Small-diameter steel tube has to do three jobs well. It must hold its dimensions, seal under pressure, and resist corrosion. A
plain welded tube from a dependable Bundy tube supplier meets these needs in brake lines, air conditioners, refrigerators, heat exchangers and compressors.
PIPECW, operated by Zhangjiagang Chewit International Co., Ltd. in Jiangsu, China, supplies
plain welded Bundy tube to international buyers. This guide covers what the tube is, how it is made, which specifications we list, how the coatings differ, and what to check before you send an inquiry. Importers, distributors, OEM buyers and procurement teams can use it as a practical checklist when they compare a
Bundy tube manufacturer in China.
What Is a Plain Welded Tube? (Plain Welded Bundy Tube Explained)
A
plain welded tube is a small-diameter, low-carbon steel tube. The maker forms it from steel strip and joins the edges with a longitudinal weld. The result is a round tube with consistent dimensions and a reliable seal.
Our
plain welded Bundy tube focuses on structural stability and practical use. It suits general hydraulic circuits, and it works in hydraulic brake systems, AC units, refrigerators, heat exchangers and compressors.
Buyers use several names for this product family: Bundy tube, Bundy pipe, welded steel tube and precision steel tubing. These terms usually describe the same type of small fluid-line tube. PIPECW groups these items in its
Bundy Tube range, which also includes zinc coated and copper coated versions.
How Is a Plain Welded Tube Made? Forming, Welding and Surface Treatment
Production follows a clear sequence. Exact settings depend on your order, so send your drawing and ask our team to confirm the route.
• Strip selection: the maker chooses low-carbon steel strip that matches the target outside diameter and wall thickness.
• Forming: rollers shape the strip into a round tube.
• Welding: a precise welding process joins the seam. This step controls dimensional consistency and sealing performance.
• Sizing and cleaning: the tube is sized to tolerance, and the inside surface is cleaned to limit residue.
• Surface treatment: the tube receives copper plating or zinc coating, depending on the specification.
Why the process matters to buyers
Weld quality affects roundness, wall thickness and leak rate. A clean inside surface protects compressors, valves and refrigerant circuits from contamination. When you compare suppliers, ask how they control each step, not only the final product.
Plain Welded Tube Specifications: OD 4–8mm and Wall Thickness 0.5–0.65mm
The table below lists the sizes shown on our product page. Each size pairs an outside diameter (OD) with a wall thickness (WT).
| OD (mm) |
WT (mm) |
Zinc coating method |
| 4 |
0.5 |
Hot-dipped galvanizing |
| 4.76 |
0.6 |
Hot-dipped galvanizing |
| 4.76 |
0.65 |
Hot-dipped galvanizing |
| 6 |
0.6 |
Hot-dipped galvanizing |
| 6 |
0.65 |
Hot-dipped galvanizing |
| 8 |
0.6 |
Electro zinc coating |
Coating rule: tubes with an OD below 8mm use hot-dipped galvanizing. Tubes with an OD of 8mm or more use electro zinc coating (galvanizing).
Do you need another size? Send your drawing, quantity and application. Our team will check whether we can supply it.
Dimensional Tolerance of Plain Welded Tube: ±0.05mm on OD and Wall Thickness
Tight tolerance keeps assembly smooth. Our
plain welded tube lists the following dimensional tolerance:
• Outside diameter (OD): +0.05mm / -0.05mm
• Wall thickness (WT): +0.05mm / -0.05mm
Why does this matter? Fittings, flares, bends and brazed joints all depend on a tube that stays close to nominal size. Stable dimensions reduce rejects on your assembly line and help your engineers keep leak paths under control.
Buyer tip: request a sample and measure OD and WT with your own gauges before you place a bulk order.
Mechanical Properties: Tensile, Yield Strength and Elongation
Mechanical properties show how the tube behaves when you bend, flare or pressurize it. Our product page lists these minimum values:
• Tensile strength (Rm): ≥325 N/mm²
• Yield strength (Rel): ≥208 N/mm²
• Elongation (A): ≥42%
Tensile strength is the maximum stress the tube can carry before it breaks. Yield strength marks the point where permanent deformation begins. Elongation measures ductility, which matters when your process includes bending or flaring. Compare these numbers with your drawing or customer standard before you approve a sample.
