Material take-off and estimate¶

cheme assess mto counts the bulk materials of the committed 3D model (layout/plant-model.yaml, layout-model.md); cheme assess estimate prices them with the project's unit rates (estimate/rates.yaml, kind rates) by the factor method. GET /api/mto serves both for a revision. Code: domains/assessment/mto.py, estimate.py, schemas.py, gates.py, package data domains/assessment/data/steel-sections.yaml; skill mto-estimate; tests tests/test_assessment_mto.py (counts against a small model counted by hand).

The take-off reads the model as a file (the documented contract), so assessment imports no spatial code. It is deterministic: the same model gives the same rows in the same order. cheme-as-code holds no prices: every rate and factor comes from the plant repository, each with status (ASSUMED or QUOTED), source and year. The file cheme init writes is an example (example: true, currency XXX) and prices nothing.

Take-off rows¶

One row per category, item, DN (and second DN), pipe class, spec and group, summed:

category	unit	item	counted from the model
`pipe`	m	`pipe`	each `pipes[]` polyline's length, by `dn`, `class.code` and insulation (`spec`: `bare` or `insulation <mm> mm <jacket>`); the length of a `buried` pipe in the ground (its top at or below grade, a riser to where it leaves the ground) in rows of its own, `group: buried` (coating, trench); `count`: pipes
`elbow`	ea	`elbow 90`, `elbow 45`, `bend <deg>`	every change of direction above 1 degree inside a pipe's polyline, and where two pipe ends meet at an angle (at the larger DN)
`tee`	ea	`tee`, `reducing tee`	a pipe end on another pipe's run (run: that pipe; `dn` the larger, `dn2` the smaller DN); three pipe ends at one point (run: the two largest); n > 3 ends: n - 2 tees
`reducer`	ea	`reducer`	two pipe ends of different DN at one point (`dn` x `dn2`); a placed `inline` reducer elsewhere (`dn` of its pipe)
`flange`	ea	`weld neck flange`	one pipe flange per `flange-<k>` and `outlet-flange` part of an `inline` item (two for a valve, check valve or safety valve without parts; the outlet flange at the DN of the item's other segment), and one per nozzle whose `point` is a pipe's end
`gasket`	ea	`gasket and bolt set`	one per flange (one per flanged joint)
`valve`	ea	the DEXPI class (`BallValve`, ...)	`inline` items of kind `valve`, `check_valve`, `safety_valve`, at their pipe's DN and class
`inline`	ea	the DEXPI class	the other `inline` items (silencers, filters, instruments)
`steel`	t	the section (`HEB300`, ...)	every `member` part: length x mass per metre (`steel-sections.yaml`); `spec`: the part's `material` (`steel`, `handrail`, `crane` for the runways), `length_m`: total length, `count`: members; the overhead crane itself (bridge, end carriages, crab) is a machine and not counted
`grating`	m2	`grating`	plan area of `grating` parts (`box`: dx x dy; `annulus`: ring area over its arc)
`insulation`	m2	`pipe insulation`, `equipment insulation`	outer surface of insulated pipes, pi (OD + 2 t) L; side surface of `insulation` cylinders
`concrete`	m3	the part's name without numbers and sides (`plinth`, `foundation`, `ring-wall`, `saddle-pad`; `bund wall` in a bund area)	volume of `concrete` parts (`box`, `cylinder`, `annulus`)

group says where a part is: rack, structure, building, platform, step-over, equipment, support, support-steel (declared posts and T-posts under pipes), area, and stair or ladder for the parts of a structure's, rack's or platform's stairs and ladders. Proposed valve access platforms and proposed support steel (whole objects of source: generated) are left out until they are pinned. Points closer than 2 mm are one point.

Not counted (the model does not draw them): unrouted lines, field-run small bore, vents and drains not on the P&ID, olets and couplings, flanges at spool breaks, steel without a section (shoes, guides, chairs, base plates, connections, tank and platform handrails drawn as rings or cylinders), equipment insulation beyond the drawn cylinders, paving, piles, sumps. The estimate carries them as factors or explicit rates.

