Tulisan ini membahas tentang pengaruh adanya wind load terhadap pressure Vessel Design, diambil dan dirangkum dari Forum Migas Indonesia Bulan April 2008.

Untuk pressure vessel (vertikal), perhitungan wind load terletak pada bagian yang diterpa angin dan sebaliknya. Stress yang dialami vessel di titik yang diterpa angin (upwind) = tension akibat internal pressure - compression akibat berat vessel + tension akibat hempasan angin.


Stress yang dialami vessel di titik di balik terpaan angin (downwind) = tension akibat internal pressure - compression akibat berat vessel - compression akibat hempasan angin.

kedua nilai ini harus dibawah compression dan tensile strength dari vessel. Jika nilainya negatif, berarti stress yang dihasilkan adalah compression. Jika positif adalah tensile stress. Untuk desain, ketebalan vessel akan didapatkan dari perhitungan ini (perlu diingat, menambah tebal juga menambah berat, jadi perlu dihitung lagi, terutama untuk compressionnya)


Perhitungan Wind Load (Shear & Moment) pada Pressure Vessel akan mempengaruhi desain untuk Pondasi Vessel tersebut, terutama sizing & quantity dari Anchor Bolt.
Sebenarnya ada 2 yang paling menentukan Desain Pondasi yaitu : Wind Load & Seismic Load.
Untuk perhitungan Wind Load ada beberapa Code yang dipergunakan antara lain: ANSI / ASCE-7, UBC-97, etc.

Namun jika ditarik kesimpulan ringkas, inti dari perhitungan Wind load adalah :

Wind Shear = Luasan Area yang terkena Angin x Wind Pressure note :

1. Wind Pressure disetiap titik area berbeda-beda, semakin tinggi suatu area maka semakin tinggi pula Wind Pressure.
   
2. Wind Pressure ditentukan oleh Wind Speed, tergantung dimana lokasi Vessel itu erection.

Wind Moment = Wind Shear x Height of Vessel dari base plate.

Dari hasil perhitungan wind load tersebut dipergunakan sebagai basis untuk mendesain Pondasi Vessel.

Referensi lebih lengkapnya bisa di lihat pada Pressure Vessel Handbook, Eugene F Megyesy.

Wind Load punya pengaruh besar dalam desain sebuah pressure vessel, khususnya untuk desain supportnya baik itu saddle type, leg type, atau skirt type.

Selain itu dari perhitungan wind load dan perhitungan pada support, akan didapatkan parameter untuk menentukan jumlah dan size achcor bolt yang akan dipakai oleh civil sebagai "dudukan" vessel.

Adapun referensi-referensi buku yang bisa dipakai adalah:

• Pressure Vessel Handbook by Eugene F Megyesy
• Pressure Vessel Design Handbook by Hendry H Bednar
• Pressure Vessel Design Manual by Dennis Moss
  

Sedangkan International Standard Code untuk Wind Load yang kerap dipakai berkaitan dengan desain pressure vessel adalah:

• ASCE-7
• Uniform Building Code (UBC)
  

Jangan lupa untuk memasukkan dari sisi dinamisnya, terutama untuk pendesainan vessel yang tinggi dan langsing... Kalau tinggi langsing, kena angin yang sepoi sepoi saja akan ada goyang… nah kalo goyangannya itu punya frekuensi yang sama dengan frekuensi naturalnya… bisa repot. Masalah ‘bergetarnya’ sesuatu itu nampak kecil, tetapi kalo terus menerus, masalah fatigue harus jadi konsen. Pernah lihat cerobong yang tinggi langsing putih yang ada ‘pemecah anginnya’? .
Kalo ada vessel langsing,harus dicek vortex shed. Alur leeward ketika dia mulai pecah akan mengakibatkan vibrasi.

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A pressure vessel is a closed container designed to hold gases or liquids at a pressure different from the ambient pressure. The end caps fitted to the cylindrical body are called heads.

Pressure vessels are used in a variety of applications. These include the industry and the private sector. They appear in these sectors respectively as industrial compressed air receivers and domestic hot water storage tanks, other examples of pressure vessels are: diving cylinder, recompression chamber, distillation towers, autoclaves and many other vessels in mining or oil refineries and petrochemical plants, nuclear reactor vessel, habitat of a space ship, habitat of a submarine, pneumatic reservoir, hydraulic reservoir under pressure, rail vehicle airbrake reservoir, road vehicle airbrake reservoir and storage vessels for liquified gases such as ammonia, chlorine, propane, butane and LPG.
Steel Pressure Vessel
Steel Pressure Vessel

In the industrial sector, pressure vessels are designed to operate safely at a specific pressure and temperature, technically referred to as the "Design Pressure" and "Design Temperature". A vessel that is inadequately designed to handle a high pressure constitutes a very significant safety hazard. Because of that, the design and certification of pressure vessels is governed by design codes such as the ASME Boiler and Pressure Vessel Code in North America, the Pressure Equipment Directive of the EU (PED), Japanese Industrial Standard (JIS), CSA B51 in Canada, AS1210 in Australia and other international standards like Lloyd's, Germanischer Lloyd, Det Norske Veritas, Stoomwezen etc.

Pressure vessels can theoretically be almost any shape, but shapes made of sections of spheres, cylinders and cones are usually employed. More complicated shapes have historically been much harder to analyse for safe operation and are usually far harder to construct

Generally, almost any material with good tensile properties that is chemically stable in the chosen application can be employed.

Many pressure vessels are made of steel. To manufacture a spherical pressure vessel, forged parts would have to be welded together. Some mechanical properties of steel are increased by forging, but welding can sometimes reduce these desirable properties. In case of welding, in order to make the pressure vessel meet international safety standards, carefully selected steel with a high impact resistance & corrosion resistant material should also be used.

Some pressure vessels are made of wound carbon fibre held in place with a polymer. Due to the very high tensile strength of carbon fibre these vessels can be very light, but are much trickier to manufacture.

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