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Corrosion is an electrochemical phenomenon and, therefore, can be controlled by altering the electrochemical condition of the corroding interface. For external wall surfaces, altering the
electrochemical nature of the corroding surface is relatively simple and is done by altering the voltage field around the pipe. By applying a negative potential and making the pipe a cathode, the rate of corrosion (oxidation) is reduced (corrosion is mitigated) and the reduction process is accelerated. This means of mitigating corrosion is known as cathodic protection (CP).
CP is achieved in practice by one of two primary types of CP systems, including sacrificial anode (galvanic anode) CP and impressed-current CP. Sacrificial anode CP utilizes an anode material that is electronegative to the pipe steel. When connected to the pipe, the pipe becomes the cathode in the circuit and corrosion is mitigated. Typical sacrificial anode materials for underground pipelines are zinc and magnesium.

Tanya – Sadikin, Indera

Dear rekan2 milis,

Mohon pencerahannya apa material sacrificial anode yang cocok untuk struktur baja di darat (outdoor). Apakah aluminum anode bisa diaplikasikan? Thanks
sebelumnya.

Tanggapan 1 – Teguh Santoso

Kenapa nggak di coating (cat) saja pak? apa strukturnya terpendam?

Tanggapan 2 – pepen pepen

Tergantung dari hasil survey awal, karena parameter korosi banyak yang diantaranya restivit tanah, PH, luas area yang akan di protec, bisanya yang sering di pakai di darat magnesium anode. Untuk Alumunium anode biasanya dipasang sub marine. Thanks.

Tanggapan 3 – Sadikin, Indera

Betul Pak Teguh. Sebagian struktur terpendam dan juga ada beberapa moving part yang tidak bisa dicoating (roda, bearing, dll.).

Tanggapan 4 – Isya Muhajirin

Pak Indera,

Untuk struktur yg terpendam dalam tanah, bapak bisa mengaplikasikan metoda sacrifial anode maupun impressed current. Jika sacrifial anode yg dipilih maka pemilihan anode material juga harus diperhatikan. Pada umumnya, anode yang digunakan adalah magnesium anode yang di-backfill. Dibandingkan dengan aluminium anode, Mg anode memiliki potential yang lebih tinggi. Hal ini berakibat pada waktu polarisasi yang lebih cepat dan kemampuan untuk memproteksi yang lebih baik dari Al anode untuk aplikasi CP di darat. Silahkan buka recommended practice dari NACE untuk spesifik equipment (bottom tank, underground piping, and other metallic structures).

Tanggapan 5 – Mahatrisna

Urun rembuk nih… kalo untuk moving parts kena tidak coba pakai Flourocarbon coating… saya memang tidak punya pengalaman langsung, tapi beberapa literatur bilang coating ini cukup feasible.

Flourocarbon coating adalah termasuk keluarga Flouropolymer coating, merupakan specialized coating yang cure-nya bekerja dengan cara polymerization (sederhananya lapisan coating dibentuk dari proses kimia yang menggabungkan dua atau lebih molecules dengan type berlainan, membentuk jaringan molecules yang lebih besar). Flouropolymer coating umumnya dapat dikenali dari trademark mereka di pasaran seperti Kynar (PVDF), Halar (ECTFE), dan Teflon (PTFE)…
kalo yang terakhir ini sering denger khan.

Dan berikut adalah nama kimia mereka sekeluarga:

PFA – Per Fluoro Alkoxy

PTFE – Polytetrafluoroethylene

FEP – Fluorinated Ethylene Propylene

ECTFE – Ethylene Chlorotrifluoroethylene

PVDE – Polyvinyl Flouride

PVDE adalah ‘the low end’ dan PTFE adalah ‘the high end’. Coating ini memiliki corrosion dan temperature resistance yang tinggi (200- 500 deg F in Extremely corrosive environment) karena kadar flourine yang tinggi. Flouropolymer juga menunjukkan flexibility, solubility, gloss, hardness, dan weather resistance, include immersion condition yang lebih baik dari pada galvanized atau cadmium plating. Memiliki adhesion yang bagus pada plastic, copper, aluminum, galvanized, ataupun concrete, dan coefficient friction yang tinggi (non slip). Biasanya digunakan sebagai coil coating, metal cladding di roof atau wall, moving parts, chemical atau pharmachemical instruments, oil and gas, drilling rigs, cookware, sampe senar pancing kualitas tinggi.

