• ByRouging Solutions Editorial Team  ·  27 October 2026

Data Center Liquid Cooling: A Guide to Stainless Pipe Care

Servers built for AI run hot. Many new data halls now pipe liquid coolant straight to the chips. Data center liquid cooling depends on one thing people rarely see: the inside of the stainless steel pipe. If that pipe is dirty on the day it is filled, the dirt goes straight to the servers.

India is building fast. The country had about 375 MW of data center capacity in 2020. By 2025 it had around 1,500 MW, says Digital India, a site run by the IT ministry.

What Does Data Center Liquid Cooling Ask of Stainless Pipe?

It asks the pipe to stay clean and to keep the coolant clean for years. The loop that feeds the servers is called the technology cooling system, or TCS. It runs from coolant distribution units (CDUs) through row manifolds to each rack. There, small metal cold plates sit on top of the chips.

The Open Compute Project (OCP) is a group of big server buyers and makers. It shares designs and guides that anyone can use. Its guidelines for pre-commission preparation of TCS row manifolds were written by engineers from member companies. They assume the pipework will be "stainless steel, minimum grade 304."

The loop also mixes metals. OCP's PG25 coolant guidelines describe "copper cold plates, stainless steel piping" in the same loop. PG25 is a coolant made of 25% propylene glycol in water, with added corrosion inhibitors. Those inhibitors protect the metal, but they work best in a loop that starts out clean.

The PG25 guide also says "Quick connects made of stainless steel should be used." It advises against plated quick connects until they are proven, because the plating can wear off with use. Bare metal under worn plating can then corrode faster. So the guide favors stainless steel even for small fittings, and that steel's surface needs care.

This care matters more each year, because India keeps adding data center capacity.

Why Does Data Center Liquid Cooling Need Clean Pipe?

Because the channels inside a cold plate are tiny. OCP's manifold guidelines put them at about 100 microns, which is a tenth of a millimeter. Cleaning and flushing must leave the system "free of corrosion by-products, dirt, and construction debris" that could block those channels. One blocked plate means one chip runs hot.

New pipe arrives with more dirt than people expect. Cutting, grinding and welding leave metal dust, oil and scale inside. Dust blows in through open ends on a building site, too. OCP's PG25 guide notes that job-site work "often introduces additional contaminants such as dust, debris or flux residues".

Rust is the other risk. Steel with free iron on its surface, the loose iron specks left by tools, can stain and shed fine particles once water fills the loop. Our guide on pickling and passivation explains where that free iron comes from and how acid treatment removes it.

What Should Happen to the Pipe Before It Reaches Site?

It should be welded with care and then cleaned at the workshop, with pickling where needed. OCP assumes the pipe arrives treated to a cleaning standard such as ASTM A380, which covers removing scale, oil and grease. It also assumes welds are made under inert gas "to minimize heat tint". Heat tint is the colored band beside a weld.

Order matters at this stage. ASSDA, the Australian body for the stainless steel trade, warns that acid will not remove grease or oil. Its pickling and passivation guide says "it may be necessary to use a detergent or alkaline clean before pickling or passivation." After the acid step, it says, "all acids are thoroughly removed by rinsing".

Our guide to ASTM A380 covers that cleaning standard in plain words. Note that A380 is written for new parts, equipment and systems, which suits fresh pipe spools well. OCP only assumes this cleaning was done, so confirm it with your supplier.

How Is a Liquid Cooling Loop Cleaned Before Fill?

In stages, with the servers kept out of the loop until the end. OCP's guide assumes the CDUs and rack manifolds are not yet connected. Teams fill the pipe and test it for leaks. Then they clean and flush it through a skid with a pump and filter, using finer filters as the water gets cleaner.

Here is the usual order, based on the OCP guidance:

1. Isolate the pipe. Leave CDUs and racks unconnected, and link the ends with temporary loops.
2. Pressure test for leaks. OCP calls this hydrotesting, and it should be planned together with the flush.
3. Clean and flush with a skid. Start with coarse filters of 50 to 100 microns, then step down. OCP recommends a final rating of 5 microns.
4. Watch the solids. Take water samples during the flush until suspended solids stay low.
5. Passivate if your spec needs it. Then rinse well and drain all the water before the coolant goes in.
6. Fill with coolant through a fine filter. The PG25 guide suggests "5–10 micron absolute" filters as the coolant goes in.
7. Keep a sample. Take one in the first one to three days and keep it for the life of the fluid.

Timing matters as much as the steps. OCP says the flush should follow the leak test straight away. It also warns against water sitting still in the pipe, so the gap between flush and fill should be kept short.

Fresh coolant needs care, too. The PG25 guide warns that "Even new, pre-mixed fluids may introduce particulates into the system." So filtering on the way in is part of the job.

Is Passivation Always Needed for Data Center Liquid Cooling?

Not always. OCP's PG25 guide says the system is filled after the pipe is "cleaned, passivated (if required)" and drained. Pipe made off-site "may have undergone pre-cleaning or passivation" and may not need much more work. Pipe welded on site often picks up more dirt, so it needs closer attention.

The guide gives one clear instruction here. Before any cleaning on site, check with your suppliers and fabricators. Ask them "what cleaning and passivation processes have already been completed off-site." That one answer decides how big the job is.

When passivation is needed, citric acid is one option, and ASTM A967 includes citric methods. Citric acid passivation removes free iron and helps the steel's thin chromium oxide layer form again. Our citric acid passivation service works on installed pipe at your site, or on spools at our own premises.

What Records Should You Keep Before You Fill?

Keep a record of every chemical and step that touched the pipe. The PG25 guide asks teams to "Record the date, passivation method used, chemical concentrations, exposure time and test results." It also suggests keeping supplier certificates of analysis (COAs) where they are available. These records help you trace the cause if the coolant goes bad later.

Keep two samples if you can. One comes from the system in its first days, as in step 7. The guide also suggests keeping a sample of fresh coolant that never touched the system. Later tests can then be compared with a clean baseline.

How Rouging Solutions Helps With Liquid Cooling Pipe

We clean, descale and passivate stainless steel pipe and spools at your site or at ours. Our inspection team checks the surface first, using imported tools that are fully calibrated. Every job comes with all the relevant documents. Where weld zones or pipe faces are rough or discolored, we also offer mechanical polishing and electropolishing.

Here is a made-up example of how a good record helps. Say a spool fabricator near Navi Mumbai ships manifolds for a new data hall. In November, the contractor asks what cleaning and passivation the spools received. The fabricator sends a record with the method, the chemical, the contact time and a free iron test result for each batch. That record helps the site team set the scope of on-site cleaning.

Fabricators who make many spools can bring this work in-house. Our service for the establishment of a passivation system helps pipe and spool makers set up their own passivation system at their workshop.

Our teams work across the West, South and North of India. Our three directors bring 60+ years of combined industry experience. You can read more on our cleaning service for installed systems.

Where to Start

Remember one thing: the cleanest coolant cannot fix a dirty pipe. Whatever is left inside on fill day will travel to the cold plates. So this week, ask your pipe supplier one simple question. What cleaning and passivation did these spools get before they left the workshop, and where is the record?

If the answer is unclear, plan for a fuller clean on site. Keep every record from the flush, too, because you will need it later. If you want help with that, our team can visit and check the pipe first. Then we can tell you what the job needs. We reply within 24 hours.

Frequently Asked Questions