Introduction
The Nepal Bureau of Standards and Meteorology (NBSM) introduced the code NS40 to regulate the quality of HDPE pipe production and guide its use.
It was first published in 2042 B.S., revised in 2075 B.S. as the fourth revision, and a new code circulated in 2079 B.S. The old codes are now invalid.
The new code introduced a new polymer resin, expanded the pipe diameter range, added performance requirements, and test methods.
Technicians’ and Engineers’ Problem
In Nepal, people working in the water supply sector were used to the color coding of HDPE pipes. Many are also confused about PE, PN, and SDR.
With the new standard and removal of color coding, many technicians find it difficult to identify the pipes and understand/interpret the code.
This article explains the code in a simple way so that every technician can understand HDPE pipes easily and use them correctly.
This article also gives examples on HDPE pipe and a Calculator for Weight and Cost.
HDPE Pipe Calculator: CLICK HERE
Old code and new code
In this article, new code means NS40:2079 (latest version) and old code means NS40:2042, Third Amendment.
Color Coding of HDPE Pipe
What is the color coding of the HDPE pipe?
NS40:2042 (OLD): The HDPE pipes are black in color. However, there is an identification line of color in it as per the code.
| Pressure Rating | Marking Color |
| PN-2.5 | Red |
| PN-4 | Blue |
| PN-6 | Green |
| PN-10 | Yellow |
| PN-12.5 | Purple |
| PN-16 | White |
NS40:2079 (NEW): The color of pipe shall be black with blue identification stripes for all HDPE pipes.
| Pressure Rating | Marking Color |
| PN (ALL) | Blue |
Minimum Required Strength (MRS)
What is the Minimum required strength of the HDPE pipe?
Minimum required strength (MRS) is the minimum strength required for Polyethylene (PE) resin at 20 Degrees Celsius for 50 50-year life.
Minimum required strength is the same for both new and old standards.
| Material Grade | MRS (MPa) | MRS (Kg/cm2) |
| PE-63 | 6.3 | 63 |
| PE-80 | 8.0 | 80 |
| PE-100 | 10.0 | 100 |
Pressure rating (PN)
What is the Pressure rating (PN) of the pipe?
In simple terms, PN is the maximum operating pressure from the flow internally, which will be safe.
Pressure rating is the same for both old and new standards. However, more pressure ratings are included in the new NS40:2079 standards.
PN ratings according to NS40:2042
| Pressure Rating | Max allowable Operating Pressure (MPa) | Max allowable Operating Pressure (Kg/cm2) |
| PN-2.5 | 0.25 | 2.5 |
| PN-4 | 0.40 | 4.0 |
| PN-6 | 0.60 | 6.0 |
| PN-10 | 1.00 | 10.0 |
| PN-12.5 | 1.25 | 12.5 |
| PN-16 | 1.60 | 16.0 |
PN ratings according to NS40:2079
| Pressure Rating | Max allowable Operating Pressure (MPa) | Max allowable Operating Pressure (Kg/cm2) |
| PN 2 | 0.20 | 2.0 |
| PN 2.5 | 0.25 | 2.5 |
| PN 3 | 0.30 | 3.0 |
| PN 3.2 | 0.32 | 3.2 |
| PN 4 | 0.40 | 4.0 |
| PN 5 | 0.50 | 5.0 |
| PN 6 | 0.60 | 6.0 |
| PN 8 | 0.80 | 8.0 |
| PN 10 | 1.00 | 10.0 |
| PN 12.5 | 1.25 | 12.5 |
| PN 16 | 1.60 | 16.0 |
| PN 20 | 2.00 | 20.0 |
Nominal Diameter (DN)
What is the nominal diameter of an HDPE pipe?
In simple terms, the nominal diameter written as DN is the outer diameter of the HDPE pipe.
The nominal outer diameter, as per the old and the new code, is that the new code gives the range of diameter up to 2000mm, whereas the old code has pipe diameter only up to 1000mm.
| NS40:2042 | 16,20,25,32,40,50,63,75,90,110,125,140,160,180,200,225,250,315,355,400,450,500,560,630,710,800,900,1000 mm |
| NS40:2079 | 16,20,25,32,40,50,63,75,90,110,125,140,160,180,200,225,250,315,355,400,450,500,560,630,710,800,900,1000,1200,1400,1600,1800,2000 mm |
Wall Thickness of Pipe
The thickness of the pipe wall is an important factor for determining the weight of the pipe and hence the cost of the pipe.
The thickness depends on the grade of resin (PE), pressure rating (PN), and outer diameter of pipe (DN).
