According to ASTM A333 your reply is correct.
But Most of the Engineer companies proposed A671(EFW) material For the above 16"(Without consideration of Thickness) .
Note: The main different is Manufacturing Process(Welding)===>With & Without filler metal.
Seamless pipe up to 24" has been readily available in the past. I only new of one mill hat could produce seamless up to 36" but that was some time ago.
As you see Practically,companies proposed A333 ,up to 16" as SMLS, and A671 for above 16" as welded.
However, There is no limitation in A333 STD up to 16" .
You seem to be interested in the economic choice between seamless lower strength pipe and welded slightly higher strength pipe and not how large a diameter that A-333 6 pipe can be obtained. And you don't state the source of the Table shown. Per Owner's request, I can assure you that larger diameters of seamless A-333 6 has been specified, purchased and installed in low temp petrochemical facilities.
I think you misunderstood me. I simply meant to say that welded pipe in larger diameters is less expensive than seamless in the same diameters. At least it was in the past. I've been retired for over 6 tears and thus unable to comment on today's pricing.
The economics of smls vs wld are largely driven by wall thickness.
The heavier the wall the closer the prices will be.
And for some very heavy walls smls will be the only option.
Just as for very light walls likely only available as wld and if smls is available it will be much more expensive.
There is more quality variation in wld pipe than in smls.
With good HF welds and NDT the welded pipe will be at least as good as the best seamless.
The consistent wall thickness makes welded easier to work with.
In wld product you should focus on weld integrity.
In smls the biggest issues are ID surface and wall variations.
There are apparently some quality issues with producing thick wall A333. As such, for more common "standard pressures", typically high, that translates into diameter limitations. But if you can find a mill that will make the wall thickness you want and guarantee quality, and you can accept welded pipe, then there are no diameter limits, except for what max diameter the mill can produce.
If you order from a supplier, you may find the smaller diameters that are limited to those in stock, typically used for the common max standard pressures. If your pressure is not so high and you can use walls of normal easily produced thickness, you can probably get larger diameters when purchased through a direct mill order, but you'll need to make a large order to do that..
Normally ,According to Companies Experience for the Above 16" ,They propose Welded type with SAW Welding method
According to 4. of ASTM A333 :
4.Materials and Manufacture
4.1 Manufacture—The pipe shall be made by the seamless or welding process with the addition of no filler metal in the welding operation. Grade 4 shall be made by the seamless process.
Clearing mentioned the welding type is EW(ERW).
However ,Scope of ASTM A671 is :
1. Scope*
1.1 This specification covers electric-fusion-welded steel pipe with filler metal added,....
This is why that the Engineering Companies will not propose A333 for bigger sized.
Now it is true that up to certain sizes, seamless is easier to find, but I don't understand why the piping index you list doesn't simply use A333 welded pipe above whatever arbitrary size the company wants to choose below the generally recognised limit for seamless of 24"
The other pipe material might just be more commonly available in your part of the world. I don't know. Have you asked the "Engineering Company"?
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
