Pipes For Seawater Desalination

What are Pipes For Seawater Desalination

Desalination pipelines are primarily categorized into corrosion-resistant metal pipes and non-metallic pipes.
During the desalination process,because both the raw seawater and the resulting brine are highly corrosive,the choice of pipe material depends on the specific process stage,pressure requirements,and budget.

  • Pipe For Seawater Desalination

Core Strengths of Pipes For Seawater Desalination

The primary challenge in seawater desalination is the high concentration of chloride ions,which can cause rapid pitting corrosion,crevice corrosion,and stress corrosion cracking in ordinary metals.Marine-grade metal pipes are effective in resisting localized corrosion caused by seawater.
High-Pressure Resistance:
The reverse osmosis process requires extremely high operating pressures.Super duplex stainless steel has a yield strength approximately twice that of standard austenitic stainless steel,allowing for thinner pipe walls while ensuring safety,thereby reducing system weight.
Biofouling Resistance:
Modern piping can be manufactured with extremely smooth inner walls,which significantly reduce the attachment of marine organisms and minimize fluid friction resistance,thereby saving energy during pumping.
While the initial investment in high-performance piping may be higher,compliant products typically have an exceptionally long service life spanning several decades.High-performance materials can significantly reduce costs associated with downtime for maintenance and frequent pipe replacements.For example,duplex stainless steel has a service life more than twice that of 316L stainless steel.

Common Standards of Pipes For Seawater Desalination

Critical StandardsDescription/Usage
ASTM A790 / A928The primary specification for Seamless and Welded Duplex/Super Duplex Stainless Steel Pipes.It defines the chemical composition and mechanical strength required for high-pressure reverse osmosis sections.
ASTM G48A rigorous Corrosion Testing Standard used to verify the resistance of stainless steel pipes to pitting and crevice corrosion when exposed to chloride-rich environments like seawater.
ISO 14692The international standard for Glass-Reinforced Plastic Piping.It covers everything from design and manufacture to installation for non-metallic pipes used in seawater intake and brine discharge.
ASTM D3350 / D3261Standards for High-Density Polyethylene Materials and Fittings.These specify the cell classification and pressure ratings for flexible thermoplastic pipes used in seawater intake and outfall lines.
AWWA C950The American Water Works Association standard for Fiberglass Pressure Pipe.It is widely used to ensure the structural integrity of large-diameter pipes conveying seawater and treated water.
ASME B31.3The Process Piping Code,which provides the overarching engineering requirements for the design,materials,fabrication,and testing of the entire desalination plant piping network.
NSF/ANSI 61A critical health standard for Drinking Water System Components.It ensures that any pipe material in contact with the final “product water” does not leach contaminants into the drinking supply.

The desalination methods used include seawater freezing,electrodialysis,distillation,reverse osmosis,and ammonium carbonate ion exchange;currently,reverse osmosis and distillation are the mainstream methods in the market.These processes place high demands on the material quality and corrosion resistance of seamless pipes made of stainless steel and corrosion-resistant alloys.

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Applications of Pipes For Seawater Desalination

  • Brine Outfall/Discharge
  • ERD Piping
  • RO Pressure Vessel Connections
  • High-Pressure Pump Manifolds
  • Seawater Intake Lines
  • Flush & CIP Systems
  • Post-Treatment & Remineralization
  • Product Water/Permeate Lines
  • Pre-treatment Filtration
  • Chemical Dosing Lines

Main Application Specifications and Materials

CategoryGradesStandardsSize Range
Austenitic Stainless Steel304/304L, 304H, 304N/304LN, 310, 316/316L, 316H, 316Ti, 316N/316LN, 317/317L, 321/321H, 347/347HGB/T 14976, GB/T 12771, ASME SA312Outside Diameter (OD):
Φ6 – Φ762
Duplex/Super Duplex SteelS31803, S32205 (2205), S32750 (2507)GB/T 21833, GB/T 21832, ASME SA790
Super Austenitic Stainless Steel904L, S31254 (254SMO), N08925, N08367ASME SB677, SB690
Nickel-based AlloysN08800/10/11, N08020, N06600, N06601, N06625, N04400, N08825, N02200/01ASME SB165, SB167, SB407, SB423, SB444, SB729
HastelloyC276, C22, C2000ASME SB622

Manufacturing Processes Of Pipes For Seawater Desalination

The manufacturing process for seamless pipes for seawater desalination begins by heating the pipe billet and extruding it through a die.The hot-rolled pipe is then subjected to further cold drawing or cold rolling at room temperature.Solution annealing is the most critical step.The pipe is heated and then rapidly water-quenched to eliminate internal stresses and ensure that the ratio of ferrite to austenite in the duplex steel meets the required specifications.
Welded pipes for seawater desalination are suitable for medium- and low-pressure pipelines as well as large-diameter transmission lines.TIG or plasma welding is commonly used.After welding,the welds must be smoothed. Internal welds are cold-worked and flattened to ensure they are flush with the base material, thereby preventing dead corners that could lead to crevice corrosion.
Desalination pipelines have extremely stringent requirements for surface condition;any scratches or scale can serve as corrosion initiation sites.Appropriate surface treatment must be performed.
Pickling & Passivation:
An acid solution is used to remove surface scale and form a dense chromium oxide passivation layer on the surface.This is the final step in ensuring the PREN value is effectively achieved.
Electropolishing:
For certain high-performance freshwater collection systems,an electrochemical process is used to achieve a mirror-like finish on the inner walls of the pipes.
As a responsible stainless steel pipe manufacturer in China,we test every pipe before it leaves our factory.This includes,but is not limited to,eddy current and ultrasonic testing,hydrostatic testing,and ferrite content testing. We provide Material Test Reports (MTRs) for our products and can even assist with customs clearance.Please feel free to contact us at any time.

Should I use Seamless or Welded pipes For Seawater Desalination?

Seamless:
Preferred for the High-Pressure RO feed lines (70–85 bar).Because there is no weld seam, the structural integrity is uniform,reducing the risk of failure under cyclic pressure.
Welded:
Used for low-pressure intake or large-diameter headers.Modern “Class 1” welds with 100% X-ray testing are highly reliable and more cost-effective for sizes above 8 inches.

What is the difference between 316L and Duplex 2205 in desalination?

The main difference is chloride resistance.
316L is suitable only for fresh water or water with extremely low salinity.In untreated seawater,316L will develop severe pitting and crevice corrosion within a few months.
2205 is the “workhorse” for medium-salinity or brackish water.Compared to 316L,it offers higher strength and significantly better resistance to SCC.

How do stainless steel pipes compare to Titanium in desalination?

Titanium:
Technically superior (zero corrosion in seawater),but extremely expensive and difficult to source in large quantities.
Super Duplex SS:
Offers the “Best Value”—it provides sufficient corrosion resistance for the 25-year life of a plant at a fraction of the cost of Titanium.

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