Carma® Piston Corer
The newly-designed Carma® Piston Corer has been conceived to retrieve cores of large diameter (100 mm) up to 30 m long, essential for studies of sedimentary basins characterized by a large thickness of fine sediment and to sample ancient stratigraphic layers. The innovative and technological solutions used to realize the active piston allow for the reduction of compressive strength on the sedimentary strata as well as a reduction of the stress on the core top caused by the barrel’s penetration, thus avoiding breakage of the core and the liner’s implosion.
The aspiration control device of the active piston allows us to easily achieve a recovery ratio of 90%. Hvorslev (1949) defines “recovery ratio” as the ratio between the length of the sample recovered and the penetration of the barrels. Therefore with this instrument, it is possible to have at your disposal a sample that completely reproduces the original stratigraphy and composition of the sea bottom.
Main components of Carma® Piston Corer
- Head: consisting of a cylindrical iron weight (variable), providing the necessary momentum for the instrument to penetrate.
- Steering fins: a hydrodynamic structure designed to maintain the vertical position of the device during free fall.
- Barrel: composed of stainless-steel 5m-long elements of elevated mechanical strength that can be joined to make up a 10, 15 or more metre barrel.
- Liner: is in PVC with a 100 mm external diameter, 3 mm thickness, and is placed inside the barrel to be filled with sediment during core penetration.
- Nose, cutter and core catcher: the lowermost part of the barrel is reinforced by a core nose which ends with a cutter, designed to facilitate core penetration, and includes a catcher, designed to hold the sediment inside the liner when the core is pulled out of the seafloor.
- Connecting sleeves: designed to rapidly and efficiently join barrel elements by using circular straps instead of using bolts or screws.
Active Piston
The Piston is the most important component of the corer, because it allows for the attainment of long and high-quality core samples from the seabed, characterized by alternating mud and sand layers on which we can perform the study of sedimentary basins from a geological, environmental or paleoclimatic point of view, as well as other relative studies (neotectonic evolution, gravity instability and submarine landslide). These studies are of great importance to off-shore activities, as well as to the control and the limitation of exploitation of the continental platform.
The “active piston” is powered by an automatic mechanism situated at the base of the core barrel. It is able to create a strong suction on the sediment necessary to overcome the friction around the inside walls and facilitate the entrance of the core into the liner.
The piston contains a sphere interception valve controlled by a spring that opens and closes the hydraulic communication between the chambers, until the end of the penetration.
The central cylinder is equipped with some extractable pin valves that in case of a strong depression existing between the piston and the core, or in case of exceeding limits, are activated autonomously during the working phase. In fact, one or more pins can be taken out of their location to restore the right hydraulic pressure in order to avoid the breakage of the core and the liner’s implosion.
The configuration of the Piston Corer CP-20 is variable in weight (from 650 to 2150 Kg) and length (up to 30 metres), in order to choose the right setting for the physical and mechanical characteristics of the soil to be penetrated.
Coring Technique
The best technique is the new controlled penetration speed. Depending from the water depth, the new method, called “Angel Descent“, can be used in two different ways: in deep water the Carma® Winch permit the sampling following the patented methodology. In shallow water, up to 30m, is not needful the new winch.
Alternatively has been reached so far very good results using the traditional technique of the free-fall, activated by a mechanical release system applied on the main wire and hooked to the eyebolt’s corer. It consists of a trigger, a counter-weight and a wire-releaser of a determined length depending on the height of the chosen fall.
Coring data acquisition
An accessory instrument essential to the reconstruction of events during the coring is made up of a loaded cell on the snatch block and it provides a digital output for on-line acquisition of the main wire’s strength data.
This data produces a dynamometric graph, which points out the significant events during the coring phase: the corer’s descent, the release, the seabed impact, the penetration, the extraction and the recovery.
A new instrument purchased by Carmacoring for a deep study of the coring dynamics is the accelerometer. Fixed at the corer head, records the acceleration every 2 milliseconds, up to a maximum depth of 3000 metres. See the picture where is possible detect the free-fall and the penetration phase.
Graph Accelerometer
Popularization
- A. Magagnoli: “CP-20” Carotiere a pistone per carote di sedimento lunghe fino a venti metri. Technical Report n.83, CNR – ISMAR – Sez. Geologia Marina, Bologna, November 2003. (“CP-20 Piston corer for sediment cores up to twenty metres long).
- A.Magagnoli: Sistema Universale per il brandeggio di carotiere lungo venti metri. Technical Report n. 85, CNR – ISMAR – Sez. Geologia Marina, Bologna, December 2003.
Patents
Registered patent as utility model related to the Corer
Registered patent as design patent regarding the Active Piston
Holder: Research National Council – Rome, Italy
Inventor: Angelo Magagnoli – Bologna, Italy
Carma® Piston Corer
