Your excellent high frequency welded finned tubes choice for heat exchange.
Murphy Finned tubes supplies the excellent quality welded finned tubes to main markets in the worldwide. The advanced manufacturing facility, with our state-of-the-art high frequency resistance welding machines, enable us to provide professional and excellent products to fulfill the request of worldwide customer. We’re pursing the excellent quality, fast delivery, good after service and consistent technology development. The good satisfaction of customer is our goal of work. We believe we’re the best one in the market and qualified to be your good provider for heat exchange solution.

With more than 30 years in the business, we’re professional and reliable supplier & manufacturer of high frequency welded Finned tubes in the market.

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Murphy high frequency welded finned tubes, is a main welded type welded finned tubes which designed and manufactured by Murphy finned tubes.

It’s an excellent choice to provide good efficiency in heat recovery associated with boilers for power generation and in furnace applications for the petrochemical industry.

High Frequency Welded Finned Tubes (WFH)

High Frequency Welded fin tube also called solid type fin tube, use steel or stainless steel strip directly welded to tube surface by HFW. Can improving heat transfer efficiency much more than bare tube. Due to the tight welding of the fins to the base tube, these finned tubes are often used in vibrating conditions. Fin type have Serrated fin and flat fin.

High frequency welded finned tube technical parameters

The high-frequency welded finned tube is aimed at the shortcomings of the radiator made of serial and wound fins, and an efficient heat dissipation element using high-frequency welded finned tubes is improved. The thickness of the finned tube itself is 0.8 The -1mm strip steel is wound on the finned tube, and the high-frequency welding process is adopted to weld the sheet firmly on the tube to ensure the bonding strength between the tube and the fin, and the metal thermal strength has reached 1.10 ~ 1.20w/kg ℃ , The finned tube is widely used in boiler economizer, air preheater production and workshop, residential energy-saving radiator production, and as the first choice for heat pipe winding.

Spiral finned tubes are a highly efficient heat transfer element. Its heat transfer area is several times to dozens of times that of the light pipe, which can enhance heat transfer, reduce flow resistance, and reduce metal consumption, thereby improving the economy and operational reliability of heat exchange equipment. At present, spiral finned tubes have been widely used in various boilers.

 

Spiral Finned Tube SPEC Unit: mm
Tube O.D 25-159
Tube thickness 2-8
Fin thickness 0.8-2
Fin height 10-30
Fin spacing 5-20
Fin tube length ≤10000

Note:

1 Specifications other than this table can be agreed upon by the purchaser

2 The fin height h is generally ≤1/2d

3 The spiral finned tubes produced by our factory are manufactured according to JB/T6512-92 DG1020-97 and other standards.

Spiral finned tube product specification and parameter table

Steel Tube Band steel Steel pipe wrapping per meter Fin tube per meter heat exchange area (m2
Size Weight

(kg/m)

 Spacing

(mm)

SPEC

(mm)

Weight

(kg/m)

Length

(m)

Weight

(kg)

