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Types Of Elbows Based On Direction Angle

According to fluid flow direction of the pipes, elbows can be divided into different degrees, such as 45 degree, 90 degree, 180 degree, which are most common elbows. Also there are 60 degree and 120 degree elbows for some special pipelines. This degree is just an representation of the angle by which the fluid flow is going to change after flowing through the said elbow.

What Is A 5D Elbow?

The welded elbows 5D (radius two and half diameter) are used to divert the flow of the pipes. 5D-welded elbows are useful to transport granular materials and powders. In France this type of elbow is also called coude grand rayon.

Types Of Elbows Based On Length And Radius

Elbows are split into two groups which define the distance over which the flowing fluid change direction; the center line of one end to the opposite face. This is known as the “Center to Face” distance and is equivalent to the radius through which the elbow is bent.

If the radius is the same as pipe diameter (Center-to-Face dimension of 1.0 X diameter ), it called Short Radius Elbow (SR elbow) used normally for low pressure and low speed pipelines or in tight areas where clearance is the main issue. If the radius is larger than pipe diameter (Center-to-Face dimension of 1.5 X diameter) then we call it a Long Radius Elbow (LR Elbow) used for high pressure and high flow rate pipelines.

The elbow is divided into its radius of curvature and can be divided into a long radius elbow and a short radius elbow. The long radius elbow refers to the outer diameter of the tube whose radius of curvature is equal to 1.5 times, that is, R = 1.5D. A short radius elbow means that its radius of curvature is equal to the outer diameter of the tube, ie R = D. Where D is the diameter of the elbow and R is the radius of curvature. Normal use of the length of the radius Sometimes to reduce the loss of resistance or elbow wear, the elbow with a larger bending radius will be used (in fact, it is not called elbow); when there is a limit on the installation position, a short radius elbow will be used.

Long Radius Elbow VS Short Radius Elbow

When To Choose A Long Radius Elbow Or A Short Radius Elbow?

There are two types of pipe sizes for process installation, namely pipe outer diameter and nominal size. D, DN, refers to the nominal size of the pipe. It does not represent the inner diameter of the pipe or the outer diameter of the pipe. It is a nominal size designed and used. The elbow is the elbow, and the manufacturing method is divided into the push elbow, the extrusion elbow and the welded miter elbow. The structure length is 1.0D, 1.5D, 2.0D.

At present, there are two kinds of norms implemented in this area in China: metric and imperial. For example: 1.5D steel seamless elbow, DN100 outer diameter ¢108 and ¢114.3, actual structural length L152, DN200 outer diameter ¢219 and ¢216.3, actual structural length L302. In use, long radius elbow (R = 15DN): in general, should be preferred; short radius elbow (R = 1.0DN): mostly used in applications where size is limited. Its high working pressure should not exceed 0.8 times of the long radius elbow of the same specification.

Elbow (R=nDN): used to moderate the scouring and kinetic energy of the media at the bend, available to R=3DN, 6DN, 10DN, 20DN. According to different manufacturing methods, it is divided into push elbow, extrusion elbow and welded miter elbow.

Pushing elbows and extrusion elbows: Commonly used for welding mitered elbows on medium and small-sized pipes with strict media conditions: It is often used on large-sized pipes with moderate media conditions, and the bending radius is not to be less than its nominal diameter. 1.5 times. When the miter angle of the miter elbow is greater than 450, it should not be used on highly toxic, flammable medium pipes, or on pipes subjected to mechanical vibration, pressure pulsation and alternating load due to temperature changes.

So how do we buy qualified elbows? Detecting the back arc of the elbow: Seamless elbow detection of the thickness of the back arc is an important task. Many large pipe elbow manufacturers or strict engineering inspection of the back arc is a must. It is related to the safety and stability of the pipeline operation.

Everyone knows that both the seamless steel pipe and the seamless elbow are under pressure, that is, the pressure is very large when running. Under normal circumstances, the safety factor of the thickness of the seamless elbow designed and installed is about six times. For example, the 219*8 seamless elbow, the pipeline medium is ordinary water, the temperature is usually not higher than one hundred degrees Celsius, and the pressure required to blast such a seamless elbow is about 300 kg, that is to say, The pressure inside the pipeline needs to reach PN30, and the seamless elbow will be blasted, and the operating pressure of this elbow is probably about it. It is estimated that the maximum will not exceed PN6.4, which is generally around PN4.0, of course. With the corrosion of the pipeline, the seamless elbow will also be corroded to varying degrees. In order to ensure its safe operation, the necessity of overhaul is also great.

The current process of making seamless elbows will lead to the phenomenon of back arc thinning. Under normal circumstances, the wall thickness of the mouth will be about two millimeters thinner than the back arc. The common thickness and pressure are not thinner even if the back arc is thinned. There will be too many safety hazards, because the elbow has not been replaced until the elbow has a dangerous accident. But as a rigorous project, what is not the same, and the medium inside the pipeline is also responsible, not just water. There may be oil or other impurities, the temperature is high and the pressure is high, and the thickness of the back arc as the weak place determines the life of the seamless elbow. Therefore, the importance of detecting the back arc is naturally great. With the thickness gauge, read the thickness of a point at the elbow directly.

What Does Short Radius (SR) Or Long Radius (LR) Means?

