The key to successful valve selection starts from application information and process knowledge. Accurate process conditions are needed to make accurate valve selection and sizing. Valve application know-how, together with modern sizing tools, has a vital role in finding the right valve solution and being able predict possible problems beforehand. For proper valve selection, the history information of current valve installations or references from the similar applications also helps to avoid the most common selection mistakes and problems.
Different valve types have their own suitable applications
There are numerous factors that need to be taken into account when selecting the correct valve solution for an industrial process. There are also several different valve types and designs on the market. All of the different designs have their own suitable applications. Selecting the wrong type of design will jeopardize the operational life of the valve and increase the need of maintenance and spare parts. More importantly, the selection can also have a major impact on plant operation and safety.
Most commonly, valve problems are somehow related to the wrong valve and trim selection or sizing. The valve type and materials should be selected based on the real application requirement while keeping in mind the investment and total cost of the valve ownership. It is equally important to select the correct trim designs, material and coatings separately for each different application. One general trim construction might work well in one application but get damaged quickly in another. For this reason, there are several different seat constructions available, each with their own specific applications and process mediums for which they have been designed and tested.
Life-cycle costs versus purchasing cost
Traditionally, the direct purchasing cost of devices has been seen as a one source of savings, sometimes even at the expense of the device’s quality and performance. Moreover, it has been estimated by some oil & gas valve end users that only 10–30% of the total costs of control valve ownership is related to the valve purchase price, whereas 70–90% can be attributed to maintenance, repair and operation (MRO). In addition, it is important to consider the total financial impact of possible device failures on plant production. A small savings in purchasing costs upfront at the expense of device quality can cause much larger expenses through process upsets and device maintenance costs later on.
Operation and maintenance costs are affected by the correct control valve selection and sizing based on application requirements, the quality of the valve design and selected materials.
Rather than compromising the valve design quality, the correct valve sizing itself should be seen as a possible source of savings. Valve sizing should be based on real process conditions and also consider the possible infrequent operation points of the application. Unfortunately, control valves are often sized with fairly preliminary process values that may include too much of a safety margin due uncertainty or possible future reservation. This can lead to valve oversizing and a higher purchase cost of the device. Oversized valves operate with small openings, which is also one common source of valve mechanical failures and internal erosion problems.
During the early valve selection phases, process-critical, high-cost and severe service valve applications requiring special attention should be identified. It is good to invest more time and effort to make the correct and optimized valve selection, especially for these type of applications. With an optimum and application-based valve selection, you can achieve longer valve operational time, reduced maintenance costs and better valve performance, and therefore also be able to attain the highest return of investment.
Director, Control Valve Product Center