NS40:2042– In the old standard, to identify the wall thickness, there are different tables for each grade of resin (PE). Table 1(A), 1(B) and (C) for PE63, PE80 and PE100 respectively.
NS40:2079– There is just a single table for all types of HDPE pipe to determine the wall thickness of pipe. The table is based on the standard dimension ratio (SDR) rather than the type of resin (PE). Table 4 of the code gives the data.
Density of HDPE Pipe
The density is simply the weight per unit volume of the material of the PE resin. There is only a specific range of density that can be used in making HDPE pipes.
Density of Raw Material:
- NS40:2042- Minimum density of raw material should be 940 kg/m3.
- NS40:2079- Density of raw material should lie between 930 and 965 Kg/cm3.
Written Markings in Pipe
To fully know the properties of HDPE pipe, many things about the HDPE should be marked on the HDPE pipe.
- NS40:2079: The pipe should carry written information as: Manufacturer trademark, material type (PE), pressure rating (PN), Standard dimension ratio (SDR), Outer diameter (DN), Lot Number/Batch Number, and NS mark.
- NS40:2042: It is the same without the SDR.
Additional things in new code- NS40:2079
The inclusion of the Standard Dimension Ratio (SDR) makes the new code integrated. In the old code, there are separate tables for each PE material, but in the new code, there is only one table.
Also, to know the wall thickness of the pipe, the SDR just needs to be divided by the outer diameter of the pipe.
Standard Dimension Ratio (SDR)
The SDR is the ratio of the nominal outside diameter (DN) of a pipe to its nominal wall thickness (en).
SDR = DN/en
Standard Range of SDR: SDR41, SDR33, SDR 26, SDR21, SDR17, SDR13.6, SDR11, SDR9, SDR7.4 and SDR6.
There is a theoretical relation between Standard Dimension Ratio (SDR), Pressure Nominal (PN), and Minimum Required Strength (MRS).
PN = (20*MRS*fr)/(c*(SDR-1))
Where, fr is a pressure reduction coefficient whose value is 0.85 at 27 degrees Celsius. C is the overall service design coefficient that has a value of 1.25.
Let’s understand the learning’s from the examples below:
Example 1
What is the strength (Pressure Rating) of an HDPE pipe that consists of material resin PE100, and has an SDR13.6? Then, what is the pressure rating of the pipe?
Solution:
The required formula is:
PN = (20*MRS*fr)/(c*(SDR-1))
Where,
PN in Bar (1Bar = 0.1MPa = 1.0 Kg/cm2 = 10.2 meters of water head)
MRS (in MPa) = 10 MPa for PE100 Pipe
SDR (Unitless) = 13.6
C (Unitless) = 1.25 and fr (Unitless) = 0.85
Pressure Nominal (PN) = (20*10*0.85)/[1.25(13.6-1)]
PN = 10.8 Bar or PN10.8
This is a theoretical allowable pressure rating. The chart from the code gives a value of PN10, which is a safer side.
Example 2
What is the wall thickness (en) of the HDPE pipe which has an SDR of 13.6 and an external diameter (DN) of 32mm?
Solution:
The relation is, SDR = DN/en
Hence, en = DN/SDR
en = 32/13.6
Pipe Wall Thickness (en) = 2.35mm
Hence, the HDPE has a thickness of 2.35mm. It can also be directly looked at from Table 4 of the code.
Example 3
What is the weight per unit length of the HDPE pipe having SDR13.6 and an external diameter (DN) of 32mm?
Solution:
From Table 4 (or the previous example), the wall thickness of the pipe is 2.35mm.
Then, the area of the cross-section of the pipe is given by,
External diameter (D2) = 32mm
Internal Diameter (D1) = 32-2*2.35 = 27.3
Area (A) = pi/4 * (D2^2-D1^2)
Area (A) = 218.9 mm2
Volume of material in pipe (V) = 218.9*1000 mm3 = 0.0002189m3
Density of HDPE pipe (from code) = 940*0.0002189 = 0.206 Kg/m
Thus, one meter of 32mm pipe of SDR13.6 weighs 0.206 Kilograms.
Example 4
What is the price of 1 Bundle (200 meters) HDPE pipe of 32mm external diameter and SDR13.6 with a rate of HDPE per Kg of NRs 315?
Solution:
Weight per meter of pipe (from previous example) = 0.206 Kg
Rate of 1 Kg of HDPE = NRs 315
Cost of 1 Bundle of Pipe = 0.206 * 315 * 200 = NRs 12,978
Hence, 1 bundle of HDPE pipe of diameter 32mm and SDR13.6 (or PN10) will cost NRs 12,978.
