Artifex Engineering Inc. | Riser & Umbilical Engineering

U.S. Patent: 10066445, September 4, 2018

European Patent: EP 3 389 919 B1, October 13, 2021

		Description: A Flared and Thickened End assembly for tubular joints to improve
		the fatigue performance and increase the fatigue life of tubular connections subjected cyclic loading such as connections encountered in but not limited to offshore steel catenary risers (SCRs) and steel lazy wave risers (SLWRs)

APPLICATION

One example is mitigating fatigue in SCRs and SLWRs

BENEFITS

		Overcomes the limitation of traditional upset ends (which have the same ID as
		the pipe) imposed by the thickness that can be welded

		Eliminates weld qualification of excessive wall thickness using traditional upset
		ends and associated risk, time, and cost

Reduces offshore welding time and cost

Provides an alternative to using costlier materials such as titanium

		Provides an alternative to using non-established connections for steel catenay
		risers (SCRs) and steel lazy wave risers (SLWRs)

		Renders simple SCRs with Flared and Thickened Ends a robust alternative to
		SLWRs

BENEFITS OF SIMPLE SCRs WITH FLARED AND THICKENED
ENDS COMPARED TO SLWRs

		Significantly simpler to analyze and design (eliminate the effort and time
		required to establish the proper configuration of SLWRs and changes in configuration as a function of content variation and floater offsets)

Eliminate the high cost of buoyancy modules (several million US dollars)

		Eliminate installation complexity, limitation on choice of installation methods and
		vessels, and associated high cost impact

		No gaps in strakes which exist in the "hog bend" section of SLWRs (section with
		buoyancy modules)

		Better short- and long-term integrity with no buoyancy modules to worry about
		especially for insulated risers and straked risers

		Eliminate the environmental impact of buoyancy modules' raw materials,
		fabrication, shipping, and disposal

FABRICATION

Can be fabricated either as a separate forging or integral with the pipe

		Fabrication as separate forgings requires WPQ, fatigue testing, and AUT
		qualification/validation of the

		Pipe-to-forging welds
		Forging-to-forging welds

		Fabrication integral with the pipe requires WPQ, fatigue testing, and AUT
		qualification/validation of the

		Flared and Thickened End-to-Flared and Thickened End welds
		This would likely eliminate the WPQ, fatigue testing, and AUT
		qualification/validation of the SCR pipe welds--would definitely eliminate it for thickness of the integral Flared and Thickened Ends within certain code limits of the SCR pipe thickness

EXAMPLE

In this example, the SCR pipe is 7.25in ID X 1.75in WT. The fatigue life is low and
Flared and Thickened Ends are needed to provide a factor of 4 in order to meet the
design life.

		Keeping the same pipe ID (traditional upset ends) requires a 7.25in ID X 2.3in
		WT upset ends--this thickness is excessive for fatigue quality welding especially offshore

		Keeping the same pipe wall thickness requires 8.997in ID X 1.75in WT flared
		ends--this increase in ID is probably excessive

Alternative Flared and Thickened Ends are

		8.469in ID X 1.90in WT--this increase in ID is more reasonable
		8.139in ID X 2.00in WT--this increase in ID is yet more reasonable and the
		increase in WT is also reasonable for welding

Other Flared and Thickened End configurations are possible as desired

FLOW VELOCITY

Q = V1 * A1 = V1’ * A1’ =>

V1’ = V1 * (A1/A1’) = V1 * (D1/D1’)

Thus, as the diameter increases, the velocity decreases

Example

		SCR pipe: 7.25in ID X 1.75in WT
		Flared & Thickened Ends: 8.139in ID X 2.00in WT
		V1’ = 0.79 V1

FLOW PRESSURE

From Bernoulli’s Equation

P1 + ρ g h1 + ½ ρ V1

2 = P1’ + ρ g h1’ + ½ ρ V1’

P1’ = P1 + ρ g (h1 – h1’) + ½ ρ (V1^2 - V1’^2)

Thus, as the diameter increases, the pressure increases

Example

		SCR pipe: 7.25in ID X 1.75in WT
		Flared & Thickened Ends: 8.139in ID X 2.00in WT
		ρ = 1.71 lb.sec^2/ft^4 (55 pcf oil)
		P1 = 10 ksi
		h1 – h1’ = ~ 2.5ft Length of Flared & Thickened Ends
		V1 = 11.33 ft/sec (corresponds to production of 50 Mbpd)
		V1’ = 8.95 ft/sec
		P1’ = 10.0012ksi

POTENTIAL EROSION

Potential Erosion on Transition from Flared & Thickened Ends-to-Pipe

From DNVGL-RP-O501, annual surface thickness loss

Example

		SCR pipe: 7.25in ID X 1.75in WT
		Flared & Thickened Ends: 8.139in ID X 2.00in WT
		ρm = 881 kg/m^3 (55 pcf Oil)
		ρt = 7800 kg/m^3 (487 pcf , steel pipe)
		P1 = 10 ksi
		V1 = 11.33 ft/sec (3.45 m/sec, corresponds to production of 50 Mbpd)
		V1’ = 8.95 ft/sec (2.73 m/sec), V1 is used conservatively
		mp = 0.015 kg/sec (0.033 lb/sec, mass rate of sand)
		dp = 0.0005 m (0.5mm, ~20 mils, sand particle diameter)
		As Velocity increases, measures to control mass rate of sand increase
		The transition thickness can be increased to accommodate potential erosion, e.
		g., 0.29mm for 30-yr riser life and 1:4 transition slope
		Erosion is not an issue for export SCRs
		CFD analysis can be performed for better prediction of potential erosion

IMPACT ON FLOW

The impact of the Flared and Thickened Ends on the flow is negligible (if any) for the following reasons

		The Flared and Thickened Ends will be placed in the high fatigue zones such as
		the sagbend and hangoff, i.e. their number will be small (e.g. ~13 for a 500ft long high fatigue zone in the sagbend--not considering multi jointing)