ASME B16.5 vs HG 20592 Flange Standards

ASME B16.5 and HG 20592 are two flange standards, the first North American and the second Chinese. They differ in how sizes, pressure classes and facings are designated, so a flange made to one does not reliably mate with a flange made to the other.

Vector Components quotes flanges to either, or to the client's own standard. The published range is DN15 to DN2000, in Class 150 to Class 2500, to ASME B16.5, ASME B16.47, HG 20592 to 20605, HG 20615 to 20626, or the client's own standard, in carbon, alloy and stainless steel.

What Does Each Standard Actually Specify?

Both fix the same categories of dimension, with different numbers in them.

The American Society of Mechanical Engineers (ASME) B16.5 covers pipe flanges and flanged fittings in nominal sizes up to 24 inches, by pressure class. ASME B16.47 picks up the larger diameters above that.

HG 20592 is a Chinese chemical industry standard, part of a series that runs from HG 20592 to 20605, with a second series from HG 20615 to 20626. It covers the same ground for the same kinds of plant.

Each standard fixes the bolt circle diameter, the number and size of bolt holes, the flange outside diameter and thickness, the hub dimensions, and the facing. Each also sets which material grades go with which rating.

Neither is a variant of the other. They are two complete, independently maintained systems that happen to describe the same component.

Where Do the Two Diverge in Practice?

At designation, at facing, and at the bolt pattern.

Designation is the first trap. ASME works in pressure classes; the HG series uses nominal pressure, written PN. A drawing that says "Class 150" and a drawing that says "PN 16" are not describing the same flange even where the dimensions happen to be close.

What a PN number permits depends on the material and the temperature, so it is not a figure to convert against an ASME class by arithmetic. Specify the standard and let its own table govern.

Facing is the second. Raised face, flat face and ring-type joint all appear in both systems, but the facing dimensions and the gasket that seats on them are set by the standard. A correct flange with the wrong facing does not seal.

The bolt pattern is the third and the most visible. Two flanges of the same nominal size to different standards can differ in bolt circle diameter and hole count, which means they will not bolt together regardless of what else is right.

None of this is a statement about where the flange was made. Flanges to ASME B16.5 are manufactured in China routinely and correctly. What causes a mismatch is a drawing that names a size and a class without naming the standard, and leaves the choice to whoever reads it.

Which Range Is Available to Either Standard?

DN15 to DN2000, Class 150 to Class 2500, in carbon, alloy and stainless steel.

Nominal diameter (DN) is the metric designation, and the range covers everything from a small instrument connection to a large plant header. The specification table on the flanges page carries the full combination of size, class and material.

The client's own standard is also quoted. Company standards usually depart from a published standard in a small number of specific dimensions rather than throughout, so sending the standard document or referencing it on the drawing is what makes that work.

Parts are made by the partner factories Vector Components represents. Vector does not own or run a factory, and each factory in the network has an agreement authorizing Vector to serve as its overseas sales department.

What Has to Be on the Drawing?

Six things: the standard, the nominal diameter, the pressure class, the facing type, the material grade, and ideally the component it mates to.

Facing is the one most often left off, and it matters as much as the bolt circle because the gasket seats on it.

The mating component is the most useful addition. A flange specified against the thing it bolts to can be checked before it is made, and that check catches the designation mismatch described above.

Vector's team works with the production engineers in their native language. A question about which standard a drawing meant is answered against the drawing rather than guessed at, which is where a standards mismatch usually gets caught or missed.

Which Standard Should You Order To?

Whichever the mating equipment uses.

That is the whole answer, and it is worth stating plainly because the question often arrives framed as a quality comparison. It is not one. Both standards produce flanges that work; mixing them produces flanges that do not fit.

If the plant is North American, ASME. If the equipment came from a Chinese supplier and the existing flanges are HG, HG. If the project has both, say so on the drawing and specify each line separately rather than letting one standard be assumed across the order.

Standard parts made to exact specification typically ship within two weeks. Material grade and pressure class move that more than size does, because the higher classes need thicker forged stock.

Send computer-aided design (CAD) drawings and specifications with the standard and the mating component named. A quotation follows within one business day, quotations are free, and payment terms are NET 30.

Send the drawing and the mating part.

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