12. SAVJETOVANJE O ZAŠTITI MATERIJALA I INDUSTRIJSKOM FINIŠU

Odgovor na prisutne štetnosti (nečistoće) u prirodnom plinu polja Molve i posljedično korozijsko okruženje CO₂ - H₂S - RSH - Hg - H₂O - O₂ - Cl^- - bakterije - viši ugljikovodici, a pri izboru optimalne tehnologije s ekonomskim naglaskom, bio je kompleksni sustav s rđajućim, nerđajućim i aluminijskim konstrukcijskim materijalima sa sekcijama predkondicioniranja plina, uklanjanja CO₂/H₂S aMDEA postupkom, LO-CAT odsumporavanjem i ekstrakcijom C₂₊.

Praćenje korozije ostvaruje se direktnim mjerenjima na 14 izabranih najkritičnijih točaka pomoću elektrootpornih sondi, vodikove sonde, ultrazvuka, te praćenjem parametara procesnih analizatora i ostalih parametara, kao i vizualnim pregledom za vrijeme stajanja radi uvida u stanje materijala i opreme (filtri, erozija) i indirektnim mjerenjima uzimanjem uzoraka za laboratorijske analize kao npr. bušotinski fluid, procesne otopine, dodatna voda, test kuponi, biofilm, talozi i mulj.

Može se zaključiti da instrumenti i probe reagiraju u skladu s očekivanom agresivnošću sredine, tako da su očitani rezultati najveći gdje je agresivnost veća i obratno.

U trogodišnjoj praksi stanje opće korozije je zadovoljavajuće i u području je zanemarive i vrlo niske korozivnosti, ali lokalno je definirano nekoliko problema koji zahtijevaju poseban nadzor i studiranje kao npr. izmjenjivač aMDEA otopine s pojavom pitinga uslijed klorida, erozija sondi u sustavu stripera aMDEA, mikrobiološka korozija LO-CAT pumpi i pojava galvanske korozije na filteru za pranje vodom.

Rano predviđanje stanja i utjecaja promjena u procesu, ocjena optimuma zaštite i nadopunjavanje novim spoznajama u dinamičkom sustavu procesiranja prirodnog plina pridonose uspjehu u borbi protiv korozije i na taj način ostvaruje se svrha praćenja korozije u smislu ostvarenja znatne ekonomske dobiti sa sigurnosno-ekološkom komponentom.

The complex system, involving carbon steel, stainless steel and aluminium structure material and consisting of gas preconditioning section, removal of CO₂/H₂S by aMDEA process, LO-CAT desulphurization process and C₂₊ extraction, was a response to impurities, i.e. CO₂ - H₂S - RSH - Hg - H₂O - O₂ - Cl^- - bacteria - higher hydrocarbons - present in natural gas at Molve field. It was also a result of consideration regarding the most appropriate technology from commercial and ecological standpoint.

The corrosion monitoring program covers direct measurement at selected 14 most critical points by electrical resistant probes, hydrogen probes and ultrasonics. Moreover, utilization of process analyzers and close monitoring of other parameters, as well as visual inspections during stand-by periods lead to conclusions regarding the true condition of material and equipment (erosion, filters). The indirect measurements involve collection of well stream, process solution, make-up water, precipitate and sludge samples, test coupons and biofilm.

The conclusion is that the instruments and probes react according to expected hostility of the environment, i.e. the highest readings are taken at the points of strongest severity and vice versa.

During the three-year operation, the general corrosion condition is satisfactory, since it is held within range of negligible or very low corrosiveness. However, some of discovered local problems require closer supervision and examination: the chloride induced pitting at the aMDEA solution exchanger, erosion of probes stated within aMDEA stripper system, micro-biological corrosion of LO-CAT solution pumps and signs of galvanic corrosion atack found on the water wash system filter.

The fight against corrosion has to be supported by early prediction of conditions and influences resulting with changes in process parameters, optimal safety measures and consistent incorporation of latest understanding related to dynamics of natural gas processing. Thus, corrosion monitoring accomplish the ultimate purpose - provide substantial economic benefit to the user with safe and ecologically acceptable environment.