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Pressure Tightness

Technical Perspective

Pressure-tightness, or leak tightness, is likely the most misunderstood, and yet one one of the most important quality attributes in casting manufacturing today.

Misperception #1: All porosity leaks, and all leaks imply porosity.

While from a broad perspective this can be true, it is quite often not the whole story. Depending upon the application, porosity not even visible to the naked eye (ie molecular dendritic arm spacing) can cause leaking if the application is stringent enough, such as in the case of low atomic weight gases at very high pressures. Furthermore, large porosity, if it is isolated, can promote very sound surrounding metal which is actually more pressure-tight, such as in the case of hypo-eutectic alloys. Bottom line is the correlation between porosity and the leak-paths in your specific application can only be analyzed on a case-by- case basis, where every application should be viewed independently.

Misperception #2: Pressure-tightness is pressure-tightness.

Nothing could be further from the truth! How stringent your application is depends upon many factors, such as:

  • Pressure

  • Media

  • Time Duration of Test

  • Thickness

  • Detection Method

  • Allowable Leak rate

  • Salvage Method

All the above factors need to be considered when judging the difficulty of a particular application. Casting an 1/8" wall pressure tight to a decay rate with SF6 gas is harder than casting a 1/4" wall that needs to be tight to 5 psi water.

Consider our calculator to get a feel for how demanding your application may or may not be.

Misperception #3: All leaks are a sign of a defective casting.

Again, this is a severe oversimplification of what pressure-tightness really is, and why it occurs. For very stringent applications, failure rates of as high as 5-10% can be perfectly acceptable, while for other situations a zero tolerance is perfectly achievable.

What also needs to be considered here is the foundry's ability to detect leaks. Detection becomes much easier when the foundry can also machine and pressure-test the component under one roof, thereby continually managing and improving the process.

Case Studies

  • SFMT Rear Cover

    Engineered Cover for High Voltage Circuit Breakers

    Pressure tight to SF6 gas at 100 psi+

  • 760 Enclosure

    Engineered Flow Control Enclosure used in Energy Sector

    Various chambers pressure tight to 80 psi air without cross talk and low permissible decay

  • Vapor Valves

    Valve for Liquid Fuel Transport Application

    Various chambers pressure tight to 80 psi air without cross talk and low permissible decay

  • 600A Cold Plate

    Battery Cover for Earth Moving Equipment

    Entire internal chamber weather tight to ambient moisture and air

  • Subaru Outlet Tank

    Radiator Tank for Automotive Application

    Leak-tight with pressurized anti-freeze

  • Filter Base

    Heavy Equipment Air Supply Filtration

    All internal passages 100% tested to 80 psi air with bubble test

  • Stator Cap 109

    Valve for Liquid Fuel Transport Application

    Leak-tight to 150 psi Air with regulated decay

  • 62XX Body

    NEMA Rated Enclosure for Oil & Gas Chromatograph

    Explosion proof casting per NEMA

  • EHA 11in Housing

    High Level Hydraulics

    Extended length sealing pressure chamber tight to 6000 psi oil burst

  • Filter Head Large

    Large Filter for Mining Industry

    O-ring groove pressure tight to 600 psi burst

  • Dynamometer Body

    Precision Handheld Health Device

    Leak-tight with oil in internally cast hollow

  • Oil Fill Boss

    Transmission Outlet Cover for Recreational Motorsport Market

    Leak-tight with Hydraulic Oil to 5000 psi burst with Welded Seams

Degree of Difficulty Calculator

Select your specifications below to view Degree of Difficulty

100°

Very Stingent

Pressure:

5 PSI

30 PSI

80 PSI (STD LINE)

150 PSI

1000 PSI

3000 PSI

10-5 Torr (Vacuum)

Media:

Oil

Water

Air

SF6 Gas

Helium

Hydrogen

Duration of Test:

10 Secs

30 Secs

60 Secs

2 Mins

2 Mins +

Wall Thickness:

< 1/8"

1/8"

1/4"

3/8"

1/2"

1/2" +

Detection Method:

Soapy Water

Underwater Bubble

Molar Decay Meter

Visible Oil Leak

Allowable Leak Rate:

None

Slight Molar Decay

Intermittent Bubbles

Permissable Salvage Method:

None

Impregnation

Weld Repair

Degree of Difficulty:

100°

Very Stingent

Degree of Difficulty Key

Moderate: Score of < 29

Challenging: Score of 30-49

Demanding:Score of 50-79

Very Stringent: Score of 80-100