25×3 1.63 5 1.2×15 0.141 25.15 3.55 0.833
25×3 1.63 6 1.2×15 0.141 20.94 2.96 0.707
25×3 1.63 7 1.2×18 0.169 19.30 3.28 0.773
25×3 1.63 8 1.2×20 0.188 17.70 3.33 0.787
32×3 2.15 6 1.2×15 0.141 24.61 3.48 0.839
32×3 2.15 7 1.2×17 0.160 21.99 3.52 0.848
32×3 2.15 8 1.2×20 0.188 20.42 3.85 0.917
32×3 2.15 10 1.2×22 0.207 16.69 3.51 0.847
38×3.5 2.98 7 1.2×20 0.188 26.05 4.91 1.161
38×3.5 2.98 8 1.2×20 0.188 22.80 4.30 1.031
38×3.5 2.98 10 1.2×20 0.188 18.25 3.44 0.849
42×3.5 3.32 7 1.2×20 0.188 27.84 5.25 1.246
42×3.5 3.32 8 2×10 0.157 20.44 3.21 0.540
42×3.5 2.32 10 1.2×20 0.188 19.50 3.67 0.912
48×3.5 3.84 7 1.2×17 0.160 29.19 4.67 1.143
48×3.5 3.84 8 1.2×17 0.160 25.55 4.09 1.019
48×3.5 3.84 10 1.2×20 0.188 21.39 4.03 1.006
51×3.5 4.10 8 1.2×17 0.160 26.72 4.28 1.069
51×3.5 4.10 10 1.2×17 0.160 21.39 3.43 0.887
51×3.5 4.10 12 1.2×20 0.188 18.61 3.51 0.905
57×3.5 4.62 8 1.2×20 0.188 30.25 5.70 1.389
57×3.5 4.62 10 1.2×20 0.188 24.21 4.56 1.147
57×3.5 4.62 12 1.2×20 0.188 20.18 3.80 0.986
60×3.5 4.88 10 1.2×20 0.188 25.15 4.74 1.194
60×3.5 4.88 12 2×20 0.314 20.97 6.58 1.027
70×3.5 5.74 10 1.6×20 0.251 28.29 7.11 1.352
70×3.5 5.74 12 2×20 0.314 23.58 7.40 1.163
76×4.0 7.10 10 1.6×20 0.251 30.18 7.58 1.446
76×4.0 7.10 12 2×20 0.314 25.15 7.90 1.245
83×5.0 9.62 10 1.6×20 0.251 32.27 8.13 1.556
83×5.0 9.62 12 2×20 0.314 26.97 8.47 1.340
89×5.0 10.38 10 1.6×20 0.251 34.26 8.51 1.650
89×5.0 10.38 12 2×20 0.314 28.55 8.96 1.422
108×5.0 12.70 10 1.6×20 0.251 40.22 10.01 1.948
108×5.0 12.70 12 2×20 0.314 33.53 10.63 1.680
133×5.0 15.75 10 1.6×20 0.251 48.08 12.08 2.341
133×5.0 15.75 12 2×20 0.314 40.07 12.58 2.021
Material: ordinary carbon steel, stainless steel, corrosion-resistant steel

Base pipe: seamless steel pipe, high frequency electric welded steel pipe

Technical specification for high frequency resistance welded finned tubes

High frequency resistance welded spiral fin tubes

  1. Scope

This standard specifies the requirements and regulations for the material, manufacture, inspection, marking and packaging of high frequency resistance welded spiral finned tubes.

This standard applies to spiral wound finned tubes manufactured by high frequency resistance welding in boilers and pressure vessels.

  1. Reference standards

The following standards contain provisions which, through reference in this standard, constitute provisions of this standard. At the time of publication of the standard, the edition to which it belongs was valid. All standards are subject to revision and parties using this standard should explore the possibility of using the latest edition of the following standards.

GB/T716 Carbon structural steel cold rolled strip

GB/T3522 High-quality carbon structural steel cold-rolled strip

GB4239 Stainless Steel and Heat Resistant Steel Cold Rolled Strip

GB/T11253 Carbon structural steel cold-rolled sheet and strip

GB9948 Seamless steel pipes for petroleum cracking

GB3087 Seamless steel tubes for low and medium pressure boilers

GB5310 Seamless steel pipe for high pressure

GB/T8163 Seamless steel pipes for conveying fluids

GB13296 Stainless steel seamless steel pipes for boilers and heat exchangers

GB/T14976 Stainless steel seamless steel pipe for fluid transportation

GB150 Steel Pressure Vessel

GB151 Shell and Tube Heat Exchanger

Pressure Vessel Safety Technology Supervision Regulations Issued by the former National Bureau of Quality and Technical Supervision

  1. Materials

3.1 The steel strips used for finned tubes shall comply with relevant standards (GB716, GB3522, GB/T11253, GB4239); T14976) and the material, and the elongation of the material should not be less than 30%. The surface of the steel strip should be bright, without wrinkle marks, and there should be no obvious burrs, gaps and other defects on the edge. The thickness deviation of the steel strip shall comply with the provisions of Table 1.

