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Cara Memilih Material Pipa

"PIPA SEAMLESS" Material pipa ada berbagai jenis. Bagaimana cara untuk menentukan material yang harus digunakan? Untuk dapat menentukan material, terutama untuk bidang industri, faktor yang paling penting adalah fluida apa yang akan mengalir didalamnya. Selain itu, kondisi luar dari pipa juga akan mempengaruhi. Dan terakhir, tentu saja dalam sisi ekonomi juga akan menjadi dasar pemilihan material.
Pipa juga dapat dibagi menjadi 2 bagian besar. Pipa dari logam dan non-logam. Logam telah terdiri dari carbon steel, stainless steel, aluminium, nickel dan lainnya. Berikut ini adalah contoh dalam desain pipa untuk pabrik industri gas alam, minyak, atau pabrik kimia lainnya.
Pertama, insinyur proses harus bisa menghitung apa dan berapa banyak macam kandungan yang akan melewati pipa. Pada dasarnya, semua pipa untuk proses biasanya harus memakai pipa logam dan dimulai dari material carbon steel yang paling murah.
Akibat aliran fluida, bagian dalam pipa akan mengalami korosi, dan salah satu cara untuk dapat menetapkan kecepatan korosi adalah memakai grafik de Waard – Milliams nomograph. Grafik ini membantu untuk dapat menentukan berapa kecepatan korosi (mm/tahun) yang telah disebabkan adanya kandungan CO2 dalam fluida.
Problem disebabkan korosi juga dapat diatasi dengan menambah ketebalan pipa sebesar kecepatan korosi dikali tahun lamanya pabrik didesain. Tetapi, jika total ketebalan yang dibutuhkan untuk dapat mengatasi korosi itu terlalu tebal, pipa akan menjadi sangat tebal dan tidak efektif dalam pembangunannya. Untuk keadaan ini, pipa dari stainless steel telah menjadi pilihan selanjutnya.
Selain korosi, suhu fluida juga dapat menentukan material pipa. Semakin rendah suhu, logam akan menjadi mudah mengalami retakan. Ini karena sifat brittle (getas)  logam bertambah pada suhu rendah . Stainless steel merupakan salah satu yang tahan akan suhu rendah. Karena itu, untuk cryogenic service (fluida dengan suhu operasi dibawah -196 degC) stainless steel adalah material yang cocok dibandingkan dengan carbon steel.
Stainless steel sering disebut juga corrosion resistance alloy (campuran logam tahan korosi) dan tentunya akan lebih mahal jika dibandingkan carbon steel. Stainless steel bisa dibagi menjadi beberapa jenis, contohnya austenitic, feritic, martenistic, duplex dan high alloy stainless steel (campuran tinggi logam stainless steel). Sayangnya, stainless steel tidak tahan terhadap semua jenis korosi, terutama korosi yang disebabkan oleh klorida, sulfida serta fluida asam (sour fluid) lainnya.
Untuk sistem pipa yang mengalirkan fluida asam (piping system for sour service) biasanya di desain berdasarkan standar NACE (National Association of Corrosion Engineers) MR0175. Mulai tahun 2003, standar NACE MR0175 bersatu dengan ISO 15156 dan yang telah memiliki syarat desain yang sulit dibandingkan edisi tahun sebelumnya.

Berdasarkan NACE MR0175/ISO 15156, penggunaan austenitic stainless steel telah dibatasi oleh kombinasi dari kadar khlorida, H2S (hydrogen sulfide) dan suhu fluida. Jika austenitic stainless steel tidak dapat digunakan, maka penggunaan duplex atau high alloy stainless steel merupakan pilihan selanjutnya. Jika duplex atau high alloy stainless steel juga tidak dapat digunakan, maka pilihan selanjutnya adalah menggunakan logam campuran nikel seperti incoloy dan inconel.
Semakin tahan terhadap berbagai korosi, semakin mahal harga material tersebut. Untuk dapat mengurangi biaya, pengaplikasian cladding atau overlay juga merupakan salah satu alternatif. Misalnya dengan menggunakan pipa dari carbon steel dengan dilapisi logam mahal pada bagian dalamnya saja yang bersentuhan langsung dengan fluida sumber korosi akan bisa menekan biaya tanpa mengurangi ketahanan terhadap korosi.
Pemilihan material ini bukan hanya untuk pipa, tetapi juga berlaku untuk bejana (vessel), katup (valve) dan elemen pipa lainnya. Untuk katup, walaupun material dari badan katup bisa memakai carbon steel, tetapi bagian dimana korosi tidak diperbolehkan untuk dapat menjaga kemampuan katup untuk menyekat (sering disebut sebagai trim, seperti bagian valve seat, stem dan lainnya), maka penggunaan stainless steel atau logam tahan korosi lainnya menjadi keharusan.
Pada saat melakukan pemilihan material yang sebenarnya, mungkin tidak akan semudah yang dijabarkan diatas, tetapi secara umum, begitulah proses pemilihan material pada saat mendesain pabrik industri.


Editor : Dian Sukmawati

CARA MEMILIH MATERIAL PIPA

Over the last five years or so, it seemed there was little that Dean G. Skelos, the majority leader of the New York Senate, would not do for his son.

He pressed a powerful real estate executive to provide commissions to his son, a 32-year-old title insurance salesman, according to a federal criminal complaint. He helped get him a job at an environmental company and employed his influence to help the company get government work. He used his office to push natural gas drilling regulations that would have increased his son’s commissions.

He even tried to direct part of a $5.4 billion state budget windfall to fund government contracts that the company was seeking. And when the company was close to securing a storm-water contract from Nassau County, the senator, through an intermediary, pressured the company to pay his son more — or risk having the senator subvert the bid.

