In plumbing inspection, this appears to be simple.
However, many people continue to make mistakes on the job.
Which one is seamless?
Which is welded?
Which code applies?
What exactly should be inspected?
Let us make it realistic.
Seamless pipes:
No weld seams.
Made from solid billet (piercing and rolling).
More uniform construction.
Welded pipes:
Has a longitudinal weld seam.
Made from a plate or coil, then rolled and welded
Includes weld metal and HAZ.
Simple understanding:
Seamless means there are no weld seams, making it more uniform.
Welded seams pose the most risk
𝗖𝗼𝗺𝗺𝗼𝗻 𝗦𝗵𝗼𝗿𝘁 𝗙𝗼𝗿𝗺 (𝗦𝗶𝘁𝗲 𝗧𝗲𝗿𝗺)
SMLS = Seamless.
ERW: Electric Resistance Welded.
SAW: Submerged Arc Welded.
HAZ: Heat Affected Zone.
WT = wall thickness.
OD: Outside Diameter
MTC: Mill Test Certificate.
Inspectors must understand these, which should always appear on pipe markings and paperwork.
𝗖𝗼𝗱𝗲 and 𝗦𝘁𝗮𝗻𝗱𝗮𝗿𝗱
ASME B31.3.
ASME B31.4.
ASME B31.8.
Material Specifications:
ASTM A106.
ASTM A-53
API 5L
Welding and NDT:
API 1104
ASME Section IX.
ASME Section V.
Do not make guesses. Verify.
Pipe Marking (SMLS, ERW, SAW)
Mill Test Certificate (manufacturing technique specified).
Visual check (welded seam vs. no seam)
NDT records for welded pipes.
If you’re doubtful, always use MTC rather than assumptions.
For seamless pipes, material integrity is a key consideration.
Marking versus MTC
Outer diameter, weight, and tolerance
Surface conditions (cracks, lamination, pitting)
UT thickness and lamination
Heat number traceability
Welded pipe (focus on weld and material):
All seamless inspections.
A visual examination of welded seams
Weld Profile and Reinforcement
NDT as specified (RT / UT / MT / PT).
WPS, PQR, welder qualification.
HAZ condition.
Key Point:
Most problems occur during welding.
𝗖𝗼𝗺𝗺𝗼𝗻 𝗠𝗶𝘀𝘁𝗮𝗸𝗲𝘀
No MTC verification.
Treating welded pipes as seamless.
Ignore weld seam.
Not referring to code and specifications.
Seamless means focusing on the material.
Welded = attention on weld and substance.
Always verify against:
Code, Specification, and Drawing.
It’s not about seamless versus welded.
This is about:
Manufacture quality.
Welding Quality
Inspection quality.
This is the distinction between checking and real inspection.
If you’ve worked on-site, you’ve witnessed this.
