Seamless Steel Elbow VS Welded Steel Elbow

12 Nov

Seamless Steel Elbow VS Welded Steel Elbow

2018-11-12

What is a seamless elbow?

The most common raw material for seamless elbow is seamless steel pipe. The tube blank of the elbow is cut by waterjet cutting, hot cutting, etc., and is pushed by the intermediate frequency pushing machine, and then pressed and finished by a hot press, and then subjected to subsequent processing such as groove and non-destructive testing. After leaving the factory, the raw material for rolling seamless elbow is a round tube blank, which is cut by a cutting machine into a billet having a length of about one meter and sent to a furnace for heating via a conveyor belt. The billet is fed into a furnace and heated to a temperature of approximately 1200 degrees Celsius. The fuel is hydrogen or acetylene. Furnace temperature control is a critical issue. After the round tube blank is released, it is subjected to a through-hole punching machine. The more common perforating machine is a conical roller perforating machine. This perforating machine has high production efficiency, good product quality, large perforation expansion, and can wear a variety of pipe fittings. After perforation, the round billet is successively rolled, rolled or extruded by three rolls. After extrusion, the tube should be sizing. The sizing machine is rotated at a high speed by a conical drill bit into a steel core to form a seamless elbow.

1 Manufacturing Process of Seamless Elbow 3 Manufacturing Process of Welded Elbow 5 Size 7 Short radius (SR) elbows 9 Wall Thickness of Elbows
2 What is a welded elbow 4 Standards 6 Long radius (LR) elbows 8 Application of pipe elbows 10 Seamless Steel Elbow VS Welded Steel Elbow

Classification of seamless elbows

Seamless elbows are divided into hot-rolled (extrusion) seamless elbows and cold-drawn (rolled) seamless elbows due to their different manufacturing processes.

Manufacturing Process of Seamless Elbow

The manufacturing process of seamless elbow usually contains heating bending and clod bending. One of the most common methods is using hot mandrel bending from straight steel pipes. Applying hot mandrel bending can manufacture a wide size range seamless elbows. After heating the steel pipe at a elevated temperature, the pipe is pushed, expanded, bended by the inner tools of mandrel step by step.
When compared to other bending method type the advantages of hot bending elbows include smaller thickness deviation and stronger bending radius. Meanwhile, using bending instead of prefabricated bends substantially reduces the number of welds needed. This reduces the amount of work required and increases the quality and usability of pipes.
Cold bending is a quick and inexpensive bending method. It is a competitive option for making pipelines and machine parts. Cold bending is the process to bent the straight steel pipe at normal temperatures in a bending machine. Cold bending is suitable for pipes with an outer diameter of 17.0 to 219.1 mm, and wall thickness 2.0 to 28.0 mm. The recommended bending radius is 2.5 x Do. Normally at a bending radius of 40D. By using cold bending, we can get small radius elbows, but we need to pack the internals with sand to prevent wrinkling.

Forming method of seamless elbow

  1. Forging method: The end or part of the pipe is punched out by a swaging machine to reduce the outer diameter. The common forging machine has a rotary type, a link type and a roller type.
  2. Rolling method: Generally, the mandrel is not used, and it is suitable for the inner edge of the thick-walled tube. The core is placed in the tube, and the outer circumference is pressed by a roller for round edge processing.
  3. Stamping method: The pipe end is expanded to the required size and shape with a tapered core on the press.
  4. Bending forming method: There are three methods that are more commonly used. One method is called stretching method, the other method is called pressing method, the third method is roller method, there are 3-4 rollers, two fixed rollers, one adjusting roller, and adjustment. With the fixed roll distance, the finished pipe is curved.
  5. Inflating method: one is to place rubber in the tube, and the upper part is compressed by a punch to make the tube convex and convex; the other method is to form a hydraulic bulge, fill the middle of the tube with liquid, and the liquid pressure drums the tube into the required The shape, the production of bellows is mostly used in this way.

The advantages of seamless elbow

Seamless elbow has the following advantages: hygienic non-toxic, light weight, good heat resistance, good corrosion resistance, good heat preservation, good impact resistance and long service life.

