Digital Feature: Guiding a chopper valve application
S. GAVINI, Valin Corporation, Chandler, Arizona
A large refinery in California (U.S.) was conducting a turnaround and utilized an outside engineering firm to oversee the process. During this phase, the engineering firm discovered the refinery needed new emergency safety shut-off valves (chopper valves) as part of their regeneration process. The refinery was working with an engineering firm to assist with this process who, in turn, contacted the author’s company. After the author’s company’s team reviewed the specifications, it held an in-depth strategic session with both the engineering firm and the refinery.
The redundant control system. During the discussion and analysis, it was determined that the refinery would specifically need process valves for their chopper valve application. These chopper valves demand redundant solenoid valves to pilot them. However, if not designed properly, these valves can have a higher rate of failure due to the nature of their operation.
With most solenoid valves, the O-rings will be in direct contact with the walls of the chamber while the plunger is in motion. This is what ultimately creates the seal. This means that before moving, the plunger must first overcome the stiction between the O-rings and walls. Thus, if the valve is resting for an extended period, the stiction increases beyond a level where the forces generated by the solenoid coil can overcome it. Furthermore, when any level of water and/or oil is introduced to the mix, the stiction gets even worse. With all these potential concerns in play, the valve’s probability of failure-on-demand (PFD) is increasingly higher. The risks of explosions increase when this happens, resulting in more safety concerns and the likelihood of an unplanned shutdown.
For this reason, it makes logical sense to periodically test solenoid valves to ensure that stiction does not become a significant problem. However, to test the valve, one must bring it through a single cycle. This means you must take the safety instrumented system (SIS) offline. This, in turn, causes costly downtime. This fact was enough to prevent many plant owners from participating in this kind of preventative maintenance. The way to circumvent this is by adding a second solenoid valve to the design. By using this approach, one can test each solenoid individually. Additionally, a controller can be programmed to run periodic tests automatically. This can further prevent valve stiction and lower the average PFD. This is the point where the author’s company’s team assembled a valve package that included a proprietary redundant control systema (RCS) (FIG. 1).
FIG. 1. A view of the proprietary RCSa.
The RCS is the only pilot valve system that has no single point of failure that could result in an unwanted closure of the process valve. The RCS is also fit-for-use in SIL 3 applications and greatly reduces false trip rates. By using a redundant, fault-tolerant architecture, high diagnostic coverage and automated testing, the RCS achieves a higher level of process safety and reliability. It is available in a variety of constructions as well, providing valve diagnostics through automated, online testing.
By adding two solenoid valves to the SIS, the refinery took the proper steps to keep its equipment, facility, and personnel safe and its system online.
Certification. Due to stringent safety rules in California (U.S.), the author’s company’s team was asked to add a third party Class 1 Div. 2, Group B, C and D certifications on the RCS solution. As a standard, the proprietary RCS vendor does not offer this certification. However, the author’s company partnered with a third party to provide certification to meet the refinery specifications. These certifications were traditionally completed by field verifications where the third party brings their own personnel, verifies the product and certifies the solution by sticking a label on them. This is a time-consuming process and neither the refinery nor the engineering firm was interested in going through this process due to past experiences. Detailed meetings were held with various certification providers and the best certifier was determined to fit the customer needs.
Through collaboration, a limited product certification (LPC) plan was developed to opt out from field certification and ship out the RCS with class rating labels on them. This certification offers UL 508:2018 Ed.18, UL 508A:2018 Ed.3+R and UL 1203:2013 Ed.5+R to make the RCS a Class 1 Div 2, Group B, C and D rated product. This process benefited both the refinery and the engineering firm by saving time and eliminating the need for third-party companies to come out and perform field certifications.
This offered a one-stop-shop solution with competitive pricing to both the engineering firm and the refinery for both the process valves and the proprietary RCS with UL certification. The author’s company’s solution assisted the customer in overcoming issues they had gone through in the past with other vendors who took a significantly longer time to get panels approved with the class ratings at a significantly higher price.
NOTE
a Emerson’s ASCO™ Redundant Control System
About the author
Srinivas Gavini is the Business Development Manager for Industrial Automation at Valin Corporation, a leading technical solutions provider for the technology, energy, life sciences, natural resources and transportation industries. Valin offers personalized order management, onsite field support, comprehensive training and applied expert engineering services utilizing automation, fluid management, precision measurement, process heating and filtration products.
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