Materials (including welding consumables) entering the factory shall be inspected in accordance with the relevant provisions of JB/T3375. When using foreign materials, it shall comply with the relevant provisions of relevant national regulations and standards. When the steel pipe for manufacturing finned tubes is selected from materials outside the scope of GB9948, it shall comply with the provisions of the design documents. Substitute materials shall be handled in accordance with relevant regulations.

Table 1 Thickness deviation of steel strip

Steel strip thickness (unit mm) Thickness deviation (unit mm)

0.8-1 ±0.05

>1-1.6 ±0.10

>1.6-2 ±0.15

>2-2.5 ±0.17

>2.5-3.5 ±0.20

 

3.2 The steel pipe and fin material shall have the ex-factory quality certificate. Re-examination should be performed in any of the following situations:

(1) The content or items of the quality certificate are incomplete;

(2) The manufacturing unit has doubts about the quality of the material;

(3) The user requires additional inspection items;

⑷ When specified in the design documents.

All re-inspection results shall comply with the provisions of relevant standards and design documents before they can be used.

3.3 The written consent of the design unit should be obtained when the substitute materials are used.

4 Manufacturing

4.1 Preparation before manufacture

4.1.1 Blanking

Cut the seamless steel pipe to the required length according to the requirements of the drawing, and use the polishing machine to derust the pipe. The surface of the pipe should be thoroughly cleaned of rust, oxide scale, grease, and other defects that affect the welding quality. Alloy steel pipes should be subjected to spectral analysis one by one and marked. The straightness of the pipe should meet the maximum deviation of 2mm per 3m section, and the maximum deviation of the entire pipe length is 4mm.

The connection between the steel strip and the steel strip shall be butt weld, the surface of the weld shall be ground after welding, and there shall be no defects affecting the quality of the weld after visual inspection. The width dimension deviation of the processed steel strip should not be greater than 0.3mm. The weld surface of the base pipe and the steel strip shall be free of defects and impurities that affect the quality such as coating, rust, pits, etc.

The base pipe should avoid splicing as much as possible. If splicing is required, the following requirements should be met:

(1) The shortest pipe length for splicing shall not be less than 2m;

(2) The splicing of the base pipes of each tube bundle should be in the same position, and the fins should be blocked by baffles to avoid air leakage;

(3) Other requirements for base pipe splicing of finned tubes used in shell and tube heat exchangers shall comply with the provisions of Article 6.3.3 of GB151.

(4) The base pipe splicing of finned tubes used in steel pressure vessels shall meet the requirements of GB150. When the base pipe length is not more than 12m, splicing is generally not allowed; if the base pipe length is more than 12m, splicing is allowed, and there are no more than 2 welded joints. When the base pipe length of the finned tube used in the boiler is not more than 7m, splicing is generally not allowed; when it is greater than 7m, one splicing weld is allowed. The requirements for the butt joint of the pipe shall comply with the provisions of JB/T1611, the butt weld shall be ground to be flush with the pipe, and 100% radiographic inspection shall be carried out, and it shall be qualified according to the provisions of JB/T4730.2 Class II.

4.1.2 Machine debugging before welding

(1) Preheat high-frequency heating equipment

Start the GP.200 high-frequency induction heating equipment, turn on the cooling water source and preheat the filament according to the operating procedures of the GP.200 high-frequency induction heating equipment.

(2) Adjust the welding machine

①Install the seamless steel pipe on the welding machine, insert the steel strip into the guide wheel, the high-frequency electrodes are in contact with the steel pipe and the steel strip respectively, and connect to the cooling water source.

②The steel strip and the steel pipe are positioned and fixed by arc welding.

4.2 High frequency welding

4.2.1 The welding of finned tubes shall be subject to the process qualification of high-frequency resistance welding, and can be put into production only after passing the test.

4.2.2 The welding between the steel strip and the tube of the finned tube shall be good, and the fusion thickness of the welding seam shall be greater than or equal to 90%. The length of the welded seam between the steel strip of the finned tube and the tube should be greater than or equal to 95%.