  1. Hygienic and non-toxic: The material is composed entirely of carbon and hydrogen. No toxic heavy metal salt stabilizer has been added. The hygienic performance of the material has been tested by the national authorities.
  2. Light weight: stamping elbow density of 0.89-0.91g / cm, only one tenth of the steel pipe. Due to its light weight, it can greatly reduce the transportation cost and the construction strength of the installation.
  3. Good heat resistance: when the working water temperature is 70 degrees, the softening temperature is 140 degrees.
  4. Good corrosion resistance: in addition to a few hydrogenating agents, can withstand the erosion of a variety of chemical media, has excellent acid, alkali, corrosion resistance, will not rust, will not corrode, will not breed bacteria, no electricity Chemical corrosion.
  5. High impact: because the unique impact strength performance is significantly improved than other solid wall tubes, the ring stiffness is equivalent to 1.3 times the real wall.
  6. Long service life: the pipe at the rated use temperature and pressure, the service life of more than 50 years, with anti-UV, anti-radiation, so that the product does not fade.

What is a welded elbow?

The weldedelbow is the “shrimp bend”, which can be welded after cutting and cutting on the pipe or steel plate, and the specification can be very large. The number of bends and the bend radius are freely determined by the producer. The welding bend is not very round, and the bending radius of both is not large, generally about 1 times the diameter of the pipe.


Elbows Inside welded

Manufacturing Process of Welded Elbow

Welded elbows are made from the steel plates, so there is a weld seam on it. Use a mould and press the steel plate to the shape of the elbow, then weld the seam to be a finish steel elbow. It is the old production method of the elbows. Recent years the small sizes elbows are almost manufactured from the steel pipes now. For the big size elbows, for example, it is very difficult to produce elbows over 36” OD from the steel pipes . So it is commonly made from the steel plates, pressing the plate to the shape of half elbow, and welding the two halves together. Since the elbows are welded in its body , the inspection of the welding joint is necessary . Commonly we use the X-Ray inspection as the NDT.

Advantages of welding elbows

  1. The stamping process of welding elbow has high production efficiency, easy operation and easy mechanization and automation. This is because stamping relies on die and stamping equipment to complete the processing. The number of strokes of ordinary press is up to several per minute. Ten times, high-speed pressure can reach hundreds or even thousands of times per minute, and each stamping stroke may result in a stamping.
  2. Stamping generally has no chip scraps, less material consumption, and no need for other heating equipment. Therefore, it is a material-saving and energy-saving processing method, and the cost of stamping parts is low.
  3. Stamping can process parts with large size range and complicated shape, such as stopwatches with small clocks, large automotive longitudinal beams, covering parts, etc., plus cold deformation hardening effect of materials during stamping, strength and rigidity of stamping. Both are higher.
  4. When stamping, the size and shape accuracy of the stamping part are guaranteed, and the surface quality of the stamping part is generally not damaged, and the life of the mold is generally long, so the quality of the stamping is stable, the interchangeability is good, and it has “the same” feature.
  5. No need for tube blanks as raw materials, which can save the cost of pipe making equipment and molds, and can obtain push elbows with any large diameter and relatively thin wall thickness. The material of the stamping elbow is special, and it is not necessary to add the raw material of the tube blank, and it is easy to control during processing.
  6. The billet for processing stamping elbow is flat or expandable surface, so the material is simple to cut, the precision is easy to guarantee, the assembly and welding are convenient, the raw materials are easy to control during processing, the operation is relatively simple, there is no complicated process, and the welding and assembly are convenient.

Standards

Some widely used pipe fitting standards are as follows:

ASME: 

American Society for Mechanical Engineers

This is one of the reputed organizations in the world developing codes and standards.

