How Wide Should a Flange Guard Be? Measure the Gap, Not the Flange

A stainless steel flange spray shield, also called a flange guard or flange safety shield, does not need to cover the full width of both flanges or the projecting bolts. What matters is the gap between the two flange faces. The shield needs at least 10 mm of mesh contact on each flange, so the minimum shield width is the gap plus 20 mm. A standard 50 mm RAMCO Spray Control (RSC) shield therefore suits flange gaps of up to 30 mm.

It is one of the questions our technical team answers most often: "Does the shield need to cover the full width of both flanges?" The answer is no. The diagram above shows why.

The width rule: shield width ≥ gap + 20 mm

Measure the gap between the two flange faces, rim to rim. Add 20 mm, which is 10 mm of mesh contact for each flange. The result is the minimum shield width when the shield is centred over the joint.

Minimum shield width = flange gap + 20 mm

The overall thickness of the flange pair and the length of the projecting bolts do not change this calculation.

Quick reference: which flange guard or spray shield width for which gap?

What does the mesh do?

RSC metal safety shield uses multi-layer stainless steel mesh to diffuse spray pressure at the flange joint. If a gasket fails, the mesh reduces the force of the escaping spray, helping to protect personnel and nearby equipment. To do that reliably, the mesh must sit on both flanges. For width selection, that means at least 10 mm of mesh contact on each flange.

Three flange gaps, explained

Standard raised-face joint: 8 mm gap

The first illustration shows an 8 mm gap with a standard 50 mm shield. That leaves 42 mm of shield width overlapping the flanges, or 21 mm of mesh contact on each side.

A typical ASME B16.5 Class 150 or 300 raised-face connection has a 1.6 mm raised face on each flange and a gasket of roughly 3–4.5 mm, giving a gap of about 6–9 mm. A centred 50 mm shield leaves more than 20 mm of contact per side.

Spacer or spectacle blind fitted: 30 mm gap

The middle illustration shows a spacer increasing the gap to 30 mm. The same 50 mm shield still gives 10 mm of mesh contact on each flange, which meets the minimum.

The flange bodies are the same thickness as in the first illustration. They have simply moved further apart to make room for the spacer; the shield width has not changed.

Wafer check valve (non-return valve) fitted: 40 mm gap

The third illustration shows a wafer-type non-return valve increasing the gap to 40 mm. A centred 50 mm shield would leave only 5 mm of contact per side, which is below the minimum, so a wider shield is needed.

Using the rule, 40 mm + 20 mm gives a minimum width of 60 mm. The next standard size, 70 mm, gives 15 mm of mesh contact on each flange when centred.

Do thicker or higher-pressure flanges need a wider spray shield?

Not necessarily. Higher pressure classes, such as ASME Class 900 and 1500 or EN 1092-1 PN 64 and PN 100, have thicker flange bodies, but the gap between the flange faces is not much larger.

For example, ASME B16.5 Class 400 and above use a 6.4 mm raised face on each flange. With the gasket, that puts the gap at around 16–17 mm: still well within a standard 50 mm shield.

Projecting bolts can also make the overall assembly much wider than 50 mm. The shield does not need to cover the bolts or conceal the complete flange pair. Measure the gap before specifying a wider shield.

How to measure the flange gap for a spray shield

Measure the distance between the two flange faces at their outside edges, rim to rim. Include any gasket, spacer, spectacle blind or wafer valve between them.

Take the measurement at several points around the joint and use the largest figure.

Add 20 mm to find the minimum shield width, then choose the next standard width up.

Confirm the flange outside diameter and the application details (media, pressure, temperature) so the shield diameter and specification are also correct.

Available RAMCO spray shield widths

We manufacture stainless steel RSC flange spray shields in 50, 70 and 90 mm widths with a single clip, and in widths of 100 mm and above with two clips. Width is one part of the specification. The correct diameter and application specification must also be confirmed; the safety shield selection guide covers pressure, temperature, chemical compatibility and inspection requirements.

Not sure which width you need?

Send us the gap measurement and details of the connection, and we will recommend a suitable shield. Request a quote or ask our technical team.

Frequently Asked Questions

Does a spray shield need to cover the whole flange pair?

No. A flange spray shield needs at least 10 mm of mesh contact on each flange. It does not need to cover the full flange thickness or the projecting bolts.

How do I work out the spray shield width I need?

Measure the gap between the flange faces and add 20 mm. For a 40 mm gap, the minimum width is 60 mm, so a 70 mm shield is specified.

What is the maximum gap for a 50 mm spray shield?

30 mm, when the shield is centred over the joint. That leaves 10 mm of mesh contact on each flange.

Do Class 900 or PN 100 flanges need a wider spray shield?

Not necessarily. Higher pressure classes have thicker flange bodies, but the gap between the flange faces usually stays well under 30 mm. Measure the gap before choosing a wider shield.

Do I need a wider shield if there is a spacer or check valve in the joint?

Only if the gap exceeds the shield's limit. A 50 mm shield suits up to 30 mm; above that, use the width rule (gap + 20 mm).

Is a flange guard the same as a flange spray shield?

Yes, in most cases. Flange guard, flange shield, flange safety shield and spray shield are all names for a cover fitted around a flanged pipe joint to help manage spray from a leak. The sizing rule in this article applies to RAMCO's stainless steel RSC shields.

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