You will often hear SR45 elbow or LR45 elbow. The 45 or 90 refers to the angle of the bend for buttweld fitting to change the direction of flow. A long radius elbow (LR 90 Elbow or LR 45 elbow) will have a pipe bend that will be 1.5 times the size of the pipe. So, a 6 inch LR 90 has bending radius that is 1.5 x nominal pipe size. A short radius elbow (SR45 or SR90) has a pipe bend that is equal to the size of the fitting, so a 6” SR 45 has a bending radius that is 6” nominal pipe size.

What Is A 3R Or 3D Elbow Pipe Fitting?

First, the terms 3R or 3D are used synonymously. A 3R butt weld elbow has a bending radius that is 3 times the nominal pipe size. A 3R elbow is smoother than SR or LR fitting.

Types Of Elbows Based On Connection With Pipe

As per the connection with pipe, elbows could be classified as Butt Welded Elbow, Socket Welded Elbow and Threaded Elbow.

Types Of Elbows Based On Material Of Construction

Stainless Steel Elbow : ASTM A403 WP Gr. 304, 304H, 309, 310, 316, 316L, 317L, 321, 347, 904L

Carbon Steel Elbow : ASTM A 234 WPB, WPBW, WPHY 42, WPHY 46, WPHY 52, WPH 60, WPHY 65 & WPHY 70.

Low Temperature Carbon Steel Elbow : ASTM A420 WPL3, A420 WPL6

Alloy Steel Elbow : ASTM / ASME A/SA 234 Gr. WP 1, WP 5, WP 9, WP 11, WP 12, WP 22, WP 91

Duplex Steel Elbow : ASTM A 815, ASME SA 815 UNS NO S31803, S32205. Werkstoff No. 1.4462

Nickel Alloy Elbow : ASTM / ASME SB 336 UNS 2200 ( NICKEL 200 ), UNS 2201 (NICKEL 201 ), UNS 4400 (MONEL 400 ), UNS 8020 ( ALLOY 20 / 20 CB 3, UNS 8825 INCONEL (825), UNS 6600 (INCONEL 600 ), UNS 6601 ( INCONEL 601 ), UNS 6625 (INCONEL 625), UNS 10276 ( HASTELLOY C 276 )

Wall Thickness Of Elbows

The weakest point on an elbow is the inside radius. ASME B16.9 only standardizes the center to face dimensions and some "squareness" dimensional tolerances. The wall thickness at the weld line location even is standardized, but not through the rest of an elbow. The standard states that the minimum tolerance will be within 12.5% of the minimum ordered wall thickness of the pipe. A maximum tolerance is specified only at the ends of the fitting.

Many providers of buttweld elbows (and tees) provide one schedule greater thickness so that sufficient wall thickness, after forming, remains.

Steel Pipe Elbow Coating

Along with build quality, the longevity and reliability of steel pipe elbows are highly dependent on the type and quality of the coating used. However, applying coatings to pipe elbows is not just about preventing corrosion, but can affect the evenness of flow through the pipe and the need to prevent contamination of pipe contents ((e.g. foodstuffs or drinking water). We offer corrosion resistance coating service for steel pipe elbow, our coating service includes light oiling, black painting, FBE coating, 2 layers or 3 layers PE coating, hot-dip galvanizing.

ASME / ANSI B16.9 dimension

ASME B16.9 Standard covers overall dimensions, tolerances,ratings, testing, and markings for factory-made wrought buttwelding fittings in sizes NPS 1⁄2 through NPS 48 (DN 15 through DN 1200).

Tolerances Of Welded Fittings

All dimensions are given in inches. Tolerances are equal plus and minus except as noted.

1. Out-of-round is the sum of absolute values of plus and minus tolerance.
2. This tolerance may not apply in localized areas of formed fittings where increased wall thickness is required to meet design requirements of ASME B16.9.
3. The inside diameter and the nominal wall thicknesses at ends are to be specified by the purchaser.
4. Unless otherwise specified by the purchaser, these tolerances apply to the nominal inside diameter, which equals the difference between the nominal outside diameter and twice the nominal wall thickness.

The ASME B16.9 pipe fittings can be used under the jurisdiction of the ASME Boiler & Pressure Vessel Code (BPVC) as well as the ASME Code for pressure piping. Referencing pressure ratings of flanges per ASME B16.5, they can be designated as Classes 150, 300, 600, 900, 1500 and 2500. The allowable pressure ratings for ASME B16.9 pipe fittings may be calculated as for straight seamless pipe of equivalent material in accordance with the rules established in the applicable sections of ASME B31 Code for pressure piping.

Design Of Fittings

The design of butt welding pipe fittings made to ASME B16.9 shall be established by one of the following methods: (a) mathematical analyses contained in pressure vessel or piping codes; (b) proof testing; (c) experimental stress analysis with hydrostatic testing to validate experimental results; (d) detailed stress analysis with results evaluation.

Standard Marking

Generally, ASME B16.9 pipe fittings shall be marked to show the following details: “trademark + material grade + wall thickness + size + heat number”. For example, “M ASTM A234 WP5 SCH80 6″ 385“. When steel stamps are used, care shall be taken so that
the marking is not deep enough or sharp enough to cause cracks or to reduce the wall thickness of the fitting below the minimum allowed.

Material & Manufacture

The ASME B16.9 fittings may be made from an extensive range of mateirals covering (1) carbon and low-alloy steels in accordance with ASTM A234 and ASTM A420; (2) austenitic and duplex stainless steels in accordance with ASTM A403 and ASTM A815; (3) nickel alloys in accordance with ASTM B366; (4) aluminum alloys in accordance with ASTM B361; and (5) titanium alloys in accordance with ASTM B363.

Pipe Fittings Dimensions Tolerance As Per ASME B16.9: