1、1 TR-19/2007 Chemical Resistance of Thermoplastics Piping Materials 105 Decker Court, Suite 825, Irving, TX 75062 P: 469-499-1044 F: 469-499-1063 www.plasticpipe.org 1 CHEMICAL RESISTANCE OF THERMOPLASTICS PIPING MATERIALS Foreword This report was developed and published with the technical help and
2、financial support of the members of the PPI (Plastics Pipe Institute, Inc.). The members have shown their interest in quality products by assisting independent standards-making and user organizations in the development of standards, and also by developing reports on an industry-wide basis to help en
3、gineers, code officials, specifying groups, and users. The purpose of this technical report is to provide information on the transport of various chemicals using thermoplastic piping materials. This report has been prepared by PPI as a service of the industry. The information in this report is offer
4、ed in good faith and believed to be accurate at the time of its preparation, but is offered without any warranty, expressed or implied, including WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. Consult the manufacturer for more detailed information about the particular weathering
5、 package used for its piping products. Any reference to or testing of a particular proprietary product should not be construed as an endorsement by PPI, which do not endorse the proprietary products or processes of any manufacturer. The information in this report is offered for consideration by indu
6、stry members in fulfilling their own compliance responsibilities. PPI assumes no responsibility for compliance with applicable laws and regulations. PPI intends to revise this report from time to time, in response to comments and suggestions from users of the report. Please send suggestions of impro
7、vements to the address below. Information on other publications can be obtained by contacting PPI directly or visiting the web site. The Plastics Pipe Institute 469-499-1044 www.plasticpipe.org September 2007 2 This report has been developed as an informative guide on resistance of thermoplastic pip
8、ing materials to chemical attack. It is divided into two main sections: (1) a discussion of chemical resistance and general considerations for end use applications and (2) a listing of chemical resistance data (table) for several thermoplastic piping materials applicable to non-pressure applications
9、. Determination of suitability for specific applications under stress (pressurized service) is beyond the scope of this report. SECTION I: CHEMICAL RESISTANCE IN GENERAL Thermoplastic materials generally are resistant to attack from many chemicals which makes them suitable for use in many process ap
10、plications. The suitability for use in a particular process piping application is a function of: I. Material A. The specific plastic material: ABS, CPVC, PP, PVC, PE, PB, PVDF, PEX1, PA11, PK B. The specific plastic material physical properties as identified by its cell classification according to t
11、he appropriate ASTM material specification. II. Product and Joint System A. Piping product dimensions, construction, and composition (layers, fillers, etc.). B. Joining system. Heat fusion and solvent cementing do not introduce different materials into the system. Mechanical joints can introduce gas
12、kets such as elastomers, or other thermoplastic or non-thermoplastic materials used as mechanical fitting components. C. Other components and appurtenances in the piping system. III. Use Conditions - Internal and External A. Chemical or mixtures of chemicals, and their concentrations. B. Operating t
13、emperature maximum, minimum, and cyclical variations. C. Operating pressure or applied stress maximum, minimum and cyclical variations. D. Life-cycle information such as material cost, installation cost, desired service life, maintenance, repair and replacement costs, etc. 1Once cross-linked, PEX is
14、 no longer considered a thermoplastic material; however, it is included in this report as convenience for the reader. 3 Types of Chemical Attack on Plastics In general, chemicals that affect plastics do so in one of two ways. One effect is chemical solvation or permeation; the other is direct chemic
15、al attack. Chemical Solvation or Permeation In the case of solvation or permeation, physical properties may be affected, but the polymer molecule structure itself is not chemically changed, degraded or destroyed. In solvation or permeation, gas, vapor or liquid molecules pass through the polymer, ty
16、pically without damaging the plastic material itself. If the solvating chemical can be removed completely, the plastic is generally restored to its original condition. However, removal of the chemical is not always possible, and, in such cases, these chemical solvation effects may be permanent. Some
17、times the polymer itself may not be soluble, but it may contain a soluble compounding ingredient that may be extracted from the polymer compound. This is rare because such extractable ingredients are either not used in pipe compounds, or they are chemically bonded to the molecular polymer matrix and