Example 5
A manufacturer wants to produce an HDPE pipe of 32 mm, which needs to hold just 0.6 MPa (6Kg/cm2) of pressure safely. How will the pipe be produced?
Solution:
This one is for the manufacturer. So, there are three types of materials that can be chosen, which are PE63, PE80, and PE100.
This means that the material will have a Minimum required strength (MRS) of 6.3MPa, 8.0MPa, and 10.0MPa.
Let’s choose the material PE100.
Now, the manufacturer needs to choose the strength of the pipe. As only 0.6MPa or 6kg/cm2 needs to be held. The safe pressure rating of PN6 will be okay.
(Burst Pressure: The pressure that will explode/rupture the pipe will be much higher than the PN rating of the pipe for safety, ~2.7MPa, where design is at a maximum of 0.6MPa. Annex E (Page 22) of the code gives the method to determine the rupture test).
The chosen PN rating of the HDPE pipe is PN6.
Now, from Table 4 of NS40:2079 (or can also be calculated from the formula), the SDR17 is to be taken.
Again, from the same Table 4, the minimum and the maximum thickness of the wall of the pipe will be between 1.9mm and 2.2mm for a 32mm HDPE pipe.
Thus, the final values are:
- Material Type (PE): PE100
- Nominal Diameter (DN): DN 32mm
- Pressure Rating (PN): PN6
- Standard Dimension Ratio (SDR): SDR17
- Wall Thickness (en): Between 1.9mm and 2.2mm
The weight and cost of the pipe can also be calculated similarly to the previous example.
❓ Frequently Asked Questions
General Knowledge
1. What is HDPE pipe?
HDPE (High-Density Polyethylene) pipe is a flexible, durable plastic pipe made from thermoplastic polymer. It’s used for water supply, irrigation, drainage, and gas distribution due to its excellent chemical resistance, flexibility, and long lifespan.
2. What is NS 40 standard in Nepal?
NS 40:2049 is the Nepalese standard for high-density polyethylene pipes, established by Nepal Bureau of Standards and Metrology (NBSM). It specifies requirements for manufacturing, testing, and quality control of HDPE pipes in Nepal.
3. What is the difference between PE 80 and PE 100?
PE 80 has a minimum required strength (MRS) of 8.0 MPa with maximum pressure of 1.25 MPa, while PE 100 has MRS of 10.0 MPa with maximum pressure of 1.6 MPa. PE 100 offers superior strength, durability, and pressure resistance for demanding applications.
4. What sizes are available for HDPE pipes in Nepal?
HDPE pipes in Nepal are available from 20mm to 500mm outer diameter (OD) according to NS 40 standards, covering various applications from household water supply to large municipal projects.
5. What is the expected lifespan of HDPE pipes?
HDPE pipes have a designed lifespan of 50 years at 27°C when properly installed and maintained. Their durability and resistance to corrosion ensure long-term reliable performance.
Technical Specifications
6. What does SDR mean in HDPE pipes?
SDR (Standard Dimension Ratio) is the ratio of pipe’s outer diameter to wall thickness. Lower SDR means thicker walls and higher pressure capacity. Common SDRs include 9, 11, 13.5, 17, 21, and 26.
7. What is PN rating in HDPE pipes?
PN (Pressure Nominal) indicates the maximum operating pressure in bars at 20°C. Common ratings are PN 6, PN 10, PN 12.5, and PN 16, corresponding to 6, 10, 12.5, and 16 bar pressure capacity respectively.
8. How do I calculate HDPE pipe weight?
Pipe weight depends on outer diameter, wall thickness, and length. Weight per meter = (OD – wall thickness) × wall thickness × 0.0246 (for PE material). Use manufacturer charts for accurate weights.
9. What is MRS in PE pipe specifications?
MRS (Minimum Required Strength) is the long-term strength of polyethylene material at 20°C over 50 years. PE 80 has MRS of 8.0 MPa, PE 100 has 10.0 MPa, determining pressure capacity.
10. Can NS 40 HDPE pipes handle hot water?
HDPE pipes are not recommended for continuous temperatures above 60°C for liquids. For hot water applications, consider PPR (Polypropylene Random) or CPVC pipes designed for higher temperatures.
Applications & Uses
11. What are the main applications of HDPE pipes in Nepal?
HDPE pipes are used for potable water supply, bore wells, lift irrigation, sprinkler systems, drip irrigation, sewerage, drainage, industrial effluents, and agricultural applications across Nepal.
