Can Long Tubes be Coated to Improve Corrosion Resistance?

November 08 2019 Corrosion

Tubing coils blog header

At SilcoTek, we coat lots of tubing with our corrosion resistant and inert coatings.  But what's the longest tube I can have coated?  That all depends on the tube.  Read on to learn more.

Can Long Tubes be Coated to Improve Corrosion Resistance?

First let's talk about the tubing coating process.  SilcoTek's CVD coating process is able to treat 2 tubing configurations, coiled rolled tubing and straight sticks.  Our chemical vapor deposition process has some limitations relating to each tubing configuration. 
For coiled tubing we're able to treat longer rolls by filling the internal diameter of the roll with our corrosion resistant and inert process gasses.  The tube is heated to enable the coating reaction and allowing our silicon coatings to bond to the inner tube surface.  In order to reliably coat the internal surface, we limit the maximum coil length as summarized below.

Coiled/Rolled Tubing  Coiled Tubing

  • Coated internally-only 
  • Maximum continuous length: 
Max coil length table
We also have some general tube roll limitations to assure we're able to properly load tubing coils into our process ovens.  We ask that coiled tubing be shipped either on metal spools or bound with metal wire to be sure we don't damage the coil while processing.
  • Maximum coil OD for tubing > 1/16" OD: 36"
  • Maximum coil OD for tubing 1/16" OD or smaller: 18"
  • Must be shipped on a metal spool or bound with metal wire.  No spools made of wood, plastic, or other flammable materials.

Coating Straight Tubing

The coating process for treating straight tube sticks is a bit different.  For straight sticks, we load the tube stick into a process reactor and coat both the inside and outside of the tubing.  So reactor size and oven size limit the tube length.

Straight Tubing Sticks  

PAC Stainless tubing- Coated both internally and externally

- Maximum length: 80"


What About Tubing ID?

Our unique chemical vapor deposition process is performed in the gas phase, so even the smallest channels and tightest tolerances will be adequately coated along with the rest of the part.  We also have the ability to coat certain tube configurations internally-only.  If we can get our process gasses into the tube we're able to coat the part.  But for long but extremely narrow tubes we'll restrict the tube length to be sure we're able to achieve the desired coating performance.  

We proved coating aspect ratio capabilities by coating a 1/16" OD, .4mm ID tube with multiple bends both internally and externally.  After coating, the tube was cut open to examine the coating at the center-most point inside the tube.  In addition to the external coating on the tube, a quick visual inspection shows the vibrant purple-colored SilcoTek coating inside the narrow bore.  



The thickness of the coating throughout the tube was verified by a Filmetrics F40-Series Thin Film Analyzer and it was confirmed to meet our specifications.  SilcoTek coatings are not applied with line-of-sight processes that lead to inconsistent deposition and uncoated areas.  With our process, 100% of your parts are coated, even if the design is complex or the pathways or tortuous.  




Corrosion Resistance of Tubing

A CVD coating like Dursan®, for example, will improve the corrosion resistance and inertness of tubing, offering a multitude of benefits. The chemical vapor deposition process used to coat stainless steel flow paths will prevent disruption of grain boundaries and act as an inert barrier to aggressive and sticky compounds.  Dursan coated analytical flow paths will prevent HCl, sulfuric acid, bleach, and other corrosives from pitting and attacking stainless steel surfaces.  Here are some examples of how Dursan and Silcolloy® can improve corrosion resistance.

Corrosion data summary.jpg

Click here to learn more about improving the corrosion resistance and durability of analytical systems.

Dursan offers inertness, durabilityfouling, and carryover contamination benefits for process analytical, gas supply, process sampling, stack and flare sampling.  Want to learn how our coatings improve purity and yields?

Get Our Corrosion Resistance Application Guide


Dursan Corrosion Resistance Data.  How a Chemical Resistant CVD Coating Can Protect Stainless Steel From Corrosion in Gas Delivery Systems.

Dursan® can increase corrosion resistance by 10x or more through preventing interaction of the analyte or process fluid and the stainless steel surface. Dursan exceeds typical metal passivation capability. Immersion testing in 6M hydrochloric acid (HCl) shows that Dursan coated surfaces prevent surface attack and protect stainless steel from rust by orders of magnitude compared to passivated stainless steel, preventing gas supply system corrosion.


Sulfuric acid can form in process analytical sampling systems and stack sampling systems that transport stack emissions or hydrocarbon flare samples. When exposed to water and heat, sulfur compounds commonly found in stack samples can form sulfuric acid and corrode and contaminate sample systems. Inert coatings like Dursan reduce the risk of corrosion, even when exposed to sulfuric acid.



HBr corrosion resistance

Comparative HBr corrosion testing shows that Dursan and Silcolloy coated stainless steel surfaces improve flow path corrosion resistance by up to an order of magnitude over uncoated stainless steel.  Virtually all stainless steel surfaces can be coated including small and large bore tubing, regulators, stainless steel frits, fittings and valves.



Get more corrosion application information and benefits for your process or products.  Get our corrosion presentation.

Get Our Latest Corrosion Solutions Presentation

Protecting analytical flow paths from rust can revolutionize the reliability of process and analytical sampling.  Contact our technical service team to discuss your application.  Need an inert hydrophobic surface?  How about an anti-fouling surface that's wear resistant?  Our team can help match the best coating for your application.

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