Your web browser will no longer be supported by Restek.com as of 30 June 2021.
To avoid any interruption in access or functionality, install a current-generation web browser now. Learn more.

Maximum Usable Pressures for our MXT Tubing

23 January 2023
By
  • Tim Herring
  • Share:

We 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.

blog-maximum-usable-pressures-for-our-MXT-tubing-01.jpg

"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.

P = (2*S*t)/D
P = (2*195,000 psi)(0.105mm) / (0.74mm) = 55,338 psi
Max working pressure = 30% of P = 16,601 psi

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.

Related Articles

Maximum Working Pressure of Restek Stainless Steel Tubing

Read Article

GC capillary tubing – things you may not know

Read Article
Comments

Sign In and be the first to comment.