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March

2017

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ontinuing economic pressures on the refining

industry are persuading refiners to evaluate, or

re-evaluate, processing lower priced opportunity

crudes in order to improve profit margins.

Opportunity crudes now encompass a large range of

crudes, from heavy, high solids crudes (Canadian,

Venezuelan, etc.) and high acids crudes to the light tight

crude oils. These crude oil slates may be available for as

much as 10% less than similar characteristic feedstock. In

many cases, the refiner’s largest concern is not necessarily

with the crudes themselves, but rather the blend of the

crude oils that destabilise asphaltenes in the final crude

blend. This incompatibility can result in less efficient

desalting and increased corrosion downstream (e.g. crude

tower overhead, vacuum tower overhead lines). Another

major issue is the use of triazene-based H

2

S scavengers and

the impact their byproducts have on downstream fouling

and under-deposit corrosion in middle-side cuts that have

historically been mildly corrosive. Newer naphthenic-acid

crudes impact the lighter stream-like diesel and

atmospheric gas oils, as well as the historical crude tower

bottoms and vacuum gas oils.

Although problems with these types of corrosion have

impacted the refinery industry for many years,

1

there have

been significant advances in the past decade regarding the

accuracy of online monitoring of the pressure-boundary

components (such as piping) in overhead and higher

temperature side-cuts service. This newer generation of

non-invasive, online ultrasonic (UT) wall thickness

measurement systems are capable of reliably obtaining

actual wall loss data, and have been doing so for more than

15 years in these services. Additionally, the data is now

obtainable in many formats – both wireless or wired.

2

In

comparison to corrosion probes, online UT probes provide

Bruce Pellegrino,

Sensor Networks, Inc.,

USA and Mike Nugent,

E

2

G, USA,

examine a new

technology for online

corrosion monitoring and

control when processing

opportunity crudes.