The main turning hardware between the crane and the load
APP: Dry & Subsea Lifting
Offshore crane Component
STANDARD: up to 400 t
CUSTOM: 400-2000 t
ABS-DNV-LRS approved
Swivels are used in lifting, mooring and anchoring applications, and consequently are considered critical lifting component from a safety point of view because is the main turning hardware between the crane and the load.
The main difference between a swivel hook and a hook block are pulleys: a swivel hook does not need sheaves and the main reason is that there are certain lifting operations where straight lifting is necessary with enough weight and protection to turn.
The key component of the Swivel Hook is the COVER: this part protects inner machined parts, bearing and thread to guarantee a full turning and proper rotation of the load, and at the same time gives the necessary weight to avoid rope outlet and crane incidents. Weight and rotation are the main functions of a swivel.
Regularly these kinds of products are used in Offshore environments, where swivels could have two main purposes:
For subsea lifting, the crane is regularly located on the top site, even if recently semi-submergible and submergible cranes are being designed and installed. These kinds of Offshore cranes regularly do subsea operations even if there are dry cranes too: most of them do in shallow water, but others do deep water e.g. manifolds recovery, seabed pipeline maintenance or repair. It is possible to do operations up to 4.000 m subsea. For this application, regular swivel hooks are used.
For long-term mooring lines, the main technology to fix floating structures into the seabed, forged swivels are a great product to link two chains, chain with rope, rope with sling… or any technology used for floating structures mooring lines. Recently other technologies beside steel chain are being used and recommended by installation companies based on two criteria:
* Weight of mooring line in deep water.
* Cost of commissioning & installation.
The mooring line is being a combination technology in recent projects, combining steel with fibre products: steel chain, steel wire ropes, synthetic ropes and textile slings. Combination of all 4 technologies is reducing commissioning costs and reducing weight. Hooks and other links are in between different technologies to ensure a permanent steel-fibre, steel-steel or fibre-fibre join or linkage. For this application regularly Eye-Eye and Eye-Clevis Swivels are used.
In both cases, with hook or without hook, swivels are working submergible and to avoid salty water getting into the inner parts, cover part and sealings are used to guarantee a long lifetime. Additionally when operation is held in deep water, outer & inner pressure difference is a big issue and sealings are a key factor to avoid any problem and guarantee the bearing is rotating correctly.