Design First – Build Later

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Design First!

Sounds simple. It makes sense. But far too many people do not do this. They put together an idea, a process, but fail to take the design to completion before starting to build. Cutting corners always comes at a price. There is an old saying in Project Management, “You can have it Good, Fast or Cheap, pick any TWO”. Cutting corners will bump your cost, decrease quality, or possibly both.

A while ago I was tasked with designing and building a system for groundwater and soil remediation. The science was basic. The groundwater contained multiple hydrocarbons including both light ends and DNAPLs and the soil above the water line also contained volatile hydrocarbons that were creeping up from the contaminated water. We had made many of these in the past, and since. The issue was not the remediation science, the issues were in the complexity of the system and the physical constraints of the project.

I have made countless containerized systems, where you fit the equipment into standard, or in some cases high cube, 40 foot long ISO shipping containers. This is a very effective method as it allows the system to be easily shipped anywhere while providing a safe, robust enclosure for the system to operate. ISO containers are also quite plentiful, and reasonably priced, making the economics of their use is advantageous.

The First Issue

The container needed to be compartmentalized. We were going to be bringing in groundwater that contained various hydrocarbons, some of which were light end and volatile. The part of the container that housed the incoming feed piping from the wells, the oil water separator, and the double wall tank for hydrocarbon storage was a Class 1 Div 1 enclosure. The remainder was General purpose and housed the valve banks, the controls, and an air compressor to run the Sparge Lines.

Noise was not allowed. Seriously, the system was to be used close to a residential area and we had to make it run at below 60 dB. This complicated the space issue. We built a small room around the compressor, and then had to install multiple acoustic attenuators within the container including a Helmholz Resonator on the ventilation fan and on the intake louver for ventilation. Each box was six feet long, four feet high, and two feet wide.

Real estate was at an absolute premium. Which leads to:

The Second Issue

The second issue tying in with the first was the complexity of the system. We needed to control the whole system from within the General Purpose room. Therefore, every incoming line had to pass through the barrier between the two rooms, receive its necessary process controls and be measured, then pass back to the Class 1 Div 1 room. We accomplished this with two separate Valve banks. One on either side of a quarter inch A36 steel plate with full couplings welded into it. The plate was a eloquent solution that was removable for maintenance.

Class 1 Div 1 Valve Bank
Class 1 Division 1 Valve & Gauge Bank

The first picture shows the Class 1 Div 1 side of the enclosure. The operators needed to be able to monitor pressures in real time and have full, instant shut off control of each line from within that enclosure. The solution was simple, robust, effective and practical. It looks simple, and it is, but it is what we had on the other side that makes it somewhat, insane.

controls and instrumentation valve bank
Controls & Instrumentation

And here we have the backside. Each line incorporated both controls and instrumentation. The operators have full system knowledge and oversight from the control room. Being general purpose, the solenoid valves were demonstrably more economical than their Class 1 Div 1 counterparts would have been. Considering the number of them, this saved the Client a small fortune. The blue plate in the first picture can be seen high up on the wall. This was an extremely complex piping spool to build. The secret to the success of the build was the effort put into the design. Design First. Then Build.

And just to be complete, here is the third valve bank in that system.

valves and gauges
Valves & Gauges on Pump Lines

The SolidWorks Advantage

The shear number of components, the routing, the supports, make this virtually impossible to design by hand. Not only did everything have to fit, it must be easy to operate, and easy to maintain. We always design with the Operator and Maintainers in mind.

Using the 3D CAD package, SolidWorks, we were able to complete a full design, and test that design for operational requirements. It is also quite handy that SolidWorks will generate an accurate and complete Bill of Materials to make Purchasing happy.  There are a number of high quality 3D packages out there, I simply prefer SolidWorks.

Moral of the Story

Generally, the later in the Project lifecycle that we make mistakes, the more costly those mistakes are. For example, any work done in the field costs at least three times as much, in both time and money, as work in the shop. It is better to make your mistakes on a computer screen where the correction only costs you a few minutes, then it is during testing when you have to rip out a Valve Bank and delay delivery to the Client.

Design first – Then Build Later. That sounds simple, but many do it backwards, and pay for it. If halfway through the build your tradesmen are coming to you with suggestions of how to better design the system, you have already failed. A good designer will always run his ideas by his colleagues on the floor and get their input while the design is still on the screen. These guys work hands on eight hours a day, five days a week. They know what works and what doesn’t. They are one of your most valuable assets as a Design Engineer. Once completed, hand the drawings to the Manufacturing Manager to be red-lined, then to the Quality Manager for a similar review. Yes it will take an hour or two of their time, but they will invariably catch mistakes, or make suggestions, that will save many more hours and dollars during the build, and may frustrations for the Operators down the road.

Design First – Then Build.


