The ACET Corrosion Risk Assessment module assesses the Risk of failure by looking at the Probability (likelihood) of a failure and the Consequence of that failure should it occur

The Qualitative approach assesses the Probability of Failure descriptively, using terms such as very likely, unlikely, possible, probable, or highly probable

Considerations taken into account during the assessment of the probability of failure include:

Corrosion Rate
Remaining Life
Threats (including failure mechanisms)

The Quantitative approach determines single numerical values for the Probability of Failure. These values can be obtained from experience, generic failure data, workbooks of questions with weighted answers, engineering judgement, or as a result of numerical analysis.

Basically the Quantitative approach used to determine the probability of failure is more comprehensive than the Qualitative approach in two ways:

The assessment is specific to the equipment and not generalised across a group of equipment with similar characteristics.
The assessment considers a much wider range of criteria likely to affect the probability of failure of the item including specific failure mechanisms.

However the final score is once again assigned a level of significance (score) between 1 and 5 where the highest or maximum score is used in conjunction with the consequence to determine the overall risk.

The following threats (failure mechanisms) and plant conditions are considered by default. The user can add any number of additional threats as required.

Internal Corrosion (Inspected Data); CO 2; O 2; Process Fouling; Bacterial SRB / GAB’s; HIC; Erosion; Cavitation; Crevice; External Corrosion; SCC; SSCC; Fatigue (vibration); Fatigue (thermal); Under Insulation; Creep; Galvanic; Overpressure (MOP); Temperature Induced Embrittlement Low; Additional user determined threats Other 1, Other 2, etc.

If a particular failure mechanism is not available in the set of default tables within ACET the user can simply create and save their own table with a set of considerations and their significance or weighting.

The Qualitative approach assesses the Consequence of Failure descriptively, using terms such as very low and very high.

A list of options (outcomes) for the consequence of failure in relation to Safety, Economics and the Environment are available and have been assigned a level of significance (1 to 5). This is then used as the system set of defaults, but the client or end user has the ability to add their own set of outcomes and their significance.

The consequence is derived from Safety, Economics and Environmental considerations.

Safety is set as the driver for the consequence assessment. The set up for the final value used for the consequence assessment will either:

Use the highest (worst case) significance from Safety, Economics or the Environment.
Apply a user set weighting to the consequence values to derive a final combined significance. If a weighting is applied there will be an additional option, which permits the user to set a rule up as follows:

If the final weighted significance is < [Pick list of: Safety, Economics, Environment, etc] then assign that value.

Applying a weighting to the consequence factors permits the user to attach more significance to one or more of the consequence factors; safety, economics, environment, etc.

The Quantitative approach determines single numerical values for the Consequence of Failure for each individual item. These values are obtained from experience, generic failure data, workbooks of questions with weighted answers, engineering judgement, or as a result of numerical analysis.

Basically the Quantitative approach used to determine the consequence of failure is more comprehensive than the Qualitative approach in two ways:

The assessment is specific to the equipment and not generalised across a group of equipment with similar characteristics.
The assessment considers a much wider range of criteria likely to affect the consequence of failure of the item.

However the final score is once again assigned a level of significance between 1 and 5 where the highest or maximum significance is used in conjunction with the probability of failure to determine the overall risk.

The user is able to create their own set of questions and weighted answers and add their own consequences of failure (in the form of an outcome).

The Risk from equipment failure is the combination of the assessed probability and the consequence. This is achieved by combining the highest value for the Probability of failure with the highest (or weighted) value for the Consequence of failure through a risk matrix.

The Matrix adopted for both Qualitative and Quantitative approaches is a numeric 5 x 5 matrix. ACET incorporates a default matrix. The user can customise the Matrix used in ACET as follows:

The user can change the values contained in the matrix to be numeric or textual.
The user can choose a value or meaning for any one of the 25 matrix outcomes.
The user can create a custom matrix.

The selection of an Examination Interval and a Confidence Factor allocation is a matter for experienced judgement by personnel thoroughly familiar with all aspects of the equipment and its duty and should be approved by a competent person.

The Inspection Frequency is determined from the risk in combination with a confidence factor. The end user or client can override the system-generated frequency. The system stores the history of override, which identifies the user, date, the system value; the new override value and the reason or justification.

The value on any particular threat is used to recommend the best NII method or methods to be used for the inspection. Understanding the types of damage can help the inspector select the appropriate inspection method and location for a particular application.

An NII reference table is available to assist with the selection of the most appropriate NII method or methods.


The output from the RBA Module is a transparent and auditable inspection plan based on a proactive risk assessment. It recommends inspection frequencies, inspection methods and where to apply these methods. It is simple in relation to its technical content and usability as well as being visually clean. In addition, the process is completely flexible and capable of meeting the requirements of most clients without any customisation.

