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6 Reasons to Review Your Pressure Safety Devices

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6 Reasons to Review Your Pressure Safety Devices

Pressure Safety Device Rendering

Pressure vessel accidents caused 127 fatalities between 2000 and 2010, according to the National Board of Boiler and Pressure Vessel Inspectors. It’s a worst case scenario – one of your mechanical systems malfunctions and someone gets injured.

A typical manufacturing facility has many safety systems, controls, and procedures to prevent injuries from happening. One often-overlooked component is pressure safety devices. These “last resort” devices exist in the background and are designed to do their job only under the most extreme circumstances. In order for these devices to continue to provide the safety measure for which they were installed, you and your facility manager should understand how and why your pressure safety devices are installed.

What is a pressure safety device?

safety relief valve

Pressure safety devices protect your systems and equipment from overpressure situations. If you have a pressurized tank with a rated pressure limit of 125 psig*, and the system pressure increases above 125 psig, a pressure safety device is there to relieve the excess pressure in a controlled manner and protect the vessel from rupturing. Many pressure-rated vessels are provided with pressure safety devices pre-installed.

Two common pressure safety devices

A large portion of pressure safety devices fall into two main types:

  1. A Pressure Safety Valve (PSV) is sometimes called a Safety Relief Valve (SRV) when used for vapor relief, or a Pressure Relief Valve (PRV) when used for liquid relief (not to be confused with a Pressure Reducing Valve). These valves can open when pressure is too high (above set point) and close when the pressure returns to normal (below set point).
  2. A rupture disk or burst disk (sometimes called a Pressure Safety Element, or PSE). Rupture disks are small, typically metal disks mounted inside a vent pipe, specifically designed to rupture or burst at a certain pressure. Below that set point pressure, the system operates normally and there is no flow in the relief pipe. Above the set point pressure, the rupture disk releases and the excess pressure is relieved into the vent line. A failed rupture disk must be replaced.

Why you should understand your pressure safety devices

You might be asking, “Why should I be concerned about this? The safety devices were installed with the systems or equipment. Everything was stamped and passed inspections. Why would there be a problem now?”

Here are six scenarios in which you may have a problem with your safety relief devices and not even know it:

  1. Your discharge piping runs too far. Even though your safety device is sized correctly for your pressure vessel, the discharge piping from the outlet of the device could affect its operability. Chemicals or high-energy systems such as steam need to be vented to a safe location. Long discharge piping runs will increase the back pressure on the relief system when the valve opens. If the back pressure is great enough, the relief system may not be able to function properly. The solution to this may be a shorter pipe route, or a larger discharge pipe.
  2. Multiple relief devices tie into a single discharge pipe. When multiple relief devices tie into a single discharge pipe, most mechanical codes will require that the relief piping is sized so that all the devices can flow their full capacity simultaneously. While all the relief devices may be properly sized, combining the discharge pipes together can compromise the safety of the overall system. Analysis with a flow modeling program such as AFT Fathom can easily verify whether the combined discharge piping system can handle all the scenarios that may occur.
  3. Your system has expanded or changed. As processes at your facility change, or the facility itself grows, the conditions used for the original design of your mechanical systems may change as well. Projects that modify mechanical systems should include a review of the associated pressure safety devices. If the design conditions used to select the devices are no longer valid, a new calculation—and possibly a new device—is required.
  4. Your safety device may be too old. Pressure safety valves are built to sit idle for years at a time until called upon in an emergency. Environmental conditions can nonetheless affect the ability of the valve to do its job over time. Many facilities include pressure safety valves in their preventative maintenance programs with a replacement scheduled every five to ten years. A white paper by Exida (a process safety and security company) noted the useful life for pressure relief valves as 4 to 5 years. With no moving parts, rupture disks are less likely to become ineffective over time, but corrosion could result in an unintended release.
  5. The safety device rating is not appropriate for your system. The pressure set point of a safety relief device is typically stamped on the device itself. It is often easy to verify whether the current set point is appropriate for your system. However, it is surprisingly common to find an existing safety valve whose set point is well above the maximum allowable working pressure (MAWP) of the vessel the valve protects!
  6. A shut-off valve is blocking your safety relief. Most mechanical codes will require that safety reliefs be connected to the system with no isolation valve that can prevent safe discharge of an overpressure situation. In some cases, a valve is installed inadvertently. A valve in front of a safety relief device is particularly worrisome. Since the safety relief does not operate under normal conditions, a shut-off valve could be left closed without the system, or anyone else, noticing. In an overpressure situation, the safety relief valve has been rendered useless.

