Mechanical Steam Control Valve Problem Holds Up Commissioning
It was during the commissioning process at the end of a large project when it was discovered that several mechanical steam control valves were not performing reliably. Operating as both pressure-reducing and steam-regulating valves between high- and low-pressure systems, accuracy and repeatability of the spring-operated, mechanically-adjustable valves with stainless-steel diaphragm was found to be unreliable. This caused pressure control problems and negatively affected the commissioning effort.
The solution was to replace all of the valves in kind, which solved the problems in the short term, but within a short period of time, anomalies with steam pressure and high-pressure condensate flash-off began occurring once again. The manufacturer was called in, but they were unable to fix the problem, so the decision was made to bring in a respected steam engineer to assess the problems.
The steam engineer advised that, in his experience, mechanical control valves were not ideal for the type of steam design employed. Even when the mechanical valves were set up properly in this type of application, they tend to drift out over time, causing poor steam control for the process.
Omni Instrumentation & Electrical Services, Inc. having been involved in the commissioning effort, recommended replacing the mechanical steam control valves with a quality 4-20 mA pressure transmitter with pneumatically-powered, electrically-operated control valves. Once we received the OK, we were able to quickly locate the new pressure transmitters and control valves and have them delivered to the job site within one week for installation by the mechanical contractor.
With utmost safety in mind, Omni wired and tubed the control valves, then carefully loop-checked and tested them at 10% intervals. Because they were wired back to the process control system, we were also able to trend-log their performance 24/7. The new steam valves were controlled with a PID loop and were found to be controlling within one-tenth of one PSI, and a 3-point pressure check was successfully performed on the pressure transmitter, allowing the commissioning team to close the control issues that were holding up the process. Insulation was installed, valves were tagged, and labeling was completed.
Omni Instrumentation & Electrical Services, Inc., located in New Jersey and Maryland, is a premier instrumentation and electrical contractor, providing superior total care solutions since 1986. Services include instrument installation, tubing installation, instrument calibration, control loop testing, startup and commissioning, power and lighting, process control wiring, BMS wiring, telecommunications and data wiring, fire alarm wiring, security wiring, process network wiring, and control panel fabrication. Omni Instrumentation & Electrical Services, Inc., is certified in Foundation Fieldbus, Profibus, DeviceNet and ASI-Bus installation.