Select LocaleWe sometimes get calls in tech service asking about maximum pressures for our MXT guard columns, which are often used in applications other than traditional chromatography, where pressures can potentially be much higher.
"Barlow's Formula", which relates the internal pressure that a pipe can withstand to its dimensions and the strength of its material, is used to obtain these maximum pipe or tubing pressures. Here is a Barlow’s Formula calculator.
P= (2•S•t)/D,
where P = burst pressure (psi), S = allowable stress (see tubing supplier test report or mill cert for reported tensile strength) (psi), t = wall thickness, and D = outside diameter.
The industry standard is for the recommended maximum working pressure to be 30% of this calculated burst pressure. Further an "engineering safety/design factor" of 80% is typically applied for a final “customer usable working pressure“.
i.e.
Customer usable working pressure = engineering safety/design factor (0.8 for MXT tubing) x actual maximum working pressure (30% of burst pressure)
| MXT Tubing ID (mm) | Maximum customer usable working pressure (psi/bar/kPa) |
|
0.18 |
27,120 / 1870 / 186,986 |
|
0.25 |
20,700 / 1427 / 142,722 |
|
0.28 |
25,800 / 1779 / 177,885 |
|
0.32 |
13,090 / 903 / 90,252 |
|
0.53 |
13,280 / 916 / 91,563 |
Here is the relevant portion of an example mil cert (also called the material certificate or certificate of conformance) for our 0.53 MXT tubing below.
MECHANICAL TESTS
| Tensile Strength (psi) | Yield Strength (psi) 0.2% offset | % Elongation | Hardiness | Straightness | Surface Finish (µin) | ||
| OD | ID | ||||||
| Max. | |||||||
| Min. | |||||||
| Results | 195,000 | 155,190 | 6% | N/A | Passed | N/A | N/A |
Testing is in accordance with ASTM A370 and individual specification. Other requirements:
CHEMICAL COMPOSITION WEIGHT %
| Heat Number | C | Si | Mn | P | S | Cr | Ni | N | Mo | Co |
| Max. | 0.03 | 0.75 | 2.00 | 0.040 | 0.030 | 20.00 |
13.00 |
0.10 | ||
| Min. | 18.00 | 8.00 | ||||||||
| SE25260 | 0.03 | 0.55 | 1.12 | 0.033 | 0.0020 | 18.26 | 9.05 | 0.03 | 0.00 | 0.23 |
Chemical composition meets ASTM A249 / A269 / A270 / A632. Remarks: Composition complies to ASTM A908 & F899
It the Tensile Strength listed in the Mechanical Tests section of the cert that is used for the “S” (allowable stress) in Barlow’s formula.
An example using Barlow’s formula follows for our 0.53mmID MXT tubing.
An engineering safety factor (20% less) is applied to obtain a customer usable working pressure of 13,280 psi.
Here are a couple of other related blog posts on our larger SS tubing pressures and available MXT dimensions.
