Article: Rethink Your Control Valve Servicing

Reduce Turnaround Time and Effort

Emerson Automation Solutions Senior Engineers Scott Grunwald and Karl Lanes recently published an article in the September 2022 issue of Chemical Processing. It is titled “Rethink Your Control Valve Servicing,” and it describes techniques to better focus shutdown efforts and reduce costs. A summary of the article follows.

Shutdowns, turnarounds and outages (STOs) are a stressful time for plant personnel. Production is stopped and every minute costs the company thousands of dollars. This article examines the STO process from pre-planning through execution, providing methods to save time and reduce costs.

STO chaos
During a typical STO, operations staff balloons to hundreds of workers, and all are competing for personnel and equipment resources. Maintenance departments usually takes the opportunity to pull and repair hundreds of valves. Invariably, unexpected damage is found, creating unplanned surprises, extending the STO, and exceeding the budget.

Ways to address the problem
Historically there have been a couple of theories of valve repair:

  1. Run valves to failure
  2. Overhaul every valve during every STO.
  3. Repair by replacement, where valves are proactively replaced based on their age, service, etc.

Option 1 is cheap in the short term but invariably cost much more in the long term. Option 2 dramatically reduces unplanned surprises, but it comes at a very high price. Option 3 requires a lot of guesswork because valves tend to unexpectedly fail.

But there is a fourth option, as the authors explain:

Another method of tackling the STO problem is to only pull and overhaul the control valves that require service. Many valves operate in relatively benign conditions and can go years without any maintenance at all, so there is no reason to needlessly pull them. Of course, the challenge to this method is knowing which valves have problems and which do not.

This method has proven to save significant STO costs, but it requires the plant to predict when valves need attention. The plant needs to know:

  • What control valves are installed, including sub-components.
  • A history of how the valve has been operating to date.
  • An indication of how the valve is performing now.

Armed with that information, it is straightforward to assess which valves should be overhauled now and which repairs can be deferred. Even using this procedure, there is always a risk that a valve could unexpectedly fail, so certain critical and severe service valves are typically pulled during every shutdown.

STO execution
If the data is available, the control valve STO becomes a much more manageable exercise, as shown in Figure 1.

Figure 1: If the right information is available, control valve STO efforts are much less onerous. Data is used to create the list of valves that require repair, and pre-planning ensures the necessary parts and resources are available.

Ideally the health of each valve is evaluated using data and equipment inspections to create a list of valves to overhaul. Critical valves are added to the list. Then the list is re-evaluated to determine what equipment upgrades might be best incorporated during the repair.

With the STO scope defined, the team plans the logistics of the event, orders the parts, and works out repair details. A carefully planned STO becomes much less challenging, with cost and schedule overruns reduced or eliminated. While this alternative method has many benefits, it is ultimately predicated on complete information on the valves. But what does a plant do if it lacks that data?

Gathering field data and reducing emissions
If valve information is unavailable, many plants start by walking down each valve and gathering information. Many plants also use this walkdown as an opportunity to address fugitive emissions by specifically targeting valves handling volatile organic materials and/or restricted materials. The authors explain:

Leakage results in lost product, generates increased testing requirements under the Environmental Protection Agency’s Leak Detection and Repair program, and can ultimately generate fines. The findings of the environmental walkdown can be used to generate a target list of valves for repair and/or improvements during the STO.

Diagnostic performance data
Actual valve performance data may be available from existing digital positioners already installed on the valves. These positioners can gather performance data, flag developing problems, and transmit the information to an asset management software package. There it can be alarmed, and then internally handled, or externally reviewed by Emerson’s automation experts, who can highlight developing problems in periodic reports sent to plant staff (Figure 2).

Figure 2: Valve diagnostic data from operating valves can be captured and monitored by third-party experts. Serious issues are immediately addressed, while slowly developing problems are captured in monthly reports.

Walk downs, repair histories, and valve diagnostic data are all used to help guide the STO planning process. When evaluating repair versus upgrade versus replace options, consult with your valve vendor and lean on their expertise as they can usually provide a list of alternatives, and provide cost comparisons to determine the best solution.

Planning the repair logistics
The authors also mentioned one remaining STO planning step:

The last critical step prior before starting an STO is formulating a detailed plan for executing the repairs. The sheer logistics of pulling hundreds of control valves, overhauling them, re-installing them, and returning them to service is not to be taken lightly.

Most facilities lack the staff to handle this effort, so contracting with a valve repair company for STOs is common. The firms should be chosen carefully since some lack the technical training to perform the repairs, and others are prone to use non-OEM repair parts to cut corners. Many plants complete the repair by obtaining an “as left” stroke signature that can be compared against future performance (Figure 3).

Figure 3: During commissioning, it is important to capture a post-repair control valve stroke signature. This data can be used to spot developing problems in advance of the next plant outage.

STO savings
These techniques for pre-planning and executing plant outages have generated substantial savings:

  • After a failed STO, a facility utilized these techniques to better plan and focus the next STO, finishing 46% ($485,000) under budget.
  • A combined-cycle power plant used upgraded digital valve positioners and diagnostic alert software to focus their outage efforts and saved $68,000 in one outage alone.
  • Similar programs in other plants have generated average savings of $1200 per valve.

All figures courtesy of Emerson

About the Authors

Scott Grunwald is a director of global business development at Emerson Automation Solutions in Marshalltown, Iowa, where he’s responsible for shutdown, turnarounds, and outages for Emerson’s final control products.

Karl Lanes is senior director of lifecycle services at Emerson Automation Solutions in Marshalltown, Iowa, where he’s responsible for global parts distribution for Emerson’s final control products.