304 SS bulging

[demsha]

Hello everyone,

Vertical plates which supports downwards trend of the flow in digester (pulp and paper making) has been bulged. Those bulges are quite large. The plates made of 304L SS. The temperature in this area falls between 300 - 320 F. Can anyone tell me what was cause for bulging to occur?

Thanks

 

[metengr]

What is the thickness? Thin 304L plates can warp resulting in bulging because of residual stresses from forming,installation or service conditions.

 

[EdStainless]

Or if they are tightly constrained and then heated the thermal expansion must go somewhere.
And 304 has a large thermal expansion.

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P.E. Metallurgy, Plymouth Tube

 

[MintJulep]

Quite possibly force > yield strength.

 

[weldstan]

Based on the cyclic operation of digesters, I agree with Ed.

 

[demsha]

The thickness of the plate is 1/4". During April 2013 shutdown never experienced any bulging of these plates but found in September 2014 shutdown. Besides this digester has been in the service since 1972.

 

[metengr]

It sounds like you had some type of over-pressure event since 2013. You need to review your operating process to determine if over-pressure was possible given bulging versus warpage. Your recent post above does not sound like any previous installation or constraint concerns.

 

[davefitz]

thermal ratcheting is a common problem in 304 SS ; the components apparently are constrained and prevented from free thermal growth. Low temperature creep is also an issue with 304L

"Nobody expects the Spanish Inquisition!"

 

[racookpe1978]

In service that long?

Dirty slides or assemblies in the hangers or supports mean expansion joints that used to work jammed.
As mentioned, a transient or over-temp due to error or failure in another system (controller, pump, burner, flow meter, sensor, etc.) Things break that old.

 

[EdStainless]

It is called wear and tear for a reason.
My hunch in that either crud or a mild deformation caused binding, and then thermal expansion took over.

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P.E. Metallurgy, Plymouth Tube

 

[weldstan]

Digesters are routinely repaired throughout their lifetimes. Any of which may have contributed to the condition. Still believe that restraint coupled with thermal cycling and thermal are primarily responsible.