The schedule number for pipe fitting starts from ASME/ANSI B16. The various classifications of ASME/ANSI B16 standards for different pipe fittings are as follows:

  • ASME/ANSI B16.1 – 1998 – Cast Iron Pipe Flanges and Flanged Fittings
  • ASME/ANSI B16.3 – 1998 – Malleable Iron Threaded Fittings
  • ASME/ANSI B16.4 – 1998 – Cast Iron Threaded Fittings
  • ASME/ANSI B16.5 – 1996 – Pipe Flanges and Flanged Fittings
  • ASME/ANSI B16.11 – 2001 – Forged Steel Fittings, Socket-Welding and Threaded
  • ASME/ANSI B16.14 – 1991 – Ferrous Pipe Plugs, Bushings and Locknuts with Pipe Threads
  • ASME/ANSI B16.15 – 1985 (R1994) – Cast Bronze Threaded Fittings
  • ASME/ANSI B16.25 – 1997 – Buttwelding Ends
  • ASME/ANSI B16.36 – 1996 – Orifice Flanges etc.

ASTM International:
American Society for Testing and Materials

This is one of the largest voluntary standards development organizations in the world. It was originally known as the American Society for Testing and Materials (ASTM).

  • ASTM A105 / A105M – Specification for Carbon Steel Forgings for Piping Applications
  • ASTM A234 / A234M – Specification for Piping Fittings of Wrought Carbon Steel and Alloy Steel for Moderate and High Temperature Service
  • ASTM A403 / A403M – Specification for Wrought Austenitic Stainless Steel Piping Fittings
  • ASTM A420 / A420M – Standard Specification for Piping Fittings of Wrought Carbon Steel and Alloy Steel for Low-Temperature Service

AWWA
American Water Works Association

AWWA About – Established in 1881, the American Water Works Association is the largest nonprofit, scientific and educational association dedicated to managing and treating water, the world’s most important resource.

  • AWWA C110 – Ductile-Iron and Gray-Iron Fittings, 3 Inch Through 48 Inch (75 mm Through 1200 mm), for Water and Other Liquids
  • AWWA C208 – Dimensions for Fabricated Steel Water Pipe Fittings

ANSI: 
The American National Standards Institute

ANSI is a private, non-profit organization. Its main function is to administer and coordinate the U.S. voluntary standardization and conformity assessment system. It provides a forum for development of American national standards. ANSI assigns “schedule numbers”. These numbers classify wall thicknesses for different pressure uses.

MSS STANDARDS 
Manufacturers Standardization Society

The Manufacturers Standardization Society (MSS) of the Valve and Fittings Industry is a non-profit technical association organized for development and improvement of industry, national and international codes and standards for: Valves, Valve Actuators, Valve Modification, Pipe Fittings, Pipe Hangers, Pipe Supports, Flanges and Associated Seals

  • MSS SP-43 – Wrought Stainless Steel Butt-Welding Fittings Including Reference to Other Corrosion Resistant Materials
  • MSS SP-75 – Specifications for High Test Wrought Buttwelding Fittings
  • MSS SP-73 – Brazing Joints for Copper and Copper Alloy Pressure Fittings
  • MSS SP-83 – Class 3000 Steel Pipe Unions, Socket-Welding and Threaded
  • MSS SP-97 – Integrally Reinforced Forged Branch Outlet Fittings — Socket Welding, Threaded, and Buttwelding Ends
  • MSS SP-106 – Cast Copper Alloy Flanges and Flanged Fittings Class 125,150, and 300
  • MSS SP-119 – Factory-Made Wrought Belled End Socket Welding Fittings

Difference between “Standard” and “Codes”:

Piping codes imply the requirements of design, fabrication, use of materials, tests and inspection of various pipe and piping system. It has a limited jurisdiction defined by the code. On the other hand, piping standards imply application design and construction rules and requirements for pipe fittings like adapters, flanges, sleeves, elbows, union, tees, valves etc. Like a code, it also has a limited scope defined by the standard.

Factors affecting standards:

“Standards” on pipe fittings are based on certain factors like as follows:

  • Pressure-temperature ratings
  • Size
  • Design
  • Coatings
  • Materials
  • Marking
  • End connections
  • Dimensions and tolerances
  • Threading
  • Pattern taper etc.

BSP: 
British Standard Pipe

BSP is the U.K. standard for pipe fittings. This refers to a family of standard screw thread types for interconnecting and sealing pipe ends by mating an external (male) with an internal (female) thread. This has been adopted internationally. It is also known as British Standard Pipe Taper threads (BSPT )or British Standard Pipe Parallel (Straight) threads (BSPP ). While the BSPT achieves pressure tight joints by the threads alone, the BSPP requires a sealing ring.