Section masses (steel-sections.yaml): HEB, HEA, IPE, UPN (also written C200) and equal angles at the EN 10365 nominal masses; RHS and flat bars named without a wall thickness at the values given there (ASSUMED). A name is compared without blanks and in upper case. A member of another section is left out and reported (cheme.mto-section-unknown, warning).

estimate/mto.csv columns: category, item, dn, dn2, class, spec, group, count, quantity, unit, length_m (numbers to 3 decimals, empty when not applicable). estimate/mto.md: the totals, one table per category, the findings, and the model's provenance.output_sha256.

`estimate/rates.yaml` (kind `rates`)¶

currency: EUR            # ISO 4217; XXX: no currency (the template's example)
cost_year: 2026
example: false           # true: example numbers, the estimate warns, gate `rates` fails
basis: "Class 4 estimate of the bulk materials, basic engineering"
rates:                   # the FIRST rate of a row's category whose where: matches prices it
  - {id: pipe-cs-small, category: pipe, unit: m, rate: ..., where: {dn_max: 50, class: "PN16"},
     status: QUOTED, source: "<supplier> quotation <ref>", year: 2026}
factors:
  - {id: piping-erection, kind: direct, factor: ..., applies_to: [pipe, elbow, flange, valve],
     status: ASSUMED, source: "<estimating handbook, edition>", year: 2025}
  - {id: engineering, kind: indirect, factor: ..., status: ASSUMED, source: ..., year: 2026}
  - {id: contingency, kind: contingency, factor: ..., status: ASSUMED, source: ..., year: 2026}

A rate's unit must be its category's (above). where: filters, all optional: item (glob), dn_min, dn_max, class (glob on the pipe class), spec (glob), group (glob). cheme schema rates prints the JSON Schema; cheme validate checks the file.

The estimate¶

materials: each row x its rate (rounded to 0.01); a row without a rate stays unpriced;
direct: each kind: direct factor x the material cost of its applies_to categories (all materials when empty); direct cost = materials + direct factors;
indirect: each kind: indirect factor x the direct cost;
contingency: each kind: contingency factor x (direct + indirect).

Total = direct + indirect + contingency. Findings (file estimate/rates.yaml): cheme.estimate-example-rates (warning), cheme.estimate-unpriced (warning, rows without a rate), cheme.estimate-rate-year (info: rates and factors of another year than cost_year, used without escalation), cheme.estimate-rate-unused (info: a rate no row uses, usually shadowed by an earlier one), cheme.estimate-no-rates (error: no or an invalid file).

estimate/estimate.csv columns: section (material, direct, indirect, contingency), id (the take-off row's key, e.g. pipe DN100 PN16 bare, or the factor's id), description, quantity (a factor's base cost), unit, rate (or the factor), basis (the rate's or factor's id), cost, status, source, year.

Commands¶

command	does
`cheme assess mto [--csv \\| --json] [--write \\| --check]`	the take-off (Markdown by default); findings on stderr; exit 1 without a model
`cheme assess estimate [--csv \\| --json] [--write \\| --check]`	the estimate (Markdown by default); exit 1 without a model or valid rates

--write writes estimate/mto.csv and estimate/mto.md (estimate/estimate.csv and .md); --check writes nothing and exits 1 when they are not what the current files give. --json is the payload below plus source (git commit, dirty inputs, fingerprints of the model and the rates).

Python: mto_report(root) -> MtoReport (rows, findings, takeoff, source, payload()) and take_off(model_document) -> TakeOff; estimate_report(root) -> EstimateReport and estimate(takeoff, RateFile) -> Estimate (lines, totals(), findings).

The gate `kind: mto`¶

require takes any of:

mto-current: estimate/mto.csv is the take-off of the current layout/plant-model.yaml (byte for byte);
rates: estimate/rates.yaml loads, is not an example, and prices every take-off row;
estimate-current: estimate/estimate.csv is the estimate of the current model and rates.

The template's gate mto (stage basic) requires mto-current; a project adds rates and estimate-current once it prices its plant. The gate does not judge the quantities or the rates: that is the estimate review's (skill mto-estimate).

