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Inspection is the practice of examining the physical condition of materials, components, or entire pieces of equipment in order to determine if and for how long it will operate as intended. Inspection plays a vital role in any asset integrity management program. Inspection provides information about the current condition of the equipment in question and may provide information to validate the reliability prediction for the equipment (i.e. validate the accuracy of the equipment remaining life estimation).

Types of Inspection

Nondestructive Testing

Nondestructive testing (NDT) uses a variety of inspection techniques in order to locate and monitor defects without causing damage to the component. External and internal corrosion and cracks are often found using NDT methods. Some examples of common NDT methods include: radiographic testing, ultrasonic testing, magnetic particle testing, electromagnetic testing, and many more. When selecting an NDT method to use for a piece of equipment, the following four considerations should be accounted for:

  • The type of damage mechanism to be inspected for
  • The size, shape, and orientation of the defect
  • Where the defect is located (external or internal)
  • The sensitivities and limitations of the NDT method

Destructive Testing (Mechanical Testing)

In contrast to NDT, destructive testing causes damage to the test specimen. The purpose of destructive testing, also known as mechanical testing, is to reveal material properties when external forces are applied dynamically or statically. Important material properties of interest include: tensile strength, elasticity, elongation, hardness, fracture toughness, fatigue, and resistance to impact. Common mechanical tests that provide information about those properties include tensile testing, compression testing, torque testing, bend testing, hardness testing, charpy impact testing, and shear testing.

Inspection for Reliability and Remaining Life

The purpose of performing inspection is to provide information on the current state of a piece of equipment or provide information for remaining life calculations. Risk-based inspection (RBI) and fitness-for-service (FFS) assessments are two standards used in the oil and gas and chemical processing industries.

Risk-Based Inspection

RBI is a process that uses a combined system of methods to identify and understand risk. Put simply, risk can be defined by two elements: the consequence of failure (CoF) and the probability of failure (PoF). The CoF considers and evaluates the consequences of various outcomes (e.g. health and safety, environmental damage, equipment damage, and economic loss). The PoF is the likelihood that a piece of equipment will fail at a given time. Furthermore, both the CoF and the PoF involve qualitative and quantitative assessments. The fundamental concept of RBI is “How much confidence do I need to have in what I believe to be the true damage state of the equipment [1]?” RBI can be used to reduce uncertainty about the damage state of a piece of equipment by prioritizing inspection-related techniques. This is usually done by means of NDT. Learn more about RBI.


FFS is a recommended practice and industry standard that evaluates in-service equipment for structural integrity. The purpose of FFS is to determine if a component is suitable for continued service. There are three levels of FFS assessments, each increasing in level of detail, analysis, and complexity. Typically, data from NDT and mechanical testing provide critical inspection information used for FFS assessments. The outcome of an FFS assessment, as it relates to inspection, is to establish inspection intervals for specific equipment in order to monitor and eliminate potential failures. Establishing inspection intervals improves the overall safety, reliability, and efficiency of aging equipment. Learn more about FFS.

Inspection for Quality Assurance and Quality Control

Quality assurance (QA) and quality control (QC) are often confused as being the same process. However, the two processes are distinct.

Quality Assurance

The purpose of QA is to inspect the process that manufactures products. In other words, QA is a process that looks to improve the product development in order to eliminate defects in manufactured products. Inspection relating to QA does not typically involve NDT nor mechanical testing but rather, uses qualitative methods to identify gaps and anomalies in the process.

Quality Control

QC is carried out after QA and involves inspection of the product. The QC process involves activities such as NDT to ensure the quality of the product will operate as intended and for a specified number of cycles (if applicable) before failure. Mechanical testing may also be performed on one part per batch or per “X” number of batches. The number of batches is up to the company and individuals involved in the manufacturing process. The purpose of QC is to detect flaws and to determine if the defect is acceptable or rejectable for service.

Codes and Standards

Relating to NDT and Mechanical Testing

Since there are hundreds of standards relating to NDT and mechanical testing, it is best to list the organizations that develop and publish standards pertaining to inspection. The following standards bodies are well known in the inspection community:

Relating to RBI and FFS

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