The criminal complaint, unsealed on Monday, lays out corruption charges against Senator Skelos and his son, Adam B. Skelos, the latest scandal to seize Albany, and potentially alter its power structure.

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Preet Bharara, the United States attorney in Manhattan, discussed the case involving Dean G. Skelos and his son, Adam. Credit Eduardo Munoz/Reuters

The repeated and diverse efforts by Senator Skelos, a Long Island Republican, to use what prosecutors said was his political influence to find work, or at least income, for his son could send both men to federal prison. If they are convicted of all six charges against them, they face up to 20 years in prison for each of four of the six counts and up to 10 years for the remaining two.

Senator Kenneth P. LaValle, of Long Island, who serves as chairman of the Republican conference, emerged from a closed-door meeting Monday night to say that conference members agreed that Mr. Skelos should be benefited the “presumption of innocence,” and would stay in his leadership role.

“The leader has indicated he would like to remain as leader,” said Mr. LaValle, “and he has the support of the conference.” The case against Mr. Skelos and his son grew out of a broader inquiry into political corruption by the United States attorney for the Southern District of New York, Preet Bharara, that has already changed the face of the state capital. It is based in part, according to the six-count complaint, on conversations secretly recorded by one of two cooperating witnesses, and wiretaps on the cellphones of the senator and his son. Those recordings revealed that both men were concerned about electronic surveillance, and illustrated the son’s unsuccessful efforts to thwart it.

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Adam Skelos took to using a “burner” phone, the complaint says, and told his father he wanted them to speak through a FaceTime video call in an apparent effort to avoid detection. They also used coded language at times.

At one point, Adam Skelos was recorded telling a Senate staff member of his frustration in not being able to speak openly to his father on the phone, noting that he could not “just send smoke signals or a little pigeon” carrying a message.

The 43-page complaint, sworn out by Paul M. Takla, a special agent for the Federal Bureau of Investigation, outlines a five-year scheme to “monetize” the senator’s official position; it also lays bare the extent to which a father sought to use his position to help his son.

The charges accuse the two men of extorting payments through a real estate developer, Glenwood Management, based on Long Island, and the environmental company, AbTech Industries, in Scottsdale, Ariz., with the expectation that the money paid to Adam Skelos — nearly $220,000 in total — would influence his father’s actions.

Glenwood, one of the state’s most prolific campaign donors, had ties to AbTech through investments in the environmental firm’s parent company by Glenwood’s founding family and a senior executive.

The accusations in the complaint portray Senator Skelos as a man who, when it came to his son, was not shy about twisting arms, even in situations that might give other arm-twisters pause.

Seeking to help his son, Senator Skelos turned to the executive at Glenwood, which develops rental apartments in New York City and has much at stake when it comes to real estate legislation in Albany. The senator urged him to direct business to his son, who sold title insurance.

After much prodding, the executive, Charles C. Dorego, engineered a $20,000 payment to Adam Skelos from a title insurance company even though he did no work for the money. But far more lucrative was a consultant position that Mr. Dorego arranged for Adam Skelos at AbTech, which seeks government contracts to treat storm water. (Mr. Dorego is not identified by name in the complaint, but referred to only as CW-1, for Cooperating Witness 1.)

Senator Skelos appeared to take an active interest in his son’s new line of work. Adam Skelos sent him several drafts of his consulting agreement with AbTech, the complaint says, as well as the final deal that was struck.

“Mazel tov,” his father replied.

Senator Skelos sent relevant news articles to his son, including one about a sewage leak near Albany. When AbTech wanted to seek government contracts after Hurricane Sandy, the senator got on a conference call with his son and an AbTech executive, Bjornulf White, and offered advice. (Like Mr. Dorego, Mr. White is not named in the complaint, but referred to as CW-2.)

The assistance paid off: With the senator’s help, AbTech secured a contract worth up to $12 million from Nassau County, a big break for a struggling small business.

But the money was slow to materialize. The senator expressed impatience with county officials.

Adam Skelos, in a phone call with Mr. White in late December, suggested that his father would seek to punish the county. “I tell you this, the state is not going to do a [expletive] thing for the county,” he said.

Three days later, Senator Skelos pressed his case with the Nassau County executive, Edward P. Mangano, a fellow Republican. “Somebody feels like they’re just getting jerked around the last two years,” the senator said, referring to his son in what the complaint described as “coded language.”

The next day, the senator pursued the matter, as he and Mr. Mangano attended a wake for a slain New York City police officer. Senator Skelos then reassured his son, who called him while he was still at the wake. “All claims that are in will be taken care of,” the senator said.

AbTech’s fortunes appeared to weigh on his son. At one point in January, Adam Skelos told his father that if the company did not succeed, he would “lose the ability to pay for things.”

Making matters worse, in recent months, Senator Skelos and his son appeared to grow wary about who was watching them. In addition to making calls on the burner phone, Adam Skelos said he used the FaceTime video calling “because that doesn’t show up on the phone bill,” as he told Mr. White.

In late February, Adam Skelos arranged a pair of meetings between Mr. White and state senators; AbTech needed to win state legislation that would allow its contract to move beyond its initial stages. But Senator Skelos deemed the plan too risky and caused one of the meetings to be canceled.

In another recorded call, Adam Skelos, promising to be “very, very vague” on the phone, urged his father to allow the meeting. The senator offered a warning. “Right now we are in dangerous times, Adam,” he told him.

A month later, in another phone call that was recorded by the authorities, Adam Skelos complained that his father could not give him “real advice” about AbTech while the two men were speaking over the telephone.

“You can’t talk normally,” he told his father, “because it’s like [expletive] Preet Bharara is listening to every [expletive] phone call. It’s just [expletive] frustrating.”

“It is,” his father agreed.

Dean Skelos, Albany Senate Leader, Aided Son at All Costs, U.S. Says

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