4.2.3 Finned tube There should be no unfused phenomenon within the range of 150mm from the start and end of the fin (excluding the part of the bare tube). And the starting end and the terminal can not be fixed by manual arc welding (NB/T47030 regulations, HG/T3181 regulations can be fixed by arc welding). When the non-continuous welding length of the heating wire is larger than the diameter or larger than 50mm, there are more than 2 local unfused parts of the finned tube per meter, and the defect spacing is less than 300mm, repair welding should be used to improve the welding rate. Repair welding finned tubes should be hydrostatically tested.

4.2.4 During the winding process of the finned tube, the welding seam at the joints of the steel strips (including the broken steel) is not fused. , The splicing length of the steel strip should be greater than the long winding length of the 300mm steel pipe, and it is also necessary to ensure that the surface of the pipe at the joint of the steel strip is free from any traces and defects caused by arcs.

4.2.5 The steel strips at the beginning and end of the fins of the finned tubes shall be mechanically removed along the radial direction of the finned tubes, and the sharp corners of the ends shall be removed.

4.2.6 The post-weld heat treatment shall meet the following requirements:

(1) Heat treatment is generally not required after welding of finned tubes made of carbon steel, stainless steel and low alloy steel;

(2) The finned tube of Cr-Mo alloy steel (Cr≥1.25%, and Mo≥0.65%) should be heat treated if it meets one of the following conditions after welding:

①, the nominal diameter of the pipe is greater than DN100;

②, the upper limit of carbon content of the material is greater than 0.15%;

③ The thickness of the welded finned tube is greater than 3mm.

For the above finned tubes that need heat treatment, if the manufacturer has verified that the heat affected zone of the tube welding is beyond the minimum required thickness of the tube wall, the finned tube may not be heat treated.

4.3 Dimensional deviation

4.3.1 Dimensional deviation shall meet the following requirements:

(1) The fins should be spirally wound on the steel pipe, the fins should be perpendicular to the surface of the steel pipe, and the allowable deviation of the perpendicularity is 5°.

(2) The average pitch deviation of the fins within 10 pitches should not be greater than ±0.5mm, the total deviation of the full length of the finned part of the finned tube should not be greater than ±10 mm, and the deviation of the total number of fins should be Not more than ±1.5%.

(3) The deviation of the height of the fins should be no more than ±0.5 mm, and the deviation of the thickness of the fins should be no more than ±0.1 mm.

(4) The height of the frills on both sides of the fin should not be greater than the thickness of the fin. The thickness of the welding flash of the fin should be less than the width of the fin, and the height should be less than 0.3mm. The allowable deviation of the straightness of the finned tube is 0.1% of its length, and shall not exceed 8mm.

(5) The length deviation of each finned tube should not be greater than ±2.0 mm. Except for stainless steel, anti-rust oil should be applied to the welding grooves at both ends of the steel pipe. In addition to stainless steel, the outer surfaces of steel pipes and fins should be coated with anti-rust paint.

See the figure below for details.

5 Inspection

5.1 10% (but not less than 1) finned tubes from each batch shall be selected for inspection according to the provisions of Article 4.3 of this standard. Each batch shall consist of finned tubes of the same material, the same specification, and the same manufacturing process, and the finned tubes manufactured within 6 months are one batch. When unqualified, in addition to picking out the unqualified, double samples should be taken from the same batch for re-inspection. If the re-inspection results are still unqualified, the batch of finned tubes is unqualified.

5.2 Articles 4.11 and 4.12 should be checked root by root.

5.3 The finned tubes shall be inspected by scratching sound one by one. The method is to gently scrape the fins on the outer ring of the fins along the length of the finned tube with a thin steel sheet with a thickness of 1 to 2 mm, such as sound.

The frequency is high and crisp, and the sound is consistent, indicating that the weld quality is good. If the sound is hoarse, the quality of the weld is poor and should be inspected in accordance with the provisions of Article 4.4 of this standard. When the defects exceed the requirements of Article 4.4, repair welding shall be carried out by qualified welders.

