Skid Cost

What Drives Process Skid Cost and How to Build a Defensible Quote

A money-focused breakdown of what really drives skid cost per unit, how to structure a quote that holds, and the estimating errors that erode margin on packaged plants.

On a shop-fabricated process skid, labor, not material, is where quotes are won or lost. A typical mid-size carbon-steel skid splits roughly 30 to 40 percent material, 35 to 45 percent shop labor, 10 to 15 percent I&C and integration, and the balance in engineering, testing, and overhead. Structural steel and pipe are commodity buys you can firm from a mill quote within days; the risk sits in the labor hours, which swing 20 percent or more on welder productivity and rework. The Skid Total Cost calculator rolls component count, a blended unit rate, a capture factor, and fixed shop cost into one fully loaded number to anchor the bid.

Piping labor is the single largest movable cost. Price it in diameter-inches, not per spool, because a 12 inch header weld carries five times the hours of a 2 inch line. At a fully burdened welder cost of 65 to 95 dollars per hour and a shop rate of 8 to 14 DI per hour on carbon steel, each diameter-inch lands near 5 to 12 dollars of direct labor, before overhead. Stainless GTAW can push that to 12 to 20 dollars per DI. A 600 DI skid therefore carries 3,000 to 12,000 dollars of weld labor alone, so the material spec drives the quote far more than the pipe tonnage does.

I&C and integration are the scope estimators most often underbid. The Instrument Loop Labor and Panel Integration Cost calculators exist because terminations, loop checks, and cable dressing eat hours a flat per-panel price misses. Budget 1.5 to 3 hours per simple loop and three to five times that for SIS or analyzer loops. Panel integration commonly runs 40 to 55 dollars per panel-hour fully burdened, and a control panel with 200 terminations can absorb 30 to 60 hours. Carry a fixed setup and test-gear line separately so it does not vanish into a per-unit rate on small skids, where it dominates cost per loop.

Commissioning and FAT are cost centers that outlast the shop. The Commissioning Labor calculator prices field checkout per tag, where mobilization and standby can add 250 dollars or more of fixed cost per trip regardless of tag count. A completed shop FAT is the lever that shrinks this: every punch item closed on the shop floor at 75 dollars an hour avoids the same fix in the field at a field productivity penalty of 1.5 to 2 times shop hours, plus travel and standby. Quote the FAT window explicitly, because a witnessed test that overruns holds the client, inspectors, and the skid itself past ship date.

Scrap and rework are real dollars, not a rounding line. On weld-heavy skids, a first-pass yield of 95 to 97 percent still means 3 to 5 percent of joints get cut out and rewelded, each repair costing two to three times the original weld because it adds excavation, re-NDE, and schedule. The Rework Allowance calculator sizes the margin between hours you budgeted and hours a punch list actually consumes. A defensible bid carries 5 to 10 percent of fab hours as rework contingency; drop it to zero and you are quoting a perfect build that has never happened on a first-of-a-kind skid.

Overhead and margin turn cost into price, and this is where quotes quietly go negative. Shop burden, engineering, documentation, and G and A typically load 25 to 40 percent on top of direct cost before any profit. Apply margin on the fully burdened number, not the bare labor, or you give away the overhead. On competitive packaged-plant work, gross margin often sits at 12 to 20 percent, thinner on repeat designs and fatter on first-of-a-kind scope that carries real risk. The Skid Total Cost and a margin step let you see the quoted price and the point at which a discount request eats your contingency.

The most expensive estimating error is scope you priced against the wrong basis. Bidding gross spool count instead of net deliverable count promises welds you cannot produce on time. Counting instruments instead of loops overstates I&C labor by the number of devices per loop, often 2 to 3 times. Folding installation into a per-loop check rate hides real hours. And blending simple and complex spools into one average rate systematically underprices the large-bore lines where most weld hours live. Each of these shifts the quote 10 to 25 percent in the direction that loses money.

Build the quote bottom-up and reconcile it top-down. Sum material from firm mill and vendor quotes, labor from diameter-inches and loop counts at your demonstrated rates, then add rework contingency, commissioning, overhead, and margin. Cross-check the total against a dollars-per-DI or dollars-per-loop benchmark from a recent completed skid; if your new bid lands more than 15 percent off that history without a scope reason, an input is wrong. A quote that ties bottom-up detail to a top-down sanity check is the one you can defend in a bid review and hold through the build.

Published 2026-07-01.