JIS: 
Japanese Industrial Standards

This is the Japanese industrial standards or the standards used for industrial activities in Japan for pipe, tube and fittings and published through Japanese Standards Associations.

NPT:
National Pipe Thread

National Pipe Thread is a U.S. standard straight (NPS) threads or for tapered (NPT) threads. This is the most popular US standard for pipe fittings. NPT fittings are based on the internal diameter (ID) of the pipe fitting.

BOLTS & NUTS

We are manufacturer of Flange bolts & Nuts and supply high quality

  • A193 = This specification covers alloy and stainless steel bolting material for pressure vessels, Valves, flanges, and fittings for high temperature or high pressure service, or other special purpose applications.
  • A320 = Standard Specification for Alloy-Steel and Stainless Steel Bolting Materials for Low-Temperature Service.
  • A194 = Standard specification for nuts in many different material types.

AN:

Here, “A” stands for Army and “N” stands for Navy

The AN standard was originally designed for the U.S. Military. Whenever, a pipe fitting is AN fittings, it means that the fittings are measured on the outside diameter of the fittings, that is, in 1/16 inch increments.

For example, an AN 4 fitting means a fitting with an external diameter of approximately 4/16″ or ¼”. It is to be noted that approximation is important because AN external diameter is not a direct fit with an equivalent NPT thread.

Dash (-) size

Dash size is the standard used to refer to the inside diameter of a hose. This indicates the size by a two digit number which represents the relative ID in sixteenths of an inch. This is also used interchangeably with AN fittings. For example, a Dash “8” fitting means an AN 8 fitting.

ISO: 

International Organization for Standardization

ISO is the industrial pipe, tube and fittings standards and specifications from the International Organization for Standardization. ISO standards are numbered. They have format as follows:

“ISO[/IEC] [IS] nnnnn[:yyyy] Title” where

  • nnnnn: standard number
  • yyyy: year published, and
  • Title: describes the subject

A standard hose guide is given

Hose Size In Nominal ID Inch Dash Size Standard Dash Size
1/4 3/16 -04
3/8 5/16 -06
1/2 13/32 -08
3/4 5/8 -12
1 7/8 -16
1 ½ – –
1 ¼ 1 1/8 -20

Flanges: Ratings in Classes and Pressure Numbers (PN)

Flange Class 150 300 600 900 1500 2500
Flange Pressure Number, PN 20 50 100 150 250 420

Size data of pipe elbows


An elbow is a pipe fitting installed between two lengths of pipe or tubing to allow a change of direction, usually a 90° or 45° angle, though 22.5° elbows are also made.

The ends may be machined for butt welding, threaded (usually female), or socketed, etc. When the two ends differ in size, the fitting is called a reducing elbow or reducer elbow.

  • Pressure: SCH5 to SCH160
  • Size range: 1/2 to 56 inches (DN 15 to DN 1,400mm), 22.5 Deg, 45 Deg, 90 Deg, 180 Deg
  • Manufacturing standards: ANSI, ISO, JIS and DIN
  • Process: butt welding, seamless, threaded , or socketed

Long and Short Radius Elbow

By default, there are 5 opportunities, the 45°, 90° and 180° elbows, all three in the “long radius” version, and in addition the 90° and 180° elbows both in the “short radius” version.

Long radius (LR) elbows

Radius is 1.5 times the pipe diameter

Short radius (SR) elbows

Radius is 1.0 times the pipe diameter

  • S/R 45°Elbow
  • S/R 90°Elbow
  • S/R 180°Elbow

Elbows are split into two groups which define the distance over which they 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.

Here below, for example, you will find the center to face distance of NPS 2 elbows (the A distance on the image)

  •  90°-LR : = 1½ x 2(NPS) x 25.4 A=76.2 mm
  •  180°-LR : = 2 times the 90° LR elbow A=152.4 mm
  • 90°-SR : = 2(NPS) x 25.4 A=50.8 mm
  • 180°-SR : = 2 times the 90° SR elbow A=101.6 mm

The center to face distance for a “long” radius elbow, abbreviated LR always is “1½ x Nominal Pipe Size (NPS) (1½D)”, while the center to face distance for a “short” radius elbow, abbreviated SR even is to nominal pipe size.

