtained with the Corrator correlated
better with mass loss and electrochemical corrosion rates than Corrosometer
results.
Corrosion rates increased with an increase in dissolved oxygen content level
of the solution and with additions of chloride, but sulphur additions rendered
lower corrosion rates.
A water phase process stream received from SASOL showed that the
corrosion rate increased with temperature and levelled out towards 200°C
The corrosion characteristics of the received stream can be simulated by
acetic acid with the same acid number.
Die hoofondersoek het bestaan· uit die bepaling van korrosietempo's van
laekoolstofstaal ( A lSI 1020 ) wat blootgestel word a an ontlugte stagnante
oplossings van organiese sure in water by verskillende temperature en
suurgetalle. Die korrosietempo's is bepaal deur gebruik te maak van
massaverliestoetse.
Die temperatuurgebied wat ondersoek is, was van 25 °C tot 250°C. Dit is
waargeneem dat die korrosietempo aanvanklik toeneem met 'n toename in
temperatuur en daarna is 'n afname in die korrosietempo waargeneem. Die
afname word toegeskryf a an 'n dik multi-laminere-korrosieprodukfilm wat op
die monsteroppervlak gevorm het. Hier is waargeneem dat die
beheermeganisme be"invloed word deur die teenwoordigheid van
korrosieprodukfilms terwyl eienskappe van die films afhanklik was van die
tipe suur, asook die temperatuur waarby eksperimente gedoen is. Die
suurgetalgebied wat ondersoek is, was vanaf 0 tot 25 mg KOH/g oplossing.
Korrosietempo's het toegeneem met 'n toename in suurgetal ongeag die
beheermeganisme wat bestaan het. Die korrosiwiteit van die suuroplossings
het afgeneem met 'n toename in organiese molekuullengte, waar geen
korrosieprodukfilm teenwoordig was nie. Die teenwoordigheid van
korrosieprodukfilms het komplekse korrosietempo-tipe suur verhoudings by
konstante temperature opgelewer.
Elektrochemiese toetse is gedoen op sekere sistema by 'n temperatuur van
25 °C. Korrosietempo's verkry deur gebruik te maak van elektrochemiese
toetsmetodes vergelyk baie gunstig met massaverliestoetsresultate. Die
gevolgtrekking wat dus gemaak is, was dat 'n elektrochemiese
korrosiemeganisme bestaan.
Newe-ondersoeke is gedoen op sekere .organiese suursisteme en het die
volgende ingesluit: Turbulensie het geen effek op die korrosieproses gehad nie. Dit is tipies wat
verwag word van 'n aktiveringsbeheerde sisteem waar geen
korrosieprodukfilms teenwoordig is op die monsteroppervlak nie.
Mengsels van die sure het getoon dat die korrosietempo's 'n gemiddelde
waarde van die individuele korrosietempo's van die suiwer suursisteme
oplewer.
In die moniteringstudies het die Corrator resultate beter gekorreleer met
massaverlies en elektrochemiese toetsresultate as Corrosometer resultate.
Die korrosietempo het verhoog met 'n toename in opgeloste suurstofinhoud
van die oplossing asook met die byvoeging van chloriede, terwyl 'n afname
in korrosietempo waargeneem is met die byvoeging van swael.
'n SASOL waterfase produkstroom het getoon dat die korrosietempo
toeneem soos die temperatuur toeneem tot ongeveer 200°C waarna 'n
afplatting in korrosietempo waargeneem is. Die korrosiekarakteristiek van die
SASOL waterfase produkstroom word redelik goed verteenwoordig deur 'n
asynsuur sisteem met dieselfde suurgetal.
