Instrument Steam Pressure Taps Primary Block Valves Glands and Bonnets Leaks

Instrumentation engineering root cause analysis (RCA) of instrument Steam Pressure Taps Primary Block Valves (PBV) Glands and Bonnets too soon leaks and this delays the commissioning of a plant.

Article Type:Root Cause Analysis (RCA)
Category:Instrumentation
Equipment Type:Transmitters
Author:S. Raghava Chari

Note: This root cause analysis (RCA) is from real-time scenarios that happened in industries during the tenure of two or three decades ago. These articles will help you to improve your troubleshooting skills and knowledge.

Instrument Steam Pressure Taps Valves Leaks

Steam taps’ Primary Block Valves (PBV) glands and bonnets within a month or even sooner leaks problem need an immediate solution:

Root Cause Analysis (RCA)  

Q- Why even reputed vendors’ correct rated ¾” weld end steam instrument Tap PBVs’ (fig 1) Bonnet and Gland leaks; but not those of the far below taps located three-way manifold valves

Instrument Steam Pressure Taps Valves Glands and Bonnets Leaks

Flashed Answer – Only cold condensate wets those of the latter, but a steam condensate mixture of those of the former.

Few days thinking flashed solution from the above RCA

Few days thinking flashed solution from the above RCA was; shift the at taps valves 200 mm below pipe CL. Now cold condensate only would wet their gland packing and bonnet gaskets; maybe these would last forever as the manifold valves.

A plant section allowed a short shutdown (SD) for trial. The trial was a great success.

RCA Solution Benefits

RCA Solution Benefits are

  1. No leaky PBVs and the associated below described benefits:
  2. Accurate Instrument readings and resultant smooth plant operation,
  3. Steam Savings
  4. Saved housekeeping costs
  5. No plant shutdowns from excessive leaks
  6. Extending this idea, displacer chambers steam PBVs welded bonnet downwards (fig 3) are leak free. Benefits 1a-1e apply to Level transmitters too.
  7. The plant saves welding 300 Nos. new steam ¾” PBVs, and 25 Nos. displacer chamber steam side 2” valves every turnaround (TA) and several between TAs.

Author: S. Raghava Chari

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