Red Seal Steamfitter/Pipefitter cheat sheet

Pipe sizing: Q = A × v; for a given flow, halving diameter quadruples velocity and roughly 16× the friction loss per unit length (Darcy-Weisbach, h_f ∝ 1/d^5 at constant Q).

Allowable stress basis: ASME B31.1 uses S = lesser of 1/3.5 × tensile at temperature or 2/3 × yield at temperature; B31.3 uses the same concept with its own tabulated values - always use the code edition cited in the contract.

Minimum wall thickness: t_m = t + c, where t = PD/(2(SE + PY)) for straight pipe under internal pressure; c accounts for mechanical, corrosion, and erosion allowance.

Thermal expansion: ΔL = L × α × ΔT; carbon steel α ≈ 6.5 × 10⁻⁶ /°F (11.7 × 10⁻⁶ /°C). A 100 ft carbon steel line at 300°F ΔT grows about 2.3 in.

Hydrostatic test pressure per B31.3 is 1.5 × design pressure × (allowable stress at test temp / allowable stress at design temp); test fluid temperature must stay below the ductile-brittle transition limit.

Weld joint efficiency E values: seamless = 1.00, ERW = 0.85, furnace butt weld = 0.60 (B31.3 Table A-1B); the value drives required thickness, so confirm the pipe spec before calculating.

Pipe schedule numbers are nominal wall-thickness indicators only; actual wall varies by NPS, so use tabulated OD and wall values (ASME B36.10M carbon, B36.19M stainless) for mass and stress calculations.

Support spacing rule of thumb for Schedule 40 water-filled carbon steel: ~10 ft for 1 in, ~12 ft for 2 in, ~15 ft for 3 in, ~17 ft for 4 in, ~21 ft for 6 in; verify against project specs and code.

Steam quality x = (h_actual − h_f)/h_fg; saturated steam at 100 psig has h_f ≈ 298 Btu/lb and h_fg ≈ 880 Btu/lb, so a 95% quality mixture carries about 44 Btu/lb less than dry saturated steam.

Steam velocity guideline: 4,000–6,000 ft/min in distribution mains, 6,000–10,000 ft/min in process lines, and under 1,500 ft/min in condensate-return lines to limit water hammer and erosion.

Flash steam fraction = (h_f at higher pressure − h_f at lower pressure) / h_fg at lower pressure; condensate from 100 psig to 0 psig flashes roughly 13%.

Drip leg sizing: use full line size for the drip and a length equal to at least the pipe diameter plus 4 in, with the trap takeoff from the bottom of the leg, not the side.

Steam trap selection: thermostatic traps for end-of-main drip points, inverted bucket or float-and-thermostatic for process heat exchangers, thermodynamic for high-pressure drip and tracing.

Two-pipe vs one-pipe: gravity return requires the return main sized with slope in the flow direction and an adequate flash/vent receiver; pumped returns allow smaller lines and lift.

Safety valve capacity: ASME Section I requires the valve to relieve the boiler's maximum generating capacity at MAWP; set pressure plus accumulation must not exceed 6% above MAWP for power boilers.

Pipe expansion loop leg length: L = √(3EDΔL/S_A) using the guided-cantilever formula; check the anchor loads, not just the leg length, before committing the layout.

Butt-weld fit-up: root gap per procedure (typically 1/16–1/8 in for GTAW root), land 1/16–1/8 in, and bevel 37.5° ± 2.5° per side gives a 75° included angle.

Preheat for carbon steel per ASME B31.3 Table 330.1.1: 50°F minimum below 0.30% C, 175°F for 0.30–0.40% C, and 250°F above 0.40% C, with thickness thresholds raising the requirement.

Post-weld heat treatment thresholds (P-No. 1 carbon steel): required above 3/4 in nominal thickness per B31.3 Table 331.1.1; hold time is 1 h per inch of thickness, minimum 1 h.

Weld symbols: a fillet weld is shown as a triangle on the reference line; the size precedes the symbol, length follows, and the tail carries the process or procedure reference.

Hydrogen bake-out for low-alloy steels: hold at 400–500°F for at least 2 h immediately after welding when specified, to allow hydrogen diffusion before cooling.

Pipe bending: minimum bend radius is commonly 5× OD for hot bends and 3× OD for cold bends; ovality must not exceed 8% of nominal OD per B31.3.

Branch connection reinforcement: the required area is the metal removed from the run pipe opening; reinforcement must lie within a zone extending 2.5 × run wall thickness from the outside surface.

Threaded joint makeup: use PTFE or pipe dope on male threads only, engage 3–4 threads by hand, and leave 1–2 threads exposed; over-tightening splits fittings and cracks cast iron.

