Special Fasteners with Geomet 500B Coating for Offshore Cranes and Shipyards

Fasteners with Geomet 500B coating are widely used in offshore and marine sectors for applications exposed to corrosion, vibrations, dynamic loads and low temperatures.

In this article, we present two real supply projects managed by EFS | European Fasteners Solutions for offshore cranes and shipbuilding applications. More specifically, the projects involved two large-size special fasteners, both subjected to post heat-treatment impact testing and protected with Geomet 500B coating.

The images also show two different production stages:

• fasteners before surface coating, ready for tensile and impact testing
• inspected fasteners returned after Geomet® 500B coating

The first project involved a quenched and tempered 42CrMo4 fastener for offshore applications; the second concerned a large-size class 10.9 special fastener for shipbuilding and structural applications.

As with all special fastener supplies, EFS coordinated the entire project: selection of qualified manufacturers, laboratory inspections, surface treatments, dimensional controls and full batch traceability.
EFS operates as project manager for custom-made fasteners and is certified by TÜV SÜD according to ISO 9001:2015.

42CrMo4 Fasteners with Geomet® 500B for Offshore Cranes

The first case concerns special fasteners for offshore applications. EFS managed a supply consisting of:

• UNI 5737 M42 x 440 bolts
• Quenched and tempered 42CrMo4 material
• Geomet® 500B coating

UNI 5737 bolts are hex head fasteners with partially threaded shank, commonly used in heavy structural steelwork, port structures, cranes and lifting systems.

In offshore environments, they are frequently employed in:

• marine cranes
• port infrastructures
• handling systems
• steel structures exposed to salt atmosphere
• applications subjected to vibration and cyclic loading

Why 42CrMo4 is used

42CrMo4 is a chromium-molybdenum alloy steel widely used in heavy mechanical and highly stressed structural applications.

After quenching and tempering, this material provides:

• high mechanical strength
• good toughness
• excellent fatigue behaviour
• reliable performance under dynamic loading

For this reason, it is commonly selected for offshore applications where fastening systems must maintain long-term reliability under continuous vibration and severe mechanical stress.

Impact testing at -40°C ≥ 42 Joules

After heat treatment, the batch was subjected to Charpy impact testing with the following requirements:

• test temperature: -40°C
• required average value: ≥ 42 Joules

The test measures the energy absorbed by the material before fracture.

In offshore applications, toughness is a critical parameter because low temperatures may increase the risk of brittle failure.

Impact testing therefore confirms that the material maintains adequate toughness even under severe environmental conditions.

M39 Class 10.9 Fasteners with Geomet 500B for Shipyards

The second project managed by EFS involved:

• UNI 5737 M39 x 580 bolts
• Class 10.9
• Geomet® 500B coating
• Post heat-treatment impact testing

This was a non-standard special fastener both in diameter and, above all, in its 580 mm length.

These geometries are typically used in:

• shipyards
• structural steelwork
• cranes and lifting systems
• heavy-duty steel structure

What property class 10.9 means

Property class 10.9 identifies high-strength fasteners according to ISO 898-1.

This class is selected when fastening systems must withstand:

• high static loads
• dynamic stresses
• vibrations
• significant tightening loads

Class 10.9 fasteners are normally quenched and tempered to achieve the correct balance between strength and toughness.

For oversized dimensions such as those involved in this project, production process control becomes even more critical.

Challenges of long-size fasteners

Special fasteners with non-standard dimensions, particularly in length, introduce additional manufacturing and inspection challenges.

During production, the following parameters must be carefully monitored:

• straightness
• heat-treatment consistency
• thread quality
• dimensional tolerances
• surface coating uniformity

Geomet® coating itself must maintain consistent thickness along the entire fastener in order to avoid assembly issues or uneven performance.

For this reason, EFS coordinates the entire supply process as technical project manager, selecting qualified manufacturers and specialised partners for every production stage.

Geomet ® 500B: advantages for offshore and marine sectors

Geomet® 500B is a water-based zinc-flake coating developed for applications requiring high corrosion resistance.

In offshore and marine sectors, it represents a reliable alternative to traditional zinc plating.

Compared to conventional galvanising, it:

• does not introduce hydrogen
• reduces the risk of hydrogen embrittlement
• provides more uniform coating thickness
• offers high corrosion resistance.

Compared to other zinc-flake systems, Geomet® 500B provides:

• longer service life in marine environments
• improved long-term stability
• good friction coefficient repeatability
• effective protection even on complex geometries.

For these reasons, it is widely used on special fasteners for offshore cranes, shipyards, port structures, marine steelwork and lifting systems.

Discover more about the treatment, coating and mechanical machining services that EFS can coordinate.

Certified special fasteners for marine applications

As clearly shown by these two projects, fastener quality does not depend only on the final component itself, but also on the management of the entire production process.

Material selection, heat treatment, surface coating, dimensional inspections and mechanical testing must all be coordinated carefully to ensure long-term reliability.

EFS, certified by TÜV SÜD according to ISO 9001:2015, supports offshore, marine, lifting and heavy structural industries in the supply of custom-made special fasteners, including bolts, stud bolts, nuts and high-strength special components with dedicated treatments and inspection procedures.