November, 2003

200301NovAll DayBut the pressure rating was OK!Process Safety Beacon | Temperature and Pressure Ratings - usually an inverse relationshipLessons:Asset integrityLanguage:EN Origin: CCPS Document Type:Bulletin


Here’s What Happened:

In this case, the line down stream of the rotameter had a history of plugging. Several times in the past, 150 psig steam was used successfully to clear the plug. When it plugged again, steam was used but this time the outcome was different!

How Did This Happen?

The Facts:
• The rotameter was rated for 175 psig at 200oF. At 360oF, the rating drops to only 80 psig. Steam used to clear the plug was 150 psig and 360o F.
• The rotameter failed because it could not withstand the steam pressure at the elevated temperature.

The History:
• Using steam to clear this line had been done many times in the past but was officially discontinued approximately two years ago. However, it was practiced “un-officially” during off-shifts.
• The supervisor was uncertain of the pressure rating of the piping and rotameter and had second thoughts. When he saw that the steam hose was already connected, he decided to proceed.

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