Proteksi katodikKorosi Prinsip • Menurunkan potensial sampai daerah imun • dengan menghubungkan logam dengan logam lain yang potensial reduksinya lebih negatif anoda korban (SA) • Dengan mengalirkan arus arus terpasang (IC) E0 pipa minyak di lepas pantai. tangki penyimpanan.Prinsip • Proteksi katodik adalah suatu metode perlindungan korosi pada permukaan logam dengan membuat katoda dengan logam lain (anoda korban) atau suatu rangkaian listrik • Proteksi katodik digunakan untuk melindungi pipa dalam tanah. . dan lain-lain. kapal. aboveground storage tanks bottoms. concrete pressure pipes. . tower footings. grounding systems. sewage treatment clarifiers. above ground storage tank bottoms. underground piping. internal surfaces of water storage tanks. watermains and effluent discharge piping • Reinforced concrete structures: bridges. heat exchangers and storage well casings • Marine: ships.Aplikasi proteksi katodik • Petroleum & Petrochemical: underground piping and storage tanks. offshore drilling and production platforms • Pulp & Paper: effluent clarifiers. offshore pipelines. penstocks. iron and steel watermains. steel or reinforced concrete dock structures. buoys. condensers. parking garages and foundations • Municipal: foundation pilings. barges. foundation pilings. sewage pump stations • Electrical Power Industry :cooling water pipelines & intakes. • polarisasi minimum 100 mV. • -850 mV potensial polarisasi terhadap CSE. .Kriteria Proteksi • 850 mV terhadap proteksi katodik yang diaplikasikan. . . Proteksi katodik Anoda Korban . Pk Anoda korban . . . Prinsip Proteksi katodik Anoda korban • Menghubungkan logam yang diproteksi dengan logam yang dilindungi • Logam yang dikorbankan mempunyai potensial elektroda lebih negatif • Tidak memperlukan arus dari luar . 0.363 .0.828 -1.Anoda korban E Zn 2+/Zn Zn 2+ + 2e = Zn 2H2O + 2e = H2 + 2OHE Al3+/Al Al +3 +3 e = Al .2.662 E Mg2+/Mg Mg 2+ + 2e = Mg .763 . Diagram Polarisasi . Diagram polarisasi seng (Zn) . . Persyaratan • Mampu menurunkan potensial logam yang diproteksi ke daerah imun • Memerlukan biaya murah • Mampu dibentuk sesuai dengan ukuran yang diinginkan • Mengalami korosi merata . Short chunky shapes are suitable for low resistivity areas.000 ohm-cm and 5. but long slender shapes should be employed in higher resistivity areas • Aluminum anodes are not commonly used in earth burial applications. Short chunky shapes are suitable for low resistivity areas.000 ohm-cm. Some proprietary aluminum alloy anodes work well in a sea water environment . but long slender shapes should be employed in Higher resistivity areas • Zinc anodes are also available in many shapes and sizes. Favorable environments are sea water and salt marshes.Tipe anoda • Typical materials for sacrifical anodes are Magnesium (for soil) and Aluminium/Zinc /Galvalum / Indium alloys (for seawater or seabeds) • Magnesium anodes bervariasi bentuk dan ukuran dengan berat 17 Anoda Mg untuk resistivitas tanah 1. They are appropriate in soils with very low resistivities (750 ohm-cm to 1500 ohmcm). Hub Anoda Korban & Resistivitas • Jenis anoda Al Zn Mg Resistivitas (OhmCm) < 150 150-500 >500 . 8 1200 50 Zn 7.7 0.7 1.10 0.25 2700 95 .Sifat Anoda Jenis anoda 1.5 1.V 4.E (V/SCE) 3.25 780 95 Al 2.05 0.dorong.Masa jenis 2.Teg.7 1-1.Efisiensi (%) Mg 1. Kapasitas (AH/Kg) 5.6-0. Backfill • Kantung pembungkus anoda yang berisi gypsum 75% bentonit 20% natrium sulfat 5% Resistivitas anoda yang dihasilkan 50 Ohm-Cm Fungsi Backfill • Memberikan lingkungan yang merata arus keluaran tetap • Menurunkan resistivitas dari fasa anoda dengan tanah • Mencegah kontak langsung antara anoda dengan tanah Keuntungan • Self-powered so no external power source is required. • Easy field installation. • Low maintenance requirement. • Less likely to cause stray current interference problems on other structures. • When the current requirement is small, a galvanic system is more economical than an impressed current system. Low maintenance requirement. Not an economical source of large amounts of CP current. • Very Little capacity to control stray current effects on the protected structure. Limited to use in low resistivity soils.Kelemahan • • • • Low driving voltage. . Contoh . . Pemasangan anoda . . . Pemantauan . . . Pemantauan . • Sistem Impressed Current Cathodic Protection menggunakan anoda yang dihubungkan dengan sumber arus searah (DC) yang dinamakan cathodic protection rectifier.Proteksi katodik arus terpasang • Untuk struktur (bangunan) yang lebih besar. anoda korban tidak dapat secara ekonomis mengalirkan arus yang cukup untuk melakukan perlindungan yang menyeluruh. . Arus terpasang . Peralatan • Rectifier (current supply) • Counter electrode • Reference electrode . Instalasi . . → H2(g) eq .