CALM Buoy_Chinese Lantern Configuration

CALM Buoy / Chinese Lantern Configuration

Trelleborg brings over forty years of experience and expertise to the development and qualification of offshore offloading hoses for oil applications. Trelleborg combines in-depth industry knowledge and innovation to create customized oil handling solutions that are safe, efficient and reliable, and adhere to the latest OCIMF guidelines. What follows are descriptions and explanations of Trelleborg vision about the Catenary Anchor Leg Mooring (CALM) buoy/ Chinese Lantern configuration.


Chinese Lantern Configuration

What is a ‘Chinese Lantern’?

A Chinese Lantern is a submarine configuration, used under a CALM buoy when the water deep varies from 30 to 60 meters. Chinese lantern configuration is composed of 2 submarine strings permanently connected to a Pipeline End Manifold (PLEM) on the seabed and a floating CALM Buoy moored with chains. Each string is made with hose sections (from 3 to 6 sections, and 30 to 40 feet long).

The curved shape of the strings is made with additional buoyancy modules, fitted on the hoses. The shape depends of the fluid properties, environmental conditions (currents), and the weight and behavior of each type of hose. The hoses connected at both ends of each strings are reinforced to support the loads of this connection.

The Chinese Lantern configuration remains the most difficult and aggressive configuration for hoses, and must be perfectly calculated and adjusted to avoid excessive loads, stresses, and abnormal fatigue as a consequence of these factors.

When possible, we recommend to use Steep S or Steep Wave configuration which is less restrictive for the hoses.

Hose design selection table

Main characteristics & hydrodynamic analysis results

Lot of studies performed by recognized engineering companies show that the performance of the nippleless hoses are consistently  higher than the nipple hoses. This is because of their notable increased flexibility (axial and bending stiffness values) and weight, since nippleless hoses are on average up to 30% lighter than the nipple design.

Nippleless hose design with:
- compact nippleless flanges and protection against corrosion,
- specific reinforced flanges with integrated bending stiffener for PLEM and CALM buoy connections,
- continuous inner liner and integrated gaskets,
- reinforced structure with steel cable layers and individual steel rings, 
provides a flexible string with progressive distribution of bending loads, to avoid stress concentration, and limit fatigue in the hose structure and flange areas. Consequently, this design solve the main causes of failure during service life, the subsequent risk of leak and guarantees a long service life.

The Chinese Lantern configuration should be perfectly built (hydrodynamic analysis). If input data are missing or wrong, all advantages of the nippleless technology are not fully exploited. The recommendations during installation, operation, and maintenance should also be strictly respected. Phenomena, such as a twist during installation or shrink during operation, should be completely avoided to preserve the hoses and the configuration.

Methodology Principle

All hose designs are qualified in accordance with the GMPHOM 2009 (last OCIMF guideline for Marine hoses), and Trelleborg uses the nippleless hose design to achieve the API Spec 17K requirements (ISO 13628-10 Specification for Bonded Flexible Pipe), which can guarantee 10 years of service life for the hose strings.