3D elbows as an example, are calculated with: 

3(D) x 2(NPS) x 25.4

Note:

  • 90 Degree Elbow – where change in direction required is 90°
  • 45 Degree Elbow – where change in direction required is 45°
  • L/R – Long radius, S/R – Short radius
Nominal pipe size Outside Diameter 
at Bevel  		Center to End Center to Center Back to Faces
45° Elbows 90°Elbows 180°Return
H
        F
       P
       K

DN

INCH

Series A Series B LR LR SR LR
SR
LR
SR
15
1/2
21.3
18
16
38
–
76
–
48
–
20
3/4
26.9
25
16
38
–
76
–
51
–
25
1
33.7
32
16
38
25
76
51
56
41
32
11/4
42.4
38
20
48
32
95
64
70
52
40
11/2
48.3
45
24
57
38
114
76
83
62
50
2
60.3
57
32
76
51
152
102
106
81
65
21/2
76.1(73)
76
40
95
64
191
127
132
100
80
3
88.9
89
47
114
76
229
152
159
121
90
31/2
101.6
–
55
133
89
267
178
184
140
100
4
114.3
108
63
152
102
305
203
210
159
125
5
139.7
133
79
190
127
381
254
262
197
150
6
168.3
159
95
229
152
457
305
313
237
200
8
219.1
219
126
305
203
610
406
414
313
250
10
273.0
273
158
381
254
762
508
518
391
300
12
323.9
325
189
457
305
914
610
619
467
350
14
355.6
377
221
533
356
1067
711
711
533
400
16
406.4
426
253
610
406
1219
813
813
610
450
18
457.2
478
284
686
457
1372
914
914
686
500
20
508.0
529
316
762
508
1524
1016
1016
762
550
22
559
–
347
838
559
Note:

1. Do not use the figures in the parenthesis as far as possible2. Please first select A series. 

600
24
610
630
379
914
610
650
26
660
–
410
991
660
700
28
711
720
442
1067
711
750
30
762
–
473
1143
762
800
32
813
820
505
1219
813
850
34
864
–
537
1295
864
900
36
914
920
568
1372
914
950
38
965
–
600
1448
965
1000
40
1016
1020
631
1524
1016
1050
42
1067
–
663
1600
1067
1100
44
1118
1120
694
1676
1118
1150
46
1168
–
726
1753
1168
1200
48
1220
1220
758
1829
1219

Weight of elbows

NPS
inches 		ELBOWS
LR 90° 		ELBOWS
SR 90°
Sch.
5S 		Sch.
10S 		Sch.
40S 		Sch.
80S 		Sch.
5S 		Sch.
10S 		Sch.
40S 		Sch.
80S
1/2 0.05 0.06 0.08 0.10 0.03 0.04 0.05 0.07
3/4 0.06 0.07 0.09 0.11 0.04 0.05 0.06 0.07
1 0.09 0.15 0.18 0.20 0.06 0.10 0.12 0.13
1 1/4 0.13 0.20 0.25 0.35 0.09 0.13 0.17 0.12
1 1/2 0.18 0.30 0.40 0.50 0.12 0.20 0.27 0.33
2 0.30 0.50 0.70 0.90 0.20 0.33 0.47 0.60
2 1/2 0.60 0.85 1.35 1.80 0.40 0.60 0.90 1.20
3 0.90 1.30 2.00 2.90 0.60 0.90 1.35 1.90
4 1.40 2.00 4.00 5.90 0.90 1.35 2.65 3.90
5 2.90 3.60 6.50 9.70 1.95 2.40 4.35 6.50
6 4.00 5.00 10.5 16.0 2.70 3.35 7.00 10.5
8 7.40 10.0 21.5 33.5 4.90 6.70 14.5 22.5
10 13.6 16.8 38.5 52.5 9.10 11.2 25.6 35.0
12 23.4 27.0 59.0 79.0 15.6 18.0 39.5 53.0
14 29.0 35.0 70.0 94.0 19.3 23.5 47.0 63.0
16 41.3 47.0 95.0 125 27.5 31.5 63.5 84.0
18 51.8 59.0 120 158 34.5 39.5 80.0 105
20 73.0 85.0 146 194 49.0 57.0 98.0 129
24 122 140 210 282 82.0 94.0 140 188
Approximate weights in kg, density 8 kg/dm3