→ 4OH2H+ + 2e.Reaksi • Carbon steel and stainless steel (depending on the temperature) exposed to seawater will suffer from corrosion. • The following reactions will occur on the surface : • Anodic reaction: Fe → Fe 2+ + 2e• Cathodic reactions: O2 + 2H2O + 4e. PK arus terpasang . Polarisasi dalam air laut . Overvoltage diagram for steel in seawater with protection current IP included . Prinsip . Keuntungan • • • • • Flexibility Applicable to a variety of applications Current output may be controlled Not constrained by low driving voltage Effective in high resistivity soils . Kelemahan • Increased maintenance • Higher operating costs • May cause interference on other structures . Graphite. Mixed Metal Oxide.Tipe anoda • Anodes for ICCP systems may be in cylindrical. rod shaped. Silicon-Cast Iron anodes are the most economical. Materials may be Silicon-Cast Iron. Platinum or Titanium coated alloys. but also crack easily. tubular or ribbon form. wire. . Flush mounted. Bracelet .Jenis anoda : Stand off. Thus these anodes are used where high driving voltage is required. Graphite anodes are one of the most commonly used anodes for impressed current systems. its use is no critical Platinized Titanium anodes take advantage of the low consumption rate and high current density. Breakdown of the niobium oxide film occurs at approximately 120 Volts. Voltages in excess of 10 Volts will result in severe pitting of the titanium core causing premature failure. Nonuniform consumption. High Silicon Cast Iron anodes are widely used in underground applications in both shallow and deep ground beds. Graphite anodes are suitable for deep. Platinized Niobium/Tantalum anodes also take advantage of the properties of platinum. • • • . high rate of consumption. Although the performance is Improved with coke breez . and discoloration of surrounding structures are distinct disadvantages. or horizontal ground beds with carbonaceous backfill. shallow vertical. but avoid the low driving voltage restriction of platinized titanium anodes. Specially formulated high silicon cast iron anodes are also used in seawater. Most common applications are to protect underground structures.Type anoda • • Scrap iron is sometimes used as an anode simply because it is available. .providing a consistently low resistance anode .• Magnetite anodes are quite expensive but have an extremely long life. The titanium serves as a support for the oxide coating. As a result of this low consumption rate. When applied on titanium. measured in terms of milligrams per year. The mixed metal oxide is a crystalline. electrically-conductive coating that activates the titanium and enables it to function as an anode. the coating has an extremely low consumption rate. They are therefore an economical choice for some applications. the tubular dimensions remain nearly constant during the design life of the anode . • Mixed Metal Oxide anodes consist of a high purity titanium substrate with an applied coating consisting of a mixture of oxides. Karakteristik anoda . . Banyak aplikasi menanam anoda hingga kedalaman 60 m (200 kaki) dengan diameter lubang 25 cm (10 inchi) serta ditimbun dengan conductive coke (material yang dapat meningkatkan performa dan umur dari anoda). Terminal positif dari output DC tersebut dihubungkan melalui kabel ke anoda-anoda yang ditanam di dalam tanah. .50 ampere dan 50 volt.Instalasi • Tipe sistem ICCP yang umum untuk jalur pipa terdiri dari rectifier bertenaga arus bolak-balok (AC) dengan output arus DC maksimum antara 10 . . Pemasangan anoda (ground Bed) . . mempunyai dua fungsi: • menjadi sebuah resistivitas yang sangat rendah. dan dipadatkan di sekitar anoda. dan memiliki efek meningkatkan ukuran anoda dengan mengakibatkan penurunan resistansi terhadap tanah • sebagian besar akan diteruskan ke backfill dari anoda melalui kontak langsung sehingga sebagian besar konsumsi material akan terjadi di tepi luar kolom backfill.Karbon yang ditanam. 5 mA/m2. . pipa dengan cat/coating ditambah dengan isolasi 0. yakni pipa tanpa proteksi 20 mA/m2. pipa dengan cat/coating 2 mA/m2.Kebutuhan arus proteksi • Kebutuhan arus proteksi pada pipa mengacu pada densitas arus proteksi yang diperlukan. IP = AP x i • IP = Arus proteksi untuk melindungi pipa (ampere) • AP = Luas permukaan yang akan dilindungi (m2) • i = Densitas arus proteksi yang diperlukan (mA / m2 ) 20 mA / m2 untuk pipa tidak dilapisi 2 mA / m2 untuk pipa yang dicoating 0.5 mA / m2 untuk pipa yang dicoating dan diisolasi . Pemantauan • Elektroda acuan CSE . Multi meter . . isolasi .6 mA/m2. dan jembatan • Jelaskan prinsip perlindungan korosi metode proteksi katodik • Jelaskan perbedaan PK anoda korban dan arus terpasang • Sebutkan isi backfill dan apa fungsinya • Hitung kebutuhan arus proteksi dan anoda korban untuk pipa dengan luas 8 km2 jika rapaat arus nya 0. • Jelaskan persyaratan logam yang dapat digunakan sebagai anoda korban. anoda. • Gambarkan dengan diagram E Vs log (i) PK anoda korban dan arus terpasang! .Tugas • Hitung efisiensi anoda Mg dan Zn • Berdasarkan praktikum PK 1 dan 2 buatlah analisa dari hasil percobaan bagamana kondisi pipa.