Fighting Stress

By Elena Zhuk, December 20, 2013

The search for effective anti-corrosion methods is one of the major challenges in providing reliable operation of Russia’s nationwide gas transportation network 

Gazprom’s gas transportation system (GTS) is more than 168,000 kilometers long. It is the world’s longest grid and providing its operational reliability is an issue of critical importance for the national gas industry and Russia’s economy. According to Vladimir Kharionovsky, chairman of the Thesis Board at VNIIGAZ, for over 50 years this R&D Center has been successfully developing the technological reliability segment, creating optimal conditions for gas transportation while taking into account the system’s uniform operation mode and ensuring that performance targets be met. Things are different with structural reliability as this sector came to VNIIGAZ’s attention later, in the 1970s. In this field experts have relied on the work of oil industry scientists and the VNIIST R&D Center, Kharionovsky noted in his presentation at the 5th International Scientific Conference “Gas Transportation Systems: Present and Future,” held Oct. 29-30 in the Moscow suburb of Razvilka.

Linking Technological and Structural Reliability

GTS reliability is monitored by several systems, including the Integrity Control System (SUTSC). VNIIGAZ experts started shaping up the system in 2009 and two years later the work on regulatory support, structural changes and the database was completed. “So far we have insufficient resources to run the system for all gas transportation companies, so we are adjusting the timetable for gas pipeline overhauls, taking into account the SUTSC-based suggestions of the subsidiaries,” Sergei Nefedov, director of the of GTS Health and Integrity Management at VNIIGAZ, told the conference. The adjustment produces good results. Postponing major overhauls even for a year usually boosts expenses by 7 to 10 percent, but the use of SUTSC facilitated targeted distribution of detection and repair expenses, ensuring cost optimization. While the project financing in 2011–2013 was reduced by about a third, the SUTSC-related adjustments helped complete 50 percent of the plan.

According to Kharionovsky, technological reliability is a multifaceted issue, especially in the context of hardware. “And while in the 1970s even top-notch experts had no idea about the stress-strain state, today such knowledge is commonplace,” the scientist adds. In his view, the main methodological problem lies in providing a sound integration of technological and structural reliability through regulatory measures.

Caution: Stress Corrosion!

To ensure structural reliability, professionals are increasingly focusing on stress corrosion, or the so-called stress corrosion cracking (SCC). Twenty-three years ago, the VNIIGAZ R&D Center identified the problem of pipeline stress corrosion at the first topical conference attended by Soviet and U.S. experts. While the mechanism of stress corrosion is still unknown, scientists decided to focus on studying the metal microstructure.

The research was greatly helped by field work. Studies have been run to identify stress corrosion susceptibility levels for the pipes made of various grades of steel, with special focus on the choice of high-strength pipes for pipeline projects in challenging environments. High reliability was demonstrated by X80 grade steel, which was tested on the Kopeysk site and used