PRODUCT NOTE

Tech Note ORI-T003 August, 2004

MLI Branch Connection ComparisonFull-Bore / Full Penetration vs. Extruded Tee

Magnetic Liquid Level Indicators

This application note provides a comparison of Orionsfull-bore/full penetration (conventional) branch connec-tions and extruded tee branch connections as used onMagnetic Level Indicators (MLIs).

The fundamentals of branch connectionsFull-bore/full penetration connection is a machinedopening in the chamber with a fitting welded to it.

Extruded tee connection is an opening in a chamberthat is formed by either internally or externally forcingthe chamber wall material to form a collar.

Achieving the stylesFull-bore/full penetration connections are made bycutting a circular opening into the chamber, machining afitting (coupling/nipple) to theprecise curvature of the chamberand welding that fitting to thechamber. Fittings can be forged(Bonney couplings or a saddledpipe nipple), machined fromround stock or pipe.

Extruded tee connections are made by cutting a pilot holeinto the chamber material. A forming head withretractable pins is inserted into the chamber through thepilot hole. The retractable pins are then extended and thehead begins to revolve. While the pins are revolving theforming head is pulled through the pilot hole forcing thereshaping of the chamber material into the extruded teeconnection.

Important points to consider1. Extruded tee connections do not produce a superiorMLI. The primary purpose behind this method is toreduce welding and other fabrication costs for themanufacturer.

2. Extruded tee process connections cannot be achievedwith schedule 80 and 160 stainless steel pipe. Full-bore/full penetration branch connections must beemployed in these cases.

3. Extruded tees will always fail prior to a similar full-bore/full penetration branch connection when taken tomaximum pressures. This is due to reduced materialthickness at the extrusion.

Full Bore Extruded Tee

Full Bore

Extruded Tee

Drilling of Pilot Hole Forming Pins Extended Forming of Collar

Important points to consider4. Unlike full-bore/full penetration connections, extrudedtees result in visible thinning of the process connectionmetaltypically a reduction in thickness of 25 to 30percent. To achieve ASME (American Society ofMechanical Engineers) code compliance, maximumallowable pressures must be reduced. In addition, thethinner material results in a mismatch in materialthickness between the extruded tee and the branchconnection. It is typically noted that internal diametersof the extruded tee and the process connection willmatch. Additional weld metal must be applied to com-pensate for the mismatched outside diameter.

5. Perhaps the most important issues with extruded teesinvolve corrosion and stress-cracking. The end usershould be aware:

A. There will be less corrosion allowance due to thereduced material thickness.

B. Due to Work Hardening during the cold formingprocess, increased hardness of the formed outletproduces internal stress in the area of the processconnection. This will result in a reduction of corro-sion resistance at the formed process connection.

An explanation from the ASM (American Society forMetals) International Handbook Volume 13 Corrosionapplies:

Processes such as cold working, in which thematerial is plastically deformed into some desiredshape lead to the formation of elongated and highlydeformed grains and a decrease in corrosion resist-ance. Cold working can also introduce residualstresses that make the material susceptible tostress-corrosion cracking.

It is therefore logical that cold-formed branch connec-tions will add yet another potential area of failure into analready complex equation of corrosion.

6. The purported advantage of extruded tee branch con-nections is the ability to x-ray 100% of the branchconnection weld. A more preferred option would be toutilize butt-weld tee fittings that produce 100% x-rayquality welds. This method does not require de-ratingof the MLI chamber.

7. Through the use of proper tooling, welding techniques,and sufficient material thickness Orions full-bore/fullpenetration connections eliminate the possibility ofchamber bowing.

Note: MLI process connections provide a structuralfunction in that the entire mass of the instrument issupported at these points. Application of extrudedtee technology should be approached with cautiondue to the increased pipe strain and reduced struc-tural strength.

SummationOrions full-bore/full penetration method is time-provenand the widely accepted industry standard that providesthe strongest most durable branch connections.

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Performance specifications are effective with date of issue and are subject to change without notice.

BULLETIN: ORI-T003.0EFFECTIVE: August 2004

Full Bore Extruded Tee

ReducedThickness

StressedArea

Orion Tech Note ORI-T003MLI Branch Connection ComparisonFull-Bore / Full Penetration vs. Extruded Tee

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