Hose + Coupling World is pleased to present Part Two of our interview with John-Paul Schmidt, Piping Stress Leader at Dow Chemical. Further to our conversation about calculating acceptable risk, mentorship, and common types of equipment he uses in his day-to-day, we cover fluid hammer, tips for the proper design, installation, and maintenance of expansion joints, as well as the best and most challenging aspects of the job.
By Editorial Team
Raised in the small chemical plant town of Mont Belvieu, Texas, where nearly everyone in town worked in the plant, John-Paul Schmidt was exposed to the industry at a young age, quickly discovering a passion for engineering and “creating something useful out of something worthless”. After obtaining his BSc in Chemical Engineering from Lamar University and an MBA with a focus on Project Management, Procurement, and Project Finance from the University of Houston, Schmidt recently obtained his PE license — considered the highest standard of competence in the engineering profession.
Today, Schmidt works in a mechanical engineering capacity at Dow Chemical but has prior experience working in a variety of roles in both capital and maintenance projects. Schmidt works out of the Houston office, guiding the day-to-day activities of a handful of designers and engineers, as well as supporting clients on capital and maintenance projects. One of his primary responsibilities is to review the proposed designs of the 18 designers on his team to ensure that the physics are sound, and the design is safe.
“I check the thermal growth, the weight, and flow phenomena like transient flow, water hammer, flow-induced vibration, acoustically-induced vibration and all the different rigors that we put the pipes through,” explains Schmidt. “I want to make sure that there are absolutely no unplanned events.”
In Part One of the series, we discussed Schmidt’s involvement with valves in different Dow facilities, and he let us know that one of the first things he asks the process engineers on a site is whether a valve is fast opening or closing. It turns out, this is critical information for a man whose primary responsibility is predicting the unpredictable.
Fluid hammer
Fluid hammer also called water hammer or hydraulic shock is a pressure surge or wave caused when a fluid in motion is forced to stop or change direction suddenly. It often occurs when a valve closes suddenly at an end of a pipeline system, when steam from one pipe mixes with condensate from another, or two-phase flow occurs producing a pressure wave in the pipe. This pressure wave can cause major problems, from noise and vibration to pipe rupture.
“The equipment is never designed to handle fluid hammer, neither is the pipe. It is unpredictable and dangerous,” explains Schmidt. “Fluid hammer can cause the pipe to fail, the pump to fail and it can destroy the surrounding steel and damage the internals of valves.”
A properly designed, operated and maintained steam system rarely, if ever, suffers a fluid hammer event — however, by its very nature, it is impossible to plan for it. Avoiding fluid hammer requires both a thorough understanding of its causes and contributing factors and following good design, operations, and maintenance protocol. Other strategies for reducing the effects of fluid hammer pulses include accumulators, expansion tanks, surge tanks, and pressure relief valves.
“My primary job is to make sure there are no unplanned events,” he adds, “to make sure the designs our designers create are safe. Fluid hammer is unpredictable, and we try to avoid it but if it is going to happen we want to be as safe as we can and put in extra support.”
There are many factors that can contribute to fluid hammer, the examples below are a few of the most common causes:
Steam flow water hammer, or two-phase flow, can occur if condensate accumulates in low sections of steam and condensate piping. The steam creates ripples on the surface of the water in a pipe and if the water level is high enough for the ripples to fill the pipe, they are transformed into a slug of water the steam carries down the pipe at upwards of hundreds of feet per second.
Condensation-induced water hammer is caused either by steam entering a piping system that contains water (cooled condensate) or by the injection of water into a piping system containing steam. This type of fluid hammer is caused by a four-step sequence which involves: rapid condensation; a sudden void caused by the steam changing to liquid form; and a dramatic drop in pressure in the pipe, producing a local pressurized pulse of fluid shooting down the pipe.
Water-flow water hammer is a sudden decrease or stop of flow velocity that can occur in any water system. It is s caused by a similar mechanism described in the steam flow water hammer.
Tips for proper design, installation, and maintenance of expansion joints
In terms of design, the most important lesson Schmidt wants us to learn is that we cannot assume that the equipment in use in a massive piping system will behave the same way as it would in a small-scale operation.
“Say you have an expansion joint or a hose in your house,” demonstrates Schmidt. “You can move it, you can compress it or extend it. But when that hose is 20 inches in diameter and has 150 psi inside of it, the pneumatic force involved is astronomically different. We’re talking ℼr2, so 3 x 10 x 10 x the pressure, which means the pneumatic force on the expansion joint would be 47 kip (47,000 lbs). It is not going to be able to compress and extend along the axis in the same way, and a lot of people forget that because it doesn’t match what you experience on a small scale.”
During installation, expansion joints are typically shipped with shipping bars that protect them from being overly compressed during transport. When they arrive at their destination, the shipping rods are cut off and the expansion joint is ready for installation in the field. Here’s the thing: to counteract pneumatic force, many expansion joints are designed with tie rods to hold them in place so that they can shift from side to side, but not compress or extend.
“It is very important that the pipefitter knows to cut off the shipping bar, which is disposable, and leave the tie rod, a critical part of the joint, intact to ensure the safe installation of the joint,” says Schmidt.
Expansion joint materials
The expansion joints at Dow come in a variety of metals, with different metals for different parts. Flanges are typically the same material as the rest of the pipe, which is decided during the design phase. Pipes run the gamut from carbon steel, stainless steel, duplex stainless, fiberglass reinforced plastic (FRP) and other non-metallics, but expansion joint flanges are always metal if they exist at all. In some cases, rubber expansion joint will exist that has a metal backing ring instead of a flange.
Bellows, where the movement and flexing actually occurs, is typically a thin, noble material, such as zirconium or nickel-based steel Hastelloy. This is because stresses in the bellows are made worse by thick material, so the thicker the material, the more stress gets transmitted to the material.
The human factor
As the reader can imagine, coordinating a team of 18 engineers, consulting on capital projects and providing on-site support is no easy feat. Of all his daily responsibilities, Schmidt says the most challenging are the human factors; understanding how to communicate with and align with the goals of his co-workers.
Coordinating people, training and motivating them is an amazingly difficult thing to do in any profession, but Schmidt believes in the importance of counterpoints; alternate points of view and people who will challenge our ideas and inspire us to work hard and make progress.
“I need my co-workers, even though sometimes it is difficult to deal with them,” he laughs. “But without people to challenge us, we stagnate.”
For Schmidt, the best parts of the job are the freedom to learn new technical information, and the opportunity to interact with peers, inside and out of the company. “I interact with ASME professionals and professors, read technical journals, etc. I have been given a lot of leeways to collect a vast sphere of knowledge and then apply it to real-world problems, which is exciting and gratifying.”
One of his favorite experiences working with Dow was being called out to a job site at 2 o’clock in the morning on a Sunday. “When I arrived, there were about a dozen very angry pipefitters who had encountered an unforeseen problem with the design of a maintenance project. When I left two hours later they were smiling because they had a clear solution. Helping people find a solution to a problem is gratifying. The next morning, I had an encouraging email from the group leader waiting for me, which I still have pinned to my wall today.”
“I’m proud to say that I work for a safety-conscious company,” concludes Schmidt. “I admire this company and what it stands for. The employees can hold a capital project or maintenance operation if they feel that something is unsafe. Safety is our primary concern at Dow, but in an unplanned event we’re motivated to get the plant up and running or the project back on schedule.”