# Bolt Preload for Piping connection

**URL:** <https://prepomax.discourse.group/t/bolt-preload-for-piping-connection/835>\
**Category:** General Questions\
**Created:** [April 18, 2023, 6:25am UTC](https://prepomax.discourse.group/t/bolt-preload-for-piping-connection/835 "2023-04-18T06:25:32Z")\
**Posts on this page:** 1\
**Showing post:** 16

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**Author:** ![datsnl](https://avatars.discourse-cdn.com/v4/letter/d/8e7dd6/32.png) [@datsnl](https://prepomax.discourse.group/u/datsnl)\
**Post date:** [May 15, 2023, 1:44am UTC](https://prepomax.discourse.group/t/bolt-preload-for-piping-connection/835/16 "2023-05-15T01:44:53Z")

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One more attempt. Input file is here  
[P5701178-02-214\_BoltedConnectionFEA.zip](https://prepomax.discourse.group/uploads/short-url/rcNdAXlqfFEX2kIgjFJ4HRgOzMb.zip) (1.5 MB)

Metal to metal contact, no gaskets involved.

There are 4 bolts in L pattern.

First assumption is that they are M10 Class 4.6 bolts with Proof strength of 225MPa and for Pre-Load we go upto 90% of proof strength thus Pre-Load = 15.9kN  
Contact pressure I get for this is shown below. Pressure = 1.094 Pascals

 ![image](https://global.discourse-cdn.com/free1/uploads/prepomax/original/2X/8/8ae27fb093ec89279f3755e159569c419594a629.jpeg)

For second assumption bolts are M10 Class 8.8 with Proof strength of 600MPa and Pre-Load = 42.4kN  
Contact pressure I get for this is shown below. Pressure = 3 Pascals

 ![image](https://global.discourse-cdn.com/free1/uploads/prepomax/original/2X/a/a50f2f661c89a25ab651bad75ff1148e0af531a9.png)

Pressure increased from around 1 Pascals to 3 Pascals as the Pre-Load increased from ~15kN to ~42kN

My question is, why is the contact pressure so small?

What can I do to get realistic results?

Thanking in advance.

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