Life Assessment of Steam Header

Running Head: LIFE ASSESSMENT OF STEAM HEADER
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Part 2: Life Assessment of High-Temperature Header Piping and Tube System
Student Name
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LIFE ASSESSMENT OF STEAM HEADER 2
Project II: STEAM HEADER LIFE ASSESSMENT
INTRODUCTION
Steam power generation plants are always associated with very high temperatures of about
5500C. High-temperature components are prone to failure due to fatigue, creep, thermal fatigue,
and creep-fatigue. Cracks are initiated and grow due to the creep and fatigue mechanisms, and
ultimate failure may eventually occur at any temperature. A key consideration in the selection for
steam power plant components is the fracture toughness of the material. Life assessment of the
components is necessary to predict the remaining life of the high-temperature components in
steam power plants for both safety and economic purposes (Kumar, Pandey & Das, 2014).
Low alloy steels are used extensively for high-temperature components such as steam pipes and
headers in power generation plants due to their excellent resistance to hydrogen attack and
oxidation together with good elevated temperature creep strength. The creep and fatigue
developed due to thermal stress are the main life-limiting factors of the steam pipes and header's
useful life. This paper presents the life assessment of a super-heater header using the ASME
pressure vessel design codes (Aronson et al., 2010).

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LITERATURE REVIEW
In steam power plants, the high-temperature components are prone to failure due to fatigue,
creep, thermal fatigue, and creep-fatigue. Cracks initiation and growth are due to the creep, and
fatigue mechanisms and ultimate failure may eventually occur at any temperature (Nicholas,
2017)
Creep Damage
Creep is the main high-temperature failure in main steam pipes and headers and can take several
forms. Dimensional changes as a result of creep deformation may cause loss of clearance,
distortions, and wall thinning in pipes and headers. When a material is continuously exposed to
high operating temperatures, brittle failure may occur due to crack growths at the welds and high
stressed crack regions. The available creep life prediction approaches for power plant
components can be classified broadly into post-service examination approach and operational
approach. Life prediction methodology is more appropriately based on essential creep
deformation data, such as the relationship between creep rate and stress (Miller & Priest, 2017.
The creep curve
The rate of creep increases with the increase in stress and temperature of the material as shown
in figure 2.1 (Kumar, Pandey & Das, 2014)

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Figure 2.1: Creep rate as affected by temperature and stress.
The creep strain curve shown in figure 2.2 divides the creep process into three phases, with the
creep strain rate as the slope of the curve. The three distinct phases are the primary creep,
secondary creep, and the tertiary creep (Lukáš & Klesnil, 2011).