HDPE pipes are the superior solution for countless fluid flow applications, with a major benefit being that they are resistant to attacks from chemicals. Sandale Ontario has compiled this guide to help you better understand how chemicals react to plastic and how HDPE pipes are the superior option.
Did you know that HDPE pipes and fittings are resistant to chemicals? Sandale Ontario’s HDPE pipes are highly resistant to chemicals, making them a frequent choice for transporting corrosive substances and ensuring long-term durability in various industrial, commercial and municipal applications.
Understanding Chemical Attacks on Plastics Like HDPE
Knowing the exact fluids that flow in your pipes will help to determine the optimal type and design of the pipes themselves. Why? Because the specific material used in pipes and fittings impacts its chemical resistance. Metal will react differently than PVC, which will react differently than cast iron and even concrete.
Then there’s the design of the pipe that plays a factor in how chemicals react. You need to consider pipe dimensions, such as wall thickness, construction and composition (layers, fillers, etc.).
Even the fittings in your pipe joining system can affect the performance of the pipe system in handling chemicals. In the case of Sandale Ontario’s HDPE pipes, heat fusion is often the primary joining technique and does not introduce different materials into the system. This helps to limit issues in system operations since adding components in any piping system can have different chemical resistances. Even gaskets that use elastomers have their own unique resistances.
Types of Chemical Attacks on HDPE Pipes
Permeation of Chemicals
Chemicals can permeate through pipe walls through the free volume of the polymer matrix without significant change in the material properties. Permeability is especially concerning if the pipe is a less resistant material than HDPE (e.g., fibreglass or steel), where the pipe is moving hazardous substances, or where the pipe is installed in contaminated soil.
Absorption of the chemicals into a pipe may result in pipe swelling, plasticization or solvation. In these cases, physical properties may be affected, but the pipe itself would not be chemically changed. That being said, swelling may also result in plasticization, which can soften the material material, which can lead the failure. HDPE pipes are resistant to chemicals more than many other materials.
Another thing to keep in mind is that permeating chemicals can be entrained in the material and may be released with heat fusion. Thus, heat fusion may be unreliable if performed on permeated HDPE pipes. Caution should always be used in performing these processes if solvation or permeation is suspected.
Environmental Stress Cracking
Environmental stress cracking does not result in chemical alteration of the HDPE pipe; it is caused by a chemical agent in combination with mechanical stress, such as constant internal pressure or mechanical stress cycles.
When the pipe is subject to continuous applied mechanical stress or to combinations of chemicals, testing that duplicates the expected field conditions, as closely as possible, should be performed on samples of the pipe product to properly evaluate that HDPE pipe for use in this application.
Chemical Acceleration
Chemical attacks are increased when temperature or stress are increased or when temperature or stress are varied. When the application is installed at elevated temperatures or high concentrations, some salt solutions may attack some plastic materials through either oxidation or chemical substitution when they would be benign at lower temperatures and concentrations
The resistance of a particular plastic to a specific chemical will decrease with an increase in concentration. For example, for some materials, dilute sulfuric acid may be acceptable, whereas 95% sulfuric acid may not be acceptable.
The chemical resistance of a particular plastic often decreases with stress increases. This is further accelerated with stress cracking.
Chemical Resistance Testing for HDPE Pipes
In some cases, combinations of chemicals may cause damage where the individual chemicals do not. If you’re not sure what the reaction will be, the pipe should be tested in the complete chemical mixture in question.
For applications that involve chemicals, it is advisable to perform compatibility testing to ensure that HDPE pipes will not react adversely with the chemicals they will encounter. Manufacturer data sheets and chemical resistance charts should be consulted to guide these assessments.
Chemical Resistance Data for Plastic Piping in Non-Pressure Applications and Data Table
Much of this information derives from the Plastic Pipes Institute, the major North American trade association focused on advocacy and education for plastics used in pipe, conduit and infrastructure solutions. This is a member-driven organization that improves the quality of plastic pipes, and without their support, the industry wouldn’t be where it is today.
Please note that additional information may be needed when using HDPE in chemically sensitive environments, especially with regard to unusual or special applications. Reach out to your team at Sandale Ontario for more information.
Resistance Codes
Code | Meaning | Typical Result |
R to xx⁰F | Plastic material is generally up to the temperature (⁰F) indicated by code and may have limited resistance at higher temperatures | Swelling <3% or weight loss <0.5% and elongation at break not significantly changed. Typical performance properties not significantly affected. |
L to xx⁰F | Plastic material has limited resistance at the temperature (⁰F) indicated by code. Compatability at lower temperatures should not be assumed. | Material may experience swelling in the range of 3-8% or weight loss of 0.5-5% and/or reduction in elongation at break by >50%. Some effect on performance properties. |
N | Plastic material is not resistant. | Material may experience swelling >8% or weight loss >5% and/or reduction in elongation at break >50%. |
P | Pure concentration. | |
---- | Data not available. Check with piping manufacturer. |
The following cautions apply to this table:
This table may not be fully applicable to pressurized applications
Data Sources. The information has been obtained from numerous sources, including the Plastic Pipe Institute. The data are based primarily on plastic material test specimens that have been immersed in the chemical and evaluated, and to a lesser degree, on field experience. In most cases, detailed information on the test conditions (e.g. exposure time), and on test results (e.g. change in weight, change in volume, and change in strength) was not available. Therefore, this information is best used only for comparison of different plastic materials.
Combinations of chemicals. Chemicals that individually do not have an effect may affect the pipe if combined with certain other chemicals. The list of possible combinations of chemicals is endless. This table does not address chemical combinations.
Composite piping. Layered composite piping may have chemical resistance that differs from that of the individual materials in the layers. This table is not applicable to layered composite piping products.
Applicability to fibreglass and filled materials. This table is not applicable to reinforced epoxy resin (fibreglass) pipes and to plastic pipes containing significant percentages of filler materials.
Concentrations. Where no concentrations are given (indicated as ‘P’), the commercially pure material is indicated, except in the case of solids where saturated aqueous solutions are indicated.