12. Is HDPE pipe safe for drinking water?
Yes, NS 40 certified HDPE pipes made from virgin PE 100 material are safe for potable water. They don’t leach chemicals, resist bacterial growth, and maintain water quality throughout their lifespan.
13. Can HDPE pipes be used underground?
Yes, HDPE pipes are ideal for underground applications. Their flexibility allows them to withstand ground movement, they resist corrosion from soil chemicals, and can be bent to follow terrain contours.
14. What is the minimum bending radius for HDPE pipes?
HDPE pipes can be bent to a radius of approximately 25 times the pipe diameter without fittings. This flexibility eliminates many joints, reducing leak points and installation costs.
15. Can HDPE pipes replace metal pipes?
Yes, HDPE pipes are superior replacements for metal pipes. They don’t corrode, are lighter, easier to install, have lower friction losses, require less maintenance, and are more cost-effective long-term.
Installation & Joining
16. What are the joining methods for HDPE pipes?
Common methods include butt fusion welding (for larger pipes), electrofusion, socket fusion, and mechanical compression fittings. Fusion welding creates homogenous joints as strong as the pipe itself.
17. Do HDPE pipe joints leak?
Properly welded joints are leak-proof and have the same properties as the pipe. Fusion joints create a molecular bond, making them stronger and more reliable than mechanical joints in other pipe systems.
18. What equipment is needed for HDPE pipe installation?
Basic tools include pipe cutters, fusion welding machines (for larger pipes), compression fittings tools, and measuring instruments. HDPE installation requires less specialized equipment than metal pipes.
19. How much labor is required for HDPE pipe installation?
HDPE pipes require significantly less labor than metal pipes due to their light weight, flexibility, and fewer joints needed. This reduces overall project costs and installation time.
20. Can I install HDPE pipes in winter?
Yes, HDPE pipes have excellent cold resistance and can be installed in low temperatures. However, fusion welding requires specific temperature conditions, so follow manufacturer guidelines for winter installation.
Quality & Standards
21. How can I verify if HDPE pipe meets NS 40 standards?
Look for NS mark certification from Nepal Bureau of Standards (NBSM) on the pipe. Certified manufacturers display specifications including NS 40:2042, PE grade, PN rating, and size on the pipe surface.
22. What is the difference between virgin and recycled HDPE?
Virgin HDPE uses new polymer granules ensuring consistent quality, strength, and safety. Recycled material may have variable properties and isn’t suitable for potable water. Always use virgin PE 100 for drinking water.
23. What quality tests are performed on HDPE pipes?
Tests include tensile strength, hydrostatic pressure testing, dimension verification, visual inspection, density testing, and material composition analysis to ensure compliance with NS 40 and ISO 9001:2015 standards.
24. Why is pipe color important?
HDPE pipes are typically black with smooth surfaces. Black color provides UV protection for outdoor storage and above-ground installations, preventing degradation from sunlight exposure.
25. What is ISO 9001:2015 certification?
ISO 9001:2015 is an international quality management standard. Manufacturers with this certification follow systematic quality control procedures throughout production, ensuring consistent product quality and reliability.
Maintenance & Troubleshooting
26. Do HDPE pipes require regular maintenance?
HDPE pipes require minimal maintenance. They don’t corrode, scale, or rust. Periodic visual inspection for damage and ensuring proper support are usually sufficient for long-term performance.
27. Can HDPE pipes be repaired if damaged?
Yes, damaged sections can be cut out and replaced using fusion welding or mechanical couplings. Small leaks can be repaired with specialized clamps, though fusion welding provides the most reliable repair.
28. How do I store HDPE pipes properly?
Store pipes on level ground with adequate support to prevent sagging. Stack height should not exceed 1.5 meters. Protect from prolonged direct sunlight if not UV-stabilized, though black pipes have inherent UV resistance.
29. What causes pressure loss in HDPE pipe systems?
Common causes include air pockets, undersized pipes for the flow rate, excessive fittings creating friction, clogged filters, or pump issues. HDPE’s smooth interior reduces friction losses compared to metal pipes.
30. Are HDPE pipes affected by chemicals in soil?
No, HDPE pipes have excellent chemical resistance to most acids, alkalis, salts, and organic compounds found in soil. This makes them ideal for aggressive soil conditions where metal pipes would corrode.
You can download the standards NS40:2042 (4th revision) and NS40:2079 from the downloadable files below, which are obtained from https://nbsm.gov.np/ne/.