Given the important role that safety relief devices play in your mechanical systems, periodic review of their age, condition, settings, and system functionality is well worth your time and effort.

Find out more

Applied Engineering has provided field surveys, calculations, and documentation for hundreds of safety relief devices in water, steam, compressed air, refrigeration, and other systems. Please contact us if you would like to find out more!

Doug Walker, PE, is an Associate with Applied Engineering Services.

*psig = pounds per square inch gauge

CFD Modeling Now Offered

CFD Modeling Now Offered

We are pleased to offer Computational Fluid Dynamics (CFD) modeling as one of our engineering services. CFD modeling is an excellent tool for understanding and solving airflow patterns in critical environments such as operating rooms, isolation rooms, and cleanrooms. Further, CFD modeling allows our engineers to understand temperature gradients in the built environment such as in data centers, tall lobbies, and protective environment spaces like a burn center.

There are many applications for CFD modeling that include:

  • Airflow patterns in critical environments
  • Temperature gradients
  • Age of air (e.g., operating rooms, isolation rooms)
  • Dilution (e.g., diesel exhaust entering an air intake louver)
  • Air quality – pollutants or flammables
  • Capture velocity (e.g., ensuring researcher safety at face of fume hood)

CFD modeling makes our engineering stronger by validating the configuration of the airflow devices to maximize effectiveness. Let Applied model your critical environment with CFD!

This video is a particle trace showing a one pass airflow to return grilles.


This CFD model of a surgery suite shows no recirculated air, which was the goal – one pass of air from the ceiling diffusers to low return grilles.




Day in the Life of an Onsite Project Engineer

Day in the Life of an Onsite Project Engineer

Loren Horan DITLHave you ever wondered what our engineers actually do all day? This year, we’re continuing our “Day in the Life” series started in 2014. Each quarter, we will feature someone within the firm who will provide insight into their typical day. This quarter showcases one of Applied’s owners, Project Engineer Loren Horan, PE, RCDD, LEED AP.

As a project engineer, my day is typically laid out in one of the following three ways. The first option is a day in the office where I work on designs, specifications, review shop drawings, collaborate with team members, and perform engineering calculations. The second option is a day where I am in the field to attend construction meetings, observe construction in progress, perform a site survey for a new project, meet with clients to determine their needs and requirements, and collaborate with architects, structural engineers, and civil engineers at their offices. The third option is somewhere in between the first two. I chose to write about a day where I was onsite.

7:00 am – My day starts as I leave home directly for Purdue University.

8:30 am – Arrive at Purdue University and head over to Lynn Hall to start our observation of the sprinkler system hydrostatic pressure test. I meet the contractor and owner at the site and we watch each sprinkler zone get pumped up to 200 psi of hydrostatic pressure and confirm that there aren’t any leaks.

9:00 am – The pressure gauges on the sprinkler zones have been initially recorded.  I now walk around the building to perform my construction observation.

9:30 am – Stop in at a student commons area to get a cup of coffee and open up my computer to respond to emails. I am able to remotely connect into the office, so I am also able to perform some lighting design and calculations for an industrial client.

11:00 am – Meet up with the contractor and owner to review the pressure gauges and confirm that the sprinkler lines are still holding the same pressure.

11:30 am – I have a few minutes before my lunch meeting, so I work on some specifications for an industrial client that is creating a new headquarters within Indianapolis.

