As a Corrosion Expert, this report centred around the failure investigation of a shell and tube heat exchanger due to corrosion mechanisms.
The different types of corrosion, its effect resulting to the failure and possible solutions and recommendations were submitted to the client for further action. The report also sheds light on the alloys used for the design and better alternatives to be used to prevent future degradation of the shell and tube heat exchangers.
Table of Contents
Introduction
Methodology
Failure Investigation
Material Description
Inspection and Tests
Operational Conditions of the heat exchanger
Effect of the Operational conditions
Effects of Corrosion
Detected Corrosion
Crevice Corrosion
Stress Cracking Corrosion
Pitting Corrosion
Conclusion
Recommendation
Research Objectives and Core Topics
The primary objective of this investigation is to identify the root cause of recurrent failures in a C22 tube bundle within an offshore HP gas cooler heat exchanger. By evaluating historical operational data, material properties, and environmental stressors, the study aims to establish effective rectification and preventative maintenance strategies.
- Failure analysis of C22 alloy tube bundles.
- Impact of operational variables (temperature, velocity, pressure) on structural integrity.
- Mechanisms of corrosion, including crevice, stress-related, and pitting types.
- Evaluation of maintenance and material selection procedures.
Excerpt from the Book
INTRODUCTION
According to Aliya (2002), failure analysis is an investigative process carried out to determine the leading factors of an unwanted loss in functionality. The failure of structures, components or machines can be addressed, depending on the approach and base knowledge of materials engineering. Therefore, the application of failure investigation plays a key role in determining the root cause of failures. In carrying out failure investigation there are variables that guide in these assessment termed the ‘HUFIEMOODS’ this is used in evaluating the entire industry processes in order to reach the base cause of failure and design an effective solution.
In this failure investigation, we are going to be assessing the failure of a C22 tube bundle of a HP gas cooler heat exchanger. This heat exchanger is situated offshore and has undergone a series of repairs, servicing and materials upgrade within the last ten years, it currently has a tube leak after six months from its last repair. Our client Zonko Petroleum has supplied documents of defect assessments carried out by Eddy Current. We have also acquired further information from our client like; results of prior test analysis, thermal data sheet and the material analysis. This will serve as a guide in finding the root cause of failure and effective measures to rectify and prevent such failure.
Summary of Chapters
Introduction: Outlines the scope of the investigation into the C22 tube bundle failures and the utilization of the HUFIEMOODS framework.
Methodology: Details the sequence of analysis, including testing, operational assessment, and material design reviews.
Failure Investigation: Covers the material properties of C22 alloy and the mechanical characteristics observed under room temperature conditions.
Inspection and Tests: Describes the physical inspection techniques and cyclic passivation/crevice corrosion testing performed on the materials.
Operational Conditions of the heat exchanger: Presents the design and operating temperature parameters for the heat exchanger system.
Effect of the Operational conditions: Analyzes how thermal expansion, contraction, and fluid-induced vibrations impact the integrity of tube-plate joints.
Effects of Corrosion: Discusses the susceptibility of C22 alloy to various corrosive factors present in the North Sea environment.
Detected Corrosion: Focuses on the identification of specific corrosion sites, particularly at the production gas inlet and non-welded contact zones.
Crevice Corrosion: Explains the mechanisms of deterioration in confined spaces and the impact of chloride concentration.
Stress Cracking Corrosion: Investigates the stages of crack propagation resulting from cyclic thermal stresses and fatigue.
Pitting Corrosion: Examines the electrochemical reactions leading to localized surface degradation of the tubes.
Conclusion: Summarizes that the failure resulted from a simultaneous occurrence of multiple corrosion types driven by extreme operational conditions.
Recommendation: Proposes improved material assembly standards, such as API 660, and water treatment protocols to mitigate future failures.
Keywords
Heat Exchanger, C22 Alloy, Failure Investigation, Crevice Corrosion, Pitting Corrosion, Stress Corrosion Cracking, Offshore, Material Engineering, Tube Bundle, Corrosion Fatigue, Thermal Stress, Eddy Current, Salt Deposition, Passive Behavior, Maintenance.
Frequently Asked Questions
What is the primary scope of this technical report?
This report investigates the root causes behind the repeated structural failures of a C22 alloy tube bundle within an offshore high-pressure gas cooler heat exchanger.
What are the central themes discussed in the study?
The study focuses on the interplay between material science, operational environmental conditions (such as high pressure and velocity), and various corrosion mechanisms.
What is the core research objective of this work?
The main goal is to determine the underlying reasons for tube leaks occurring shortly after repairs and to provide actionable recommendations for preventing future damage.
Which scientific methods are utilized for the investigation?
The author employs visual inspection, material analysis, thermal data review, and specific corrosion tests like the Cyclic Passivation test and ASTM G48 classification C tests.
What topics are covered in the main section of the report?
The main section covers the mechanical properties of C22 alloy, the influence of operational stresses, and a detailed breakdown of different corrosion types identified in the system.
Which keywords best characterize this work?
Key terms include Heat Exchanger, C22 Alloy, Crevice Corrosion, Pitting Corrosion, Stress Corrosion Cracking, and Failure Investigation.
How does the sea water environment specifically impact the heat exchanger?
Sea water acts as a bulk electrolyte that promotes corrosion, causes salt deposition, and creates an oxygen-rich environment that facilitates crevice and pitting attacks.
Why did the maintenance team struggle to prevent recurrent leaks?
Recurrent leaks were largely due to a combination of improper sealing, cumulative fatigue from repeated tube expansions, and the simultaneous occurrence of different, reinforcing types of corrosion.
- Quote paper
- Austin Mwana (Author), 2018, Heat Exchanger Failure, Munich, GRIN Verlag, https://www.grin.com/document/424143
