FAQs

FAQ
  1. Why can’t I get SDR 11, UL listed conduit?
  2. Why isn’t 3” Schedule 40 available in UL listed conduit?
  3. Why can’t we get 4” Schedule 40 on a reel?
  4. What is the difference between UL certified resin and ASTM F2160 resin?
  5. How many cables can I fit into an innerduct or conduit?
  6. What about the number of HDPE conduit innerducts in a casing pipe?
  7. What is PE 4710 resin?
  8. What does the cell classification of HDPE mean?
  9. What is regrind?
  10. What is coex (co-extruded) pipe?  Why is the interior black?
  11. Why does HDPE Conduit have a memory?
  12. What is the recommended SDR for HDD (horizontal directional drilling) pipe?
  13. What does SDR stand for?
  14. What does ASTM stand for?
  15. Is my order taxable?
  16. What is the pressure rating of Schedule 40 pipe?
  17. Can conduit per ASTM F2160, UL 651 and NEMA TC7 be used for pressure pipe?

FAQ

1. Why can’t I get SDR 11, UL listed conduit? Top
  UL, Underwriters Laboratories, has strict guidelines, requiring us to exactly manufacture according to their specifications.  UL 651B, Continuous Length HDPE Conduit, and UL 1990, Nonmetallic Underground Conduit with Conductors, have four categories of pipe thickness: EPEC A, EPEC B, Schedule 40 and Schedule 80.  SDR11 is not a wall thickness dimension ratio listed and therefore not allowed within the UL listing.

We understand, especially when used in directional drilling, a heavier pipe is required.  In 1 ¼” diameter through 3” diameter, a schedule 80 pipe will match up very closely to SDR 11 wall thickness and provide the extra pull strength required.  Refer to our sizing tables for further information.
  
2. Why isn’t 3” Schedule 40 available in UL listed conduit? Top
  There is an anomaly in the UL 651B specifications.  UL used relative crush values for PVC, when the HDPE specification was written.  No manufacturer can meet the crush test values (only for 3” Schedule 40) listed in the specifications.  Blue Diamond is a member of PPI (the Plastic Pipe Institute) and as an association we are working with UL to correct the specification.  
3. Why can’t we get 4” Schedule 40 on a reel? Top
  Theoretically, we can put 4” schedule 40 on a reel.  However, we don’t recommend it.  As the pipe is extruded, it is wound on a reel.  As it is wound, the top of the pipe is in tension, while the bottom is in compression.  This causes the pipe to oval.  It is much more apparent in the larger diameters.  ASTM F2160 acknowledges the effect and allows for it in the specification.  4” Schedule 40 is a relatively thin wall, and so it (and Schedule 40 diameters above 4”) can have a tendency to buckle.  That’s why BDI does not recommend 4” Schedule 40 on a reel.  We can easily provide those diameters in stick pipe.  
4. What is the difference between UL certified resin and ASTM F2160 resin? Top
  Not much in reality.  Both resins are quality resins and the properties are virtually the same.  However, UL runs fingerprint testing on the final product of which we are certified.  Therefore, we are bound to use the same resin we have submitted to UL for approval.  Essentially, we are locked in to the exact resin we have the certifications for.  
5. How many cables can I fit into an innerduct or conduit? Top
  It depends on the size and quantity of the cable.  The NEC (National Electric Code) has guidelines on the number of conductors allowed in a HDPE Conduit.  With one conductor, it can “fill” 53% of the inside diameter of the conduit.  For 2 wires 31% and over 2 wires 40% fill ratio is allowed.  Simply multiply the area of the conductors by the quantity and compare to the inside area of the pipe.  See our “Fill Ratio Chart”. (web link)

The same general rules apply for fiber optic cable.		  
6. What about the number of HDPE conduit innerducts in a casing pipe? Top
  This is highly dependant on the installation.  The straighter and shorter the run, the more you can fill the casing pipe.  The longer and more complex the casing installation is, the less fill is applicable.