Tanggapan 6 – abdi raja

External Corrosion

Corrosion is an electrochemical phenomenon and, therefore, can be controlled by altering the electrochemical condition of the corroding interface. For external wall surfaces, altering the
electrochemical nature of the corroding surface is relatively simple and is done by altering the voltage field around the pipe. By applying a negative potential and making the pipe a cathode, the rate of corrosion (oxidation) is reduced (corrosion is mitigated) and the reduction process is accelerated. This means of mitigating corrosion is known as cathodic protection (CP).

CP is achieved in practice by one of two primary types of CP systems, including sacrificial anode (galvanic anode) CP and impressed-current CP. Sacrificial anode CP utilizes an anode material that is electronegative to the pipe steel. When connected to the pipe, the pipe becomes the cathode in the circuit and corrosion is mitigated. Typical sacrificial anode materials for underground pipelines are zinc and magnesium. Impressed-current CP utilizes an outside power supply (rectifier) to control the voltage between the pipe and an anode (cast iron, graphite, platinum clad, mixed metal oxide, etc.) in such a manner that the pipe becomes the cathode in the circuit and corrosion is mitigated. CP is most often used in conjunction with a coating. There are always flaws in the coating due to application inconsistencies, construction damage, or the combination of natural aging and soil stresses. If left unprotected, corrosion will occur at these coating flaws (holidays). Often the rate of attack through the wall is much higher at the holiday than the general attack of a bare steel surface. The use of a coating greatly reduces the total amount of current required to achieve protection of the pipeline system; therefore, CP and external coatings are utilized together wherever possible.

CP can be used to mitigate all types of corrosion previously discussed (general, stray current, MIC, and SCC). Sometimes it is difficult to determine the level of CP necessary to mitigate the different corrosion mechanisms and to identify which type of corrosion is present. Stress corrosion cracking presents additional problems. First, the high-pH form of SCC is only found on pipelines protected with CP. The products that result from cathodic reactions occurring on the pipe surface during CP in conjunction with soil chemistry produce the environment necessary for high-pH SCC. Since high-pH SCC only propagates in a very limited potential range, maintaining the potential of the pipe surface outside of this range by proper CP control will prevent growth of the high-pH SCC cracks. In addition, it has been established that proper CP control can inhibit the growth of near-neutral SCC cracks.

Internal Corrosion

Internal corrosion is also an electrochemical process; however, CP is not a viable option for mitigating internal corrosion in a pipeline. One of the first defense systems against corrosion for transmission pipelines is to ensure that the product being transported is free of moisture. Dry, deaerated natural gas and moisture-free oil and petroleum products are not corrosive. For corrosion to occur, there must be moisture, CO2, oxygen, or some other reduction reactant, such as one produced by microbes. Operators typically control moisture, oxygen, and CO2 contents of the transported product, but these constituents can enter the pipeline through compressor or pump stations, metering stations, storage facilities, or other means. Gathering lines in production fields have a much more significant problem with internal corrosion than the typical transmission pipeline. Appendix E – Gas and Liquid Transmission Pipelines E8.

One option available for mitigating internal corrosion is chemical treatment of the product being transported.
Chemical inhibitors for mitigating corrosion and biocides to prevent microbiological activity are used. Both of these methods can be effective in either natural gas or liquid pipelines. The cost of
either the inhibitor or biocide the treatment is significant. Recall that large volumes of products are continuously flowing through the pipeline. To mitigate corrosion through chemical treatment requires continuous injection or regular batching of the inhibitor or biocide. Appendix E – Gas and Liquid Transmission Pipelines.

Tanggapan 7 – roeddy setiawan

Dear Pak Sadikin,

Kalau struktur nya buried, tentu saja sacrificial anode bisa juga di apply cuman perlu study yang agak lanjut, karena resistivity dll sampai the soil wetness berubah rubah, jadi umumnya dipakai proteksi berlapis, sesudah coating, soil conditioning bisa di pakai sacrificial anode… cuman ngak begitu populer di indonesia…. bisanya yang banyak di pakai impress current….

Kalau strukturnya tidak buried saya kira coating is the best way, cheaper, dan intervensi nnya sederhana.

Kalau buat tangki liquid yang ada air nya sacrificial anode sering di pakai di bagian dalam, untuk menghilangkan resiko pitting karena coating imperfection,,,,, atau bagian dalam jangan di coating sama sekali to get even metal loss, then sac anode.

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