Mechanical Stress Improvement Process (MSIP)

In considering the stress corrosion cracking problem in the heat affected zone of field welds in BWR primary pumping, Dr.’s Bill O’Donnell and Janek Porowski developed a reliable Mechanical Stress Improvement Process (MSIP) which applies compressive stresses and is easy to control and verify. MSIP was developed with supporting finite element analysis and tests which show that it provides compressive stress fields in both the axial and circumferential directions at the inner surface of weldments.

MSIP works by using a hydraulically driven clamp to squeeze the pipe on one side of the weldment. The permanent contraction produces a concave contour at the weld section and results in a corresponding reduction (typically <1%) in pipe circumference. Once the tool is removed, the weld area remains in hoop and axial compression through approximately half the wall thickness.

The Process was developed for pipe-to-pipe, pipe-to-discontinuity (such as valve body) and pipe-to-vessel nozzle configurations – and first applied in 1986 to mitigate Intergranular Stress Corrosion Cracking (IGSCC) in BWR recirculation piping.

The benefits of MSIP include:

1. Early application can eliminate need for pipe replacement
2. Reduces required inspection frequency
3. Makes the welds in the system immune to corrosion damage
4. Saves a utility money

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A few related published articles include:

Advanced Methods of Improving Resistance to Stress Corrosion Cracking in BWR Piping Systems J. S. Abel, J. Titrington, R. Jordan, J. S. Porowski, W. J. O’Donnell, M. L. Badlani, and E. J. Hampton, presented at the American Society of Mechanical Engineers Pressure Vessels and Piping Conference, June 19 – 23, 1988, PVP Vol. 13, 1988. 

Use of Mechanical Stress Improvement Process to Mitigate Stress Corrosion Cracking in BWR Piping Systemsby J. S. Porowski, W. J. O’Donnell, M. L. Badlani, and E. J. Hampton. Nuclear Engineering and Design 124, pp. 91-100, Elsevier Science Publishers, February 1990.

Use of Mechanical Stress Improvement for Weldments with Cracks J. S. Porowski, W. J. O’Donnell, M. L. Badlani, and E. J. Hampton, Proceedings, SMIRT Post Conference Seminar No. 2, Assuring Structural Integrity of Steel Reactor Pressure Boundary Components Taipei, R. O. C., August 26-28, 1991.