Evaluation of the Suitability of X100 Steel Pipes for High Pressure Gas Transportation Pipelines by Full Scale Tests

Abstract

In order to increase the knowledge necessary for the utilisation of grade X100 steel pipes, and to consolidate preliminary indications regarding the safe level of toughness required to control the ductile fracture propagation event within X100 gas pipeline, an ECSC-Demonstration Project, (DemoPipe), partially sponsored by EPRG, has been performed (2001–2004) using TMCP X100 pipes with a diameter of 36”. The project examines the problems of building a new high grade steel on-shore gas pipeline, with special emphasis given to the issues of the field welding technologies and selection of consumables, girth weld defect tolerance, field cold bending, and the fracture propagation behaviour in a high-pressure natural gas pipeline. In order to achieve these stated aims, a dedicated programme of laboratory and full scale tests was included in the project. This paper presents a summary of some of the results obtained, together with a discussion regarding their applicability to future X100 pipelines.

The CTOA as a Parameter of Resistance to Crack Extension in Pipes Under Internal Pressure

“…The critical CTOA is sensitive to geometrical parameters such as thickness or ligament size and loading mode through constraints, but this is a general problem for all fracture criteria. The influence of geometrical parameters of pipes on CTOA has been proposed [7] and is given by the general form :…”

“…Since the 1990s, the use of this criterion has been extended to numerical simulations by FEM of the crack extension. Nowadays, CTOA c is used to predict crack length and pressure at arrest of a ductile running crack and particularly in gas pipes [7]. Gas pipeline fracture initiation is usually followed by extended running crack propagation.…”

Modelling Crack Propagation and Arrest in Gas Pipes Using CTOA Criterion

“…Gas pressure ahead of the crack depends only on time. This simplification is justified by the fact that the crack propagation speed is at most 200-300 m/s, which is lower than the wave speed in the pressurized gas, estimated at about 400 m/s [14]. This means that the crack cannot outrun the pressure drop wave, and the crack tip will always be in a segment of the pipe with falling pressure.…”

“…It is also sensitive to material through its flow stress σ 0 . The influence of these different parameters on CTOA has been described by [14] and is given by the general form:…”

Design of crack arrestors for ultra high grade gas transmission pipelines: material selection, testing and modelling

“…The distinction between ductile and brittle fracture propagation is particularly relevant for gas pipelines, for which the decompression of the gas during failure is an important driving force. Experimental burst tests [1] reveal that the typical crack speed during ductile fracture propagation in steel pipelines does not exceed 350 m/s. Since the acoustic velocity of gas (such as lean gas or rich methane) under the usual operation conditions is in the range of 350 -500 m/s, the decompression of the pipe is faster than the crack speed.…”