`GET /api/mto?rev=`¶

The take-off of the committed model at rev (default: the working tree), read-only:

{
  "rev": "<commit or null>",
  "model": "layout/plant-model.yaml",
  "model_sha256": "<the model's provenance.output_sha256>",
  "columns": ["category", "item", "dn", "dn2", "class", "spec", "group", "count", "quantity",
              "unit", "length_m"],
  "rows": [{"category": "pipe", "item": "pipe", "dn": 100.0, "dn2": null, "class": "PN16",
            "spec": "bare", "group": "", "count": 2, "quantity": 10.0, "unit": "m",
            "length_m": null, "key": "pipe DN100 PN16 bare"}],
  "totals": {"pipe": {"m": 812.4}, "steel": {"t": 299.5}},
  "findings": [{"file": "...", "level": "warning", "rule": "cheme.mto-section-unknown",
                "message": "...", "ids": ["XYZ1"], "hint": "..."}],
  "estimate": null
}

estimate is null without estimate/rates.yaml at that revision, else {currency, cost_year, example, model_sha256, totals: {materials, direct, indirect, contingency, total, unpriced_rows}, lines: [{section, id, description, quantity, unit, rate, basis, cost, status, source, year}], findings} (totals empty and the error in findings when the rates do not load). 404 without a model at that revision, 422 for a model that is not a YAML mapping.

The equipment estimate (`cheme assess equipment`)¶

domains/assessment/equipment_cost.py costs every item of the equipment list from the published purchased and bare module cost correlations of R. Turton, J. A. Shaeiwitz, D. Bhattacharyya, W. B. Whiting, Analysis, Synthesis, and Design of Chemical Processes, 5th ed., 2018, Appendix A (CAPCOST). The package data domains/assessment/data/turton-capcost.yaml holds the rows used, each with its table (A.1 to A.4, Figure A.19) and the second transcription it was cross-checked against; factors whose transcriptions disagree are left out on purpose, so the project supplies them with their source or the item stays partly costed.

step	how
correlation	from the DEXPI class (pump: centrifugal, reciprocating, positive displacement; compressor; fan; expander or turbine; exchanger: fixed tube sheet unless U-tube, floating head, kettle, double pipe, plate, spiral or air cooled; column: tower shell; tank: fixed or floating roof; vessel: vertical, horizontal with a length and no height), or `correlation` of the cost basis
size A	the cost basis's `size` (with `size_source`), else the datasheet (`type_specific`, `operating`, `design`: `volume_m3`, `area_m2`/`heat_transfer_area_m2`, `shaft_power_kw`/`power_kw`, `fluid_power_kw`, `gas_flow_m3_s`/`flow_m3_s`, `duty_kw`; the size source carries the value's `source`, `ASSUMED` when the datasheet marks it `assumed: true`, and `draft` for a draft datasheet, listed in the info finding `estimate-draft-size`), else a volume from the list's `dimensions` (pi/4 D^2 H, overall: an upper bound, ASSUMED)
purchased	log10 Cp0 = K1 + K2 log10 A + K3 (log10 A)^2, USD at CEPCI 397 (2001); outside A's range: `estimate-equipment-range`, not extrapolated
pressure factor	vessels and towers: ((P+1) D / (2 (850 - 0.6 (P+1))) + 0.00315) / 0.0063, at least 1; others log10 Fp = C1 + C2 log10 P + C3 (log10 P)^2 over the row's range, 1 below it; P = `design_pressure_barg`
material factor	`CS` or `SS` read from the list's `material` (only one of them, no other metal); else the cost basis's `fm`
bare module	CBM = Cp0 (B1 + B2 Fm Fp), or Cp0 FBM (compressors: the centrifugal FBM only; a class naming axial or reciprocating gets its purchased cost only, a class naming no kind the centrifugal FBM marked ASSUMED); a missing factor: `estimate-equipment-partial` (purchased cost only) unless the cost basis gives `fm`, `fp` or `fbm` with `factor_source`
escalation	x `cost_index.value` / 397 (the project's CEPCI with year and source); none: `estimate-no-index`, costs stay in 2001 dollars

estimate/cost-basis.yaml (kind cost_basis, cheme schema cost_basis):

