Marine Engineering - General

Metal locking crack repair process

What is Metal-locking?

Metal locking crack repair process – Metal-lock or metal stitching is a method of repairing fractures to castings, onsite without the use of heat. It involves sinking Metal-lock keys, perpendicular to a fracture. The fracture is then sealed and held rigid by Metal-lace studs. The result is a repair that is sealed tight and flush with the surface, recreating much of its original strength.

What types of repairs are carried out by metal-locking?

>> As a cold repair process, metal stitching is applicable where heat should not be used, and in situations where the material cannot be successfully repaired by welding.

>> Large structure:  Such as engine blocks, ‘A’ frame cracks, Auxiliaries structure which can’t be removed out for repairs easily are repaired using ML process.

>> Material Characteristics:  Where welding due to heat would introduce thermal stresses into the base metal, and also changes the grain structure of the metal crystals – altering the characteristics and the strength of that part of the equipment, ML is used.

>> Alignment: The metal stitching repair process maintains alignment of original surfaces, since the lack of heat during the repair produces no distortion of the completed repair.

>> Dampens stress:  Metal stitching dampens and absorbs compression stresses; providing a good ‘expansion joint’ for castings subject to thermal stresses.

>> Pressurized interface:  Where the repair involved a pressurized interface, the repair process has the ability to seal the join.

Procedure of Metal locking crack repair process.

Metal locking procedure is done in 5 main steps

1. Examination and preparation

– After close inspection the metal is lined as such the cracks are held together using pressure clamps.

2. Drilling & Fitting

– Using a drilling template, the holes are drilled perpendicular to the crack to the depth of castings.

– The length of holes are adjusted to the extent of crack.

 3. Connecting the holes and inserting the metal lock keys

– The holes are connected in the middle matching the shape of the keys.

– The keys are inserted and hammered to the complete depth. The keys are of slightly larger in size than the holes.

4. Applying pressure tight joint

– Holes are drilled along the line of fracture.

– The holes are then filled with studs, each stud biting into its predecessor which results in pressure tight joint of the piece.

5. Finishing

– The surface is completely ground off to give smooth finish and then the surface is cleaned and painted if it’s a painted surface.


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About Ram Govindasamy

Ram Govindasamy is a sailing marine engineer working for a leading cruise company. Ram founded Dieselship to create an online platform for Marine engineers worldwide to bond, share knowledge & Resources. He is a computer enthusiast who loves creating web based activities, web pages & programs. He is also authoring technical articles, videos for Dieselship as well as for various other maritime websites. Ram is interested in Maritime Law and Technical Operations and looks forward to meeting new people especially those who are interested in creating web based platforms, Assets maintenance & inventory programs and Planned Maintenance software etc

One thought on “Metal locking crack repair process


    Respected SIR,
    thanks so much for this solved answers, which would be very much useful for my upcoming MEO CL II examinations.
    I am highly grateful to you,
    I am conveying my best regards to you,
    yours sincerely

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