[Richard Beale]

Hi All,
My company has decided to move the fabrication of small bore piping from the field to the shop to reduce field labor. We define small bore as NPS 1 1/2 and below; this commonly being SW or threaded piping. Large bore for us is defined as NPS 2 and above and commonly is all butt-welded piping. Up to now, the large bore has always been shop spooled and the small bore has always been field run.

I’m told that shop fabrication plus shipping plus field erection of the small bore piping spools is estimated to be 30% less than the cost of a total field assembly, so expectations are that the total installed cost will still be less with this approach even after allowing for the anticipated repair of damaged spools due to transportation and handling. After thirty-eight years of working on projects where SW and threaded piping has always been field run, I’m having a hard time believing that the claimed efficiencies of shop fabrication versus field fabrication are real for the small bore SW and threaded piping. Albeit, we do model and clash detect all line sizes down to NPS 1/2, but still, my instincts are that this type of piping goes together so quickly and easily in the field that the time required to bring in the spools, figure out the configuration, repair the damage and modify for field obstructions not modeled, as opposed to just building in-situ will end up being a wash overall at best.

Don’t get me wrong, I understand the rational of wanting to reduce the field labor, and I’m not opposed to this initiative; quite the opposite in fact, I wish to be supportive. However, I am skeptical, largely because after almost forty years in the industry I’ve come to learn that those that came before us were no dummies, and if they didn’t do it then there was a good reason why. However, putting my instincts aside, I’m struggling to identify definitive reasons against this approach; not to scuttle it, but to give those making the decisions some heads-up about possible pitfalls to be aware of and to be planned around.

I’ve recommended that we at the least reduce our standard large bore piping spool length of 12m (40’) to 6m (20’) for the small bore pipe spools, and that we only do SW in the shop and still completely field run the threaded piping.

I’d like to know your opinions on this matter. Primarily, I’d like to hear the lessons learned for and against from those of you that have experience with this approach, and, if it were your decision to make, whether or not you’d do it again.

Best wishes,
Flowr8

[Richard Beale]

It’s been a long time, but as promised I have feedback for you on the success of the shop fabrication of 1½” and below SW piping. The general consensus from fabrication and construction is that it is working out well, largely due to the fact that the use of 3D CAD for the modelling of these small bore lines produces a high degree of accuracy in the pipe routing.

The negatives are that the fabricators find it a challenge to move it through the shop efficiently due to fit-up time taking longer than welding time, so they have to schedule the small bore with some larger bore to balance the shop activity. No spool fabricator would outright say it, but inference is that if all they were sent were small bore piping orders they wouldn’t be too interested in the work, but provided they have lots of large bore butt weld spools to fabricate to go along with it, they’re happy to accommodate it.

Damage in shipping and handling is more likely than that of large bore spools and consequently there’s invariably some field repair required at site. To reduce this likelihood the maximum spool length that has been adopted is 20ft (6m) as opposed to the more common 40ft (12m) for large bore.

Overall though, it does save time in the field and has proven to be a worthwhile endeavor.

[James Pennock]

Thanks for the feedback

[er.piping]

I am working on American projects since last 2 years. As per project specification all butt welded and socket welded material is to be marked as shop fab category. Only threaded material is marked as field category.
The spooling length for 2″ and above pipe is 40’X8’X8′ and for 1 1/2″ and smaller pipe it is 20’X8’X8′.

[Mark Pearson]

Very ineteresting article.

I’m interested to know if the following affects the decision to go this route;

Use of exotics.
Stress critical small bore lines.
Not all small bore is socket weld/threaded.
offshore scope.
hot work acceptance.

Cheers
Mark

[Author]

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