---
title: "Degradation Mechanisms - Classification and Definition"
slug: "degradation-classification-theory"
tags: ["PEI", "S-RBI", "Theory"]
updated: 2026-10-27T23:11:38Z
published: 2026-10-27T23:11:38Z
canonical: "ims-handbook.cenosco.com/degradation-classification-theory"
---

> ## Documentation Index
> Fetch the complete documentation index at: https://ims-handbook.cenosco.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Degradation Mechanisms - Classification and Definition

> [!NOTE]
> Take Note
> 
> This section of the Handbook introduces the theoretical underpinnings of Degradation Management in IMS. To learn more about the individual Degradation Modules used in IMS, see: [Degradation Modules Overview](/v414/docs/degradation-modules-1).

Degradation Management is about managing Degradation Mechanisms (DMs). So what really defines a DM? Let's have a look:

## Definition

According to the British Standards terminology, degradation is defined as the “*detrimental change in physical condition, with time, use, or external cause. Degradation may lead to a failure*”. Failure is the “*termination of the ability of an item to perform a required function*” and a Failure Mode (FM) is then the “*manner in which the inability of an item to perform a required function occurs*”. See [References](/v414/docs/degradation-management-theory-references) - 2.

A Degradation Mechanism (DM) is the physical, chemical, or other process that will cause a specific degradation morphology to occur, which may then lead to a failure. There are many different DMs and morphologies, and it is important to identify the correct DM to manage the degradation properly.

---

In IMS all DMs are modelled according to their location, and type. They can also be further described in terms of the morphology that they cause (designation of degradation).

## Location Types

DMs are divided into two location types:

- Internal: Process-side degradation
- External: Degradation outside pressure envelope

Note: Most DMs are Internal.

## Degradation Types

DMs are divided into three degradation types:

- Age-Related (AR): Modelled with Remnant Life (RL)
- Non-Age-Related (NAR): Modelled without RL
- Strategy Based (SB): Modelled with or without RL and pre-defined Inspection Strategy (IS)

See [Age-Related and Non-Age-Related Failure Characteristics](/v414/docs/age-related-and-non-age-related-failure-characteristics) and also [Corrosion and Remnant Life](/v414/docs/corrosion-and-remnant-life).

## Morphologies

The DMs can be further described in terms of the morphology that they cause (designation of degradation):

- General Thinning
- Localized Thinning
- Pitting Isolated
- Internal Thinning and Pitting
- Environmental Cracking – surface breaking
- Environmental Cracking – internal
- Environmental Cracking – blistering
- Fatigue Cracking
- Creep Damage
- Brittle Fracture
- Delamination
- Material Change
- Dent Buckling
- Plastic deformation

---

## Defining DMs in IMS

Degradation Mechanisms can be [defined in the CL](/v414/docs/defining-the-degradation-mechanisms).