		The assessment is carried out at both the qualitative and quantitative levels as follows: There are 3 options: Route 1: Qualitative assessment only Route 2: A Qualitative assessment followed by a more detailed Quantitative assessment. Route 3: A Quantitative assessment only.

	The Qualitative approach assesses the Probability of Failure descriptively, using terms such as very likely, unlikely, possible, probable, or highly probable Considerations taken into account during the assessment of the probability of failure include: Corrosion Rate Remaining Life Threats (including failure mechanisms) The Quantitative approach determines single numerical values for the Probability of Failure. These values can be obtained from experience, generic failure data, workbooks of questions with weighted answers, engineering judgement, or as a result of numerical analysis. Basically the Quantitative approach used to determine the probability of failure is more comprehensive than the Qualitative approach in two ways: The assessment is specific to the equipment and not generalised across a group of equipment with similar characteristics. The assessment considers a much wider range of criteria likely to affect the probability of failure of the item including specific failure mechanisms. However the final score is once again assigned a level of significance (score) between 1 and 5 where the highest or maximum score is used in conjunction with the consequence to determine the overall risk. The following threats (failure mechanisms) and plant conditions are considered by default. The user can add any number of additional threats as required. Internal Corrosion (Inspected Data); CO 2; O 2; Process Fouling; Bacterial SRB / GAB’s; HIC; Erosion; Cavitation; Crevice; External Corrosion; SCC; SSCC; Fatigue (vibration); Fatigue (thermal); Under Insulation; Creep; Galvanic; Overpressure (MOP); Temperature Induced Embrittlement Low; Additional user determined threats Other 1, Other 2, etc. If a particular failure mechanism is not available in the set of default tables within ACET the user can simply create and save their own table with a set of considerations and their significance or weighting. The Qualitative approach assesses the Consequence of Failure descriptively, using terms such as very low and very high. A list of options (outcomes) for the consequence of failure in relation to Safety, Economics and the Environment are available and have been assigned a level of significance (1 to 5). This is then used as the system set of defaults, but the client or end user has the ability to add their own set of outcomes and their significance. The consequence is derived from Safety, Economics and Environmental considerations. Safety is set as the driver for the consequence assessment. The set up for the final value used for the consequence assessment will either: Use the highest (worst case) significance from Safety, Economics or the Environment. Apply a user set weighting to the consequence values to derive a final combined significance. If a weighting is applied there will be an additional option, which permits the user to set a rule up as follows: If the final weighted significance is < [Pick list of: Safety, Economics, Environment, etc] then assign that value. Applying a weighting to the consequence factors permits the user to attach more significance to one or more of the consequence factors; safety, economics, environment, etc. The Quantitative approach determines single numerical values for the Consequence of Failure for each individual item. These values are obtained from experience, generic failure data, workbooks of questions with weighted answers, engineering judgement, or as a result of numerical analysis. Basically the Quantitative approach used to determine the consequence of failure is more comprehensive than the Qualitative approach in two ways: The assessment is specific to the equipment and not generalised across a group of equipment with similar characteristics. The assessment considers a much wider range of criteria likely to affect the consequence of failure of the item. However the final score is once again assigned a level of significance between 1 and 5 where the highest or maximum significance is used in conjunction with the probability of failure to determine the overall risk. The user is able to create their own set of questions and weighted answers and add their own consequences of failure (in the form of an outcome). The Risk from equipment failure is the combination of the assessed probability and the consequence. This is achieved by combining the highest value for the Probability of failure with the highest (or weighted) value for the Consequence of failure through a risk matrix. The Matrix adopted for both Qualitative and Quantitative approaches is a numeric 5 x 5 matrix. ACET incorporates a default matrix. The user can customise the Matrix used in ACET as follows: The user can change the values contained in the matrix to be numeric or textual. The user can choose a value or meaning for any one of the 25 matrix outcomes. The user can create a custom matrix. The selection of an Examination Interval and a Confidence Factor allocation is a matter for experienced judgement by personnel thoroughly familiar with all aspects of the equipment and its duty and should be approved by a competent person. The Inspection Frequency is determined from the risk in combination with a confidence factor. The end user or client can override the system-generated frequency. The system stores the history of override, which identifies the user, date, the system value; the new override value and the reason or justification. The value on any particular threat is used to recommend the best NII method or methods to be used for the inspection. Understanding the types of damage can help the inspector select the appropriate inspection method and location for a particular application. An NII reference table is available to assist with the selection of the most appropriate NII method or methods.