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.
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/.