Chemical Composition of Low-Carbon Plain Welded Tube (C, Mn, S, P)
Low carbon content supports good weldability and forming. Our
plain welded tube lists these chemical limits:
• Carbon (C): ≤0.11%
• Manganese (Mn): ≤0.15%
• Sulfur (S): ≤0.08%
• Phosphorus (P): ≤0.09%
Low sulfur and phosphorus help keep the steel tough and reduce the risk of brittle behavior. If your project requires a specific steel grade or standard, tell us early so we can confirm what we can supply.
Surface Treatment Options: Copper-Plated vs Zinc-Coated Plain Welded Tube
Our product page lists copper-plated, zinc-coated and “without smooth coating” surface options. If you need the last option, confirm the exact finish with our team before you order.
• Copper-plated: a clean, traditional finish for fluid and refrigeration lines. Our
Copper Coated Tube page gives more detail on this surface.
• Zinc-coated: adds corrosion protection for tubes exposed to moisture or harsher environments. Our
Zinc Coated Tube page gives more detail on this surface.
How do you choose? Start with the operating environment, your customer’s corrosion requirement and your cost target. Many buyers pick copper plating for refrigeration and AC circuits and pick zinc coating when corrosion protection matters more.
Hot-Dipped Galvanizing vs Electro Zinc Coating: Which One for Which OD?
The zinc coating method depends on the tube size, as shown on our product page:
• OD below 8mm (4mm, 4.76mm and 6mm): hot-dipped galvanizing
• OD of 8mm and above: electro zinc coating (electro-galvanizing)
Hot-dipped galvanizing applies zinc by dipping the tube in molten zinc. Electro zinc coating deposits a thin zinc layer with an electric current. The two methods give different coating appearance and thickness, so state your corrosion test requirement in your inquiry. For example, a 6mm tube and an 8mm tube in the same order may use different coating routes.
Sealing Performance: 1.6 MPa Nitrogen Airtight Test Without Leaking
Sealing performance is a key buying point for
plain welded tube. Our product page lists a seal airtight test at 1.6 MPa with nitrogen (N2), with no leaking.
Why does this test matter? A small leak can cause refrigerant loss in an AC unit or pressure loss in a hydraulic circuit. Nitrogen is dry and inert, so it tests the seam without adding moisture to the tube.
Buyer tip: ask whether test records can accompany your shipment, and tell us if your application needs a different test requirement.
Inside Surface Cleanliness: Residue Below 50mg/m²
Inside surface cleanliness protects the rest of your system. Our product page lists soluble and insoluble residue below 50mg/m².
Residue inside a tube can contaminate compressor oil, block narrow passages or damage valves. Clean tube is especially important in refrigeration and AC circuits, where moisture and debris cause failures. If your customer sets a stricter cleanliness limit, share it with us before production.
Advantages of Plain Welded Bundy Tube for Stable, Reliable Fluid Systems
A
plain welded Bundy tube gives buyers a balanced mix of performance and practicality. The main advantages are:
• Structural stability from quality base material and precise welding
• Consistent dimensions, with ±0.05mm tolerance on OD and WT
• Reliable sealing, backed by a 1.6 MPa nitrogen airtight test
• A clean inside surface, with residue below 50mg/m²
• Coating choice: copper-plated or zinc-coated, as listed
• A compact size range, from 4mm to 8mm OD, for tight assemblies
• One source for plain, zinc coated and copper coated Bundy tube
These points help procurement teams reduce rework and simplify supplier management.
Applications: Hydraulic Brake Systems, AC, Refrigerators, Heat Exchangers and Compressors
Our product page lists these main uses for
plain welded tube.
Hydraulic brake systems
Brake lines need a tube that holds its shape, seals well and resists corrosion. Check your brake standard and coating requirement before you select a specification. For related automotive fluid lines, you can also browse our
Automotive Steel Tube range.
Air conditioners and refrigerators
Refrigerant circuits need clean, leak-free tube. Sealing data and inside cleanliness matter most in these assemblies.
Heat exchangers and compressors
These systems use small-diameter tube for fluid and gas lines. Stable dimensions help assembly teams fit tubes into compact layouts.
General hydraulic circuits
The tube also suits general hydraulic circuits that need a small OD and a thin wall.
Plain Welded Tube vs Double-Wall Bundy Tube: Key Differences
Buyers often ask how a plain welded tube differs from classic double-wall Bundy tube. Industry sources describe classic Bundy tube as a double-wall, copper-brazed steel tube made from a strip that is rolled through two turns. A plain welded tube uses a single wall with one welded seam.
