Stainless steel elbow is a pipe fitting that connects two lengths of pipe or tubing to change the direction in piping and plumbing systems, there are common angles having 45 degree, 90 degree and 180 degree, 304/304L and 316/316L stainless steel elbows can withstand high pressure and resist corrosion, duplex steels and nickel alloys are available.
| ANSI Specifications | ANSI B16.9 |
|---|---|
| ASME Specifications | ASME SA-403 |
| ASTM Specifications | ASTM A-403 WPW |
| Elbow Degree | 30, 45, 60, 90, 180 Degree |
| Fitting Size | 1/2″ Up To 10″ |
| Schedule | Sch5s, 10S, 40S, 80S |
| Elbow Type | Long Radius, Short Radius, Straight |
| Material | Stainless Steel 304/304L, 316/316L, 321 |
There are various stainless steels to be adapted for pipe elbow used in different applications, as we know that stainless steel exhibits excellent properties to resist corrosion, heating and high pressure, thus, stainless steel elbow is often used in critical applications.
304 and 316L are the most used stainless steel grades, they are both high chromium austenitic grades and can be met the most cases, and other grades are available, such as 321/321H and 347/347H. Some special alloys are usually for the elbow as well, like 904L, and 2205.
| Grade | Carbon | Silicon | Manganese | Chromium | Nickel | Molybdenum | Sulfur | Phosphorous |
|---|---|---|---|---|---|---|---|---|
| WP 304 | 0,08 | 1,0 | 2.00 | 18.0 – 20.0 | 8.0 – 11.0 | – | 0,03 | 0,045 |
| WP 304L | 0,035 | 1,0 | 2.00 | 18.0 – 20.0 | 8.0 – 13.0 | – | 0,03 | 0,045 |
| WP 316 | 0,08 | 1,0 | 2.00 | 16.0 – 18.0 | 10.0 – 14.0 | 2.00 – 3.00 | 0,03 | 0,045 |
| WP 316L | 0,035 | 1,0 | 2.00 | 16.0 – 18.0 | 10.0 – 15.0 | 2.00 – 3.00 | 0,03 | 0,045 |
| WP 321 | 0,08 | 1,0 | 2.00 | 17.0 – 19.0 | 9.0 – 12.0 | – | 0,03 | 0,045 |
There are also EN steel no. for opting, these equivalents include 1.4301, 1.4307, 1.4401, 1.4404, 1.4541, 1.4550, 1.4438, and 1.4539.
Elbows are available in two radius types by length, Short radius (SR) and Long radius (LR), there are also other radiuses, for example, 2D, 3D and 4D.
Long radius elbow the radius of curvature is equal to 1.5 times the diameter of the pipe, namely, R = 1.5D, Long radius elbow is used to reduce frictional force and elbow abrasion.
Short radius elbow the radius of curvature is equal to the pipe diameter, Short-radius elbow is typically installed in limited situations and tight spaces, it will give the piping a sharper turn than a long-radius elbow, However, it is a less costly option compared to LR elbow.
2D means the bending radius is 2 times the nominal pipe size, in the same way, 3D means 2 times the nominal pipe size, they are long radius elbows as well, these long radius elbows are not like 1.5D elbows frequently used, they are smoother and used for specific applications.
There are three common angles of the elbow to use in the piping system, 45 degree, 90 degree and 180 degree, these angle types turn fluid in different directions, including right angles and return angles, there are also other angles to use, like 60 degree and 180 degree.
45 degree elbow changes the flow direction to 45 degrees, it includes long radius 45 degree elbow and short radius 45 degree elbow.
90 degree elbow changes the flow direction to 90 degrees, it also has long radius and short radius types, 90 degree elbow is the most used elbow..
180 degree elbow changes the flow direction to 180 degrees.
According to connection style, the elbow can be classified butt weld elbow, socket welded elbow and threaded elbow, butt weld elbow is a commonly used type.
Butt weld refers to connecting pipes and fittings ends by butt welding method, it has ends beveled to make it easy to weld, beveled ends should be conformed to the requirement of ASME B16.25, and the plain end is offered upon request, BW elbow dimensions can be from 1/2” to 72”, BW weld elbow can be made of both seamless and welded pipe by the process of hot forming that includes bending and forming to shape.
Butt-weld fittings allow for a smooth, flush connection that provides maximum flow, is lower cost elbow, thin wall sizes can be allowed.
45° and 90° – LR and 3D elbow conform to ASME B16.9.
| Nominal Pipe Size | 1/2 To 2.1/2 | 3 To 3.1/2 | 4 | 5 To 8 |
|---|---|---|---|---|
| Outside Diameter At Bevel (D) |
+ 1.6 – 0.8 |
1.6 | 1.6 | + 2.4 – 1.6 |
| Inside Diameter At End | 0.8 | 1.6 | 1.6 | 1.6 |
| Center To End LR (A/B) | 2 | 2 | 2 | 2 |
| Center To End 3D (A/B) | 3 | 3 | 3 | 3 |
| Nominal Pipe Size | 10 To 18 | 20 To 24 | 26 To 30 | 32 To 48 |
| Outside Diameter At Bevel (D) |
+ 4 – 3.2 |
+ 6.4 – 4.8 |
+ 6.4 – 4.8 |
+ 6.4 – 4.8 |
| Inside Diameter At End | 3.2 | 4.8 | + 6.4 – 4.8 |
+ 6.4 – 4.8 |
| Center To End LR (A/B) | 2 | 2 | 3 | 5 |
| Center To End 3D (A/B) | 3 | 3 | 6 | 6 |
| Wall Thickness (T) | Not Less Than 87.5% Of Nominal Wall Thickness | |||
Dimensional tolerances are in millimeters.
