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TOPIC: Shop fabrication of small bore piping

7 years 2 months ago #8202

  • Flowr8
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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

Re: Shop fabrication of small bore piping 7 years 2 months ago #6381

  • shrivallabha
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What I did first was to check if this is becoming a trend or had there been some more cases of the same nature.

This discussion looks at some of the points you discussed.
http://www.pipingdesign.com/archive/0805/15668.html

In my company, we always do the way its always been done i.e. at field.

However, if the company is willing to venture out on an unbeaten path, it means (in a way) that they will be willing to absorb the "extra" costs they might incur if the scheme of things doesn't work out as it was imagined / intended. In that case, there will be some lessons learned which will determine the future course of action that the company will take in this regard.

On the other hand, at this point of time, when the actual work has not been started, it would be pertinent to check the basis for comparing cost / time
  • Cost of activity [Shop Vs Field]
  • Time impact [Does it save time over the traditional technique?] [If yes, how much?]
  • Known Pitfalls of Field fab Vs Expected / Possible issues with Shop Fab.
I guess it will be a combination of these items which will decide approach. So if you could perhaps tabulate the information and then verify if the people (I think managers that be) have ticked every item in your list that you think is important or will have bearing on the final outcome.

I don't have a lot of experience to weigh in from any of the sides. I hope, I have posted something that helps some way.

Re: Shop fabrication of small bore piping 7 years 2 months ago #6430

  • Jop
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Flowr8,
You have brought up an interesting subject that has many facets that must be considered. My comments will be flavored by some experience as an Pipe Fab Shop Engineering Manager and as an Expediter in a Pipe Fab Shop along with my years in the Project engineering office and the construction site.

Points to consider include:
1. Can you find three or more competent Pipe Fab Shop that will be willing to bid on and accept such an order?
2. Pipe Fab Shops are not normally set up to do 2” and smaller fabrication and therefore they are not likely to have the space nor the jigs and fixtures for handling the small piping. Will they add a cost for leasing other Fabrication space?
3. Pipe Fab Shops do not normally have a “Shop” inventory of small bore pipe (including material selections & schedules) or fittings nor are they likely to have the warehouse space to dedicate to small bore. Will they add a cost for leasing other Warehouse space?
4. Pipe Fab Shops would have to develop and qualify Weld Procedures for all the socket weld materials and sizes. What would be the extent of and the cost of this adder?
5. Pipe Fab Shops normally have a “drafting” crew that prepares their Shop “Spool” drawings who would possibly need to undergo some training to handle socket depth and thread engagement calculations. What would be the extent of and the cost of this adder?
6. Pipe Fab Shops normally have specific Cranes and other types of transportation devices to handle the different size groupings of pipe spools. Are they going to be required to pull these items off the “Big Bore” (high value) fabrication to handle the small stuff? Or are they going to buy or lease the equipment just for this one small bore contract? What would be the extent of and the cost of this adder?
7. The manner and method the shop uses to load and ship the “small bore” piping would need to be reevaluated to reduce damage. What would be the extent of and the cost of this adder?
8. Logistics is another thing that will enter into the equation. Where is the Job Site and where is the Pipe Fab Shop? The potential for loss should be very low. However the potential for damage during shipment could be higher that for the larger sizes? Are you going to supply the field with some small bore stock so they can make repairs with out effecting start-up? What would be the extent of and the cost of this?
9. Do these Bidder Shops have any past projects they can point to so you can evaluate their performance and Client satisfaction?
10. Do these Bidder Shops even have a “Price Book” for small bore (SW & Scrd) piping that they are willing to show you?

Do your homework.

Please let us know what you decide to do and If you do choose to shop fab the small stuff let us know how it worked out when the project if completed and you have done your "Lessons Learned"


Other reading related to Pipe Fabrication Shop issues:
http://www.pipingdesigners.com/Training ... n%206b.htm
Do it once and Do it Right

Re: Shop fabrication of small bore piping 7 years 2 months ago #6574

  • Flowr8
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Jop, shrivallabha,
Thank you both for your very insightful reponses. The topic is still being discussed and I will keep you abreast of developments.

Re: Shop fabrication of small bore piping 7 years 1 month ago #6583

  • Flowr8
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Just to follow up as promised on this topic, the project decision is to proceed with the shop fabrication of small bore socket-weld piping. I can’t go into detailed explanations about the specifics of the execution strategies, as these may well be considered confidential. I did however want to thank you for your responses and insightful advice. Feedback during construction will now determine the viability of this versus the conventional approach, and I will endeavour to share the general pros and cons at a later date.

Many thanks and regards,
Flowr8

Re: Shop fabrication of small bore piping 7 years 3 weeks ago #6587

  • Peter Pyper
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I notice you come from Calgary Flow8. As you are aware much of the work that we do is modularised which breaks out into module - shop and stick built shop. It depends on how the contract is given to the vendor. Does the EPC design everything and the vendor do as instructed or does the vendor lay out, design and build from our flow sheets?
Quite often in todays world we do the latter where the vendor is responsible for design and lay out. The vendor will then spool the pipoe for the mod yard where it is installed. Even if the EPC creates the Iso's for the module it is still sent to the fab shop/Mod yard.

This includes piping down to 1/2" as it gets installed on the module. Strick built piping is kept to a minimum as it is more costly. This would previously have been field run but now is fabricated and sent to the field. The Fab shop may be welding small bore piping already so it isn't a large task for them to do stick built. On large projects we may have 3 or more fab shops working and feeding the modules. Add to this mix the fact that modules are now constructed not only in our own country but internationally. So the module arrives on site after shipping having been hydro tested and ready to be placed and welded into place on site.

Economy of scale dictates that the larger projects follow this procedure and do so but smaller projects are also following this model and shipping skids to site where practical. It is 3 times more expensive to weld in the field in Alberta than it is in the shop. Small bore now also follows under this rule.
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