5.4 The peeling inspection shall be carried out according to the following provisions:

When making finned tubes, for the finned tubes used as samples, 2 to 3 more fins should be welded at either end for stripping. When each batch is 10 or less, take 2, when 10-30, take 3, when 30-50, take 4, when more than 50, take 10%, and peel it to check the welding seam rate. The welded section is silver-white and has peeling marks. The ratio of the welded cross-sectional area of ​​the stripped fin to the total area of ​​the stripped fin cross-section is the welding ratio of the fin to the steel pipe. It is qualified when the welding rate meets the requirements of Article 4.1. When unqualified, in addition to picking out the unqualified, double samples should be taken from the same batch for re-inspection. If the re-inspection results are still unqualified, the batch of finned tubes is unqualified.

5.5 According to the provisions of GB9948 “Seamless Steel Pipes for Petroleum Cracking”, the finned tubes shall be subjected to hydraulic test one by one. The water pressure test pressure of low carbon steel, alloy steel and stainless steel finned tubes is 2 times of the design pressure or customer requirements, and the holding time is 5min.

6 Logo and Packaging

6.1 The bare tube part at the end of each finned tube must be stamped with the stamp of the steel tube material. For alloy steel, heat-resistant steel and stainless steel pipe, rounded steel stamp should be used. Imprints should be clear, and the depth should not exceed 0.3mm.

6.2 The finned tubes should be packed in groups when delivered. Each group of finned tubes is fixed separately with a fixing frame, and any two finned tubes shall not touch each other. The fixing frame should be firm during hoisting and transportation.

6.3 When packing in groups, each group of finned tubes should be marked with a label or nameplate. The content of the label or nameplate should include the steel pipe material grade, steel pipe specification, the full length of the steel pipe and the fin material grade.

Example 1 1Cr5Mo steel pipe, specification Ø127×8, total length 5.1m, fin material Q235B.

The mark is: “Finned Tube – 1Cr5MoØ127×8 – 5100 – Q235B”

Example 2 1Cr19Ni9 steel pipe, specification Ø152×8, total length 4.2m, fin material 1Cr19Ni9.

The mark is: “Finned tube – 1Cr19Ni9Ø152×8 – 4200 –1Cr19Ni9”

6.4 The nozzles at both ends of the finned tube should be protected by plastic caps.

6.5 The product should have a product quality certificate, which should include:

a), the name of the manufacturer and the date of manufacture;

b), product name and specifications;

c), material re-inspection report;

d), the test results.

The quality certificate shall have the official seal of the quality inspection department and the signature of the inspector, and indicate the inspection date.

6.6 The product delivery note should include the following:

a), the name of the manufacturer;

b), product name, specification, quantity, net weight, gross weight;

c), the name of the attached document and the number of copies;

d), ordering unit and contract number;

e), the date of manufacture.

Analysis of High Frequency Welded Finned Tubes

Abstract: The welding process of SA335P91 steel pipe and 0Cr13 steel strip spiral finned pipe is proved through the inspection of metallographic, hardness, welding rate and welding strength of finned tubes, as well as simulated working condition treatment test, impact test and hydraulic test. It is reliable, and this type of finned tube does not need heat treatment after welding.

Key words: high frequency welding; welding process; inspection; analysis

High-frequency welded spiral finned tube (hereinafter referred to as finned tube) is a high-efficiency welding method for connecting pipes and profiles developed in the early 1950s. It gradually developed and matured in the 1970s and 1980s. a welding method. Due to the larger heat transfer area of ​​finned tubes, higher heat transfer efficiency and lower pressure drop, in gas furnaces and oil-gas mixture heating furnaces, the comprehensive heat exchange performance is obviously better than that of ordinary heat exchange of the same specification and material. Tube, nail head tube. All kinds of heat exchange equipment with it as the core component are more and more widely used in electric power, fertilizer, chemical industry and oil refining equipment.

