Pipe schedules with the bore and volume figures a pigging calculation actually needs, the standard butt-weld fitting dimensions that set the geometry of the line, and — the part the dimension tables never tell you — what each fitting means for getting a pig through it.
Outside diameters and wall thicknesses to ASME B36.10M. Bore, area, volume and weight are calculated from them. Pick a size to see every schedule side by side — the highlighted row is the one carried into the summary tiles.
| Schedule | Wall | Bore (ID) | Area | Volume / length | Pipe weight | Bore as % of OD |
|---|
The one dimension that never changes with schedule. Note the break at NPS 14: below it the nominal size is a label and the OD is larger; from 14 up the OD equals the nominal size in inches.
| NPS | DN | OD (in) | OD (mm) | Schedules tabulated here |
|---|
Butt-weld elbow dimensions to ASME B16.9. The centre-to-face dimension A of a 90° elbow equals its bend radius, so a long radius elbow is 1.5 × nominal size — "1.5D". B16.9 also tabulates 3D elbows. Anything longer radius than that is an induction bend to ASME B16.49, not a fitting.
| NPS | 90° long radius (1.5D) A |
90° short radius (1D) A |
90° 3D A |
45° long radius B |
|---|
| Bend | Radius | Pigging verdict |
|---|---|---|
| Mitred / welded segment bend | — | Impassable Treat as a hard stop for anything rigid. The internal weld intrusion at each segment shears sealing elements. Foam only, and even then expect damage. |
| Short radius elbow | 1D | Avoid Not piggable for rigid bodies. B16.9 only tabulates SR up to NPS 24, and it has no place in a line intended for inspection. Foam and spheres will pass. |
| Long radius elbow | 1.5D | Conditional Conventional mandrel cleaning pigs and short caliper tools are commonly rated to pass 1.5D — several manufacturers state it explicitly. Long multi-body ILI tools generally are not. Check the tool, not the elbow. |
| 3D elbow or induction bend | 3D | Usual design minimum The normal target for a line that will be inspected. Most conventional ILI tools are specified against 3D. |
| 5D induction bend | 5D | Preferred Comfortable for long tool trains and the usual choice on new transmission lines. ASME B16.49. |
| Cold field bend | typically 30–40D | No issue Generous radius, but check local ovality: construction codes limit deformation, and a few per cent of diameter is enough to matter to a tight-fitting tool. |
Centre-to-end dimensions for equal straight tees to ASME B16.9. C is measured along the run, M along the branch — equal at every size up to NPS 36, and not equal at 42 and 48.
| NPS | C — run | M — branch |
|---|
| Arrangement | What happens to the pig | What to do |
|---|---|---|
| Unbarred equal tee | The pig takes the branch, or a sealing element drops into the opening and jams the body across the junction. The most common way to lose a pig in an otherwise clean line. | Bar it. Retro-fitting bars means cutting the tee out, so catch this at design review. |
| Barred tee | Bars bridge the branch opening so the sealing elements ride over it. | Bar spacing is set by the shortest sealing element in the train, not by the pipe size. Have the pig supplier confirm the spacing against the actual pig train before fabrication. |
| Reducing tee, branch under ~50 % of run | Usually passable unbarred — the opening is too small for a disc to enter. | The common design rule is that branches above about half the main diameter need barring. Confirm against the smallest element rather than applying the rule blind. |
| Sweepolet / extruded header | Smooth contoured branch with no internal protrusion. | Preferred on piggable lines where a full tee is not needed. |
| Set-on / set-through branch, stub-in | Set-through branches leave the stub protruding into the bore — a guillotine for cups and brushes. | Set-on only on piggable lines, with the internal weld dressed flush. |
| Thermowell, quill, sample probe | Anything reaching into the bore catches the pig outright. | Retractable fittings on piggable lines, with a positive procedure to withdraw them before the run and a check sheet that records it. Dead legs and injection points. |
Overall length H for butt-weld reducers to ASME B16.9. H depends only on the large end — a one-size and a two-size reduction from the same size are the same length, and concentric and eccentric are identical. Note the jumps at 12→14 and 18→20.
