2019 Tech Report Jan-Feb

TECHNICAL REPORT

THE

REFRIGER ATING ENGINEERS & TECHNICIANS ASSOCI ATION | JANUARY/FEBRUARY 2019

DISCHARGE FROM PRESSURE RELIEF DEVICES

Mike Axthelm - WMI Fort Wayne, Indiana

There have been multiple articles about relief valve sizing, sizing the piping for the discharge from pressure relief devices but, few if any have addressed the termination for atmospheric relief valves. IIAR-2-2014 notes in chapter 15.5 for Atmospheric Discharge, the following. (The emphasis is the authors.)

15.5.1.2 The termination of pressure relief device discharge piping relieving to atmosphere shall be not less than 15 ft (4.6m) above grade and not less than 20 ft (6.1m) fromwindows, ventilation intakes, or exits. 15.5.1.3 The discharge termination from pressure relief devices relieving to atmosphere shall not be less than 7.25 ft (2.2m) above a roof that is occupied solely during service and inspection. Where a higher adjacent roof level is within 20 ft (6.1m) horizontal distance from the relief discharge, the discharge termination shall not be less than 7.25 ft (2.2 m) above the height of the higher adjacent roof. 15.5.1.4 Discharge piping shall be permitted to terminate not less than 7.25 ft (2.2

m) above platform surfaces, such as upper condenser catwalks, that are occupied solely during service and inspection. 15.5.1.5.* The termination of the discharge shall be directed upward and arranged to avoid spraying ammonia on persons in the vicinity. 15.5.1.6 Discharge piping frompressure relief devices discharging to atmosphere shall have a provision for draining moisture from the piping. From Appendix A (Informative) Explanatory Material A.15.5.1.5 The termination of discharge is considered the final several feet of the relief piping. The vent end point of relief pipingmay include a design to prevent rain and snow from

entering. Many designs provide a method to prevent rain and snow from entering. The design at the vent end point may be a “tee” diffuser, a “double 45 degree” diffuser, a “bull’s horn” diffuser, a “spring self-closing flapper cap,” or a “sock hood cover.” The “spring self-closing flapper cap” is used on natural gas and tractor exhausts. The “sock hood cover,” which is typically bright safety yellow, orange, or red in color, has a light flexible string attached between the hood and the relief pipe stack for its containment if lifted. Another designmethod that may be incorporated has a fully open vent end point that is the “exterior stack extension” diffuser. The “exterior stack extension” diffuser has the relief termination piping extended on center up and into a separate larger-diameter stack extension. Any rain and snow that gets into the

This all makes very interesting reading but, how do I apply what it says?

extended larger-diameter stack draws to the internal surface and drops down and drains out drain hole(s) at the bottom. This keeps the rain and snow fromgetting into the relief termination piping that is on center internally.

Let’s look at some examples that do not meet the standard. These examples were discovered during a mechanical inspection. Do you have any of these problems?

Uncceptable installations

2. Here we have a discharge termination that is NOT more than 20 feet from a higher roof, it is not 7.25 feet above the adjacent higher roof, and is not directed upward and arranged to avoid spraying ammonia on persons in the vicinity. This looks like a good place to take an ammonia shower.

1. What’s wrong here? Pipe plugs in the outlet of the relief valve. These are not waterproof and contribute to corrosion of the relief valve by trapping moisture in the relief. Also note the relief termination is NOT 7.25 feet above the adjacent higher roof.

3. Here we have a common condenser relief installation. If the top rail of the guard rail is about 42 inches, a maintenance man would be looking into the discharge of the relief. This is an accident waiting to happen!

4. Here we have the same problems as before with the addition of being within 20 feet of a window or a door.

RETA TECHNICAL REPORT PAGE 2

5. Here we have a problem for many dairies. Is the top a work platform? Do you have an agitator there? If you look closely, you will see a plug in the outlet of the relief piping!

6. Here is a really problematic installation. There is a relief valve that is below working surfaces with apparently nowhere to secure a relief stack. This is a problem many older installations have. This does not excuse the installation of a relief stack that meets code.

RETA TECHNICAL REPORT PAGE 3

Let’s look at some installations that meet some of the requirements.

8. Here the downward direction is not as great but still not acceptable although the height requirements were followed.

7. On this condenser the height requirements were followed but, the termination is not directed upward.

Acceptable installations

From Appendix A: 15.5.1

The termination of discharge is considered the final several feet of the relief piping. The vent end point of relief pipingmay

include a design to prevent rain and snow from entering. Many designs provide amethod to prevent rain and snow from

entering. The design at the vent end point may be a “tee” diffuser, a “double 45 degree” diffuser, (No Picture Available)

a “bull’s horn” diffuser,

RETA TECHNICAL REPORT PAGE 4

a “spring self-closing flapper cap,”

(Note that “spring self- closing flapper caps” can become inoperable due to corrosion. Inspection, testing and maintenance should be implemented when these are used.)

The “spring self-closing flapper cap” is used on natural gas and tractor exhausts. On the condenser inspecting and maintaining the cap looks to be a challenge.

or a “sock hood cover.” The “sock hood cover,” which is typically bright safety yellow, orange, or red in color, has a light flexible string attached between the hood and the relief pipe stack for its containment if lifted.”

These are commercially available.

RETA TECHNICAL REPORT PAGE 5

“Another designmethod that may be incorporated has a fully open vent end point that is the “exterior stack extension” diffuser. The “exterior stack extension” diffuser has the relief termination piping extended on center up and into a separate larger-diameter stack extension. Any rain and snow that gets into the extended larger diameter stack draws to the internal surface and drops down and drains out drain hole(s) at the bottom. This keeps the rain and snow fromgetting into the relief termination piping that is on center internally.” These are available commercially or can be field fabricated. Designs are available by searching for “No loss stack discharge”. Lastly diffusers like these are available premade and field fabricated but, they are not recommended by IIAR-2-2014. They impose an unknown resistance on the piping system and calculating the effect on the relief piping is a guess. They also need to be engineered and documented to ensure they have adequate exhaust area.

In summary, as a designer we have many choices for the discharge from a relief system. We need to ensure it is designed, documented and installed per the design.

RETA TECHNICAL REPORT PAGE 6

The Technical Report is an official publication of the Refrigerating Engineers & Technicians Association (RETA). RETA is an international not-for-profit association whose mission is to enhance the professional development of industrial refrigeration operating and technical engineers. Don Chason Executive Editor Jim Barron Executive Director TECHNICAL REPORT THE

704-455-3551 Sara Louber Senior Director, Office Operations sara@reta.com Peggy Wiederkehr Conference Manager peggy@reta.com John Bento Assistant Education Manager john@reta.com

jim@reta.com Dan Reisinger Certification Manager dan@reta.com Dan Denton Chapter Relations Manager ddenton@reta.com

The information in this publication is based on the collective experience of industry engineers and technicians. Although the information is intended to be comprehensive and thorough, it is subject to change based on particular applications, field experience, and technological developments. The Refrigerating Engineers & Technicians Association expressly disclaims any warranty of fitness for a particular application, as well as all claims for compensatory, consequential, or other damages arising out of or related to the uses

Get your message to thousands of refrigeration professionals. Advertise in the next

of this publication. Copyright © 2019

TECHNICAL REPORT

REFRIGERATING ENGINEERS & TECHNICIANS ASSOCIATION 1725 Ferry St. SW, Albany, OR 97322 Telephone: 541.497.2955 | Fax: 541.497.2966 RETA.com

For rates and information, contact Sara Louber at sara@reta.com