This is one of those process safety questions: if 100 engineers were asked, you would NOT get the same answer from all 100. Although there may be other topics, this little fact would also hold true; this aspect of PSM is a critical path in process safety, so we need to get the FACTS on the table. In short, YES – relief valves can be installed in a horizontal position when the FOLLOWING CONDITIONS are MET…
1) Manufacturer EXPLICITLY states their RV can be installed horizontally!
I would encourage this to be in writing from the manufacturer if it is not explicitly stated as permissible in the installation/maintenance instructions. Maybe a letter from the company merely stating that they “approve” their RV being installed with the stem in a horizontal position vs. vertical.
2) ASME Section VIII, Appendix M-11 is satisfied.
M-11 INSTALLATION OF SAFETY AND SAFETY RELIEF VALVES
Spring loaded safety and safety relief valves normally should be installed in the upright position with the spindle vertical. Where space or piping configuration preclude such an installation, the valve may be installed in other than the vertical position provided that:
(a) the valve design is satisfactory for such position;
(b) the media is such that material will not accumulate at the inlet of the valve; AND
(c) drainage of the discharge side of the valve body and discharge piping is adequate.
3) The Design Basis documentation clearly states that the RV(s) that are installed on a horizontal basis are part of the design basis and that BOTH #1 and #2 above have been considered and met in the installation of the RV. Now it would not be right for me to point out the obvious…
Spring-loaded safety and safety relief valves should normally be installed in the upright position with the spindle vertical. Where space or piping configuration precludes such an installation, the valve may be installed in other than the vertical position provided that…
So it is my humble opinion that for EVERY RV installed in any orientation OTHER THAN vertical, the “design basis” needs to document that the specific RV is in that “other than vertical position” because “space or piping configuration precluded its installation.”
6/27/13 – UPDATE
Amazing how such a short article can cause such a major uproar. I have received hundreds of e-mails on this article asking for more details. It seems there may be a lot of RVs out there installed horizontally. It is what it is, the code that is! (My attempt at some Dr. Seuss writing)
It is my professional opinion, as well as many other engineers and regulatory personnel who have contacted me and thanked me for publishing this, that FIRST and FOREMOST, ALL RVs be installed with their stems in the VERTICAL DIRECTION. ONLY when there is NOT enough space OR the piping configuration, which is ALREADY IN PLACE, is such that the RV cannot be installed with its stem vertical, can we even begin to consider a horizontal installation. Then we would have to find a manufacturer that would permit their RV to be installed horizontally.
Of course, this is ALL based on the pressure vessel being an ASME-coded vessel, AND your RV design basis RAGAGEP is ASME Section VIII. If you have a different RAGAGEP for your vessel design AND RV design basis, this may very well NOT apply to your specific situation. I chose to use the ASME Section VIII in this example as it is by far the most widely used code in the USA for pressure vessel design, but if your facility is using some other RAGAGEP, my position may not hold true. However, for those who think API 576 somehow precludes you from this issue… you are WRONG. In fact, API 576 states in 5.8.4.3 …
NOTE: Pressure-relief valves should be installed vertically, with the disk or piston oriented horizontally, so that the disk or piston moves upward as the valve opens. Other orientations may permit the disk holder to become misaligned in the guide. ASME BPVC Section VIII, Division 1, Appendix M, describes under what conditions an orientation other than vertical may be acceptable.
So yes, those using API 576 as their RV RAGAGEP must also comply with ASME Section VIII, Appendix M. We can argue the merits, but it is what it is, and in many minds, this is clear. I do not apologize (Chris!) for stating what I believe to be fact. So if you ever e-mail me with comments, suggestions, challenges, etc., please correct me where you think I am wrong, and I will be most appreciated. E-mailing me and telling me I am an idiot and that my posting is somehow “causing unfounded confusion and increasing dangers to workers through my stupidity” is baffling to me.
The most common question I have received is, “Should we correct the RV(s)?”. My answer to all, regardless of the number of issues, and some stated they had hundreds of horizontal RVs, is ABSOLUTELY it/they should be corrected if they do not meet the RAGAGEP the facility has claimed as their design basis. Where this lands on your critical work plans schedule (e.g., priority) is your call, but there is NO doubt in my mind that this could be (as well as should be) cited by OSHA/EPA either under:
1910.119(d)(3)(i)(D) Relief system design and design basis;
1910.119(d)(3)(ii) The employer shall document that equipment complies with recognized and generally accepted good engineering practices
Several of those who commented asked, “Is this merely a code compliance issue, or is this truly a safety concern?” I personally do not differentiate those any longer. My position is that if it is in an engineering code that we (the facility) have adopted, then it matters not to the degree of risk. I guess it could impact the implementation schedule, as we would certainly want to take care of those issues that could cause harm before those merely dotting the “i’s” and crossing the “t’s.” But folks, it is my opinion that this issue with RV orientation is MUCH MORE than dotting the “i’s” and crossing the “t’s.” I can personally say I have dealt with this twice in my career. BOTH times, the plant manager was a ChemE, and both times, this discovery was moved way up on the corrective action list. One company actually had very high-level meetings within the company. It issued directives to all business units to audit their RVs and to have ALL corrections in place within nine months. That meant, in some cases, unplanned shutdowns of major process units. Some “engineers” actually argued that the risk of shutting down the unit to fix this problem was merely compounding the problem for an issue that was not all that serious. As it turns out, those very engineers decided that installing these RVs, although not technically correct, was an “accepted industry practice” (there is that ugly term again!).
So this will, in most all likelihood, NOT be an easy fix. Some of you have already asked your engineers about this and were “laughed out of the room.” One of you actually was told that the “code is not meant to be taken literally and to stop sticking your nose into places you do not understand.” This is why I published this article: to help Safety/PSM professionals identify items that may be outside our scope of knowledge and to learn from MY MISTAKES. The code is what it is; if an engineer chooses to dismiss it as not credible, even after the facility has stated in their PSI that it is the code for their RV design basis, that is their choice. I would have that engineer front and center, answering the relief basis design questions from OSHA/EPA.