Posts Tagged ‘doug walker’

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

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.