1. Method of Metal Magnetic Memory
Method of Metal Magnetic Memory is method of a nondestructive inspection
based on registration and analysis of distribution of self-magnetic leakage
fields (SMLF) arising on products and equipment in stress concentration zones
(SCZ) and metal defects. At that, SMLF reflect irreversible change of a
magnetization in a direction of maximal stresses action from working loads. Also
SMLF reflect structural and technological heredity of products and welded joints
after their manufacturing and cooling in a weak magnetic field (as a rule,
magnetic field of the Earth). A natural magnetization and aftereffect, which
appears as magnetic memory of metal to actual strains and structural changes in
products and equipment metal, are used in the MMM method.
2. Physical fundamentals of MMM method:
Magneto-elastic and magneto-mechanical effects.
Effect of formation of domains and domain boundaries on dislocations
clusters in stress concentration zones (magnetoplasticity).
Effect of magnetic field leakage by structural and mechanical
heterogeneities at metal natural magnetization.
3. Magnetic parameters used at inspection:
4. What is inspected in metal and welded joints by MMM method?
5. What is determined by MMM method?
6. Advantages of MMM method:
Any special preparation (metal dressing and the like) of the object to be
examined is not required.
Special magnetization is not required because the natural magnetization
formed at manufacturing and working of products is used.
MMM method can be used both at operation of the object to be examined and
at its repair.
MMM method is unique NDT method to detect stress concentration zones and
defects on the surface and in the deep layers of metal within 1mm in
At the inspection by MMM method the small-size instruments having
self-contained supply, recording device, microprocessor and up to 32MB memory
unit are used.
MMM method allows to carry out 100% quality control of engineering products
and their sorting in mass line production.
Increasing of inspection efficiency and reliability at combination of the
MMM method with conventional NDT methods.
7. Differences from conventional NDT methods (ultrasonic inspection,
magnetic particle inspection, X-ray, etc.):
MMM is method of early diagnostics of fatigue damages and pre-defect state
MMM is unique method answering to the question: "In which location to
perform metal sampling" at the equipment lifetime assessment.
MMM is second passive method after acoustic emission (AE), at which the
information on structures radiation is used. Thus MMM, besides early defect
detection additionally gives the information on actual stressed-strained state
and allows revealing the reason of developing damaging.
At the inspection by MMM method the parameters of proper magnetic leakage
fields due to dislocations accumulation in stress concentration zones are
measured unlike other known magnetic methods, at which scatterings of the
artificially created magnetic fields on defects are measured.
8. Area of MMM method application:
Quality control of metal and welded joints of products at engineering
Pipelines, vessels, equipment, any constructions and products (from
ferromagnetic and paramagnetic austenitic material) in all industries at
manufacturing, repair and maintenance.
Hoisting devices and running mechanisms.
Research of metal mechanical properties in laboratory