RE: [PipingDesign] Re: Field Weld(FW) and Fit Field Weld (FFW)

From: <bruce.r.raymond@fluor.com>
Date: Mon Jul 28 2008 - 06:53:00 EDT

I've been following this thread for a while - Field fit up can be a cost saving or cost addition to a project.

Field Fit Up implies that a construction crew actually presents the piping spool pieces, marks the Field Fit Up section - removes it , cuts and bevels the section, re-presents the Field Fit Up section, and then proceeds with the actual field welding.This can be a very a very man-hour intensive procedure
The construction crew must perform the following steps - primary rigging / presentation / marking / derigging / cutting / beveling/ and rerigging prior to actual field welding.

Example #1: replacement in kind of a 6" sch 40 cs piping section due to corrosion. No Unit Shutdown
Designer has original drawings, isos, field verifies dimensions, and adds FFW's because he didn't want to go up in the piperack and physically verify the existing piping route
# of FFW's - 2

Designer time not spent to verify piperack dimensions: 20 manhours Additional construction crew time to install piping system with 2 FFW's: 80 hours

Example #2 - replacement of a 12" sch.160 Incoloy piping system due to metallurgical upgrade: Unit Shutdown
Designer has original drawings, isos, complete laser scanning has been performed
Designer did no field verification of dimensions due to laser scanning -
# of FFW's - 0

Due to the confidence of laser scanning point clouds all spools were "pre-fabbed", with only FW's called out, but during the subsequent unit shutdown and installation there were numerous installation problems which required modifications to the original spool pieces Designer time to field verify dimensions - 0 manhours Additional construction crew and engineering time to install system - 240 hours
Actual cost impact for lack of FFW's - 2 additional days of unit shutdown @ $1,250,000 per day.

Important Comments on laser scanning - If you are working on a laser scanning driven project don't forget the following: 1) Laser scanning only "sees" the outside surfaces of piping, if you have an insulated line it will not be able to pinpoint actual pipeline center lines.
2) Laser Scanning does not take into account piping "Shrinkage" due to operating vs. shutdown temperature differentials, normally a laser scan is performed while a unit is operating, but when the actual modification is done the affected piping systems, and or equipment will be at ambient temperature

If in doubt as to the utilization of FFW's consult with your supervisor, and also with your construction group - good planning and coordination / engagement of all involved groups normally will assist in making the proper decisions.

Bruce R. Raymond
Senior Design Supervisor
Fluor

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[Non-text portions of this message have been removed] Received on Mon Jul 28 06:53:00 2008