Qingdao Haosail Machinery Co., Ltd.

At offshore wind turbine installation sites, next to the mooring systems of deep-water drilling platforms, and on the decks of subsea pipeline laying vessels, rigging consistently plays a crucial role as a "force transmitter." These seemingly insignificant "steel components" must withstand the immense pressure of hundreds of tons of equipment while resisting the corrosion of seawater and salt spray, and the repeated impact of wind and waves. Post-accident analyses of many offshore engineering incidents reveal that problems often stem from incorrect rigging selection or inadequate protection. Today, let's discuss the "selection" and "protection" of rigging in offshore engineering to help you avoid common pitfalls.

I. Selection: Not "the stronger the better," but "the more suitable, the safer"

Those new to purchasing offshore engineering rigging often fall into the trap of thinking "choosing the strongest is always the right choice." However, in actual operations, rigging that is adapted to the working conditions is the optimal solution – it avoids wasting resources and reduces safety risks from the outset. The core focus should be on these four dimensions:

1. Understand the "working condition profile" before selecting rigging

Choosing rigging without understanding the operating scenario is like buying clothes without knowing your size. You need to clarify these key questions first:

Load points and loads: Is it lifting a 150-ton wind turbine nacelle (primarily static load, with large instantaneous impact), or securing the anchor chains of a drilling platform (long-term alternating load)? The type of load directly determines the strength grade of the rigging; an additional 20%-30% safety factor is required for dynamic load scenarios.

Environmental "aggressiveness": Is it a nearshore shallow water area (high salt spray concentration, gradual temperature changes), or a deep-sea operating area (high pressure, low temperature, potential for marine organism attachment)? Even consider whether it's near an oil field (potential contact with oil) or in polar regions (risk of low-temperature embrittlement).

Operating method: Is it a single lift followed by retrieval, or does it need to be permanently fixed offshore (such as platform guardrail cables)? Does it require frequent movement and bending (such as rigging for crane pulleys)? For example, for the blade lifting of shallow-sea wind power projects, ultra-high molecular weight polyethylene fiber slings are more suitable than steel wire ropes – they are more than half lighter, making operation easier for workers, and are completely resistant to salt spray corrosion. However, for deep-sea mooring systems, high-strength alloy steel wire ropes combined with cathodic protection are better able to withstand long-term alternating loads.

2. Choosing the wrong material renders everything useless

The "corrosive magic" of the marine environment can cause ordinary steel to become heavily rusted within six months. The "durability" of different sling materials varies greatly. The following types of commonly used materials and their suitable applications and key points of use deserve special attention:

Hot-dip galvanized high-strength steel is one of the most widely used sling materials in marine engineering. It stands out for its excellent tensile strength and moderate cost, and is particularly suitable for scenarios requiring heavy loads, such as platform lifting and heavy equipment towing. However, the protection of this type of sling focuses on the zinc layer. It is necessary to ensure that the zinc layer thickness reaches at least 85 micrometers at the time of manufacture (which can be verified on-site with a thickness gauge), and anti-corrosion paint needs to be applied regularly during use to prevent the zinc layer from wearing off and losing its protective effect.

For more corrosive environments such as offshore chemical platforms and high-salt spray environments, 2205 duplex stainless steel slings are a more reliable choice. Its outstanding advantages are its resistance to pitting corrosion and stress corrosion, allowing it to maintain stable performance in complex chemical environments. However, special attention should be paid to avoiding contact with strong corrosive media such as hydrochloric acid and strong alkalis to prevent damage to the material's properties.

In scenarios with strict requirements for weight and corrosion resistance, such as wind turbine blade lifting and underwater operations, ultra-high molecular weight polyethylene material has significant advantages. It is lightweight, completely resistant to salt spray corrosion, and non-magnetic, so it will not interfere with electrical equipment. However, this type of sling also has clear usage limitations, the most crucial of which is that it cannot be used in high-temperature environments above 80°C, otherwise softening and aging problems may occur.

For special operating scenarios such as high-temperature pipeline towing and those requiring high fire resistance, aramid fiber slings are an ideal choice. They not only have a high strength-to-density ratio but also possess excellent high-temperature resistance, maintaining stable load-bearing capacity in harsh environments. However, its cost is relatively high, and prolonged exposure to sunlight accelerates aging, so shading and protection are essential when storing it outdoors.

3. Don't overlook the "small accessories," connection points are crucial

Many people only focus on the main rigging, but forget about the shackles, hooks, and connectors. Remember, the load-bearing capacity of the rigging system depends on the "weakest link." For example, when lifting a wind turbine, the main rigging might be rated for 100 tons, but if the shackles are only rated for 50 tons, it can instantly lead to a dangerous situation.