12:00 pm – Have lunch with an architect that we are working with on some classroom renovations. We catch up and review the submittals that have been issued to date on the first classroom project. We also discuss a recent change request by the owner to add some art to the second classroom project.

1:30 pm – Attend a pre-construction meeting for the second classroom project. I see familiar faces, such as the Purdue University project manager and building deputies. During this meeting, the owner describes their construction and safety requirements. The design team and contractor coordinate on how submittals will be issued.

2:30 pm – The pre-construction meeting ends and I head to a planning committee meeting for the new Innovation Design Center building. During these collaborative meetings, the clients and design team review the block layout of the proposed spaces. The design team accepts feedback from the clients and interviews the users to better understand their needs and the intended practices of the space.

5:00 pm – The planning committee meeting concludes and the architect and I have a quick 5 minute recap to ensure that we are on the same page. I check my email to determine if there are any high priority items that must be addressed prior to heading back to Indianapolis.

5:15 pm – I get into my car and leave Purdue University, ending my work day.

Day in the Life of a Project Engineer

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Day in the Life of a Project Engineer

TreySmith_DITL_B&WHave you ever wondered what our engineers actually do all day?

This year, we’re continuing our “Day in the Life” series started in 2014. Each quarter, we will feature someone in a different position within the firm who will provide insight into their typical day. This quarter showcases recent IUPUI graduate, Trey Smith. Trey started at Applied as an IUPUI co-op in 2011, and officially joined the firm after graduation last year.

8:30 AM

Arrive at work and review e-mail.

8:45 AM

I make a written list of my ongoing projects and their due dates. Tasks that I plan to complete today I list in red ink. Tasks that can be put off for another day are written in blue. This allows me to prioritize my work load and stay focused throughout the day.

9:00 AM

A project manager approaches me and informs me we have just received the latest electrical drawings for an ongoing project from another firm. He asks if I can update our arc flash model and put a report together before the day’s end. The model is fairly small, so I decide to take care of it before I begin working on my other tasks for the day. First, I check the one-line diagram to see if anything has been modified from the last submission. Nothing has changed, so I move on to determining the approximate feeder lengths between equipment and enter them into the arc flash program. When finished, I can run the arc flash analysis, coordinate breaker settings, and combine my findings into a report. The finished report is sent to the project manager, who then forwards it to the necessary parties.

11:00 AM

I shift gears to work on a replacement study for a hospital in the southern region of the state. My responsibility is to provide a cost estimate for the replacement of key electrical equipment. I can’t seem to find a reasonable price for some of the large distribution equipment after several Internet searches and referring to similar projects we’ve done in the past. I decide to ask a more experienced engineer for assistance, and am directed to a representative who handles this sort of equipment on a daily basis. When I get back to my desk, I send a brief email to the representative explaining the details of the project and the issue I’ve run into. While waiting for a response I continue working on the cost estimate, focusing on some of the smaller equipment and light fixtures.

1:00 PM

I eat lunch at my desk today, which allows me to check the latest news in the sports world.

1:30 PM

After lunch I prepare for our visit to a water treatment plant. The client would like to upgrade the existing 400 amp service to 600 amp for future replacement of their booster pumps. Also, we need to find a suitable location to install three new VFDs. Unfortunately, we are not provided a site plan so one must be made from scratch. Using pictures taken from a previous site visit, I am able to develop drawings that should provide a basis for me to work off of during our visit. During our visit I plan to fill in missing information that couldn’t be determined from the pictures. To prevent me from forgetting, I make a list of items that still need to be addressed while we’re at the job site.

2:00 PM

We leave the office and head to the site.

2:30 PM

At the job site, I am introduced to the client and a representative from the local utility company. Before we head down to the underground vault, I take pictures of the existing electrical equipment found on the surface. It is important to find nameplate information, conductor sizes, and the existing condition for the equipment that will be affected during construction. While doing this, I discuss some of the details of the project with the project manager and possible solutions to meet the client’s requirements.

Inside the vault, I again take pictures of the equipment and make notes of existing conditions. I find that the drawings I created prior to the visit do not accurately depict what’s actually inside the vault, so I do my best to markup the drawings so that I can make corrections when I return to the office.

