Swivel stack for transfer of fluid across a rotary interface and method for manufacturing such a swivel stack

Method for manufacturing a swivel stack for transfer of fluid across a rotary interface around a rotation axis between an incoming flow-line and an outgoing flow-line, the method comprising:

• providing a group of inner annular elements that comprises a lower annular element, an upper annular element and a central annular element;
• centering the lower annular element around the rotation axis with an inner radius RI1 and a first outer radius;
• centering the upper annular element around the rotation axis with the inner radius RI1 and the first outer radius;
• centering the central annular element around the rotation axis and providing the central annular element with an outer cylindrical end surface;
• positioning the central annular element between the lower annular element and the upper annular element, the central annular element having the inner radius and a second outer radius, with the second outer radius between inner radius and first outer radius, in a manner that a circular trench is present between an upward facing surface of the lower annular element and a downward facing surface of the upper annular element, the downward and upward facing surfaces each being perpendicular to the rotating axis;
• the method further comprising:
• centering an outer annular element around the rotation axis, the outer annular element having an inner end surface with a second inner radius and a third outer radius, with the third outer radius larger than the first outer radius and the second inner radius being substantially equal to the second outer radius with a gap between the outer annular element and the central inner annular element;
• the downward and upward facing surfaces of the outer annular element being directly adjacent to the upward facing surface of the lower annular element and the downward facing surface of the upper annular element, respectively;
• positioning the inner end surface of the outer annular element abutting the flat cylindrical end surface of the central annular element,
• providing a circular trench in the inner end surface of the outer annular element, such that a toroidal chamber is formed between the central annular element and the outer annular element,
• providing the upward facing surface of the lower annular element and the downward facing surface of the upper annular element with a first stepped surface;
• providing the upward and downward facing surfaces of the outer annular element with a second stepped surface;
• the first and second stepped surfaces being configured in a manner that at least two annular cavities centered around the rotation axis and having a rectangular cross-section are provided, half of the at least two annular cavities at a first interface between the downward facing surface of the upper annular element and the upward facing surface of the outer annular element and the other half of the at least two annular cavities at a second interface between the upward facing surface of the lower annular element and the downward facing surface of the outer annular element, respectively, wherein a radial width of the toroidal chamber is equal to or smaller than a height of the toroidal chamber, and the radial width of the toroidal chamber is smaller than a width of the two annular cavities combined.