Recommendation: All connecting accessories must match the rated load of the main rigging, and prioritize products with anti-loosening devices – the strong winds and waves at sea can easily loosen ordinary bolts, and shackles with pin locks provide an extra layer of safety.

II. Protection: Three parts use, seven parts maintenance - core techniques for extending lifespan

One client conducted a study: rigging that is properly protected has a lifespan 3-5 times longer than rigging that is neglected, and the subsequent maintenance costs are reduced by 60%. In a marine environment, the core of rigging protection is "corrosion prevention, fatigue resistance, and wear control."

1. Corrosion Protection: "Drawing a clear line" with seawater

The salinity of seawater is the "number one killer" causing rigging failure. Different materials require different protection methods:

- Metal rigging: Build a strong "protective layer": Hot-dip galvanizing is a basic operation, and the zinc layer thickness should be at least 85 microns (this can be measured on-site with a thickness gauge); if the rigging is immersed in seawater for a long time, it is recommended to apply another layer of fluorocarbon anti-corrosion paint. This paint can resist seawater erosion and has a validity period of more than 3 years. In addition, after each operation, rinse the surface of the rigging with fresh water to wash away salt deposits; this step is simple but often overlooked.

- Fiber rigging: Anti-aging + anti-pollution: Fiber rigging is not afraid of corrosion, but it is afraid of ultraviolet rays and oil stains. When storing outdoors, be sure to use a sunshade cover. If it gets stained with oil during operation, clean it with a neutral detergent-oil stains will decompose the fiber structure and reduce its strength. Tips: For metal rigging used in deep-sea operations, cathodic protection can be implemented using sacrificial anodes (such as zinc blocks). The sacrificial anode corrodes to protect the rigging itself, offering a very cost-effective solution.

2. Fatigue Protection: Avoiding the "Alternating Load Trap"

Due to constant wind and waves at sea, rigging is repeatedly subjected to stress like a spring. Over time, this can lead to "fatigue cracks," which are one of the main causes of rigging failure. Two key points for protection:

1. Allow sufficient safety margin during selection: For rigging subjected to alternating loads, the rated load should be at least 50% higher than the actual load. For example, if 50 tons are needed, choose an 80-ton rated rigging. Prioritize multi-strand twisted rigging structures, as they have a stronger ability to distribute stress.

2. Conduct regular "health checks": Use an ultrasonic testing device to inspect critical parts of the rigging monthly.  If cracks are found, discard the rigging immediately; do not try to "make do." Also, avoid sudden starts and stops during operation to reduce load impact.

3. Daily Maintenance: Simple Actions Extend Lifespan

Rigging maintenance doesn't need to be complicated; just follow these three steps: "cleaning, inspection, and storage":

Cleaning: After each offshore operation, rinse the rigging surface with fresh water. After drying, metal rigging can be coated with a layer of anti-rust oil.

Inspection:  Focus on checking metal rigging for broken strands, deformation, and corrosion; check fiber rigging for fraying, aging, and damage; and check for loose fittings.

Storage: Store in a dry and well-ventilated warehouse. Do not stack metal rigging to avoid deformation; fiber rigging should be rolled up and stored away from sharp objects and heat sources.

3. Real Case Study: How Important is Choosing the Right Rigging and Maintaining it Properly?

In a certain offshore wind power project, to save costs, ordinary Q235 steel rigging was used for lifting the tower sections without additional corrosion protection. Less than 3 months later, the rigging surface was severely rusted, and a minor fracture occurred during lifting. Fortunately, the operation was stopped in time, preventing equipment damage. Later, they switched to high-strength steel wire ropes with hot-dip galvanizing and fluorocarbon paint.  These ropes were washed and maintained according to requirements after each operation. They have been in use for 3 years, and the ropes are still in good condition.  It turned out to be more cost-effective than frequently replacing the ropes.

There was also an incident with an anchor cable on an offshore drilling platform. Because regular fatigue testing wasn't performed, cracks in the cable weren't detected in time. During a typhoon, the anchor cable broke, and the platform drifted more than 200 meters. The repair costs alone amounted to tens of millions of yuan – a classic example of "saving a little money but paying a heavy price."

Conclusion: Riging hardware safety is the "bottom line" of offshore engineering.

Every operation in offshore engineering involves the safety of personnel and property, and rigging hardware, as a "critical link," cannot tolerate any negligence. Taking the time to understand the working conditions during selection and performing proper daily maintenance, while seemingly tedious, is actually the most economical safety investment.

If you have any questions about rigging hardware selection for specific projects, or want to learn about the maintenance details of a particular type of rigging hardware, please contact us. Our technical team will answer your questions as soon as possible.