Metal stitching, sometimes also called cold pinning, has been around for over 100 years. It is a very well established and proven technology. It is mostly used on cast (gray) iron components such as engine blocks and casings although the repair of other materials such as aluminium and bronze is possible too.

The advantages of metal stitching are many:

  • Usually, little or no dismantling is necessary. Proper access from one side is generally sufficient.
  • Since it is a cold-repair method, no additional stresses, which over time may lead to new cracks, are introduced into the material.
  • The original alignments of the parts can be retained. There is no deformation or blemish due to the application of heat. Re-machining after repair is therefore often not necessary.
  • The repair seam helps to distribute tensile stresses over a larger area
  • If done properly, then the repaired area is liquid and gas tight. QuantiServ has successfully applied water pressure up to 12 bars (174 psi) to a test piece that was repaired by metal stitching.
Metal Stitching 2

The cracked metal is replaced with special metal stitching pins that we install by drilling and tapping to draw the sides of the crack together. This results in a continuous row of interlocking stitching pins to create a strong, pressure-tight repair. To restore the casting to its original strength, we install locks across the joint line of the pins by drilling a precision hole pattern with special drill fixtures. After the hole pattern is created, the locks are driven in, pulling the material together even tighter. Finally, the stitched area is ground to conform to the base metal contour, thus completing the repair.

A crack prior to repair
A crack prior to repair
During metal stitching
During metal stitching

If the component undergoing repair is not only cracked but if a piece is missing, then we prefabricate a new piece and lock it in place in the same manner as described above.

We are selling the majority of our crack repair tools and supplies to enable our customers to carry out small and non-complex repairs by themselves.

Stitching pins

Our metal stitching pins are equipped with special, proprietary threads that exert a radial pulling force during tightening. They therefore pull the crack together and seal it.

The majority of stitching pins that we use are made of high-grade steel. Steel pins, being stronger than cast iron, are usually used to repair cracks in cast iron bodies. For special applications, aluminum, stainless and bronze stitching pins are also available.

Locks

We install locks whenever possible. They are made of precision cut high-grade steel and are able to withstand far larger tensile forces than cast iron. Thus, the installation of locks results in an even stronger repair.

Locks should be installed perpendicular to the crack and we recommend to always use the largest lock possible for a given casting thickness. We have them available in various lengths and widths, suitable to repairs castings from 3.0 mm to 175.00 mm thick!

Our high-strength locks are available in various sizes

Over the years QuantiServ’s metal stitching experts have repaired many engine blocks, casings and other castings.  We helped their owners and operators to save a lot of money and reduce the equipment down-time from the several months that it typically takes to produce, ship and install a new part to days or weeks at most. And since most of the metal stitching repairs on board ships were carried out during the voyage, any off-hire or other interference with the vessel schedule could usually be avoided.

Case Studies

Our metal stitching specialists recently repaired an extensive damage on a 12-cylinder, 40-bore engine block on a cruise ship. All work was carried out while the ship remained in service:

The damaged was caused by a connecting rod side-kick. Here shown is the damaged engine block after dressing up.
The damaged was caused by a connecting rod side-kick. Here shown is the damaged engine block after dressing up.
With the help of 3-D scanning a precisely fitting new section was cast. Here it is shown during stitching.
With the help of 3-D scanning a precisely fitting new section was cast. Here it is shown during stitching.
The newly manufactured section is now stitched in place. The next step is the installation of the locks.
The newly manufactured section is now stitched in place. The next step is the installation of the locks.
During the installation of the locks. Notice how big and therefore strong they are!
During the installation of the locks. Notice how big and therefore strong they are!
In-situ milling, drilling and tapping completes the repair.
In-situ milling, drilling and tapping completes the repair.
The repair is hardly visible and the block is at least as strong as it was before the incident.
The repair is hardly visible and the block is at least as strong as it was before the incident.

The following photos show the repair of a marine gearbox cover by metal stitching, carried out last year in Namibia:

Severely damaged gear box cover after dressing up of the fractures
Severely damaged gear box cover after dressing up of the fractures
Fixing a prefabricated new section in place by metal stitching
Fixing a prefabricated new section in place by metal stitching
The casing after completion of the repair, before painting
The casing after completion of the repair, before painting

Here is an example of a repair of a marine gearbox foot, carried out by QuantiServ’s experts in Russia recently:

Fractured marine gear box casing
Fractured marine gear box casing
Damaged area dressed up in preparation for repair by metal stitching
Damaged area dressed up in preparation for repair by metal stitching
Prefabricated repair piece prior to installation
Prefabricated repair piece prior to installation
Repair piece installed with one M10 bolt to hold it in place
Repair piece installed with one M10 bolt to hold it in place
Metal stitching of the repair piece to the gear box casing in progress
Metal stitching of the repair piece to the gear box casing in progress
The result, approved by the customer and classification society
The result, approved by the customer and classification society