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Quotes - Engineering - SalesUSP monograph water, kept that way
What the monograph asks of the metal
The WFI monograph sets three numbers: conductivity by USP <645>, TOC by <643>, and endotoxin below 0.25 EU/mL. USP <1231> says how a system holds them, and for a heat exchanger it comes down to four things: the utility fluid cannot reach the water, the water never stands still, the surface sheds nothing, and the unit survives 80 C every hour of its life.
This page is the exchanger itself: the tube joint, the finish, rouge, endotoxin, and still-fed versus membrane-fed systems. The loop is on the Hot WFI Storage page.
Joint, finish, rouge, endotoxin and the source of the water
The tube-to-tubesheet joint is the whole argument
Every WFI exchanger has a wall between compendial water and plant steam or cooling water, and the wall is a tube 0.049 in thick. The joint where the tube enters the tubesheet is the weak point. A rolled joint weeps after enough thermal cycles. A welded single tubesheet still has one face on the steam side, and a crack there is invisible until a sample fails. HeatX builds WFI units with two tubesheets 1 in apart, tubes welded to both, the gap open at the bottom so a leak drips out where an operator sees it.
The product-side tubesheet face is a compendial-water surface too: tube welds are ground flush and polished to the tube-bore finish, because a weld crown is a crevice the borescope will find.
Finish, and what electropolishing actually does
Mechanical polishing to 15 to 20 Ra leaves smeared metal and embedded abrasive. Electropolishing removes about 0.0005 in of that layer, takes the peaks off and leaves a chromium-rich surface that passivates better and holds rouge off longer. ASME BPE SF4 calls for 15 Ra maximum mechanically polished then electropolished, and that is the finish HeatX quotes for hot WFI unless the site standard says otherwise. Every readable surface is measured with a profilometer and logged by location, because the validation package needs numbers.
Rouge is not a defect, but it is your problem
Hot WFI on stainless grows a red, blue or black iron oxide film. Class I rouge migrates from a pump or weld; Class II grows in place; Class III is the magnetite of a pure steam system. None fails the water on conductivity or TOC, but a heavy film sheds particles, and a QA group that finds red in a filter housing wants it gone. The exchanger is built so a chelant derouging solution and a passivation reach every surface and drain: vertical or a 3 degree slope, no horizontal tube, a drain at the true low point. A unit that cannot be derouged in place gets pulled, and that is a shutdown.
Endotoxin, and why bacteria are the real target
Endotoxin is the cell-wall fragment of Gram-negative bacteria; it survives 121 C and no exchanger removes it. The exchanger's job is to refuse to grow the bacteria that make it: no place for a biofilm to start, which is the finish and the welded joints; no water standing still, which is drainability and loop velocity; and the 80 C hold. A WFI exchanger that runs cold for long periods, such as a use-point cooler left full between draws, is where endotoxin excursions come from. The common mistake is validating the still and treating the exchanger as pipe.
Still-fed and membrane-fed systems
A multi-effect or vapor-compression still delivers WFI at 90 to 98 C, and its exchangers are the feed preheater, the condenser and the distillate cooler to storage temperature. Membrane WFI, allowed under the monograph with a validated RO, EDI and ultrafiltration train, delivers ambient water, so the system needs a heater rated to lift the whole make-up flow to 80 C plus a loop heater to hold it. Both are double tubesheet duties; the membrane-system heater is the larger unit because it heats every gallon made.
Send the make-up rate, storage temperature, steam pressure and finish specification.
Call and talk it through with an engineer: 1-805-484-2992 The condenser on a WFI still is covered on our WFI condenser pages.
Water for Injection exchanger process conditions
The rows set out the validated build for a WFI exchanger, from tubesheets and finish to endotoxin control and sterilization. Compare them with your validation plan and send the gaps with the quote request.
| Condition | Detail |
| Product | Water for Injection per the USP monograph |
| Flow range | 5 to 400 gpm tube side; return velocity 3 ft/s or higher |
| Temperatures in / out | Heating 65 to 80 C, or 20 to 80 C on cold start; cooling 80 C to 20 to 25 C at a use point |
| Hold | None; the loop itself is the hold at 80 C or above |
| Utility | Plant steam 15 to 60 psig, or chilled and tower water, on the shell side |
| Approach | 5 to 10 C on steam heaters; 3 to 5 C on chilled coolers |
| Construction | Double tubesheet straight tube, vertical or sloped, welded product-side joints |
| Finish / class | 316L, 15 to 20 Ra electropolished, passivated; ASME BPE SF4; ASME VIII stamp |
| Endotoxin control | No crevices, full drain, 80 C hold; no elastomer in the water path but clamp gaskets |
| CIP / SIP | Derouging and passivation in place; SIP at 121 to 135 C with the shell isolated |
Validation Questions
ASME BPE Part MJ, adopted directly by most sites, with every welder and procedure qualified under ASME Section IX. The criteria cover discoloration against the BPE color reference, concavity, misalignment and full penetration, and every tube-to-tubesheet weld on the product face is inspected because it is the surface the water sees. Heat tint beyond the allowed level is ground, repolished and re-passivated at the shop, not left for a future derouging to deal with, because tint is where rouge starts.
By a certificate naming the method and acceptance test, usually a citric or nitric treatment to ASTM A967, backed by a surface analysis where the site asks for it. The analysis is done on a coupon processed alongside the exchanger and reports the chromium-to-iron ratio of the passive layer; ASME BPE accepts 1.0 or higher on passivated surfaces and 1.5 or higher on electropolished ones. Simpler checks that some quality groups accept are the A967 water immersion or copper sulfate tests for free iron on the product surface. Ask for the coupon to be retained with the turnover package so a later derouging and re-passivation can be compared against the original.
Weekly on units that run continuously, and always after a thermal upset such as a failed steam valve. The check is visual at the gap opening and the drip point: moisture, mineral deposits or rouge staining, logged against the date. It takes about a minute, which is why the gap is built open at the bottom and lit, not sealed or hidden behind insulation. Moisture at the gap takes the unit out of service until the leaking joint is found by the in-place leak test.
The chemistry and procedure are qualified once; each cycle then runs as planned maintenance under that procedure and is documented. A chelant or phosphoric-citric solution circulates at the vendor's temperature and time, followed by re-passivation, a WFI rinse to the conductivity and TOC limits of the monograph, and a period of enhanced sampling before routine monitoring resumes. The exchanger affects the procedure through drainability and contact: solution must wet the upper tubesheet face and leave from the bottom drain, and a unit that holds liquid needs more rinse volume to clear the final conductivity check.
The exchanger is built the same way, but it carries more of the endotoxin argument. A still removes endotoxin by phase change; a membrane train relies on the integrity of its ultrafilter, so inspectors look harder at everything downstream that could let Gram-negative bacteria grow and shed endotoxin against the 0.25 EU/mL limit. That puts weight on welded product joints with no crevice, a 15 to 20 Ra electropolished finish, full drainability, and a make-up heater shown to deliver 80 C at the full membrane output with the coldest feed of the year.
Yes, from either side, using the gap as the detection point. With the product side drained and the shell pressurized with air or nitrogen, a leaking tube joint shows at the double tubesheet gap, where soap solution finds leaks down to about a thousandth of a standard cubic centimeter per second; a helium sniffer at the gap finds leaks several orders of magnitude smaller where the site has one. The reverse test pressurizes the product side with the shell open and watches the gap again. Writing both tests in to the maintenance plan gives the weekly gap inspection a defined follow-up when it finds moisture, and tells the plant whether the leak is on the steam face or the water face before the bundle comes out.
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