Generally, the recommended percentage fills are:
70% (max value recommended)
50%-short straight runs
30% longer and more complex runs.
Adjust values as needed per experience.		  
7. What is PE 4710 resin? Top
  PE 4710, is a pressure pipe resin, with a higher density and stress crack resistance than the standard PE 3608 pressure resin.  This allows higher pressures for the same SDR numbers.  Or conversely, the same pressure rating with lighter pipe.  For example, SDR 11 PE 3608 pipe has a pressure rating of 160 psi.  PE 4710, SDR 11 has a pressure rating of 200 psi.  Please note other environmental factors, such as operating temperature may lower the service pressure rating of the pipe.  Refer to the PPI Handbook of Plastic Pipe Chapter 6 (web link) for more information.  
8. What does the cell classification of HDPE mean? Top
  The cell classification is a method of identifying and specifying the raw material properties of HDPE Conduit and Innerduct.  It is a series of six numbers and one letter which describe the properties of the resin per ASTM D3350.  The numbers, in order, represent the density, melt index, flexural modulus, tensile strength, slow crack growth, hydrostatic design basis, and the letter represents whether the material is black or colored.  Blue Diamond conduit and innerduct has a standard minimum cell classification of 334420C (except the slow crack growth is >96 hrs.)  See our technical data for further information.  
9. What is regrind? Top
  As defined by ASTM D 5033, regrind is “product….that has been reclaimed by shredding and granulating for in-house use.”  Blue Diamond has pipe cut from production for our quality control testing.  Additionally, as much as we try to make perfect pipe, we have unanticipated shut downs (thunderstorms cut off the power occasionally) or manufacture the incorrect diameter, and other miscues.  BDI grinds this pipe, and uses it in new pipe production.  The reground resin is tested to make sure the properties meet ASTM specifications.  ASTM, UL, and NEMA all allow use of regrind resin in their specifications.  
10. What is coex (co-extruded) pipe?  Why is the interior black? Top
  BDI, as do other manufacturers, has the ability to co-extrude pipe.  Two extruders feed one die.  One is for an outer layer, the other an inner layer.  This allows us to change the outside color of the pipe very quickly during the manufacturing process.  The interior of the pipe is black, because that is the most common resin color for HDPE conduit and pressure pipe.  Both resins are the same quality and go through the same quality control procedures.  The layer are molecularly bonded, they cannot peel.  It is not a skin, but an integral part of the pipe.  Striped pipe is similarly co-extruded.  ASTM and other specifications allow for co-extruded pipe.  
11. Why does HDPE Conduit have a memory? Top
  Actually, if you lay HDPE conduit along a trench on a warm or hot day, the pipe will eventually relax.  Initially, the pipe will have a memory from winding on the real because the molecules align themselves during the manufacturing process of reeling, or “bending” the pipe.  You can envision, one side of the pipe will be in tension, while the opposite is in compression.  The molecules align themselves, relax and “remember” their position.  Once un-reeled, they want to relax back into the original straight positions they were during the extrusion process.  
12. What is the recommended SDR for HDD (horizontal directional drilling) pipe? Top
  Any critical project should be engineered.  Soil conditions, the length of the bore, the diameter of the bore hole, and many other factors should be considered and calculated to determine the wall thickness of the bore pipe.  PPI (the Plastic Pipe Institute) has a table (link to PPI Handbook Chapter 14, page 482) which recommends strength of pipe ranked by relative damage sensitivity.  It recommends SDR 11 as the minimum wall thickness for HDD applications.  
13. What does SDR stand for? Top
  SDR is the Standard Dimension Ratio.  Technically, it is the nominal outside diameter divided by the minimum wall thickness.  The larger the SDR the thinner the wall thickness.  See our tables (link to our spec tables) for standard SDR numbers.  
14. What does ASTM stand for? Top
  ASTM is the American Society for Testing and Materials.  It is an association of manufacturers, engineers, consultants and governmental officials who write standards for all sorts of building materials, from cement, to steel and plastic pipe.  Other important specification writing bodies are NEMA (National Electrical Manufacturers Association), UL (Underwriters Laboratories) and NEC/NFPA (National Electric Code/National Fire Protection Association).  
15. Is my order taxable?
 Top
  Blue Diamond is required by law to collect sales tax in those states where we maintain an office or business presence.  If your order is shipping to one of the following states, sales tax will be charged unless you provide a valid exemption certificate:

Florida, Georgia, Kentucky, Tennessee, Missouri

For items shipped to other states, it is the customer's responsibility to determine whether they are required to remit, directly to the state, any applicable "use" tax.  You should consult your tax advisor for further information.
  
16. What is the pressure rating of Schedule 40 pipe?
 Top
 





That is not a simple question.

The standard pressure rating of pipe is dependant on the type of resin, the diameter to wall thickness ratio, the fluid being transported, and the temperature of the application.  (Additionally, in a pipe design, fittings will affect the design pressure required of the pipe.)

The formula for pressure rating is:

PR= 2HDS Ft Af/(DR-1)

In simplest terms if Ft (service temperature) is nominal at 73 degrees F, Ft=1.0.  Also, if Af, the pipe environmental application is water, sewage or other fluids not aggressive to HDPE, then Af=1.0.

Thus the equation simplifies to PR=2HDS/(DR-1)

HDS is the Hydrostatic Design Stress.  The HDS is a rating assigned by PPI (Plastics Pipe Institute) for specific resins.  A PE 3408 resin will have an HDS of 800. A PE 4710 resin will have an HDS of 1000.  These resins are listed on the PPI website and TR-4 (Technical Report 4).

So for common SDR pipe, the results are quite easy to compute.

SDR     PE 3408     PE 4710

13.5     125 psi       160 psi

11        160 psi       200 psi

9          200 psi       250 psi

The above chart is true for any diameter of a particular SDR pipe, since the ratio of the OD to thickness remains constant.  DR=Do/t.

However, Schedule 40 and 80 pipe do not maintain the same OD to wall thickness ratio throughout every diameter.  Therefore a calculation of the ratio is required for any diameter.  For example: 2" Schedule 40 pipe is equivalent to SDR 15.4 (OD=2.375 t=0.154, so DR=2.375/.154=15.4).  So a 2" SCH 40, PE 3408 resin pipe would have a pressure rating of 111 psi.

Note that Schedule 40 and 80 pressure pipes are no longer typically produced.  ASTM D2447, the specification for Schedule 40 and 80 pressure pipe is now a "historical standard".  Most manufacturers are limiting their production to SDR pipe.

Chapter 3 and 5 of the PPI Handbook for Polyethylene Pipe is an excellent reference and gives more details on pipe design pressure applications.


  
17. Can conduit per ASTM F2160, UL 651 and NEMA TC7 be used for pressure pipe?
 Top
  The resin used in the manufacture of standard conduit is not pressure rated.  It does not have a HDS (Hydrostatic Design Stress) rating assigned by PPI Technical Report TR-4.  Or its HDS=0.  Therefore, conduit would not be recommended for long term pressure applications. 

That being said, fiber optic cable is often "blown" into conduit.  The back pressure of blowing cable does subject the conduit to air pressure.  And for a short term, conduit will certainly stand pressure.  Blowing fiber, which is a standard installation method is perfectly suitable for conduit and innerduct applications. 

Note that air pressure in plastic pipe that is not buried is a safety concern.  Contact your equipment or pipe manufacturer for further information.