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Corrosion Issues = Planning Issues

Dynamic Machine Design Homepage


Corrosion is the Fruit of Poor Planning

Rusted Out Foam Chamber
Corrosion and Erosion

Corrosion & Erosion, Hand in Hand

There indeed is a desperate need for a corrosion science. We have all seen perfect, shiny new equipment quickly rot and deteriorate in the field. Put a new motor in a pulp mill and two years later you cannot even read the label on it. String in a new stainless steel spool and a little while later you have pinhole leaks at the welds. To the right you see a fire suppression foam changer on an API 650 storage tank. It is only a few years old, but out in the wind and weather, next to the ocean, it has rotted completely away. Imagine if there was a tank fire. Do you thing that foam chamber would be effective?

In many industrial processes there is a requirement for metallurgical engineers to investigate, research and develop solutions for safe handling of chemicals. In larger industrial settings there is also a need for the assistance of corrosion specialists when integrating numerous pieces of varying equipment into a process. For example if you are transporting hydrofluoric acid at 300 Celsius through a pressurized pipe, you get an expert to tell you how. For many process situations we do have regulatory bodies and industry standard associations to help us. ASME, API, NFPA etc are perfect examples.

Outside of the Extreme

There is however another facet of the corrosion game. Many corrosion issues we face daily in industry have extremely simple solutions. Most are caused by an abject failure to educate ourselves before making decisions. All that is required is a little reading. There are untold resources, free and available at your fingertips if you have Internet and can type. There are some basic consideration that can save you a fortune and a lot of pain downstream.

Common Galvanic Corrosion

galvanically corroded boltsFirst is the problem of dissimilar metals. In general this is a BAD thing. When you are forced to use contacting dissimilar metals the first thing to note is the relative nobility of the metals. The further apart that number is, the fast one of them is going to rot away. This is further exacerbated by the amount of water present, and the amount of electrolytes in that water, and the temperature. For example if you have warm municipal wastewater, with a low pH, full of various salts as it always is, travelling through a carbon steel pipe and  you need to divert it with a hose, and decide to use an aluminium cam lock fitting. (Yes I have seen that done on more than one occasion) That decision will come back to haunt you in a few weeks. I know of another example in an oil refinery where they decided to use a titanium tube bundle in a heat exchanger. The feed pipe to the exchanger was 18 inches in diameter, to give you an idea of the scale we are talking about. The shell was about six feet in diameter and about 30 feet long. They did everything right except electrically isolating the dissimilar metals. The shell of the exchanger and the pipes feeding it were carbon steel. It was not long before they had to replace the shell and ten feet of pipe on either side.

The Process Side of Things

The next notable consideration is the chemical compatibility of your materials to your process flow. There are many tables online to help. And always, and I mean always, consult chemical compatibility tables when choosing materials for piping, fittings, tanks, vessels etc. For example, did you know that ketchup will eat through PVC piping? I didn’t either until I consulted a chemical compatibility table. What goes with what, and what doesn’t are not always intuitive. Similarly, many people mistaking think that stainless steel is stainless. It is simply corrosion resistant, under certain conditions. The rejects from a Reverse Osmosis desalination system will eat through 316 SS. You would need at the very least a 2205 duplex, or preferably a 2507 super-duplex.

Operating Conditions

Then you must consider the temperature and temperature variation. And it is not just for the acceptable temperature range of the material, you must also consider the coefficient of  thermal expansion, and the relative thermal expansion coefficients when dealing with differing materials. Laminations can peal off with heating and cooling. Piping can buckle, fitting can be snapped off. I have seen it happen. And it is not just a one time thing, it might last for a couple of months, but with each temperature cycle you get fatigue building up. Then one day, on a long weekend, you get called in to clean up because a fitting broke and nobody can figure out why.

What Else?

There is also the issue of coatings. There are many corrosion resistant coatings available for different applications. Here I definitely suggest calling the experts. And supplier of coatings should have in-house experts that will recommend the best coatings for your application if you give them accurate details up front. There are also more advanced solutions like Cathodic and Impressed Current Protection. They may seem like black magic to some, but they can work wonderfully. For example, when we replace the floor on one of our crude storage tanks, we also include a Cathodic Protection and liner. This literally adds years to the life of the tank.

Then there are things like Stress Corrosion Cracking, Corrosion Under Insulation (CUI) and Hydrogen Embrittlement, and my favourite, Microbiologically Induced Corrosion (MIC). In reality, for these you might want to consult and expert.

So for basic corrosion issues, please consult the many free and available documents that can make your life, and the life of your operators and maintainers much easier. They will thank you for it. Well, maybe not but they should. And for those funky situations where the process contains odd chemicals, high pressures etc, consult an expert and save everyone a lot of grief. Remember most corrosion issues are just the fruit of planning errors.

I hope you have found this Engineers Brief to be useful and informative. There are many more to come. Please stay tuned.


 

Please visit our homepage at:

Dynamic Machine Design

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Edmonton Office: 1-587-589-4695

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