18、 in such small amounts that they cannot be leached out to any significant extent. Permeation may do little if any harm to the material, but it may have application-related effects. The permeating chemical may transfer into a fluid on the other side of the pipe. In general, thermoplastic pipes should
19、 not be used where a permeating chemical in the environment surrounding the pipe could compromise the purity of a fluid, such as potable water inside the pipe (See also PPI Statement N on Pipe Permeation). In gas or vapor transmission service, there may be a very slight loss of contents through the
20、pipe wall. Lastly, a permeating chemical entrained in the material may be released when heat fusion or solvent cement joining is performed. Thus, heat fusion or solvent cement joining may be unreliable if performed on permeated pipes. Direct Chemical Attack Direct chemical attack occurs when exposur
21、e to a chemical causes a chemical alteration of the polymer molecules by chain scission, crosslinking, oxidation or substitution reactions. Direct chemical attack may cause profound, irreversible changes that cannot be restored by removal of the chemical. Examples of this type of attack are 50% chro
22、mic acid at 140 F on PVC, aqua regia on PVC at 73 F, 95% sulfuric acid at 73 F on PE and wet chlorine gas on PVC and PE. Direct chemical attack frequently causes a severe reduction of mechanical physical properties such as tensile strength, ductility, and impact resistance, and susceptibility to cra
23、cking from applied stress (stress cracking). 4 Chemical resistance may vary greatly from one plastic material to another (i.e., PVC, ABS, PE, etc.), and also among different cell classifications of the same plastic type (e.g. PVC 1120 to PVC 2110, PE 3608 to PE 4710, etc.). There may also be slight
24、variations among commercial products having the same cell classification. The chemical resistance of plastic piping is basically a function of the chemical resistance of the thermoplastic material, in addition to additives and other ingredients in the final compound. In general, the less inert compo
25、unding ingredients used the better the chemical resistance. Thermoplastic pipes with significant filler percentages may be susceptible to chemical attack where an unfilled material may be affected to a lesser degree or not at all. Other Considerations Chemical Families While the effect of each indiv
26、idual chemical is specific, some chemicals can be grouped into general categories based on similarities in chemical characteristics (acids, bases, alcohols, etc.). For example, water-based (aqueous) solutions of neutral inorganic salts generally have the same effect on thermoplastic piping materials
27、 as water alone; thus, sodium chloride, potassium alum, calcium chloride, copper sulfate, potassium sulfate and zinc chloride solutions have the same effect as water. However, at elevated temperatures and/or high concentrations, some oxidizing salt solutions may attack some plastic materials. Furthe
28、r, with organic chemicals in a specific series such as alcohols, ketones, or acids, etc., as the molecular weight of the organic chemical series increases, the chemical resistance of a particular plastic material to members of the specific organic chemical series frequently also increases. Thus, whi
29、le one type of polyvinyl chloride at 73 F is not suitable for use with ethyl acetate, it is suitable for the higher molecular weight butyl acetate. Accelerating factors (concentration, temperature, stress) Generally, the resistance of a particular plastic to a specific chemical decreases with an inc
30、rease in concentration. For example, at 73F polyethylene pipe can be used to carry 70% sulfuric acid but is not satisfactory for 95% sulfuric acid. Also, the resistance of a particular plastic to a specific chemical generally decreases as temperature increases, generally decreases with increasing ap
31、plied stress, and generally decreases where temperature or applied stress are varied or cycled. These effects can be greater overall in combination. Combinations of Chemicals In some cases, combinations of chemicals may have a synergistic effect on a thermoplastic material where the individual chemi
32、cals do not. It cannot be 5 assumed that an individual chemicals lack of effect would apply for combinations that include several chemicals. When the possible combined effect of several chemicals is unknown, the material should be tested in the complete chemical mixture(s) in question. Multi-Layered
33、 (Composite) Piping Some piping products utilize a multi-layered (composite) construction, in which the pipe wall is constructed of layers of different materials. The layers may consist of both thermoplastic and non-thermoplastic for example, PE/AL/PE and PEX/AL/PEX pipes, which contain a mid-wall a
