Years ago, many buyers thought:
- Seamless = higher pressure
- Welded = lower pressure
With today’s ASTM A312 welded stainless pipe, that idea is often outdated. As long as the welded pipe meets the ASTM standard and the piping code gives the weld a 1.0 quality factor, a 4” Schedule 40 welded pipe can handle the same calculated pressure as a 4” Schedule 40 seamless pipe of the same grade. The joint efficiency (E) ranges from 0.85 to 1.0 depending on the NDT method per ASME B31.3.
This presents a opportunity to help your customer, as many purchasers are familiar with both alternatives but aren’t sure when the difference counts.
Does seamless automatically mean better quality? Not necessarily — it depends on the usage and specifications.
HOW IS SEAMLESS PIPE MADE?
Seamless pipe is made without a lengthwise weld, usually by shaping a solid piece into a hollow tube.
However, seamless pipe can be a major problem child.
Wall thickness varies by +/- 12.5%
The way seamless is made is by piercing the solid billet and then rolling/extruding it. This process produces some variation in wall thickness along the length.
Reason or causes for lack of uniformity in wall thickness.
- Uneven material flow during piercing.
- Tool wear.
- Temperature changes.
- Residual stresses relief.
HOW IS WELD PIPE MADE?
Welded pipe starts as a stainless steel strip or plate rolled into a circle and joined at the seam. Today’s welding can give you very consistent, high-quality results.
Availability can vary in a big way
Welded pipe is often easier to find in larger sizes, while seamless may be harder to get depending on size, wall, and grade.
Cost counts
Seamless pipe usually costs more because of how it’s made. If your project doesn’t need it, the extra cost might not add much value.
Let the specs lead the way
Check the ASTM standard, pressure, temperature, corrosion risks, inspection needs, and what the user wants — don’t just assume seamless is better.
The Biggest Change Today
The biggest shift is that today’s welded stainless pipe isn’t like the versions from decades ago. Improvements in equipment, automation, heat treatment, forming, and testing have made it more consistent and reliable.
This doesn’t mean welded and seamless are always interchangeable—seamless still matters, especially when a spec calls for it. When both are options, pick based on your needs, availability, cost, pressure, temperature, and specs, instead of assuming seamless is always the winner.
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