Crack Growth Modeling and Life Prediction of Pipeline Steels Exposed to Near-Neutral pH Environments: Dissolution Crack
- PDF / 2,303,232 Bytes
- 12 Pages / 593.972 x 792 pts Page_size
- 93 Downloads / 198 Views
I.
INTRODUCTION
PIPELINE transportation is important to the world economy. Transporting crude oil and natural gas via pipeline is safer, more reliable, and more economical compared to rail cars and tankers. The safety and integrity of pipelines are a matter of paramount importance because of the hazardous nature of the transported substances. Stress corrosion cracking (SCC) and corrosion fatigue represent a substantial cost to pipeline companies. SCC is controlled from an integrity management point of view by in-line inspection and hydrostatic testing for oil and gas pipelines. These techniques provide protection from in-service failures when used as part of pipeline integrity management process. It has been determined that the two types of external SCC on underground pipelines are high-pH SCC (classical SCC) and NNpH SCC (Low pH SCC).[1] A common feature of both forms of SCC is that they form crack colonies consisting of up to hundreds of longitudinal surface cracks in the body of pipe that link up to form long, shallow flaws. One of the distinguishing JIAXI ZHAO, WEIXING CHEN, MENGSHAN YU, and REG EADIE are with the Department of Chemical and Materials Engineering, University of Alberta, Edmonton T6G 2G6, Canada. Contact e-mail: [email protected], [email protected] KARINA CHEVIL and RICHARD KANIA are with TransCanada Pipelines, 450 1st Street SW, Calgary, AB T2P 5H1, Canada. GREG VAN BOVEN is with Spectra Energy Transmission Ltd., Suite 1100 1055 West Georgia Street, Vancouver, BC V6E 3P3, Canada. SEAN KEANE is with Enbridge Pipelines Inc., 10201 Jasper Avenue, Edmonton, AB T5J 3N7, Canada. JENNY BEEN is with IRISNDT-Engineering, Calgary, AB T1Y 7L3, Canada. Manuscript submitted January 27, 2016. Article published online January 20, 2017 METALLURGICAL AND MATERIALS TRANSACTIONS A
characteristics between the two forms of cracking is their propagation path: NNpH SCC is transgranular, while high-pH SCC is intergranular.[2,3] Cracking failures of structural components are usually divided into three stages. Crack initiation and early-stage crack growth in Stage I, steady state crack growth in Stage II, and rapid growth leading to final failure in Stage III. During Stage III, the mechanical driving force results in rapid crack growth of a sizable crack and failure is imminent. Integrity management measures should be taken prior to reaching Stage III. Stages I and II provide the opportunity for integrity management. During these two stages, inspection of the structures and steps for the control of crack initiation and growth for service life extension can be performed. The three stages causing SCC failures of pipeline steels are often described by the bathtub model proposed by Parkins,[4] as shown in Figure 1(a). It conceptually describes the relative rate of crack growth. Crack initiation and early-stage crack growth in Stage I were visualized as occurring relatively quickly with the initial crack growth rate being fast but decreasing as the crack propagates. A steady state crack growth rate was reached in Stag
Data Loading...
