Must a chromatography column comply with BPVC? 1

[scott1971]

Hi friends,

I work for a company that manufactures liquid chromatography columns for biopharmaceutical purification. On most customer specifications that I receive for these columns, a U-stamp is requested or, at least, "conformance to Section VIII." I am also involved with the authoring of a new section for the ASME BPE (Bioprocessing Equipment Standard) dealing with the design of chromatography equipment and there are those in my group who also feel that these vessels must "comply with the relative pressure vessel codes..." as it is currently written.

For purposes of this discussion, I am talking about columns that:
[ul]
[li]Are normally filled with water or other non-toxic, "water-like" solutions with a flash point above 185°F.[/li]
[li]Are normally operated at pressures below 300 psi, usually no more than 70 psi.[/li]
[li]Are not heated in any manner.[/li]
[li]Contain no chemical process that creates gases of any kind.[/li]
[/ul]
I am also not referring to any National Board requirements or those of any state or local municipality, just ASME.

Considering the above statements, the argument I have been given for why these columns must be manufactured according to BPVC is that they could become pressure vessels, to which I say, "So could a lot of things if you set your mind to it."

There are two scenarios that describe the normal operation of one of these columns:
[ul]
[li]PURIFICATION - A column is filled with a slurry of microscopic beads which act as the chromatography medium. The column is plumbed to a piping system which conveys various liquid solutions to load a product and elute the contents. An assembly of pumps, valves, and other instruments controls and monitors the process. The pumps are equipped with hard-wired devices that remove power from the pumps in case of a higher-than-recommended pressure. The software controlling the pumps is also programmed to turn off the pumps during an overpressure event. An air sensor in the tubing that feeds the column is monitored and halts the pumps if air is detected. Also, a flow meter monitors the flow rate and stops the operation if the measured flow rate deviates too far from the programmed set point.[/li]
[li]COLUMN PACKING - This is the process of filling the column with the slurry described above. Assume, the column begins empty, filled with air at 0 psig. There are various methods of packing a column which depend on the column design and other factors. A common design is a "pack-in-place" column. In this case, the column is connected to a "packing device," which normally consists of a few valves and a couple of air-diaphragm pumps that are controlled manually (not unattended). The packing device controls all of the packing operations, which are:
[ol]
[li]Fill column with water. The water enter through a nozzle in the bottom of the column. Air exits through the "mobile-phase" outlet at the top of the column.[/li]
[li]Fill column with slurry. The slurry enters through a similar nozzle at the top of the column. The slurry volume displaces the existing water volume, which exists the column through the "mobile-phase" outlet at the bottom. The beads (see Purification above) are retained within the column by two fine-meshes at each end of the column. Click here for an illustration (this is not exactly as I've described here, but you'll get the idea).[/li][/ol]
[/li][/ul]
My understanding of the BPVC is that, in order to become a pressure vessel, one of these columns must be pressurized with liquid above 300 psi or with gas above 15 psi. Indeed, both of the modes I've described above typically involve the use of positive displacement pumps that are capable of pumping air. However, also in both modes, the column is never closed on the opposite end from the pump. In the case of the PURIFICATION mode, a number of safety features and monitors would need to catastrophically fail simultaneously to create a hazard. In the case of the COLUMN PACKING mode, the operator would need to intentionally close off one end of the column and intentionally pump air into the column. The diaphragm pumps could undoubtedly raise the internal pressure above 15 psi, but again, the process is not unattended and this situation would require operator intent—the operator would need to physically close off the open end of the column with an additional valve or blanking plate.

Section VIII, Division 1, U-1(c)(2)(f) which, among other sub-sections, identifies vessels outside the scope of the main Section, states:[ul none]"a vessel [highlight]for[/highlight] containing water under pressure, including those containing air the compression of which serves only as a cushion,..."[/ul]

Does the Code say anything about vessels that might become a pressure vessel? These columns are certainly for containing water, but they might contain air above 15 psi if someone is dumb enough to do it. How idiot-proof must a vessel be?

I recognize that, in the grand scheme of things, if one is not going to design a column according to ASME BPVC, they musk ask themselves to which standard they will design it and is that standard much more or less rigorous than BPVC. I guess I'm more concerned with the U-stamp than anything else. To me, this adds unnecessary cost to the column. Since we're are dealing with the healthcare industry here, such costs may ultimately be passed onto patients.

Thanks for taking the time to read all of this. I appreciate any comments or additional information that you can provide.



Scott
======================================
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[metengr]

Scott;
As a Purchaser, I am going to take a very simple approach here because your second statement says it all

On most customer specifications that I receive for these columns, a U-stamp is requested or, at least, "conformance to Section VIII

. The Purchaser can request whatever they please if they are willing to pay for it.
By the way,

Does the Code say anything about vessels that might become a pressure vessel? These columns are certainly for containing water, but they might contain air above 15 psi if someone is dumb enough to do it. How idiot-proof must a vessel be?

No. The Code is not an Engineering Handbook and does not provide operational scenarios. This is what Design Engineers get paid to do on their job.


We have had many vessels that were not necessarily pressure vessels by definition and we requested fabrication to Section VIII, Div 1. Why, because we wanted conformance to an existing Code or Standard for insurance purposes.

I do applaud your efforts but sometimes there is a bigger picture.

 

[scott1971]

Metengr,

Thanks for your reply. Of course, if the customer is willing to pay for it, we're willing to build it. Your statement that

The Code is not an Engineering Handbook and does not provide operational scenarios.

is what really caught my attention. If, indeed, the code does not consider operational scenarios, then from a technical fabrication perspective—which is my concern with regard to ASME BPE—it does not sound like these columns must conform to BPVC. It may be advisable to conform to BPVC or other international standards, but not necessarily a mandate. We actually follow Europe's Pressure Equipment Directive which, if I remember correctly, is actually more stringent than BPVC for our scenario. We obtain U-stamps when necessitated by the customer.


It would be interesting to know if there are any other standards out there which evaluate the fail-safe requirements vs. the likelihood of a hazard. I agree with your Purchaser perspective regarding insurance. "For every idiot proof system devised, a new, improved idiot will arise to overcome it."

Scott
======================================
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Have you read the Eng-Tips.com Forum Policies lately?

 

[JohnGP]

Scott,

Because the Pressure Equipment Directive applies to vessels operating over 50 kPag (unless covered by any of the exclusions) then you will be governed by its provisions if your columns can see more than 7 psig at any time. To satisfy the essential safety requirements I expect that you would need to design and fabricate to one of the internationally accepted pressure vessel codes. As you note, a U stamp would not be necessary if using the ASME code to satisfy the PED, but I have found that specification of U stamping tends to focus the attention of the manufacturer (particularly for foreign shops).

Just on the ASME BPVC, it cannot detail operating conditions as noted my metengr above, but expects whoever is performing the design to include such considerations - see for example the opening paragraph in U-2 of ASME VIII, which includes the requirement of "taking into consideration factors associated with normal operation, such other conditions as startup and shutdown, and abnormal conditions which may become a governing design consideration".

Just some of my thoughts……

Regards,
John