Since the early 1980s, Maoming Petrochemical Machinery Factory has developed and produced finned tubes. With the continuous improvement of finned tube production technology and production equipment technology, more and more types of finned tubes are produced. No matter in terms of product type, quality, or production capacity, it has reached the domestic leading level. At the same time, important quality indicators such as tensile strength and welding rate of welded joints have reached or exceeded the domestic “Technical Conditions for High-Frequency Resistance Welded Spiral Finned Tubes” and the professional standards of foreign countries (API standards), and have become the leading domestic manufacturer of this type of equipment. Manufacturing base.

In the production process, various types of finned tubes are inspected and tested accordingly. In this paper, through the inspection of the welding quality of SA335 P91 heat-resistant steel pipe and 0Cr13 steel strip, which is difficult to weld in finned tubes, the welding process is analyzed, in order to better develop and popularize such products.

1.Analysis of welding process performance

1.1 Basic principles

The finned tube is a steel strip wound at a certain pitch on the outer circle of the seamless steel pipe (the steel strip is perpendicular to the surface of the outer circle of the steel pipe), and the high-frequency current is used as the welding heat source, and the skin effect and electrothermal effect of the high-frequency current are used. The contact surface between the steel pipe and the steel strip and the area to be welded are heated locally to make the contact surface reach a plastic weldable state. out, so that the solid-state atomic bonding between the steel pipe and the fin material is achieved, so as to realize the plastic welding of the contact surface, as shown in Figure 1.

1.2 Weldability of SA335 P91 heat-resistant steel pipe and 0Cr13 steel strip

1.2.1 The material condition of the base metal is shown in Table 1.

1.4.2 Welding performance analysis of base metal of pipe and strip

P91 belongs to the heat-resistant steel grade in the ASME standard, which is equivalent to the domestic 9Cr1Mo steel. Due to its high alloy content, its microstructure is martensite, which has quite high air brittleness characteristics, and the supply state is normalized. In welding methods such as electrode arc welding and argon arc welding, pre-weld preheating and post-weld heat treatment are essential.

0Cr13 steel strip belongs to ferritic-martensitic stainless steel. When this type of steel is in the (α+γ) region at high temperature, when it is rapidly cooled, γ can be transformed into M (martensite), and ferrite-martensite at room temperature. Structure, because some γ is transformed into M, this type of steel has partial heat treatment strengthening effect. In general welding, welding of this type of steel has a tendency to harden cracks. When the heating time in the two-phase region is too long, the ferrite tends to grow up, which aggravates the destructive effect of welding stress on the weld.

However, in the high-frequency welding of finned tubes, due to the high concentration of the electrothermal effect of the high-frequency current during the welding process, the current penetration depth and affected area are very small, only within a narrow range of 2~3mm wide and 0.2~0.4mm deep. , the phase transition of the heat affected zone occurs, and due to the heating and heat conduction caused by the proximity effect and the electrothermal effect, the heating, heating and cooling processes continue for a certain period of time within the range of 20~50mm before and 80~120mm of the welding point on the tube. It plays the role of preheating before welding and tempering after welding, which can eliminate the tendency of hardening cracks, which can be proved in the subsequent metallographic analysis and hardness inspection.

In addition, because high-frequency welding has the characteristics of fast welding speed, short heating process, small melting amount of base metal, and basically all molten metal is expelled, the heat-affected zone is quite narrow, and it is mainly combined by atomic force, so due to material reasons The adverse effect on the base metal is relatively small. The test proved to be negligible.

2 Process evaluation

2.1 Preparation and welding of specimens

2.1.1 Preparation of welding treatment, upset wheel and electrode

Sand the pipe material to eliminate oil stains, rust, and dirt, and there should be no obvious pits; the steel width is 17.5mm to ensure that the edges are neat and free of burrs, pits, curling and pulling cracks. The preparation of the upsetting wheel should ensure that the clamping of the steel strip is uniform and moderate in the circumferential direction (about 0.1~0.2mm margin), and the inner parts rotate relatively easily. The welding between the electrode body and the contact is firm and reliable, the cooling is smooth, and there is no leakage.

2.1.2 Welding parameters (Table 2)

 

 

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