Carbon steel (ASTM A106) was mistak 2

[Alpha Charlie]

Carbon steel (ASTM A106) was mistakenly installed on very high pressure steam piping (Pressure: 108 Kg/cm2 and temp: 495C) of a ammonia-urea fertilizer plant in 1979. As per design specifications, material of construction should be A335 P11. Now in August 2021, we faced creep rupture of the dia 14"-31.75mm THK (OD: 355.6mm) pipe at one location while multiple macro cracks at 3-5 O clock along the 6 meter pipe length. One crack is approx 3.5" long and through while remaining visual cracks (almost 20) are though visible but not through. Dilation was measured along the pipe length and it was around 370mm.

We are trying to online weld a sleeve over CS pipe without welding on 6 meter long CS pipe (No Shutdown). I am interested in creep deformation rate of CS pipe at these conditions. How much time or %age dilation will fall apart the CS pipe. Current measured OD of the CS pipe is 370mm which shows almost 4% creep deformation. If anyone has any experience/knowledge of max %age creep deformation which this pipe can withstand before falling apart. Please share.
Regards

 

[Guest102023]

You (or your bosses) say 'No Shutdown'. How little does the company value the lives of its workers?

Forget about trying to manage carbon steel in an environment where it cannot hope to survive, you can't do it. That is not managing anything, it is a death watch.

Shut it down immediately and do a proper reconstruction to the ORIGINAL TECHNICAL REQUIREMENTS.

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[weldstan]

You have a pretty good idea with its currnt service life. But really, why was this nonconformance corrected at first shut down if it was only detecteed after startup. or was it only recently discovered. Anyway while you wait to make a temporary repair, catastrophy couls be immenent.

 

[weldstan]

Accelerating mechanisms for potential rupture have already occurred. The ;arger diameter plus the thinner wall thicknes impart greaater load in hoop stress at the operating/design pressure and one must assume that the pipe is no longer truly round. and that's not including metallurgical issue and the effect of existing cracks. Shut down and repair before you kill somebody.

 

[Alpha Charlie]

Thanks very much for your response.
I appreciate your concerns of catastrophic failure of the high press/temp pipe. I was just interested knowing similar failure experiences and creep deformation for my understanding. In our case pipe was taken in service in 1979 and it got failed in 2021 after giving 42 years of life. Out of specification pipe was not known to us and we came to know only after facing leakage through it.

Pipe was in tertiary creep range before it failed and . I was interested in finding creep deformation rate of this material at aforementioned process conditions. How increase in OD relate to %age of creep? Like usually at 4% creep material fails?

 

[weldstan]

It depends on what the actual operating loads were on the pipe over its 42 year life, the original strength of the pipe and chemical composition.

 

[GD2]

AlphaCharlie,
During the 42 years life of the pipe, I would imagine that the system has gone through multiple operating conditions in the creep range. You can find creep rate for the CS A106 material from many handbooks including API 579 but it will be wrong to assume one operating condition in its 42 yrs. life. Who knows, if you try to dig the past 42 years operating history log, you might end up finding no data.
There is no easy quick cookie cut way to determine creep damage and determine creep rupture life.
API 579 Part 10 gives acceptable procedures but it's no easy task. You need to engage expertise help if you want to determine rupture life.

GDD
Canada

 

There is no easy quick cookie cut way to determine creep damage and determine creep rupture life.

Not in this situation.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[weldstan]

The creep rupture failures that I have observed have essentially been short term, generally with exposure to higher temps than design design/operating. I have seen longer term creep rupture when the deaign loads were very low compared with normal ASME Code allowables.