I listen and contribute to conversations between the client and the project manager about possible ways to reach the expected outcome. Mentally, I try to visualize the sequence of construction and determine whether or not the discussed plans are practical ways to go about this project. After everyone comes to an agreement on a possible solution it’s time to head back to the office and get to work on developing drawings that show our plan for construction. The client would like to receive our plans in exactly one week.

3:30 PM

When I return to the office, I upload my pictures to the project directory and get to work updating the CAD drawings with my findings. Again, I speak with the project manager to make sure we’re all on the same page before I get too far along. During our brief discussion, I bring my concerns to the project manager’s attention and we work together to find resolutions. Once the minor details are ironed out and I feel comfortable with the design, I return to my desk to continue working on the drawings.

4:30 PM

I try to find a good stopping point for the day and make a note of where I left off for when I come in tomorrow morning. I quickly develop a list of questions and concerns for other engineers working on this project for discussion tomorrow. Looking back at my list I created at the beginning of the day, I notice there was a project that I was unable to get to. Fortunately, I still have a few more days to work on it. This will be priority number one when I come in tomorrow.

5:00 PM

Time to sign out and head home.

Day in the Life of a Project Engineer

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Day in the Life of a Project Engineer

DITL - Mike JamiesonBWHave you ever wondered what our engineers actually do all day?

This year, we’re sharing some details through our “Day in the Life”
series. Each quarter, we will feature someone in a different position
within the firm who will provide insight into their typical day. Next up is
Project Engineer Mike Jamieson, who joined Applied full-time
in 2009 after 5 years as a Co-Op student. Mike is a mechanical
engineer who works on a variety of projects for our clients.

8:00 AM

Arrive at work and review e-mail.

9:00 AM

A project manager approaches my desk and asks if I have time to work on an office building renovation project.  I do, so we plan to meet and discuss the project after lunch.  This should give me enough time to quickly look over the project proposal and any documentation we already have in the project folder on Applied’s internal network.

9:15 AM

For an unrelated project, I need to determine the lead time and cost of a 30” butterfly valve to be installed below grade. This valve may be purchased directly by the client (rather than by a contractor) so we will need to determine the best option from several manufacturers. Three manufacturers are listed on the standard specifications provided by the client, so I’ll track down information on those three. First, I need to determine which company supplies each valve in our area. I know who to call for the first valve manufacturer, but I will need to do some research to find the second and third. I find the second and third supplier on the internet.

10:00 AM

Once I have determined who I need to call, I contact each manufacturer’s representative and describe what type of valve and what options I am looking for. The lead times for each valve ranges from 4 to 6 weeks. The costs vary slightly, but are about $8,000 per valve. I put this information onto a concise spreadsheet and give this to the project manager. He is planning to meet with the client later this week. They will review the numbers and determine the next step from there. They may purchase the valve directly or hire a contractor and have them purchase. The concern with hiring a contractor to order the valve is that the lead time may cause the project schedule to slip. At this time I cannot proceed any further on this project, but will continue work at a later date after important project direction decisions are made.

11:30 AM


12:30 PM

Review the office building renovation project information before the meeting. The project proposal says we are in Phase II of a three-phase project to gut and replace the second floor of an office building which will be occupied by a new tenant. Since we are in Phase II, I assume that the tenant has already moved into the Phase I area of the building. The project directory contains drawings from Phase I and new architectural drawings showing the work for Phase II.

1:00 PM

Meet with the project manager to discuss the office renovation project. It is confirmed that Phase I of the project is complete and the tenant has moved into the Phase I area.

The project manager explains that the building has a variable air volume (VAV) system with reheat. There are two penthouses on top of the building which house two air handlers each (for a total of four air handlers). Each penthouse has a chase below it, which allows the high pressure supply and return ductwork mains to pass from floor to floor.

