Mitigating corrosion challenges from opportunity crudes

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Author: K. Wold
Date: June 2019
Publisher: Gulf Publishing Co.
Document Type: Article
Length: 1,873 words
Lexile Measure: 1610L

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High-quality crudes are not always readily available, or at a price that is acceptable to the producer's budget. Therefore, the trend toward using opportunity crudes--or spot crudes--is growing, despite the corrosion challenges that come with them.

The financial case for opportunity crudes--purchased at a significant discount per barrel--is compelling. Even a 1% use of opportunity crudes, at a discount of $6/bbl in a medium-size refinery of 300,000 bpd, can lead to crude oil cost savings of up to $6.5 MM/yr. In addition, these crude oil cost savings are conservative, considering that the typical Western Canada Select (WCS) crude discount to West Texas Intermediate (WTI) is about 25%.

However, the quality of the crude often fluctuates, depending on the field the crude originated from--with oil sand fields, in particular, producing a crude with much higher acidity, or total acid number (TAN) levels.

According to Natural Resources Canada, Canada exported 3.3 MMbpd to the US in 2017, with much of the crude coming from the Alberta oil sands. This crude is characterized as being heavy, sour and acidic, with high TAN levels and high sulfur. These characteristics--along with nitrogen and aromatics content and high viscosity--are often key elements of opportunity crudes and pose significant dangers to refinery equipment.

Such challenges are also compounded by storage tanks, which can have residue left in them from previous crudes stored there, and by the issues around blending. Opportunity crude oil properties often do not match the specifications of the refinery and process equipment and, therefore, have to be blended. With numerous crude oil feedstocks and varying properties, as well as the danger of blending too much opportunity crude into the mix, it is vital to have modern and flexible corrosion monitoring.

Finally, the aging infrastructure that characterizes many refineries brings with it another set of challenges when it comes to opportunity crudes. Maintaining any system requires deliberate planning and scheduled maintenance to remain safe and meet regulatory standards, while also remaining profitable.

While the optimal blending of opportunity crudes can have a significant impact on finances in refineries, it must be backed up by the latest corrosion monitoring and measurement technologies. This article will examine some of the recent advances in this area.

Opportunity crude corrosion challenges. What impact can opportunity crudes have on corrosion, and what are the challenges in detecting corrosion?

The causes of corrosion and the problems that are associated with it can vary. The most common forms of corrosion in refineries are caused by high TAN levels in opportunity crudes, leading to naphthenic acid corrosion (NAC), sulfuric acid corrosion, hydrochloric acid corrosion and hydrofluoric acid corrosion.

A key challenge is that these different types of corrosion often behave differently and are found at different plant locations. For example, NAC corrosion--the result of a mixture of naturally occurring cycloaliphatic carboxylic...

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Gale Document Number: GALE|A602105734