cost_index: {value: <CEPCI>, year: <year>, source: "<where it is published>"}
estimate_class: 5        # AACE 18R-97
items:
  - {tag: E-101, size: 120, size_source: "DESIGN.md D-012, thermal rating"}
  - {tag: C-101, fm: 1.7, factor_source: "<book, table, page>"}
  - {tag: X-101, cost: 250000, currency: EUR, year: 2026, status: QUOTED, source: "<quotation>"}
  - {tag: F-101, exclude: "inside the package unit X-101"}

estimate/equipment-cost.csv columns: tag, type, correlation, size, unit, size_source, cp0_base, fp, fm, fbm, cbm_base, index_ratio, purchased, bare_module, status, notes (status bare module, purchased only, project cost, excluded: <reason>, not covered). estimate/equipment-cost.md states the class and its expected accuracy range from AACE International Recommended Practice 18R-97 (class 5: -20 % to -50 % low, +30 % to +100 % high; class 4: -15 % to -30 %, +20 % to +50 %), the source, the escalation and the items covered. The bare module cost includes each item's installation materials and labour and its indirect costs, so the bulk factor estimate above is not added on top for the same scope. Python: equipment_estimate(root) -> EquipmentEstimate (lines, totals(), uncovered(), findings, payload()), estimate_equipment(equipment, datasheets, basis).

The gate kind: mto takes equipment-current (the written CSV is current) and equipment-covered (every item has a bare module cost, its own cost, or is excluded with a reason, and a cost index is given).

`GET /api/estimate/equipment?rev=`¶

The equipment estimate at rev (default: the working tree), read-only: cheme assess equipment --json of the equipment list, estimate/cost-basis.yaml and the datasheets at that revision, with rev (the commit, null for the working tree) in front (abridged, from the ASU example plant):

{
  "rev": "<commit or null>",
  "currency": "USD",
  "base": {"cepci": 397.0, "year": 2001},
  "index": {"value": 797.9, "year": 2023, "month": "annual", "source": "..."},
  "estimate_class": 5,
  "accuracy": {"low": "-20 % to -50 %", "high": "+30 % to +100 %"},
  "totals": {"purchased": 4002556.0, "bare_module": 2099909.0, "items": 39,
             "bare_module_items": 3, "purchased_only": 22, "own_cost": 0, "excluded": 0,
             "not_covered": 14},
  "lines": [{"tag": "C-1102", "type": "ProcessColumn", "correlation": "tower",
             "size": 349.895, "unit": "m3", "size_source": "datasheet type_specific.volume_m3 ...",
             "cp0_base": 215480.5, "fp": 1.3415, "fm": 1.0, "fbm": 4.6916,
             "cbm_base": 1010942.7, "index_ratio": 2.0098, "purchased": 433077.8,
             "bare_module": 2031816.6, "status": "bare module",
             "notes": "tower shell (internals not included); Fm CS"}],
  "own_costs": [{"tag": "...", "cost": 250000, "currency": "EUR", "year": 2026,
                 "status": "QUOTED", "source": "..."}],
  "findings": [{"file": "estimate/cost-basis.yaml", "level": "warning",
                "rule": "cheme.estimate-equipment-uncovered", "message": "F-1101 (GasFilter): ...",
                "line": null, "ids": ["F-1101"], "hint": "...", "key": "F-1101", "box": null,
                "crop": null, "accepted": null, "measured": null}],
  "source": {"commit": "<sha>", "dirty": [], "fingerprints": {"equipment/equipment-list.yaml":
             "sha256:..."}}
}

index is null without a cost_index; source names the inputs as served (at a revision nothing is dirty). 404 without equipment/equipment-list.yaml or when it lists no items (nothing to estimate), 422 for a list that does not load; a cost basis that does not load is the first finding. GET /api/repo says has_equipment_estimate (the list lists items).

Material take-off and estimate¶

Take-off rows¶

estimate/rates.yaml (kind rates)¶

The estimate¶

Commands¶

The gate kind: mto¶

GET /api/mto?rev=¶

The equipment estimate (cheme assess equipment)¶

GET /api/estimate/equipment?rev=¶

`estimate/rates.yaml` (kind `rates`)¶

The gate `kind: mto`¶

`GET /api/mto?rev=`¶

The equipment estimate (`cheme assess equipment`)¶

`GET /api/estimate/equipment?rev=`¶