34、luminum layer. An all-thermoplastic composite pipe may contain PVC, ABS, and PVC layers. Layered composite material pipes may have chemical resistance that differs from the chemical resistance of the individual materials. Rate of Chemical Attack Chemicals that attack plastics do so at a certain rate
35、, some slowly and some more quickly. But usually, any chemical attack is increased when temperature or stress are increased, or when temperature or stress are varied. The particular rate must be taken into consideration in the life-cycle evaluation for a particular application. It has been observed
36、in some chemical plants that while a particular application may have a relatively short service life, the overall life-cycle cost may be economically feasible and justifiable. Each combination of material cost, installation cost and service life must be evaluated and judged on its own merits. In som
37、e cases involving a slow rate of chemical attack, particularly when the application will be pressurized, simple immersion data, like that represented in the following resistance tables, may not adequately characterize performance throughout the intended design life. Longer-term testing to replicate
38、service conditions is advisable to fully measure the effects of these chemicals. 6 SECTION 2: CHEMICAL RESISTANCE DATA FOR THERMOPLASTIC PIPING IN NON-PRESSURE APPLICATIONS AND DATA TABLE When thermoplastic pipes come into contact with chemical agents, it is important to know how the pipe may be aff
39、ected. For gravity flow or non-pressure applications, where the pipe is not subject to continuous internal pressure or thermal stress, chemical immersion test data may provide suitable information. The pipe manufacturer may have additional data from similar tests, or information on previous installa
40、tions under similar field conditions. The following table provides resistance data, with the following cautions: I. Data Sources. The following chemical resistance information has been obtained from numerous sources. The data are based primarily on plastic material test specimens that have been imme
41、rsed in the chemical, and to a lesser degree, on field-experience. In most cases, detailed information on the test conditions (such as exposure time), and on test results (such as change in weight, change in volume, and change in strength) was not available. Therefore, this information is best used
42、only for comparison of different thermoplastic materials. II. Combinations of Chemicals. . Chemicals that individually do not have an effect may affect the pipe if combined with certain other chemicals. The listings that follow do not address chemical combinations. III. Composite Piping. Layered com
43、posite piping may have chemical resistance that differs from that of the individual materials in the layers. The listings that follow are not applicable to layered composite piping products. IV. Applicability to fiberglass, filled materials. The listings that follow are not applicable to composite p
44、iping products such as reinforced epoxy resin (fiberglass) pipes, or to thermoplastic pipes containing significant percentages of filler materials. V. Concentrations. Where no concentrations are given, the relatively pure material is indicated, except in the case of solids where saturated aqueous so
45、lutions are indicated. NOTE: Even though indicated as acceptable with certain temperature limitations, the use of PVC piping with liquid hydrocarbons such as gasoline and jet fuels should be limited to short-term exposure such as secondary containment systems. This piping is not recommended for long
46、-term exposure to liquid hydrocarbons. 7 Resistance Codes The following code is used in the data table: Code Meaning Typical Result 140 Plastic type is generally resistant to temperature (F) indicated by code. Swelling 8% or weight loss 5% and/or elongation at break decreased by 50%. Data not availa
47、ble. Plastic Materials Identification ABS acrylonitrile-butadiene-styrene CPVC chlorinated polyvinyl chloride PP polypropylene PVC polyvinyl chloride PE polyethylene PB polybutylene PVDF poly vinylidene fluoride PEX crosslinked polyethylene PA11 polyamide 11 PK polyketone 8 CHEMICALS THAT DO NOT NOR
48、MALLY AFFECT THE PROPERTIES OF AN UNSTRESSED THERMOPLASTIC MAY CAUSE COMPLETELY DIFFERENT BEHAVIOR (SUCH AS STRESS CRACKING) WHEN UNDER THERMAL OR MECHANICAL STRESS (SUCH AS CONSTANT INTERNAL PRESSURE OR FREQUENT THERMAL OR MECHANICAL STRESS CYCLES). UNSTRESSED IMMERSION TEST CHEMICAL RESISTANCE INF
49、ORMATION IS APPLICABLE ONLY WHEN THE THERMOPLASTIC PIPE WILL NOT BE SUBJECT TO MECHANICAL OR THERMAL STRESS THAT IS CONSTANT OR CYCLES FREQUENTLY. WHEN THE PIPE WILL BE SUBJECT TO A CONTINUOUS APPLIED MECHANICAL OR THERMAL STRESS OR TO COMBINATIONS OF CHEMICALS, TESTING THAT DUPLICATES THE EXPECTED FIELD CONDITIONS AS CLOSELY AS POSSIBLE SHOULD BE PERFORMED ON REPRESENTATIVE SAMPLES OF THE PIPE PRODUCT TO PROPERLY EVALUATE PLASTIC PIPE FOR USE IN THIS APPLICATION. *May not be fully applicable to pressurized applications* Plastics at Maximum Operating T
