V. 3 (27) / 2016 «Improving reliability of gas mains subject to stress corrosion cracking»
candidate of engineering I.V. Ryakhovskikh
doctor of chemistry A.I. Marshakov
candidate of engineering A.B. Arabei
This issue of the «Vesti gazovoy nauki» collected articles is dedicated to stress corrosion cracking phenomenon as one of the main sorts of damages in respect to the extensive systems of high-pressure subsoil trunk pipelines. In course of rather continuous studying of stress corrosion the leading world scientific schools have developed patterns which describe in detail stress corrosion cracking of the steel tubes depending on conditions and parameters of their field application. But certain aspects of this phenomenon are not investigated up to now. It occurs due to the multifactorness of stress corrosion, calling for considerable number of parameters being used in project documentation at every stage of manufacturing and operation of a pipeline, and to wide extent of the trunk pipelines subject to stress corrosion cracking.
Nowadays a working Gazprom PJSC System for Management of Technical Condition and Integrity (SMTCI) of gas pipelines provides proper control of stress-corrosion state of trunks. Nevertheless today the strong economic challenges increase significance of planning and rational allocation of resources provided for repair and restoration of the gas pipelines. So, adequacy of screening norms for tubes with stress-corrosion damages is especially topical in relation to decrease of maintenance costs. It becomes obvious that requirements to rejection of pipes with stress-corrosion cracks should differ in accordance to the real danger of defects.
Modern domestic and foreign test data on stress corrosion, including corresponding statistical rules, allow development of technical decisions aimed at increase of pipeline reliability. At the same time there is the necessity to perfect math and physical models of the phenomenon on the grounds of fundamental research of stress corrosion cracking in near-neutral soil electrolytes.
On May 25–26, 2016, by order of Gazprom PJSC a 2nd scientific-practical seminar called «Rising the reliability of trunk pipelines subject to stress corrosion cracking» was held in Gazprom VNIIGAZ LLC with a view to elaboration of complex decisions. An organizer was Gazprom VNIIGAZ being a leading Gazprom PJSC institute for coordination of all scientific and experimental works aimed at rising reliability and steadiness of gas pipelines subject to stress corrosion cracking. This seminar is to become a unique platform for exchange of information on stress corrosion between the specialists of the Gazprom PJSC Administration, industrial departments of Gazprom affiliates, scientists from universities and scientific institutes, employees of diagnostic and repair contractors, producers of innovative products and technologies.
Within the seminar some reports were made concerning the questions of diagnostics, repair and operation of the underground pipelines subject to stress corrosion. The most interesting ones were completed and inserted into this collected book within the framework of several themes, namely:
1. the results of experimental and field research of stress corrosion on account of peculiarities of trunk operation;
2. analysis, development and perfection of the regulations for operation, overhaul, and technical diagnostics of trunks;
3. forming the standards of products, materials, equipment, and technologies being used for construction, technical diagnostics and repair of trunks;
4. elaboration of software and calculative methods for estimating durability of trunk gas pipelines with corrosion-mechanical damages, and experience in application of computer-aided instruction technologies in modelling of multifactor systems;
5. application of techniques aimed at rising reliability of the trunk gas pipelines subject to stress corrosion cracking.
The papers of this collected book present contemporary concept in which way the stress corrosion cracks of pipe steel form and develop in the near-neutral electrolytic media, and the retrospective analysis of corresponding foreign and domestic research. The promising trends of stress corrosion research are shown accounting the stages of formation, development and interaction between the separate cracks within colonies.
Some issues of optimal planning in respect to repair of Gazprom PJSC gas pipelines subject to stress corrosion are revealed including the complex analysis and systematization of data on stress-corrosion damages acquired in course of the overhaul in-line and non-destructive inspection of tubes. The probabilistic-statistical models for prediction of stress-corrosion damages which are smaller than the sensitivity threshold of the in-tube flaw detectors.
On the grounds of diagnostic inspections and field tests carried out by the Gazprom PJSC affiliates the principal possibility to exploit durably the resealed sections of gas trunks with small stress-corrosive cracks on the tube surface is shown. The necessity to continue wide-scale experiments aimed at substantiation of long-term workability of the gas trunks with slight stress-corrosive cracks (not more than 10 % of a tube wall thickness) is stressed.
One will find the results of tests and the estimation of cracked pipes resistance in correlation with factual accident rate of the pipelines. There are calculated experimental dependencies between pipe resistance and geometric dimensions of stress corrosion damages, as well as methods for long-term conservation of damaged pipes during the repair works. Also, the prior Gazprom PJSC tasks and themes of further researches are listed.
These collected papers seem to become interesting for a wide range of gasoil specialists, as well as for students and postgraduates of the corresponding higher school departments.
See below English version of annotated list of articles and links to correspondent articles in Russian.