TITANIUM MATERIALS

Dalam industri kimia dan petrokimia, titanium sering dianggap sebagai material “polis asuransi”. Meskipun pengeluaran modal awal (CAPEX) lebih tinggi dibandingkan baja tahan karat (stainless steel), kemampuannya untuk menahan lingkungan agresif—terutama yang melibatkan klorida, klorin basah, dan asam pengoksidasi—menjadikannya standar untuk sistem dengan keandalan tinggi.

1. Mekanisme Fundamental: Lapisan Pasif

Kinerja titanium sepenuhnya bergantung pada lapisan oksida pasif ($TiO_{2}$).

• Pemulihan Mandiri (Self-Healing): Lapisan ini terbentuk secara instan dengan adanya oksigen atau kelembapan, bahkan dalam jumlah kecil.

 

• Stabilitas: Tidak seperti lapisan kromium-oksida pada baja tahan karat, lapisan oksida titanium sangat stabil pada rentang pH yang luas dan tetap utuh dalam aliran berkecepatan tinggi (hingga 40 m/s), sehingga kebal terhadap erosi-korosi.

 

• Pengoksidasi vs Pereduksi: Titanium sangat unggul dalam lingkungan pengoksidasi (Asam Nitrat, Asam Kromat). Namun, dalam asam pereduksi (Hidroklorida, Sulfat), lapisan oksida dapat terkikis kecuali terdapat elemen paduan (alloying) tertentu atau inhibitor.

  2. Key Grades for Process Systems

  Selecting the right grade is a balance between corrosion resistance and mechanical requirements.

  Grade	Type	Primary Benefit	Common Petrochemical Use
  Grade 2	Commercially Pure (CP)	The “Workhorse.” Excellent weldability and ductility.	Heat exchanger tubes, piping, tanks.
  Grade 7	CP + 0.15% Palladium	Superior resistance to reducing acids and crevice corrosion.	Components in high-temp, low-pH chloride environments.
  Grade 12	Ti-0.3Mo-0.8Ni	High strength and better resistance to crevice corrosion than Grade 2.	Heat exchangers and pressure vessels at elevated temperatures.
  Grade 5	Ti-6Al-4V	Very high strength-to-weight ratio.	Rotating equipment, fasteners, and high-pressure valves.

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  3. Critical Applications in Petrochemicals

  Purified Terephthalic Acid (PTA) Production

  Titanium is indispensable in the production of PTA (a precursor for polyester). The process involves Acetic Acid at high temperatures and pressures, which is devastating to most other metals.

   

  Equipment: High-pressure reactors, crystallizers, and columns are almost exclusively built with titanium or titanium-clad steel.

  Heat Transfer Systems

  Titanium heat exchangers are the industry standard for seawater cooling loops in refineries and offshore platforms.

  • Zero Pitting: It is virtually immune to pitting and stress-corrosion cracking (SCC) in seawater, unlike 300-series stainless steels.

     

  • Thin-Wall Tubing: Because of its high strength and corrosion resistance, designers can use thinner tube walls, improving thermal efficiency and offsetting material costs

  
  Chlor-Alkali Plants

  In the production of chlorine and caustic soda, titanium is used for anodes and piping handling wet chlorine gas, where it outlasts virtually all other metallic options.

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  4. Engineering & Fabrication Considerations

  Building “Titanium Systems” requires a different mindset than working with steel:

 

• • Explosion Cladding: For large pressure vessels, solid titanium is often cost-prohibitive. Titanium-clad carbon steel (joined via explosion bonding) is used to provide the corrosion resistance of titanium with the structural economy of steel.

  • Welding Purity: Titanium is a “reactive metal.” At temperatures above 427°C, it absorbs oxygen, nitrogen, and hydrogen, which causes embrittlement.

    • Trailing Shields: Welders must use secondary “trailing” gas shields to keep the cooling weld bead under a blanket of inert Argon until it drops below the critical temperature.
    • Color Check: A silver/straw color indicates a good weld; a blue or purple color suggests contamination, and a white/flaky appearance indicates a failed, brittle weld.

  • • Galvanic Protection: Titanium is a noble metal. If coupled with carbon steel or aluminum in an electrolyte (like seawater), it will accelerate the corrosion of the other metal. Proper isolation or sacrificial anodes are required.

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    5. Economic Reality: Life Cycle Cost (LCC)

    While titanium can be 3 to 5 times more expensive than stainless steel initially, its LCC is often lower due to:

    • Zero Corrosion Allowance: Designers don’t need to add “extra” thickness to account for metal loss over time.

    • Downtime Elimination: In a PTA or refinery setting, the cost of one day of unplanned shutdown usually exceeds the total price difference of the titanium components.