C70600 Tube Seamless or Welded A Complete Comparison

For most heat exchanger and condenser applications, seamless C70600 tube is the standard. It has no weld seam, so there is no risk of weld corrosion or weld failure. Welded C70600 tube is available, but it is less common. Some buyers use welded tube for non‑critical applications to save cost. Others refuse to use welded tube at all. Here is what you need to know to make your own decision.

Seamless process：

Cast solid billet (copper + nickel + iron)

Heat billet to extrusion temperature

Punch a hole through the billet (extrusion press)

Roll and draw to final size

Anneal to soften

No seam. No weld.

Welded process：

Cast a flat strip (same alloy)

Roll the strip into a tube shape

Weld the seam (usually TIG, no filler metal)

Cold draw the welded tube to final size

Anneal to soften

The weld seam is still there, but work‑hardened and heat‑treated

Why the weld seam can corrode faster：

The weld zone may have different grain structure

Welding can change local chemistry (nickel or iron may segregate)

Any defect in the weld is a place for corrosion to start

How we reduce weld seam risk：

Use same alloy for strip and filler (no filler actually, auto TIG)

Cold draw the tube after welding (work hardens the seam)

Anneal after drawing (recrystallizes the weld zone)

What ASTM B111 says：

Seamless and welded tubes are both allowed

Welded tubes must pass the same flattening and flare tests

In flattening, the weld seam must be placed 90° from the flattening direction

This tests the weld seam in tension, not compression

Real world experience：

Some users report welded tubes failing at the seam during flaring

Others have used welded tubes for years with no issues

The difference is quality of manufacturing

Welded tube is not common in seawater heat exchangers, but it does find some uses.

Applications where welded tube is used：

Low pressure, non‑critical cooling water lines

Drain lines and overflow pipes

Temporary or short‑life equipment

Fresh water heat exchangers (not seawater)

Some industrial coolers where failure is not critical

Applications where welded tube is NOT recommended：

Main condensers in power plants

Shipboard seawater heat exchangers

Offshore platform critical coolers

Any application where a leak means shutdown

High pressure or high temperature service

Why welded is cheaper：

Extruding a seamless shell is energy intensive

Rolling strip and welding is faster

Less scrap in welded process

But remember： the price difference is not huge. A 10-20% saving on tube cost is real money. But if a welded tube fails and shuts down your heat exchanger, that saving disappears fast.

Yes, ASTM B111 covers both seamless and welded tube. But most buyers specify seamless.

What ASTM B111 says：

Section 1： "This specification covers seamless and welded tube"

The same mechanical and dimensional requirements apply

Welded tube must pass the same tests as seamless

There is a separate supplement for welded tube (S4)

Why seamless is still the default：

Most mills produce seamless C70600 as their standard product

Welded C70600 is a special order for many mills

Engineers are used to specifying seamless

No one ever got fired for specifying seamless

If you want welded tube, write this on your PO：

"ASTM B111 C70600 welded tube"

Plus any weld seam testing requirements (radiograph, etc.)

Q1： Which is better for heat exchanger tubes, seamless or welded C70600?

Seamless is better for critical seawater heat exchangers. No weld seam means no seam corrosion risk. Welded tube can work for low pressure, non‑critical applications. But most engineers specify seamless for condensers and marine coolers. The small cost saving of welded is not worth the risk.

Q2： Can welded C70600 tube be used in seawater?

Yes, but with caution. The weld seam can corrode faster than the base metal in some conditions. Properly made welded tube with post‑weld drawing and annealing performs well. But seamless has no seam to worry about. For long life and reliability, seamless is the safer choice.

Q3： Is welded C70600 tube cheaper than seamless?

Yes, welded tube is typically 10-20% cheaper than seamless. The manufacturing process is faster and uses less energy. But the price difference is not huge. For a large heat exchanger bundle, the saving might be thousands of dollars. For a small one, hundreds.

Q4： Does ASTM B111 allow welded tube?

Yes, ASTM B111 covers both seamless and welded tube. But most buyers specify seamless. The standard has the same mechanical and dimensional requirements for both. If you want welded tube, write "welded" on your purchase order. If you write nothing, the mill will send seamless.

Q5： How can I tell if a tube is seamless or welded?

Look inside the tube. Seamless has no line. Welded has a thin line where the seam was welded. On larger tubes, you can see the seam from the outside too. On small diameters, look inside with a light. If you see a raised line or a color difference, it is welded. If the inside is smooth all around, it is seamless.

Q6： Does the weld seam on C70600 tube corrode faster than the base metal?

In properly made welded tube, the seam should perform nearly the same as the base metal. But in poorly made tube, the weld zone can have different grain structure or chemistry. That can lead to preferential weld attack. Seamless tube has no weld zone, so this risk is zero.

Q7： Can I flare welded C70600 tube without cracking the seam?

Yes, if the tube is well made. But the seam is the weak point during flaring. Place the weld seam 90° from the flaring direction if you are worried. Some users report welded tubes cracking at the seam during flaring. Others have no problem. The difference is tube quality.

Q8： Is welded tube available in all sizes like seamless?

No, welded tube is less common in small diameters (under 1/2") and very thin walls (under BWG 20). Most welded C70600 tube is made in larger diameters (1" and up) and medium walls. If you need a small OD or very thin wall, seamless is probably your only option.

Q9： Which tube has better fatigue resistance for vibrating heat exchangers?

Seamless has better fatigue resistance because it has no seam where cracks can start. In a vibrating heat exchanger (e.g., on a ship), the tube flexes repeatedly. The weld seam is a stress riser. Over time, a crack can start at the seam. Seamless tube has no such weak point.

Q10： Do shipyards use welded C70600 tube on new vessels?

Most shipyards specify seamless for seawater systems. Some will accept welded for non‑critical drain lines or low pressure service. But for main seawater cooling, fire main, and heat exchangers, seamless is the standard. Check your vessel's specification.

Q11： Can I weld a fitting onto a welded C70600 tube without damaging the seam?

Yes, but keep heat input low. The existing weld seam can be affected by the heat from the new weld. Place the new weld away from the existing seam if possible. Use a low heat input procedure. Annealed tube is more forgiving than hard drawn.

Q12： Which tube do most mills stock for quick delivery?

Seamless. Most mills make seamless C70600 tube as their standard product. Welded C70600 is a special order for many mills. If you need tubes fast, seamless is easier to find. If you want welded, expect longer lead times.

We start with chemistry. A spectrometer checks nickel (9-11%) and iron (1.0-1.8%). If it fails, the whole melt is scrapped.

Next, mechanical. We pull a tube until it breaks. Must hit 310 MPa. We also flatten a ring and flare a sample. No cracks. No splits.

Then eddy current. Every single tube gets probed. Any signal above the limit = reject.

You get a Mill Test Report with every order. Heat number on every tube. Third party inspection available if you want it.

Plastic caps on both ends. VCI paper between layers. Shrink wrap around each bundle. Steel straps to hold it tight.

Wooden case for small or fragile tubes. Steel on pallet for standard 6m lengths.

Waterproof label shows grade, size, heat number, quantity.

We melt, cast, extrude, draw, anneal, straighten, and test. All in one plant.

Three furnaces melt the alloy. Two casters make solid billet. Two extrusion presses punch holes through the billet. Four pilger mills reduce diameter. Eight drawing benches hit the final size. Four annealers soften the tube. Three lines straighten and cut. Two eddy current machines check every tube.

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