| Large end NPS | H | Note |
|---|
| Feature | Effect on the run |
|---|---|
| Eccentric reducer, flat side down | Correct at a trap The invert stays continuous, so the pig slides out of the oversized barrel straight along the bottom of the line. This is why trap reducers are eccentric and why the orientation is a hold point at installation — fitted flat-side-up it is worse than a concentric one. |
| Concentric reducer | Mid-line only Leaves a step all the way round. Tolerable mid-line where the pig is already moving and centred; poor practice immediately downstream of a launcher, where it leaves a lip at six o'clock for a cup to catch on. |
| Two-size step in the line | A conventional pig seals one bore. Two bores in one line means a dual-diameter pig, with sprung or hinged elements sized for both — and the tool's stated range has to cover the reducer type as well as the two sizes. Set a dual-diameter line in the calculator. |
| Wall thickness change at a girth weld | A step in bore with no fitting at all, and the one most often missing from the as-built. Heavy-wall road and river crossings are the usual culprits. Size the gauge plate on the thickest section, not the nominal. |
| Internal weld protrusion | Each unmachined girth weld takes a little bore and gives the sealing elements something to climb. Individually trivial, cumulatively the reason a tool arrives with more wear than predicted. |
| Dent, ovality or buckle | Reduces the bore locally in one plane. A caliper run quantifies it; a foam geometry pig will at least prove whether a tool can pass. Dents and gouges. |
| NPS | E — overall length |
|---|
| Item | Pigging relevance |
|---|---|
| Weld neck flange, ASME B16.5 Class 150–2500 | The bore is specified to match the pipe it is welded to, so a correctly specified weld neck is transparent to the pig. The failure mode is a flange bored for a lighter schedule than the pipe — a step at the weld. |
| Slip-on and socket weld flanges | The internal fillet weld intrudes into the bore. Not for piggable lines. |
| Raised face vs ring-type joint | No effect on the bore. RTJ matters at the trap only in that the closure and barrel joints have to be made up correctly under pressure. |
| Orifice flange assemblies | The orifice plate is a complete blockage. Any piggable line with metering needs a bypass around the meter run, with the valving arranged so the pig cannot be routed into it. |
| Spectacle blind / spacer | Blind position blocks the line and the spacer position restores bore. The single most common cause of a pig stopped dead on a plant line — verify the position, do not assume it. |
| ASME B16.5 size range | B16.5 covers NPS ½ to 24. Above that, flanges are to ASME B16.47 Series A or B — and the two series are not interchangeable, which matters when a trap spool is being replaced. |
Valves cause more pigging problems than any other single item in a line. Almost all of it comes down to two questions: is the bore full, and is the valve actually fully open.
| Valve | Piggable? | Notes |
|---|---|---|
| Full bore through-conduit ball valve | Yes | The standard choice for mainline and trap isolation. "Full bore" must be verified from the data sheet — not assumed from the tag. |
| Reduced bore ball valve | No | One or two sizes down internally. Shears sealing elements and can stop a tool outright. Common on older plant lines and easy to miss on a P&ID. |
| Through-conduit slab gate valve | Yes | Full round opening when open, with the seat protected. Widely used on pipelines. |
| Wedge gate valve | Conditional | Full bore when fully open, but the body cavity below the seat can catch a disc, and a partially closed wedge is invisible from outside. |
| Butterfly valve | No | The disc and stem sit in the bore even fully open. |
| Check valve | No | Swing and piston internals block the pig. Full-bore piggable check designs exist but must be specified as such. |
| Globe, needle, plug | No | Not piggable in any form. Acceptable only on branch and kicker lines the pig never enters. |
| Dual-plate / wafer check | No | Plates and the central hinge sit square across the bore. |
A fitting is not piggable or unpiggable on its own — it depends entirely on what you are running through it. A 1D short radius elbow is nothing to a foam pig and the end of the run for a mandrel body. Pick the pig you intend to run and the table tells you what will stop it, and why.
| Pipeline feature | Verdict | What happens to this pig |
|---|
| Pipeline feature |
|---|
One table for the design review or the piggability walk-down. If every row is green, the line is piggable. Each amber or red row needs either a change, or a decision recorded about what pig can live with it.
| Feature | Requirement for a piggable line | If it is not met |
|---|---|---|
| Bend radius | 3D minimum for inspection, 5D preferred. 1.5D acceptable for cleaning pigs and short tools if the vendor confirms it. | Foam or gel pigging only, or a short articulated tool at a cost and data penalty. |
| Mitred bends | None. | The line is not piggable with rigid bodies. No workaround. |
| Straight pipe between fittings | At least three diameters, so the pig is stable and fully re-sealed before the next feature. | Elements take repeated hits in sequence; expect wear and possible hang-up. |
| Branches over ~50 % of run diameter | Barred, with spacing checked against the shortest element in the train. | High risk of the pig taking the branch or jamming. Cut and replace the tee. |
| Valves on the route | Full bore, through-conduit, verified fully open and locked. | Sheared elements or a stopped tool. Replace, or reroute the run. |
| Bore changes | Single bore throughout, or a dual-diameter tool rated for both sizes and the reducer type. | Loss of seal, pig stalls or passes without cleaning. |
| Reducer at the trap | Eccentric, flat side down, orientation verified at installation. | The pig has to climb a step on launch. Hang-ups at low differential. |
| Internal protrusions | None. Thermowells, quills and probes retractable and logged out before the run. | Direct damage or a stuck pig. |
| Traps | Launcher and receiver sized for the longest tool planned, with full-bore isolation, kicker, vent, drain and pressure indication. | Temporary traps, or hot-tap and plug — both substantial scope. Trap hardware. |
| Minimum bore proven | Gauge plate at 90–95 % of the smallest bore returns undeformed, or a caliper run confirms the profile. | Do not run an inspection tool. The gauge run exists so you find the restriction with a £200 plate instead of a £200,000 tool. |
| As-built records | Wall thickness changes, bend radii, valve types and branch sizes all documented along the route. | Survey first — caliper or foam geometry. Assumption is how tools get stuck. |