Flange Pressure-Temperature Rating Guide

Summary

Pressure class and PN are not simple fixed-pressure promises. A flange rating depends on standard, material group, design temperature, facing, gasket route and project specification. Use this guide to prepare RFQs that let engineering and procurement compare the same duty basis.

Confirm the governing standard before reading any rating table

Match pressure class or PN with material group and design temperature

State whether the line item is ASME, EN/DIN, GOST or drawing-controlled

Do not compare quotations until rating basis, material and inspection scope match

Engineering Selection Notes

The most common RFQ trap is treating Class 300, PN 40 or Class 1500 as if the label alone defines the allowable pressure. In real projects, the usable rating is read from the standard table using material group and temperature. Two flanges with the same class can sit in different engineering conversations if material, service temperature or gasket route changes.

For export quotation, this matters because a supplier can quote the correct product name while missing the duty basis. A high-pressure RFQ should not only say Class 1500 or PN 160; it should also show the flange type, material grade, design temperature, facing and inspection expectations. That is the information QA and engineering need before committing lead time.

When buyers compare EN/DIN, ASME and GOST routes, the safest language is not a conversion claim. The RFQ should state which standard controls the order and whether any alternative standard is allowed. If conversion is needed, it should be treated as an engineering review item, not as a catalogue shortcut.

Pressure-Temperature Rating RFQ Logic

RFQ item	What buyers often send	What engineering needs	Risk if omitted
Rating label	Class 300, Class 1500, PN 40 or PN 160	Governing standard plus material group and temperature basis	Price comparison may use different rating assumptions
Material	A105, LF2, stainless or project grade	Exact material grade, condition and certificate wording	Wrong rating table or missing test evidence
Temperature	Often omitted from first RFQ	Design temperature, service temperature or MDMT note	Pressure-temperature rating cannot be reviewed cleanly
Facing	RF or RTJ sometimes added late	Facing, gasket route and ring groove note where applicable	Machining, inspection and lead time change after quote
Inspection	MTC only	MTC 3.1 plus dimensional, NDT, PMI, hardness or third-party scope as required	Offer looks cheaper because document scope is incomplete

Standard Route Reading Checklist

Route	Designation language	Rating review basis	RFQ note
ASME B16.5	NPS + Class	Pressure-temperature table by material group and temperature	State class, material and temperature basis; do not quote by class alone
ASME B16.47	NPS + Class for large diameter steel flanges	Standard-specific rating and series / drawing review	Attach drawing or line-class note for large-diameter items
EN 1092-1	DN + PN	PN route under EN project specification and material requirement	State type, PN, material and whether PED / EN 10204 documents apply
GOST / CIS project	DN + PN or project drawing	GOST table or drawing-controlled requirement	Do not convert to ASME unless the buyer approves the route

Practical Checklist

Use this list before sending drawings or line items for quotation review.

Governing standard: ASME B16.5, ASME B16.47, EN 1092-1, GOST or drawing

Size system: NPS / DN and the exact pressure class or PN

Material grade and material group where the project specification defines it

Design temperature, service temperature or MDMT note if available

Facing and gasket route: RF, RTJ, FF or drawing-controlled face

Inspection scope: MTC 3.1, dimensional report, NDT, PMI, hardness or third-party inspection

Whether substitution or standard conversion is allowed by the end user

Common RFQ Mistakes

These points often cause repeated clarification, price revisions or document mismatch.

Treating pressure class or PN as a fixed pressure value without reading material group and temperature
Comparing ASME Class and EN PN quotations as direct equivalents without project approval
Omitting design temperature on high-pressure or low-temperature service
Adding RTJ, NDT, hardness or third-party inspection only after price comparison
Quoting a drawing-controlled flange from a catalogue class label without checking bore, facing and thickness notes

FAQ

Short answers for buyers preparing this RFQ topic.

Is ASME Class the same as allowable pressure?

No. The class label is part of the rating system, but the usable pressure depends on the standard table, material group and temperature. The RFQ should include the project rating basis.

Can PN and Class be converted directly?

Do not treat PN and Class as direct replacements without engineering approval. State the governing standard first, then review any conversion against material, temperature, dimensions and project specification.

What data should a high-pressure flange RFQ include?

Include standard, size, class or PN, material, design temperature, facing, bore or drawing, NDT, MTC 3.1, third-party inspection and destination requirements.

PDF Datasheets for RFQ Review

Use these direct PDF links with the article before sending line items. The PDFs are generated from published product-page RFQ scope tables and do not invent standard dimensions.

High Pressure Flanges RFQ Datasheet

Use this PDF when class, facing, NDT, material and high-pressure inspection scope must be aligned before quotation.

Download PDF

ASME B16.5 Flanges RFQ Datasheet

Use this PDF for ASME B16.5 RFQs where NPS, class, material, facing and document scope must be stated clearly.