Heat Exchanger Failure

Investigation Report


Academic Paper, 2018
21 Pages, Grade: B+

Excerpt

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

Appendix

References

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.

METHODOLGY

To carry out a successful failure investigation, a sequence of measures must be covered.

- An analysis of all previous test is carried, to assess the result of these tests and efficiency of the provided solution.
- Assessment of the operation process and component of the heat exchanger. Note: sea water is used in the cooling effect of the heat exchanger, which deposits salt, Also high velocity and pressure flow around the walls of the heat exchanger.
- A material and design analysis of the heat exchanger to determine parts susceptible to different types of corrosion.
- A visual and internal inspection of the heat exchanger to detect other forms of corrosion and faults present in the heat exchanger.
- Information gathered from these process is then used to propose a better design or solution.

FAILURE INVESTIGATION

1.0 MATERIAL DESCRIPTION OF THE HEAT EXCHANGER

The tubing bundle was previously made up of C276 alloys but persistent corrosion lead to the use of C22 alloy. The C22 alloy is known for being resistant to oxidized and non - oxidized chemicals. It also protects materials from crevice attack, pitting and stress corrosion due to its well proven nickel - chromium - molybdenum components (Cieslak et al, 1986). The composition of C22 alloy is tabulated below based on Haynes online (2018).

Table 1. Material component

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Table 2. The mechanical properties at room temperature for the alloy sheets properties.

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Assumption: It is assumed the alloy is a shee

2.0 INSPECTION AND TESTS

In proceeding with the failure investigation, tests and physical inspection of the heat exchanger is carried to determine the operating conditions of the system. Visual inspection - usually, the use of naked eye is first used to roughly evaluate the root causes and type of failure. From figure 1 and 2, there is a development of pitting corrosion in internal surface tubing and also from figure _, a development of crevice corrosion around the cladding region.

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Figure 1: iron oxide deposit visible internal defect (case study, 2018)

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Figure 2: internal pitting underneath arrowed (case study, 2018)

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Figure 3: row 19 - tube r.h.s, typical example of a crevice corrosion

Cyclic passivation test - the test was carried out to study the behaviour of C22 alloys supplied by Haynes and Salem using the ASTM G5 under various conditions to measure the passivation behaviour. The result indicates that C22 supplied by Salem will remain passive even at a higher current and less surface area.

Crevice corrosion test - A variety of ASTM G48 classification C test with a critical pitting temperature up to 50[0]c for 72 hours was carried out to determine the better form of alloy material for the tubes to be used between C22 alloy and C276 alloy on the condition of it being used as built or over expanded. This qualifies the alloys possibility of crevice and pitting corrosion based on the nickel and chromium components at the specific temperature.

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Figure 4: A correct etching of a stainless steel sample (G2MT, 2011)

From the results at appendix b, the change of the alloy will not aid in reducing the possibility of crevice corrosion occurrence because the as built condition of the C276 has the lowest maximum depth of crevice attack.

3.0 OPERATIONAL CONDITIONS OF THE HEAT

EXCHANGER

Here are the corrosions resulting from the operation process: expansion and contraction from temperature variations, vibration from fluid flow, pressure on the tube walls from high velocity and pressure of the fluid.

From the schematic drawing of the C22 tube bundle part of the Heat exchanger, the designed and operating conditions in terms of temperature, at a rather high fluid velocity are tabulated below;

Table 3. Operational Conditions

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Excerpt out of 21 pages

Details

Title
Heat Exchanger Failure
Subtitle
Investigation Report
College
Robert Gordon University Aberdeen
Course
Oil and Gas Engineering
Grade
B+
Author
Year
2018
Pages
21
Catalog Number
V424143
ISBN (eBook)
9783668722033
ISBN (Book)
9783668722040
File size
1709 KB
Language
English
Notes
A well written and supervised academic paper hence the professional grade of B+.
Tags
CORROSION, HEAT EXCHANGER, FAILURE INVESTIGATION, CREVICE CORROSION, PITTING CORROSION, STRESS CRACKING CORROSION
Quote paper
Austin Mwana (Author), 2018, Heat Exchanger Failure, Munich, GRIN Verlag, https://www.grin.com/document/424143

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