inferTIC

Resources · Method

Published methods, cited to the page.

Three principles the code enforces: every number originates in the engine; every number carries provenance; nothing is derived from a closed-box estimator’s content. This page states the method those principles serve.

The calculation chain

Each step is a pure function. The trace object shown to the user is the record of these calls, in order, with inputs and outputs at each step.

  1. Sizing parameterUser input per item — area, volume, power, duty. A warning if it lies outside the correlation’s validity range.
  2. Purchased costFrom the library correlation at its base year and base CEPCI, or a vendor quote that bypasses the correlation and is tagged as such.
  3. Material and pressure factorsFrom the library record; multiplicative on purchased cost.
  4. EscalationCEPCI from the correlation base year to the estimate cost date. The index table is user-editable and the rows used are snapshotted into the estimate file.
  5. Location factorThe library ships the US base location; any other location is a company row or a user override with a required note.
  6. CurrencyUser-set FX rate and date.
  7. Installed costSelectable: Lang, Hand, Guthrie bare-module, or user-defined percentages.
  8. Indirects, EPCM, owner’s costPercentages, defaults by class, editable.
  9. ContingencyPercentage, default by class from a cited source, editable.
  10. Total and Monte Carlo bandTriangular or PERT per line or group, seeded; the seed is stored.

Class 3 method

AACE 18R-97 describes Class 3 as semi-detailed unit costs with assembly-level line items, prepared from preliminary quantity take-offs. The tool implements exactly that and nothing more. A bulk line carries a discipline, a quantity and a unit; quantities arrive by import of a line list or MTO, by manual entry, or by geometry from user-entered coordinates and rack polylines. Unit rates and labour norms come from a versioned company set, every row sourced, or from a public seed flagged as such. Labour is hours times craft rate times a productivity factor that the estimator states with a note.

Class 3 is claimed only when the user-stated definition level is within the Class 3 band and at least one line is quantity-priced. There is no library threshold on the quantity-priced share of cost; the share is reported so a reviewer can judge it.

Classes 5, 4 and 3 — what each one needs, what it is for

One reference plant. Three classes. One engine.

Move the slider: the app’s own capacity-scaling function runs on one checked library record and returns the figure. Switch the class: the drawing shows what a Class 5, 4 or 3 estimate has defined, and the band bracket redraws from the library’s class table. The page holds no arithmetic.

Line drawing of a reference process unit: feed pump, reactor, two shell-and-tube exchangers, distillation column with condenser, reflux drum and reboiler, bottoms pump, on a pipe rack with foundations and platform steel The class mode switch changes what the drawing highlights: Class 5 the whole unit as one block, Class 4 each sized item with the name of its size parameter, Class 3 the pipe rack, foundations and platform steel with the quantity and rate each is priced by. Cyan streams are cold, amber hot. CAPACITY × PROCESS TYPE — ONE BLOCK PIPING · LENGTH m · FITTINGS · UNIT RATE + LABOUR NORM CONCRETE · m³ · UNIT RATE CONCRETE · m³ · UNIT RATE PLATFORM STEEL · t · UNIT RATE P-101 POWER · kW R-101 VOLUME · m³ · MATERIAL · PRESSURE E-102 AREA · m² E-103 AREA · m² C-201 DIAMETER · HEIGHT · TRAYS E-203 AREA · m² V-204 VOLUME · m³ E-205 AREA · m² P-202 POWER · kW FEED DISTILLATE BOTTOMS
Illustrative reference plant — not an estimate. Tags are placeholders; each label names the parameter or quantity that class defines, never a value.

Class mode

The figure is the Class 5 screening result; Class 4 and 3 replace it with priced equipment and bulks. The slider’s ends are the exponent’s published validity window, as the engine reports it.

Record
Source
Reference point
Trace step, as the engine returns it 

            

          

        

      


      
An estimator’s brief, class by class

      

        

          
Class 5 — concept screening

          
Class 5 is the screening estimate: project definition at its lowest, the widest expected accuracy range in the practice, and an end usage of concept screening — is this worth studying at all? In this tool it needs a capacity and a published process type; the engine scales a cited unit-capacity cost by a cited exponent. Report the class, its band, and a P-value from the seeded Monte Carlo run the tool stores. Contingency is the library’s default for the class, editable, cited. Concept select, nothing firmer.

        

        

          
Class 4 — study or feasibility

          
Class 4 is the study or feasibility estimate for pre-FEED: a preferred option exists, project definition has moved on, and the expected accuracy range narrows. It needs a sized equipment list with material and design pressure. Each item is priced from a cited correlation, factored, escalated, located and installed by Lang, Hand or bare-module; a size outside a correlation’s range is flagged, never hidden. State the class and quote the P-value from the stored run. Contingency is the library’s default for the class, editable, cited.

        

        

          
Class 3 — budget authorisation or control

          
Class 3 is the budget authorisation or control estimate that carries FEED to a final investment decision: project definition well advanced, the tightest expected accuracy range this tool will ever claim. It needs the Class 4 equipment list plus quantified bulks — a line list or MTO, manual lines, or geometry from coordinates you entered — priced at unit rates and labour norms from a company set you can cite, with a stated productivity factor. Fail the gate and the badge says Class 4. State the class, the P-value, and the library’s contingency default, editable, cited.

        

      


      
AACE class bands, as stored

      
Rendered from the library’s class table, the same record the app reads and the bracket above draws from. The class is assigned from the definition level the estimator states. No class better than 3 is ever presented or implied.

      
AACE 18R-97 classes as stored in the methods library (classes.json)
ClassProject definitionExpected accuracy
Class 50–2 %-50 % / +100 %
Class 41–15 %-30 % / +50 %
Class 310–40 %-20 % / +30 %

      
The definition levels were checked against a printed reprint of the classification table; the accuracy percentages rest on the recommended practice as stated in the project brief and are noted in the record as not yet verified against a printed page of the RP itself.


      

      
Published sources

      
Equations and coefficients are implemented as methods, presented in the library’s own structure, and cited by edition, table and page. Publishers' typeset tables and figures are not reproduced. A record may carry an open item while a value is untranscribed; the release gate fails on any. The registry below is rendered from the library.

      
      
A new edition, an annual index update or a standards revision enters the library by superseding, never by overwriting: an issued estimate keeps computing on the records it names. Second reads and open items are listed in the library changelog.


      

      
What it deliberately does not do

      

      
Questions

      
Write to hello@infertic.com. The product is built by Vantis Project Intelligence Ltd.