Precision Pipeline Repair
Portable Machine Tools Speed Pipeline Repair
By Mark Leska
Figure 1: Destructive Cut
At a recent pipeline project in Superior, Wis., near Duluth, a large national pipeline distribution company used E.H. Wachs Split Frames portable pipe cutting and beveling machine tools to deliver the precise fit-ups the project required. The scope of the project included installation of a replacement section that was remotely fabricated, cold cut and weld prepped on site, lowered into its cradle and final welded.
Although this particular project used torch cutting for the destructive cuts, when it came time to cut the sections for the critical fit-ups (nicknamed the “money cuts”) the client insisted on the precision that only cold cutting can deliver. Cold cutting, or more precisely using portable machine tools to machine the cuts and bevels, can maintain critical tolerances under 1/32-in. (0.0313 in. or 0.794 mm) that are difficult or impossible to achieve using other methods.
On the Superior pipeline project torches were used to rough cut the existing pipeline section (Figure 1). Commonly referred to as “destructive cuts,” this method is used when there are no tolerance considerations, no explosive hazards and where the creation of an undesirable Heat Affected Zone (HAZ) is not a factor.
Figure 2: Precision Machining
The next phase of the Superior project involved cutting the old section to the precise length needed (Figure 2), discarding the HAZ tainted pipe stub. The Wachs Split Frames used for the project simultaneously cut and beveled a precision weld prep with a 1/16-in. (0.0625 in. or 1.59 mm) land. These preps were weld ready, requiring no further hand working. It’s worth noting that only machining can produce these precise and consistent lands.
Figure 6: OD Tracking Slider
A helpful accessory for machining a uniform prep and consistent land on larger, thin wall pipelines is the outer diameter (OD) tracking slide (Figure 6). These tool slides, used to hold the cutting and beveling bits, follow or “track” the contour of out of round pipe with a spring loaded guide wheel. Out of round is a common condition associated with thin wall, large diameter pipe due to its relatively lightweight construction that can be easily deformed during manufacturing, transit or handling.
In this particular project there were no counter bores required, but in instances where varying wall thicknesses or schedules are joined (such as heavier wall pipeline sections used underneath highways) counter boring is mandatory. Counter boring is used to match the wall thicknesses of two different schedules at the joint to a prescribed profile that does not impede flow. A typical counter boring profile is shown in Figure 7. This counter bore can only be produced by machining, never by hot cutting and hand grinding.
Figure 3: Positioning Section
Figure 4: Critical Fit-ups
In Figures 3 and 4 we see crane operators lowering the pre-fabricated section onto its new cradle, with the new section weld prepped in situ before being lowered into position ready for welding and subsequent service (Figure 5). For pipeline rehabilitation/repair projects where downtime is measured in thousands or hundreds of thousands of dollars a day in lost revenue, an investment in doing the job right the first time with Wachs cold cutting machine tools pays a huge dividend.
Figure 5: Weld Ready
Mark Leska is senior marketing coordinator for ITW Orbital Cutting & Welding, E.H. Wachs Industrial Products Division (www.ehwachs.com).
Figure 7 Counter bore spec
Comments are closed here.