Perfecting Partial Stroke Testing

The addition of an Intelligent Valve Position Transmitter as part of the Safety Instrumented System is a cost effective and efficient safety monitoring solution

Background:

Safety valves used for emergency shutdown (ESD) generally remain static for long periods - a valve that is not operated on a regular basis may be prone to sticking.

Mandatory Full Stroke Tests (FST) requiring full plant shutdowns with all the associated costs and loss of production are unlikely to be replaced, at least in the near future, by any other form of testing or technological breakthrough.

Partial Stroke Testing (PST) while considerably increasing the time span between FSTs has issues with the methods traditionally employed.

Until now the main forms PST has taken are:
The mechanical jamming of the valve via a stroke limiter, or the addition of a discrete valve controller (i.e., Smart Positioner) to the actuator.

Issues:

Mechanical Jamming, is a relatively inexpensive solution but has its disadvantages: Due to the physical presence of the jamming device the ESD Valve is unavailable during the PST, it provides no position feedback or diagnostics and reliability is dependent on procedures, training, and proper design specifications.

The Smart Positioner is the most complex of the old PST options. It is designed to generate an automatic PST function via an internal IP transducer and capture dynamic diagnostic data of the test. However, the positioner requires the use of additional devices such as limit switches or position transmitters to capture the ESD event.

Solution:

The issues associated with both the above methods can now be assigned to industrial history by adding an Intelligent Valve Position Transmitter as part of the Safety Instrumented System.

The first of this new generation to come to market is Westlock Controls’ Digital EPIC- 2 (DE2)

With only two moving parts, an analogue input and digital output (providing the main control system with exactly the data required), a unique diagnostic function to test the solenoid valve by de-energizing it and monitoring the drop in pressure (without causing any movement of the valve), the DE2 works even when the power is off and enables the valve to be used in an emergency, even during a Partial Stroke Test.

This intelligent approach to PST can also bring major cost savings by defining if a failure in the system is 'safe' and can be dealt with during routine maintenance or 'dangerous' and needing immediate action.

A new innovative transmitter from a World leading manufacturer providing a giant leap forward in safety monitoring, while giving the optimum balance of cost and functionality:

Partial Stroke Testing Perfected.

Valve & Process Solutions Ltd
Tel: 01246 220070
Web: www.vandpsolutions.com

Published: 14th May 2015