Rolling offset (equal spread): true offset = √(offset² + advance²); the fitting takeoff is subtracted from the center-to-center distance before cutting the connecting pipe.

45° fitting constants: travel = offset × 1.414, takeoff per fitting = 0.625 × NPS for a long-radius 45° elbow; for 22.5° use 2.613 and 0.254 × NPS respectively.

Miter cut angle for an equal-spread offset: cut angle = half the included angle between the two pipe runs; for a 90° turn made of two miters, each cut is 22.5°.

Pipe template development: circumference = π × OD; divide the circumference into equal parts and lay out ordinates from the sine of the angle to the cut plane to mark the wrap-around.

Parallel-line development for a tee: the branch cut line is an ellipse whose minor axis equals the branch OD and major axis equals branch OD / sin(included angle).

Grade and slope: 1/4 in per foot = 2.08%; convert slope percentage to in/ft by multiplying by 12 and dividing by 100.

Anchor-to-anchor pipe length: subtract all fitting takeoffs and valve face-to-face dimensions from the centerline dimension before cutting; record the takeoff table for the spool.

Tank or vessel nozzle orientation: use the chord and rise method - rise = R − √(R² − chord²/4) - to locate a nozzle on a curved shell from a straight-edge measurement.

Rigging: SWL of a sling leg = vertical load / (number of legs × cos of the angle from vertical); at 60° from horizontal each leg carries 1.155 × the share, at 30° it carries 2×.

Sling angle below 30° from horizontal is generally prohibited; attach above the center of gravity and use tag lines to control rotation.

Pipe weight per foot = 10.68 × wall × (OD − wall) in lb/ft with OD and wall in inches; add water at 0.34 lb/in³ of internal volume for hydro test loads.

Center of gravity of a loaded pipe rack or skid must fall inside the base footprint; check tipping moment about the edge, not just total weight.

Hydraulic torque wrench bolting: use the manufacturer's torque table for the bolt size and lubricant; torque values vary by up to 30% with lubrication, so never substitute dry for lubricated values.

Flange alignment tolerances: offset and gap within 1/16 in, and flange faces parallel within 0.06 in measured across the diameter for a raised-face joint.

Pressure test safety: pressurize in increments to half test pressure, inspect, then step to full; never exceed the lowest-rated component in the test boundary, and use a calibrated gauge in the upper quarter of its range.

Lockout: verify zero energy by attempting start and by checking gauge pressure at the isolation point; a closed valve is not a positive isolation - use a blind or spool piece.

Isometric drawing conventions: north arrow fixes orientation, line weights distinguish pipe from structural, and each spool carries a line number, size, spec, and insulation class.

P&ID vs isometric: the P&ID shows process function and instrument loops; the isometric shows physical geometry and cut lengths. A change on the P&ID must be reflected in the iso before fabrication.

Bill of materials takeoff: count fittings from the iso, add the pipe cut length from centerline dimensions minus takeoffs, and include gaskets and bolting per flange pair.

Line designation example: 6"-P-1201-A1A means 6 in nominal, process service, line number 1201, piping class A1A - the class sets material and rating.

Instrument tags: FIC, TIC, PIC, LIC denote flow, temperature, pressure, and level indicating controllers; the first letter is the measured variable.

Weld map: each weld gets a unique number traced to the welder, procedure, and NDE record; the map is the as-built quality record for the spool.

As-built markup: record field changes in red on the iso and return to engineering; the markup drives the turnover package and the next revision.

Spec break location: where a line changes piping class, the break is at the flange or weld shown on the iso; never mix ratings across a joint without an approved transition.

Use the correct PPE for the task: face shield plus safety glasses for grinding, leathers and a welding helmet with the right shade (10–13 for arc welding at 100–300 A) for welding.

Confined space entry requires a permit, atmospheric testing for O2 (19.5–23.5%), LEL (below 10%), and H2S (below 10 ppm), plus a rescue plan and attendant.

Hot work permit: clear combustibles within 35 ft, use fire blankets and a fire watch that remains 30 min after work ends per NFPA 51B.

Grinder safety: the guard stays on, the wheel RPM rating must meet or exceed the tool, and the tool rests are set within 1/8 in of the wheel on a bench grinder.

Ladder use: 4:1 rule - the base is set one unit out for every four units up; the ladder extends 3 ft above the landing and is tied off.

Fall protection is required at 6 ft or more in general industry (4 ft in some jurisdictions); inspect harnesses for cuts, fraying, and damaged hardware before each use.

Crane hand signals: the signal person is the only one who directs the operator; a stop signal may be given by anyone, and the operator must obey it.

Hazard communication: consult the SDS for a chemical before use; it lists the flash point, PPE, and first-aid measures for the product.