• Construction: double-wall tube has two layers brazed together. Plain welded tube has one wall and one welded seam.
• Production: single-wall tube is generally simpler to produce, which can help with cost and lead time.
• Selection: your drawing, working pressure and customer standard should decide the wall construction.
Tell us your working pressure and standard when you inquire. If your project needs double-wall construction, say so in your message so we can confirm what we can supply.
Why Choose PIPECW as Your Plain Welded Tube Manufacturer in China
Choosing a
Bundy tube manufacturer in China is a risk decision. Here is what you can verify about PIPECW:
• Company: Zhangjiagang Chewit International Co., Ltd., based in Jingang Town, Zhangjiagang City, Jiangsu Province, China.
• Experience: a supplier of precision steel tubes, forging and aluminum products with more than a decade of history.
• Range: carbon, alloy and stainless steel tube, hydraulic tube, automotive steel tube, aluminum products and forging parts, so you can consolidate sourcing.
• Product data: size list, tolerance, mechanical properties, chemical limits, seal test and cleanliness limit appear on the product page.
• Language support: the website offers many language versions for international buyers.
Supplier selection tips for buyers
• Send a drawing and ask for a technical review before you request a price.
• Order a sample and test OD, WT, sealing and coating on your own line.
• Compare listed data, such as tolerance and cleanliness limits, line by line.
• Confirm packaging and shipping terms for your destination.
• Judge response speed and clarity. They predict how the supplier will handle your repeat orders.
How to Order Plain Welded Tube from PIPECW: Inquiry, Samples, Packaging and Delivery
The ordering process is simple. Follow these steps:
1. Send your requirements: OD, WT, length, coating, quantity, application and any standard.
2. Technical review: our team checks your drawing and confirms the coating route by OD.
3. Quotation: you receive a quote based on your specification.
4. Samples: ask our team about sample availability before bulk production.
5. Production and inspection: the tube is made and checked against the agreed specification.
6. Packaging and delivery: share your destination so we can discuss packing and shipping options.
MOQ, lead time and packing details depend on size, coating and destination. Contact our team with your requirement to get exact terms. We welcome inquiries from importers, distributors, OEM and ODM buyers, and procurement teams in North America, Europe, the Middle East, Asia-Pacific, South America and Africa.
FAQ: Plain Welded Tube Questions from Buyers
What is a plain welded tube?
A plain welded tube is a small-diameter, low-carbon steel tube formed from strip and joined with a longitudinal weld. It is used for fluid lines in brake systems, AC units, refrigerators, heat exchangers and compressors.
What sizes of plain welded tube does PIPECW list?
The product page lists OD from 4mm to 8mm and wall thickness from 0.5mm to 0.65mm. Examples include 4 x 0.5mm, 4.76 x 0.6mm, 6 x 0.65mm and 8 x 0.6mm. Send your drawing if you need another size.
Which zinc coating method applies to which OD?
Tubes with an OD below 8mm use hot-dipped galvanizing. Tubes with an OD of 8mm or more use electro zinc coating.
What tolerance and sealing data can I expect?
The listed tolerance is +0.05mm / -0.05mm on both OD and wall thickness. The seal airtight test uses 1.6 MPa nitrogen with no leaking. Inside surface residue is below 50mg/m².
What mechanical properties does the tube have?
The listed minimum values are tensile strength 270 N/mm², yield strength 180 N/mm² and elongation 14%. The chemical limits are C ≤0.11%, Mn ≤0.4%, S ≤0.03% and P ≤0.03%.
How do I request a quotation or sample?
Email sale@chewit.cn or send a WhatsApp message to +86 18962244644. Include your OD, WT, length, coating, quantity and application, and our team will reply with details.
Conclusion: Get Your Plain Welded Tube Quotation from PIPECW
A
plain welded tube works best when its size, coating and test data match your application. PIPECW lists clear specifications for OD 4–8mm, ±0.05mm tolerance, a 1.6 MPa nitrogen seal test and a clean inside surface, so your engineers can review the facts before they order.
If you are comparing a
Bundy tube manufacturer in China, send us your drawing. Our team can help with product details, quotation, customization, samples and technical support.
Email: sale@chewit.cn | WhatsApp: +86 18962244644
+86 18962244644
SHUANGSHAN ROAD, JINGANG TOWN, ZHANGJIAGANG CITY, JIANGSU PROVINCE, CHINA
sale@chewit.cn
