Module 1: Crude Corrosivity Recap

Build a solid foundation for crude corrosivity, with information on naphthenic acid corrosion and high-temperature sulfidation, affected areas, and the evidence used to screen risk.

Module Overview

Corrosion in Refinery

Crude Corrosivity

Module 1

Crude corrosivity fundamentals

Build practical confidence through short lessons, guided decisions, and field-ready checks.

Duration10-15 minutes

FormatInteractive module

AssessmentKnowledge check

Updated30/09/2026

Module progress 0%

Complete the module quiz to record progress.

Operational Scenario

A new crude blend enters the refinery

A new crude blend changes sulfur, acidity, and operating conditions. Before selecting mitigation or inspection actions, the team must understand and distinguish the leading damage mechanism(s) and identify the evidence needed to screen affected circuits.

Topics and Subtopics

Select a topic to explore its main ideas, practical considerations, and subtopics.

Overview

What crude corrosivity means

Crude corrosivity is typically described as a joint action of naphthenic acid corrosion and high temperature sulfidation. It is present in hot sections (>230°C/>450°F) of CDU and VDU units where sulphur species and naphthenic acids may be present.

Key point: The most prominent effect of crude corrosivity is expected in vaccum gas oil sidecuts (e.g. Heavy Vaccum Gas Oil - HVGO) and vacuum residue.

Evidence to combine

Sulfidation and naphthenic acid corrosion are the leading damage mechanisms in hot sections of CDU and VDU units.
Proceeds without an electrochemical cell - no water present.
VGO, HVGO, and vacuum residue lines are particularly susceptible.

Primary drivers

Naphthenic acid and sulphur concentration and speciation.
Temperature: accelerates both mechanisms.
Local turbulence and multiphase flow: primarily intensify naphthenic acid attack; at high S level and thick loose iron sulphide scale flow will also matter.

Interactive Challenge

Interactive diagnostic case study

Select the first evidence to review

Decision point

The refinery receives a higher-acidity crude blend. Choose the evidence that should be reviewed first before declaring a new damage mechanism or changing an inspection plan.

Illustrative screening indicators

Diagnostic clues

Start with the change

Compare the new blend and operating history with the baseline period represented by the inspection data.

Locate the exposure

Use circuit conditions and metallurgy to determine where the chemistry change could become active damage.

Reveal the explanation

Screen before you prescribe

The correct first step is to join the blend change to the local operating envelope and susceptible circuit. This avoids treating a bulk assay value as proof of damage or dismissing a real change because one result appears normal.

Recommended action: Document the screening basis, identify representative monitoring points, and carry the confirmed risk drivers into the mitigation and inspection modules.

Field Checklist

Crude corrosivity screening

Use this checklist when a crude blend, operating envelope, or inspection trend changes.

0 of 5 completed

1. Confirm the crude and blend history
Record the crude sources, blend proportions, assay data, sulfur, acidity, water, and salt behavior. 2. Identify the relevant damage mechanisms
Consider naphthenic acid corrosion, sulfidation, erosion, localized attack, and any competing mechanisms. 3. Map susceptible circuits
Review temperature, flow, phase behavior, metallurgy, equipment consequence, and prior damage. 4. Check the evidence quality
Confirm measurement locations, calibration, repeatability, time period, and whether the result is local or representative. 5. Record the next decision
Assign the next assay review, monitoring point, inspection check, or engineering assessment.

Knowledge Check

Crude corrosivity fundamentals knowledge check

Select the best answer for each question, then submit it to see the reasoning. Pass mark: 70%.

Not yet passed.

Score: 0 / 2

1. What is the best starting point when a new crude blend is introduced? Compare chemistry and operating history, then screen susceptible circuits and metallurgy. Assume the most recent coupon represents every circuit. Use TAN or sulfur alone to set the inspection interval.

2. Why should the damage mechanism be linked to a specific circuit? Local temperature, flow, phase behavior, and metallurgy control how exposure becomes damage. Every component sees identical conditions when the crude is the same. Circuit mapping is only needed after a leak occurs.

Next Steps

Continue the course

Mitigation strategies

Continue to Module 2 to review operating, materials, and process mitigation options.

Next: Module 2