BUOYANT FLEXTURE FREE

tension w/1-250 k down (T min) 5ġ 1.0% In-water wt. Weight of riser string with mud in seawaterĪPI min. In practice, a lower maximum tension limit is generally applied.ĪPI riser tensions – vertical at slip ring – 9000 ft of water A maximum tension limit 90% of the installed capacity prevents the relief valves from popping under most conditions. This tension multiplied by a reduction factor for fleet angle only (in this example, the tensioner system compensates for mechanical losses, so that the estimate is 0.99) gives the maximum API tension in terms of vertical tension at the top of the riser. Maximum Tension Limit – API RP 16Q guidance is that top tension should be no more than 90% of the dynamic tensioning limit (same as rated tensioner capacity). Tensioners Down – Positive tension is maintained in the riser if one out of twelve tensioners goes down. Tolerances – 1% on the weight of steel in the riser and 1% on the net lift from the buoyancy material. For this calculation, the following information was used: The values calculated are vertical tensions at the top of the riser. The API minimum riser tensions are calculated using the installed weight of the riser with mud. Weight of riser string with mud in seawater 3įJ= flex joint WL = water line DH = diverter husing 1 Mudweight in Seawater * riser capacity * length from fflexjoint to waterline 2 Mudweight in air * riser capacity * length from waterline to diverter housing 3 Riser string weight + weight of mud (FJ to WL) + weight of mud (WL to DH) Weight of mud in air from waterline to diverter 2 Weight of mud in seawater from flexjoint to waterline 1 An added margin on tension is warranted to improve the riser performance in high seas or high currents, as will be discussed later in this chapter. In practice, the API minimum tension is rarely used as the riser's operating tension. (The ratio is often in the range of 90–99%.) All of these factors are considered in the calculation of the API minimum tension that is used to prevent buckling. API RP 16Q (1993) also distinguishes the rated capacity of a tensioner and the vertical tension applied at the top of the riser. This margin also provides adequate tension in case a tensioner fails. API RP 16Q (1993) provides guidance on this, which provides a margin to account for uncertainties in the weight of the riser steel and the lift of the riser buoyancy. To prevent buckling of the riser, criteria have been established within the industry to prevent the effective tension in the riser from going below zero. Maximum tension is established to prevent top tensions in excess of the installed capacity of the riser. Minimum tension is established to prevent buckling of the riser.

This section discusses the API guidelines that have been established for minimum and maximum tension. John Halkyard, in Handbook of Offshore Engineering, 2005 9.2.7.3.1 Minimum and Maximum API Tensions Table 4.4 shows the structural properties of syntactic foams with epoxy resin ( Chandrasekaran and Jain, 2016). When used as reinforcements in reinforced cement concrete, they can achieve both strength and buoyancy. For example, syntactic foam for 600-bar pressure possesses strength about three times higher than the concrete of 80 MPa. The presence of hollow particles results in lower density and higher strength.

BUOYANT FLEXTURE FREE

Syntactic foams, which are free from corrosion, are composite materials synthesized by filling a metal, polymer, or ceramic matrix with hollow particles, termed micro-balloons. They can be easily handled with wood-working tools. They have a high compressive and shear strength with low water absorption.

Most efficient syntactic foams use glass spheres of microscopic with an epoxy resin binder. Syntactic foams are hollow, glass spheres, dispersed in a plastic matrix. Few common applications are small submarines, oil well drill pipe, and deep-sea buoys. Such materials should possess no-water absorption, no-distortion under compression. The most common are wood and gasoline, the specific gravities of which are about 0.5 and 0.7, respectively.

Buoyancy materials have specific gravity considerably lesser than water.

Buoyant flexture