The socket weld elbow has a socket area at the end of the elbow, which can be inserted a pipe to connect together, the diameter of the socket area is matching with the outer diameter of the pipe.
Socket-connect elbows are easier to weld than butt-weld elbows because the fitting doesn’t need to align perfectly with the pipe. Slip the pipe into the socket and weld, no beveled ends are needed.
SW elbows also have 90 degree and 45 degree elbows for selecting, generally, SW elbow is used for small pipe diameter, and has three pressure ratings: Class 3000, 6000 and 9000.
Threaded elbow is similar to the SW elbow in shape, the difference is that threaded elbow has thread inside of the elbow end, this type of elbow is easier to install and remove, good for pipeline repair and maintenance.
ASME B16.9 covers overall dimensions, tolerances, ratings, testing, and markings for wrought carbon and alloy steel factory-made buttwelding fittings of NPS 1/2 through 48. It covers fittings of any producible wall thickness. This standard does not cover low-pressure corrosion-resistant buttwelding fittings.
See MSS SP-43, Wrought Stainless Steel Butt-Welding Fittings. Short-radius elbows and returns, which were previously included in ASME B16.28-1994, are included in this standard. B16.9 is to be used in conjunction with equipment described in other volumes of the ASME B16 series of standards as well as with other ASME standards, such as the Boiler and Pressure Vessel Code and the B31 Piping Codes.
ASTM A403 covers the standard for wrought austenitic stainless steel fittings for pressure piping applications. The material for fittings shall consist of forgings, bars, plates, or seamless or welded tubular products. Forging or shaping operations shall be performed by hammering, pressing, piercing, extruding, upsetting, rolling, bending, fusion welding, machining, or by a combination of two or more of these operations.
All fittings shall undergo heat treatment. Chemical and product analyses shall be performed and shall conform to the required chemical composition in carbon, manganese, phosphorus, sulfur, silicon, chromium, molybdenum, and titanium. Tension test shall be done on the fitting material to determine the tensile properties such as yield strength and tensile strength. Fittings supplied under this specification shall be examined visually for surface discontinuities, surface checks, and mechanical marks.
ASTM A960 covers the common requirements that shall apply to wrought steel piping fittings. The material shall consist of forgings, bars, plates, and seamless or welded tubular products. Ferritic steels shall be fully killed. Hollow cylindrically shaped parts up to and including NPS 4 may be machined from bar or seamless tubular material. Elbows, return bends, tees, and header tees shall not be machined directly from bar stock.
The following procedures shall be done for heat treatment: full annealing, solution annealing, isothermal annealing, normalizing, tempering and post-weld heat treatment, stress relieving, and quench and temper. Chemical analysis, heat analysis, and product analysis shall also be done. The chemical requirements shall conform to the required compositions of carbon, manganese, phosphorus, sulfur, silicon, nickel, chromium, molybdenum, vanadium, columbium, titanium, aluminum, lead, and copper. The following tests shall be done for the mechanical requirements: tension, hardness, impact, and hydrostatic tests.
ASTM A815 covers two general classes, WP and CR, of wrought ferritic, ferritic/austenitic, and martensitic stainless steel fittings of seamless and welded construction. Class WP fittings are subdivided into four subclasses: Classes WP-S, WP-W, WP-WX, and WP-WU. The material for fittings shall consist of forgings, bars, plates, or seamless or welded tubular products. The steel shall be melted by electric furnace, vacuum furnace, or electric furnace followed by vacuum or electroslag-consumable remelting. Forging or shaping operations shall be performed by hammering, pressing, piercing, extruding, upsetting, rolling, bending, fusion welding, machining or by combination of two or more of these operations.
The materials shall undergo heat treatment and shall follow the required cooling process and tempering temperature. Chemical and product analyses shall be performed and shall conform to the required chemical composition in carbon, manganese, phosphorus, silicon, sulfur, nickel, chromium, molybdenum, copper, nitrogen, and titanium. The mechanical properties of the fitting material shall conform to the required values in yield strength, tensile strength, elongation, and hardness.
EN 10253 specifies the technical delivery requirements for seamless and welded butt-welding fittings (elbows, concentric and eccentric reducers, equal and reducing tees, caps) made of austenitic and austenitic–ferritic (duplex) stainless steel without specific inspection requirements. It specifies steel grades; mechanical properties; dimensions and tolerances; requirements for inspection and testing; inspection documents; marking; handling and packaging.