The former space contained a large amount of individual offices with dedicated terminal units serving each office. The renovated space will have large open areas with cubicles.  The existing and smaller terminal units may not be compatible with the new space’s requirements. However, the terminal units which serve the perimeter of the building should be able to remain as is in most cases. We will reuse as much of the existing ductwork as possible for the new tenant, but the new space will require some rework.

Most of the work from Phase I went well. The occupants have not generated many complaints. This implies that the design was properly sized (or at least that it is not too small).

There were complaints about the temperature of a training room when it was in operation at full capacity. The temperature was too high and the terminal unit could not keep up with the load in the space. The project manager indicates that the density of people in the room was greater than anticipated when the complaint was generated. They have also installed one computer per person. It was not known that the room would have this computer load during the Phase I design. The ductwork to the training room will need to be reworked in order to compensate for the increased load.

More details and job requirements are discussed, including the project schedule. The deadline for the Phase II documents will be coming soon. We will have less than one month to put together a signed drawing set for the client, who is eager to move in. It will be a fast-paced project. Fortunately, the HVAC system is a common design found in many buildings. I’m familiar with this type of system, so I agree that this deadline will be possible.

2:30 PM

To finish the day I begin work on the office renovation project. I take a closer look at the Phase I documents to determine how the loads were calculated and what velocities and pressure drops were used in the ductwork. The air handlers are all identical and each serves one quadrant of the building. Some of the high pressure ductwork on the second floor and almost all of the low pressure ductwork (the ductwork after each terminal unit) will need to be rearranged to fit the new space requirements. Based on a quick rule of thumb check, the air handlers appear to be large enough to handle the new load requirements.

3:30 PM

Keeping the first pass, rule-of-thumb load calculation in mind, I begin a more accurate space-by-space load calculation. I won’t be able to finish this today, but I can knock out a large chunk of it.

5:00 PM

Leave for the monthly ASHRAE meeting. This month the meeting will be held at a local brewery. Woohoo!

5:30 PM

Arrive at the brewery. A professor from Purdue University will give a presentation on refrigeration concepts. He will discuss new and future compressor technology that he and his students have been developing. Before the presentation we eat and do a brewery tour.

8:00 PM

Head home.

Day in the Life of a Project Manager

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Day in the Life of a Project Manager

Have you ever wondered what our engineers actually do all day?
This year, we’re sharing some details through our “Day in the Life”
series. Each quarter, we will feature someone in a different position
within the firm who will provide insight into their typical day.
First up is Project Manager Douglas Walker, PE, who has been with
Applied since 2001. Doug is a mechanical engineer who works
mostly with our industrial clients. He recently led our engineering
efforts on the award-winning Rolls-Royce Banded Stator facility.



7:50 AM

On a typical morning, I arrive at the office, sign myself in on the computer, check my emails, and fill in yesterday’s timesheet. Some regularity in the morning helps me kick start the day.

I’m managing or tracking ten different projects currently. The clients are manufacturers who make electronics, pharmaceuticals, transmissions, fiberglass insulation, and aircraft engines. The projects are all in different phases of completion: a study of utility systems, calculations for safety relief systems, construction of a utility plant, and testing newly installed air handlers at a client site.

As much as I use the computer, I still print a schedule every other day and re-write my task list. This makes me consciously think about my work – who needs information, what decisions are pending, and what deadlines are coming up. Also, project tasks rarely are checked off as complete. Rather, they evolve into something else. Write report becomes add tables, which becomes review formatting, and so on. Rewriting my tasks every couple of days helps me to track the evolution of the projects. I prioritize my schedule so that other people can keep moving forward with their work.

8:30 AM

I review CAD drawings for a piping project. Reviewing a drawing means looking at every pipe connection, every component, every note, and making sure we – as the design engineering firm – have painted a complete and coherent picture of the system we want the contractor to build. On this project, the client was specifically interested in easy access to several important components in their new piping system. After I complete my review of the drawings, I talk through my comments and questions with the designer to brainstorm some ways to make components more accessible.

