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Engineering Calculator · 117

PREN Composition Index Calculator

Calculate the 16N version of the pitting resistance equivalent number from chromium, molybdenum and nitrogen mass percentages.

Thermal & material change
Start calculationReview the method

Live calculation

Enter the known values.

Units remain visible beside every field and result. Change any input to recalculate immediately in your browser.

01

Inputs

02

Results

PREN — 16N formula34.78index
Chromium contribution22index
Molybdenum contribution9.9index
Nitrogen contribution2.88index

Formula
PREN16=wCr+3.3wMo+16wN\mathrm{PREN}_{16}=w_{\mathrm{Cr}}+3.3w_{\mathrm{Mo}}+16w_{\mathrm{N}}

The calculation runs locally in this browser. Values are not submitted or stored by this tool.

Direct answer

What this result means

This version of PREN is Cr + 3.3Mo + 16N, with each element entered as a mass percentage. Illustrative values of 22% Cr, 3% Mo and 0.18% N give 34.78. The number compares composition on this formula basis; it does not certify a steel grade or predict corrosion in an installation.

PREN Composition Index Calculator engineering relationship diagramEnter percentages rather than fractions: 22 means 22% by mass. The three weighted contributions add to one dimensionless index. Other published PREN variants can use different nitrogen coefficients or include tungsten, so compare only values calculated on the same stated basis. This dedicated schematic represents pren weighted composition contributions and is not to scale.Cr3.3Mo16NWeighted contributions add to PRENCR + 3.3MO + 16N · TOOL 117Chromium contentPREN — 16N formula
Calculator-specific engineering relationship diagram — schematic, not a product drawing, and not to scale.

Formula & theory

Make the assumptions visible.

Enter percentages rather than fractions: 22 means 22% by mass. The three weighted contributions add to one dimensionless index. Other published PREN variants can use different nitrogen coefficients or include tungsten, so compare only values calculated on the same stated basis.

Calculation relationship
PREN16=wCr+3.3wMo+16wN\mathrm{PREN}_{16}=w_{\mathrm{Cr}}+3.3w_{\mathrm{Mo}}+16w_{\mathrm{N}}

Enter percentages rather than fractions: 22 means 22% by mass. The three weighted contributions add to one dimensionless index. Other published PREN variants can use different nitrogen coefficients or include tungsten, so compare only values calculated on the same stated basis.

Variables

wMoMolybdenum mass percentage%
wNNitrogen mass percentage%

Use sequence

From measurement to review

  1. Identify the alloy, heat report and PREN formula required for the comparison.
  2. Enter chromium, molybdenum and nitrogen percentages by mass.
  3. Keep the formula variant with the index and review service-specific corrosion evidence separately.

Limits

What this calculation does not confirm

  • Only the Cr + 3.3Mo + 16N variant is calculated; tungsten and other coefficient variants are excluded.
  • The entered constituent percentages must each lie from 0 to 100, and their total cannot exceed 100%.
  • Microstructure, fabrication, surface condition, chloride exposure, temperature and crevices affect corrosion; PREN is not a pass/fail product rating.

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Calculator FAQ

Use the number without losing the engineering context.

These answers clarify what the tool calculates and where a product-specific review still begins.

01Calculator guidanceWhich nitrogen coefficient does this PREN tool use?

It uses 16, so the formula is Cr + 3.3Mo + 16N. Check the coefficient in any comparison report; a value calculated with 30N or an added tungsten term is a different formula basis.

02Calculator guidanceDoes a higher PREN automatically make a gland suitable for seawater?

No. The index describes selected composition contributions. Temperature, chlorides, crevices, surface condition, metallurgical quality and the actual gland construction require service-specific review.

03Calculator guidanceShould I enter minimum grade limits or the measured heat composition for PREN?

Use the basis required by the specification and state it. A heat report describes the measured batch, while specified limits describe a different comparison. The calculator does not choose that contractual basis.

Product selection support

Connect the calculation with cable-entry product options.

Bepto Cable Glands can help relate a preliminary result to the product family and current model information for your application. You can start with the details you have; a complete drawing package is not needed to ask a question.

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