Journal of Failure Analysis and Prevention

, Volume 18, Issue 1, pp 189–198

# Analysis of Fatigue–Creep Crack Growth in the Superheater Header of a Power Plant Boilers and Estimation of Its Remaining Lifetime

• Seyed Ebrahim Moussavi Torshizi
• Ali Jahangiri
Technical Article---Peer-Reviewed

## Abstract

As superheater header is exposed to high pressure and temperature in power plant boilers, it is one of the most sensitive parts in a power plant.Cracks may form where tubes and main steam outlet (nozzle) are connected to reservoir. This article examines a quarter-circle crack at the corner of a nozzle junction and its propagation steps under the influence of simultaneous interaction of creep and fatigue. Header loading in each cycle includes transient steps (increase and decrease in temperature and pressure) at the beginning and at the end of a cycle and intermediate steady state (fixed pressure and temperature) during operation. For crack growth calculations, stress distribution in a track-free part was calculated. Fatigue–creep crack growth was achieved using crack growth rules and the remaining lifetime was obtained. Research result shows that creep phenomenon is responsible for maximum crack growth.

## Keywords

Fatigue Creep Header Remaining lifetime estimation Crack propagation

## List of symbols

a

Creep crack radius (mm)

da

Creep crack growth (mm)

$$\dot{a}$$

Creep crack growth rate (m/h)

$$\frac{{{\text{d}}a}}{{{\text{d}}N}}$$

Crack growth rate versus number of cycles (mm/cycle)

$$C^{*}$$

Steady state creep characterizing parameter (MPa m/h)

$$C_{\text{ref}}^{*}$$

Value of $$C^{*}$$ determined from reference stress methods (MPa m/h)

$$\varepsilon_{f}^{*}$$

Uniaxial creep rupture ductility (in % strain)

$$\dot{\varepsilon }_{\text{ref}}$$

Creep strain rate at reference stress (1/s)

$$\sigma_{\text{ref}}$$

Reference stress (MPa)

$$K_{c}$$

Stress intensity factor corresponding to the applied loading ($${\text{MPa}}\sqrt m$$)

A

Norton power law creep constant in Eq 3 (–)

n

Norton stress index in power law creep Eq 3 (–)

Eamb

Young’s modulus at ambient temperature (GPa)

Eat

Young’s modulus at operation temperature (GPa)

$$\Delta K$$

Stress intensity coefficient range ($${\text{MPa}}\sqrt m$$)

K

Stress intensity coefficient ($${\text{MPa}}\sqrt m$$)

KIC

Fracture toughness ($${\text{MPa}}\sqrt m$$)

S

Stress distribution (Pa)

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© ASM International 2018

## Authors and Affiliations

• Seyed Ebrahim Moussavi Torshizi
• 1
• Ali Jahangiri
• 1
1. 1.Faculty of Mechanical and Energy EngineeringShahid Beheshti University, A.C.TehranIran