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.
- And last but not least, our metal stitching repairs qualify as permanent repairs!
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.
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.
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.
Depending on the application, we offer two different series of stitching pins to choose from: The top-of-the line, very strong C-Series pins that are designed to not create radial spreading forces and the economical L-Series ones that are meant for applications that carry fewer structural loads.
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 repair castings from 3 mm to 200 mm (1⁄8 inch – 8 inches) thick!
Locks are meant to be stacked on top of each other. In this way it is possible to repair even very thick castings. An accurate void into which the locks are placed is created by drilling only. The special drill jigs and drills makes drilling a breeze – it is easy and fast. No chiseling is required.
The sides of the crack are pulled together during installation of the locks. The reason is that the void for the locks is slightly smaller than the locks themselves. This reduces spreading forces and increases the strength of the repair.
One to five years warranty
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.
We fully stand behind our quality and are, for the majority of cases, automatically granting a one-year warranty. We are in fact so confident that we also offer extended warranties of two, three and five years!
This warranty option extends the standard warranty from one year to a total of three years.
It requires an inspection, carried out by our technicians and chargeable to the customer, at the end of year one and at the end of year two. The customer shall bear the costs for the inspection time, travel expenses, travel time and board and lodging. QuantiServ covers the costs for supplies and labour for any necessary warranty repair revealed during the inspection.
The cost for this option is 20% of the original repair cost, without expenses.
This warranty option extends the standard warranty from one year to a total of four years.
It requires an inspection, carried out by our technicians and chargeable to the customer, at the end of year two and at the end of year three. The customer shall bear the costs for the inspection time, travel expenses, travel time and board and lodging. QuantiServ covers the costs for supplies and labour for any necessary warranty repair revealed during the inspection.
The cost for this option is 25% of the original repair cost, without expenses.
This warranty option extends the standard warranty from one year to a total of six years.
It requires an inspection, carried out by our technicians and chargeable to the customer, at the end of year two, at the end of year three and at the end of year four. The customer shall bear the costs for the inspection time, travel expenses, travel time and board and lodging. QuantiServ covers the costs for supplies and labour for any necessary warranty repair revealed during the inspection.
The cost for this option is 30% of the original repair cost, without expenses.
Read the full details of our Repair Services Limited Warranty terms here.
Metal stitching is incredibly versatile. The following pictures show some of the equipment that we repair frequently: Compressors, pumps, grand pianos, high-performance engines, marine engines, iron gates, hydro turbines, …
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 following pictures show an extensive repair that we recently carried out in Nicaragua on an 18-cylinder, 48-bore engine block that was seriously damaged due to a connecting rod side-kick. Our specialists 3D-scanned the affected areas. Based on these scans, one-of-a-kind repair patches were cast and stitched in place.
For simplicity’s sake, these pictures only show the repair that we carried out on the engine’s A-side. A similar repair was carried out on the B-side too.
The following photos show the repair of a diesel engine block with 255 mm bore and 400 mm stroke in our workshop in The Netherlands at the end of 2020. The engine block suffered a damage close to the driving end and was repaired by stitching in a CNC-machined cast iron repair patch.
In the course of a crank case inspection, a 800 mm long crack was found in the main engine bedplate on board a 15,500 TEU container vessel in 2019.
Our metal stitching specialists carried out the repair during successive port stays during the vessel’s Northern European loop. They commenced their work as soon as the vessel was alongside in port and did not stop anymore until the engine had to be restarted. They then rested during the short voyage to the next port, where they continued in the same manner. In this way they repaired over 800 mm of crack in steel plates with thickness ranging from 18 – 50 mm, without a single day of off-hire or otherwise interfering into the vessel schedule.
To repair this bed plate, metal stitching was chosen over welding because it has the following advantages:
- The vessel stayed in operation throughout the repair. The stitching was done in stages during port stays, a few centimeters at a time. With welding, this would not have been possible. The vessel would have had to be taken out of operation for around three weeks.
- Lower costs, compared to welding. A competitor proposed to carry out repair by welding in 20 days. We repaired it by stitching in 12 days. Less time spent means less costs.
- For metal stitching, a hot work permit is not normally required. Such a permit would be very difficult to get in container terminals, meaning that welding would not have been possible from a safety point of view.