This article aims to resolve the problems that can occur when high actuator torque has a negative effect on the stem of the valve in offshore service. In fact, it is important that the stem of the valve has higher torque capacity than the actuator torque. Different solutions to achieve this will be reviewed in this case study.

Valve trim materials are pressure-containing parts which should have the material quality minimum to the body of the valve. The main trim components, which are also called “wetted parts”, are closure member, seat and stem. The stem of the valve should have sufficient mechanical strength to withstand the loads implemented from the operator. Table 1 provides typical stem materials for different body material of the valves in the offshore industry.

From time to time, we are re-posting well-received or particularly valuable articles that have previously run on VALVEMagazine.com so that those who might have missed them will be able to catch up on the best of the best. This article, “Valve Positioners Offer Improved Control Valve Performance initially ran on February 16, 2016.

By closely controlling the pressure and temperature of both heating and cooling mediums within heat exchange systems, the use of an automated control valve can help assure the efficient transfer of heat.

Industries as varied as paper production, steelmaking and power generation rely on servo valves for precise motion control. A servo valve can last well above 1 billion cycles. But achieving that longevity only happens when selecting the right manufacturing techniques, mechanical designs and maintenance approach.

A Paper Chase

Paper mills, for example, use hydraulic pistons placed inside a roll to exert forces at each load zone to maintain a controlled profile across the complete width of the roll. The force exerted by each piston is controlled by a pQ (pressure and flow) servo valve that controls the position and pressure on these rolls as paper runs almost continuously through the machine shift after shift. If one spot on a roll causes a variation in pressure or position, the paper can slide or rip causing a stoppage that can shred the paper into confetti. We recently found the customized servo valves running a paper mill’s calendar rolls weren’t able to consistently control the pressure on its paper because routine repairs (by an un-authorized repair house) had not restored the valves to original condition.

According to a 1998 study released by the U.S. Federal Highway Administration, the direct costs associated with metallic corrosion in nearly every U.S. industry sector, from infrastructure and transportation to production and manufacturing was $276 billion—approximately 3.1% of the nation’s Gross Domestic Product (GDP). Bring those costs forward; in 2017 the GDP of the U.S. was $19.739 trillion, which means that last year, the direct costs of corrosion in the U.S. would be close to $600 billion.

According to that same 1998 study, the indirect cost of corrosion is conservatively estimated to be equal to or greater than the direct cost. If the indirect cost is also 3.1% of GDP, then the total cost of corrosion was $1.2 trillion in 2017. That is one of the largest single expenses in the U.S. economy, costing money in lost productivity, but also costing lives from dangerous failures.