Last update: Jan 13, 2017
Damage Mechanism (also referred to as degradation mechanism) is a general term referring to any causes of problems or failures within process equipment. These can range from corrosion, to cracking, to heat damage, and everything in between.
When assessing damage mechanisms, one must take into account the current state of the equipment, as well as any potential damage the mechanism may cause later. Equipment’s susceptibility to a particular damage mechanism is affected by a number of variables, including materials of construction, process fluids, operating conditions, external environment, etc. A good understanding of the variety of damage mechanisms that exist is a must for any mechanical integrity program.
A thorough damage mechanisms review is essential for creating an effective inspection strategy. Once damage mechanisms and morphology are understood, inspection strategists can use this information to select inspection methods with the highest probability of detecting, characterizing, and measuring potential damage. Furthermore, inspection intervals can be established using industry codes and standards such as API 510, 570, 653, API RP 579 for fitness-for-service, and API 580 and 581 for risk-based inspection.
Some of the most common damage mechanisms in the refining and chemical processing industries are:
Wet H2S Damage, which can occur when atomic hydrogen from wet H2S corrosion reactions enters and weakens the steel.
CO2 Corrosion, which is a form of degradation that occurs when dissolved CO2 in condensate forms carbonic acid, which corrodes steels.
Corrosion Under Insulation (CUI), which occurs when moisture builds up on the surface of insulated equipment.
Hydrogen Embrittlement, which happens when atomic hydrogen infuses into certain higher strength steels and causes them to become brittle.
Brittle Fracture, which is the sudden, very rapid fracture under stress where the material exhibits little or no evidence of ductility or plastic degradation before the fracture occurs.
High Temperature Hydrogen Attack (HTHA), a mechanism that can affect equipment that is exposed to hydrogen at elevated temperatures (at least 400 °F or 204 °C).
Sulfidation Corrosion, a type of corrosion that occurs at temperatures above 500 °F (260 °C) due to sulfur compounds in crude.
Damage mechanisms are detailed and covered at length in API RP 571, Damage Mechanisms Affecting Fixed Equipment in the Refining Industry. This document provides an in-depth look at over 60 different damage mechanisms that can occur to process equipment in refineries. It includes a general description of the damage mechanism, susceptible materials of construction, critical factors, inspection method selection guidelines, and control factors.
Recommend changes or revisions to this definition.
November/December 2016 Inspectioneering Journal
By Adam Gardner at PinnacleART
Beyond the financial hits, undetected degradation from corrosion can also lead to critical safety risks. To effectively manage mechanical integrity, organizations need reliable methods of identifying the current states of corrosion occurring within their assets.
September/October 2016 Inspectioneering Journal
By Kimberley Hayes at Olympus
Detecting, quantifying, and sizing indications characterized as a “crack” in critical equipment have long been the global benchmark of asset integrity programs. Therefore, the increased precision that inspection programs obtain using advanced technologies can dynamically improve the overall assessment.
October 18, 2016 By Lynne Kaley at Trinity Bridge LLC / Trinity Bridge Digital
Seasoned and knowledgeable inspectors are becoming harder and harder to keep. But using some of the industry documents in a smart way, inspectors with less experience can perform like an inspector with many more years of experience and even develop a great materials specialty with practice.
October 13, 2016 By Nick Schmoyer at Inspectioneering
Over 20 years ago, in the January/February 1996 issue of Inspectioneering Journal, we invited readers to participate in a brief survey concerning industry and non-industry topics. We recently unearthed the results to this survey and I thought our readers might get a kick out of some of the questions and responses.
InVista is a lightweight, hand-held ultrasonic in-line inspection tool (intelligent pig) capable of detecting pipeline wall loss and corrosion in unpiggable or difficult-to-inspect pipelines. The pipeline geometry inspection data captured by the InVista tool is exceptionally powerful when combined with the LifeQuest™ Pipeline fitness-for-service capabilities, providing an integrated solution set for the pipeline industry.
September 12, 2016 By Lynne Kaley at Trinity Bridge LLC / Trinity Bridge Digital
Experienced material specialists are in short supply and high demand these days. So if you are lucky enough to have one at your disposal, how can you squeeze the most out of that opportunity?
July/August 2016 Inspectioneering Journal
By Phillip E. Prueter at The Equity Engineering Group, Inc., Jonathan D. Dobis at The Equity Engineering Group, Inc., Mark Geisenhoff at Flint Hills Resources, and Dr. Michael S. Cayard at Flint Hills Resources
This article summarizes a recent finite element analysis (FEA)-based study that employs creep simulation techniques to investigate the elevated temperature response of piping with peaked longitudinal weld seams.
November/December 2015 Inspectioneering Journal
By Ralph E. King P.E. at Stress Engineering Services, Inc., and Brian Olson at Stress Engineering Services Inc.
To ensure the mechanical integrity and fitness-for-service (FFS) of equipment, facility managers, reliability engineers, and inspection technicians must understand the HTHA damage mechanism.
November/December 2015 Inspectioneering Journal
By Rick Eckert at DNV GL - North America Oil & Gas
Understanding the common factors that promote corrosion threats in the oil and gas value chain helps operators create effective inspection strategies.
September/October 2012 Inspectioneering Journal
On August 6, 2012, a piping failure occurred in the #4 Crude Unit at the Chevron U.S.A. Inc. refinery in Richmond, CA. Chevron U.S.A. would like to share some potentially significant preliminary information regarding the incident.
November/December 2004 Inspectioneering Journal
Accounts with shop validation on carbon steel samples prior to field trials, on an in-service C 1/2 Mo vessel, were reported at a recent industry conference. The studies were successful in the laboratory and appear to make sense in field trials on a C 1/2 Mo, in-service vessel.
November/December 2010 Inspectioneering Journal
The following references are from the American Petroleum Institute. They are widely used in the petroleum refining and petrochemical industries for managing equipment in HTHA service and are available in the public domain.
July/August 2012 Inspectioneering Journal
We have recently learned of one organized joint industry project (JIP) that was announced at the Spring 2012 API Refining meeting. As information has become available we have decided to present it to our readership.
AIM systems should ensure that the your facility’s MI software is accurately performing the calculations needed to calculate minimum thickness, long/short term corrosion rates and remaining life used to predict future inspection intervals. They should evaluate your MI software’s basic design and corrosion monitoring variables.
September/October 2015 Inspectioneering Journal
If we could measure, understand, mitigate, and most importantly, control corrosion, we can do a better job of keeping the product in the pipes. To accomplish this task, we needed to know what is causing the corrosion and how to control it.
September/October 2005 Inspectioneering Journal
By John Reynolds at Intertek
Temper embrittlement is another form of metallurgical degradation resulting from exposure of susceptible low alloy steels to higher temperature ranges, usually in service, but can occur to some extent even during heat treatment. And, once again, if significant temper embrittlement has occurred, the equipment may be susceptible to catastrophic brittle fracture.
May 18, 2015
This post is based on an article from the September/October 2008 issue of Inspectioneering Journal by Richard Green at Accurate Metallurgical Services. You can find the original article here.