9:30 AM

I report to one of Applied’s several principals (owners) on each of my projects. I generally check in with my principals informally a couple of times a week to make sure we’re up-to-date. Depending on the project, the principal-in-charge may be heavily involved or may leave most of it up to me. I let them know what project work has been completed recently, what may be holding us up, and whether there are any budget or schedule issues.

10:30 AM

Consultants sometimes get random questions that we know nothing about. A contractor may ask me about the nosing dimensions on a set of stairs, but all I can do is get him in touch with an architect who can help him. Today, an engineer from a site/civil consulting firm calls to ask what kind of valve I would put in a small open sight drainage line. Her client’s idea was to shut off the valve if they want to make piping modifications later. The answer: “Don’t install a valve; wait until the drain dries out.”

11:00 AM

I prefer to leave the office at lunch time. It gets me outside for a little while and I can avoid the phone and email for an hour or so.

12:00 PM

I have a meeting this afternoon with a client. We issued a preliminary report last week. He wants to review his comments with me today. Whether a meeting is a waste of time or productive often depends on how prepared you are to meet. For this meeting, I print a copy of the report, pack some backup materials, and review the main issues before I leave.

12:30 PM

I drive to the meeting early to allow time for parking, badging into the site, and walking to our meeting room. Between meetings and site visits, I spend approximately 20% – 25% of my time out of the office, on average. Getting out of the office to client sites is one of the built-in perks of consulting engineering. With a broad base of clients, I could find myself in three different manufacturing plants in the same week.

1:00 PM

At our meeting, we discuss several issues from our report, including a campus cooling water piping system, a vent gas reclaim system, and electric motor starters on pumps. Most of the client’s comments on our report are to clarify the existing condition of the systems. Contrary to popular belief, good communication skills are essential to engineers. We can analyze, research, and calculate as much as we like, but if we cannot effectively communicate the results to others – often people who are not engineers – then our work adds no value.

2:00 PM

Back at the office, I address the comments I received at my meeting – some of which are simple wording changes; others require more discussion with the engineers who contributed to the report.

I also have a meeting to set up for next week on another project. This one will be another site visit. It’s tempting to just go by myself to the site. It’s cheaper than bringing along a design engineer as well. There won’t be much to see. But no matter how many pictures I take, there is no substitute for a design engineer seeing the worksite for himself. So I decided to schedule two of us to attend.

I have a few extra minutes today, so it’s a good day to check on project budgets and hours. Applied generates a weekly in-house project sheet that summarizes the project funds available and the total charges to date. It’s helpful to look at the raw data occasionally to know who in the office has charged time to my projects and see what parts of the project are in or out of the original budget.

3:00 PM

Last week, one of my projects issued a package of drawings and specifications (narrative descriptions of structural, mechanical, and electrical systems) for general contractors to bid on (provide a price for). The project is a new utility plant for a client’s manufacturing site. There were 122 drawings and over 150 specification documents. With a large package, it is typical that contractors reading the documents will inevitably need clarifications on what the documents say. When we answer questions, we must send them to all the contractors providing bids so that everyone has the same information. I answer some of these questions this afternoon and issue a formal response to all the contractors.

4:00 PM

One of our engineers asks me about the pressure setting for a relief valve. A relief valve provides a safe outlet for the system fluid if the pressure in the piping system rises high enough to damage components. Our project is providing calculations for existing systems.

The engineer’s question is how to approach a relief valve calculation for a system with multiple components that could each have a different pressure rating. Questions like this are fun to dig into: how does the system work? How do people interact with it? These kinds of questions make us find what I think of as bedrock. What is it that officially determines or documents the limitations of a system? In this case, bedrock might be a section of the code (official government requirements), the client’s internal procedures, or a manufacturer’s stamp on a vessel.

As interesting as the question might be, part of my job as a project manager is not to answer it. I need to help the engineer working on the project arrive at an appropriate answer himself. I encourage him to check the code references, verify the raw data, read the client’s operating procedure. Knowing the source will give the engineer confidence in his conclusions.

5:00 PM

Head home. Check myself out. Today was busy, but calm. Tomorrow could be entirely different.