Plant Air Storage Tank Pressure Fluctuations Root Cause Analysis

Today in this article, we will discuss the Root Cause Analysis of pressure fluctuations in a Plant Air Storage Tank.

Air Tank Pressure Fluctuations

A Plant Air Storage Tank installed in one of the plants had a pressure fluctuation issue. The Plant Air Storage Tank had a pressure transmitter, a temperature transmitter, a PSV, an inlet control valve, and an outlet control valve.

The Plant Air Storage Tank’s pressure was fluctuating. Due to pressure fluctuations, the inlet control valve and outlet control valve also operate in auto mode to compensate for the set pressure value.

Probable Problems

Let us see what can be the possible root causes and what was the result of the root cause analysis. 

Probable Problem 1: Pressure Transmitter having calibration problem.

• Calibration of pressure transmitter checked twice with two different Tests and Calibration instruments. Both times, the pressure transmitter was found ok.

Probable Problem 2: Pressure Transmitter’s Tubing leakage. 

• Tubing was checked thoroughly, and no leakage was found.

Probable Problem 3: PSV (Pressure Safety Valve) passing issue.

• PSV also checked.  No issue was found in PSV. 

Probable Problem 4: Inlet Control Valve or Outlet Control valve having an issue.

• Stroke of both the control valves checked. Found ok. Also, during the 0% command to the control valve, no passing was observed. Checked passing for both control valves one by one.

Probable Problem 5: Leakage from any flange connected to the Plant Air Storage Tank

• All flange checked. No leakage was found from any flange.

Probable Problem 6: Leakage from any pipe or Plant Air Storage Tank itself.

• All pipes connected to the Plant Air Storage Tank were checked. All found ok. Also, no leakage from the tank was found.

Probable Problem 7: Any process parameter causing disturbance to the Plant Air Storage Tank pressure disturbance. 

• This can be a probable reason.

Plant Air Storage Tank Root Cause Analysis

Root Cause Analysis for Plant Air Storage Tank pressure fluctuating. 

1. The pressure Transmitter was checked and found ok.
2. PSV also checked and found ok.
3. All flange and pipes are connected to the Plant Air Storage Tank. All found ok.
4. While checking the trend for pressure fluctuations, one important observation came. The pressure would increase in the day time and decrease in the nighttime.
5. On opening the drain of the Plant Air Storage Tank, found minor moisture content in the Air. 
6. Also, one major observation came during the field round by the seniors that the drain point tapping was 500 mm higher than the drain line location mentioned in the standard documents. 

Hence it was confirmed that due to the moisture content in the Plant Air in the Plant Air Storage Tank, the pressure was increased when the temperature during the day was high which is a common phenomenon. And during nights when the temperature was low, the pressure came down.

The drain line tapping modification was planned and executed. Regular drain check for the Plant Air Storage Tank and other tanks scheduled.

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