Are you acquainted with flexible metal hoses? Perhaps the information below can resolve your confusions and you will find choosing metal flexible hose will be an effective and economical way to your piping problems in the long run.

Why select flexible metal hose?

Engine vibration makes flexible hoses mandatory elements of pipe systems. Flexible hoses are engineered to absorb vibration (horizontal, vertical or angular), offset misalignment of pipelines and dampen noise. These problems above all can shorten the life span of the entire systems.

There are generally options of flexible hoses - EPDM hose and corrugated metal hose. Both can act as a medium that reduce internal stress of pipelines, absorb vibration and correct misalignment. However, stainless steel flexible hose has some exceptional properties. First, it has much longer life span than the EPDM hose. The EPDM hose usually runs 10 to 15 years, while stainless steel hose will not fail all through the life of mechanical system. Second, metal flexible hose can operate at a wider range of extreme temperatures. Third, the stainless braid makes the metal hose withstand far higher pressures than EPDM hose.

What do you know about pressures?

When selecting a flexible metal hose, you may be confused about various pressures, including working pressure, test pressure and burst pressure. What do they mean? Do they have some relationships?
Maximum Working Pressure should be calculated on a continuous basis at ambient temperature of 70°F (21°C). Generally, it accounts for a quarter of nominal burst pressure.

Maximum Test Pressure refers to the maximum pressure before the corrugation of the hose start to deform. at ambient temperature of 70°F. It can be determined by multiplying the maximum working pressure by 150%.
Nominal burst pressure means that if the pressure is exceeding, the cord or braid will rupture.

T321, T304 and T316L, which one?

321, 304 and 316L are all common materials for flexible stainless steel hose. All of them belong to austenitic chromium - nickel alloys. However, there are small differences in their properties.

321 is a stabilized grade of stainless, for it is alloyed with Titanium which has a stronger affinity for carbon than chromium does at extremely high temperatures. Type 321 is the premier choice for exhaust headers.

304 is the most common stainless steel. It is similar to 321 except that 321 has an addition of Titanium. 321 is often replaced by 304 in a lot applications, such as header construction. Compared with 321, however, 304 don't have high temperature fatigue resistance.

In contrast with 321 or 304, 316L has addition content – molybdenum, which provides protection from various forms of corrosion. 316L is strongly recommended for chloride environments because it has a higher resistance to pitting and crevice corrosion.
In a word, consider the practical application before determining the exact material.

When does the hose need a liner?

Liners are designed when the velocity of liquid or gas exceeds the maximum velocity without liner. Interlock liners can decrease the turbulence posed by high speed and reduce the resonant vibration that may occur.

If the actual velocity is higher than the maximum velocity below, a liner is recommended:

Media Hose Alignment Maximum Velocity without Liner (ft./sec.)
liquid straight 75
liquid 45° bend 56
liquid 90° bend 37
gas straight 150
gas 45° bend 112
gas 90° bend 75

Conversion formulas

Definitions Feet Per Second
gph: gallons per hour (gph ÷ ID2) x 0.0068
gpm: gallons per minute (gpm ÷ ID2) x 0.4083
cfh: cubic feet per hour (cfh ÷ ID2) x 0.0509
cfm: cubic feet per minute (cfm ÷ ID2) x 3.0558
cfs: cubic feet per second (cfs ÷ ID2) x 183.35

What does safety factor refer to?

Safety factor is the ratio between the maximum working pressure with he nominal burst pressure. Generally speaking, the ratio is 25%. That is to say, the safety factor is 4:1.

What is the difference between live length and overall length?

Live length refers to the flexible or active length of a hose assembly. However, overall length means the length of the active length together with the length of fittings and braid sleeves. In a word, overall length is longer than live length.