Angularity Tolerances 

ND Max off angle Max off plane
Q P
1/2 a 4 1 2
5 a 8 2 4
10 a 12 3 5
14 a 16 3 7
18 a 24 4 10
26 a 30 5 10
32 a 42 5 13
44 a 48 5 20

Materials:

the material is selected accoding to the application use such as high temperature use,sanitary fitting,regular industrial use etc.

  • Carbon steel: ASTM A234 WPB, WPC, ASTM A420 WPL1, WPL3, WPL6, WPHY-42/46/52/56/60/65/70
  • Stainless steel: ASTM A403 WP304/304L, WP316/316/L, WP321, WP347 and WPS31254
  • Alloy steel: ASTM A234 WP1/WP12/WP11/WP22/WP5/WP7/WP9/WP91
  • Abrasion resistant material: Ceramic lined, Ceramic tile lined , Bi-metal clad pipe,
  • Manufacturing standards: ANSI, ISO, JIS and DIN.

Application of pipe elbows:

Petroleum, chemical, power, gas, metallurgy, shipbuilding, construction, etc.

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.

Seamless Steel Elbow VS Welded Steel Elbow

Comparison of seamless elbows and welded elbows

  1. Difference in appearance: The biggest difference between seamless elbows and welded elbows is the presence or absence of welds, but many weld elbows are now polished from the weld before leaving the factory, and many exporters sell such fake seamless elbows to customers. Even if the weld is polished, experienced customers can still distinguish it with the naked eye: the thickness of the seamless elbow is not uniform with respect to the thickness of the weld elbow. Currently, the false seamless elbow often appears in the area below the diameter DN600.
  2. Differences in molding process: The process of using seamless steel pipes and welded steel pipes is the same process. The difference is that the welding elbows are made of sheet steel, by bending and different welding processes.
  3. Differences in performance and usage: The seamless steel pipe elbow has better pressure bearing capacity and higher strength than the welded steel elbow. Therefore, it is widely used in high-voltage equipment, heat, boilers and other industries. Generally, the weld of the welded steel elbow is a weak point, and the quality affects the overall performance. In general, welded steel elbows can reduce working pressure by 20% compared to seamless steel elbows. This reliability is the main reason why people choose seamless steel elbows. In fact, all industrial pipes are finished with seamless pipe elbows because the elbows are subjected to extreme thermal, chemical and mechanical loads. In the aerospace, automotive and electronics industries with relatively low budgets, welding elbows are more popular, as are the working pressures on the pipeline.
  4. Differences in available sizes: For most seamless steel elbow manufacturers in China, they produce original seamless pipe elbows with a maximum outer diameter of 24 inches and 609.6 mm. In contrast, welded steel pipe elbows do not have these limitations and can range in size from 1-1 / 2 inch 48.3mm to 100 inch 2540mm.
  5. Different prices: Because the seamless manufacturing process is more complicated, the price is more expensive than the seamed elbow, and the seam is mainly made of steel plate (steel strip) for secondary welding, which is cheaper and more widely used.

Source: China Steel Elbows Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

If you want to have more information about the article or you want to share your opinion with us, contact us at sales@steeljrv.com

Please notice that you might be interested in the other technical articles we’ve published:

  • How to get high quality flanges

  • How to get high quality pipe fittings

  • How to get high quality pipe bend

  • How to Calculate a Pipe Bend

  • Stainless steel pipe bend

  • The production process of stainless steel pipe bend

  • Difference Between A Pipe Elbow And A Pipe Bend

  • What is a pipe elbow

  • How to get high quality pipe elbow

  • Use and maintenance of stainless steel elbows

References:

  • www.yaang.com

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