UHMWPE pipe

 

What is UHMWPE

 

  • Ultra-high molecular weight polyethylene (UHMWPE) is a new kind of engineering thermoplastics with more than 3 million viscosity-average molecular weight. Ultra-high molecular weight polyethylene pipe has superior performance over conventional HDPE pipe such as very high wear resistance, impact resistance, excellent resistance to internal pressure strength, resistance to environmental stress cracking, intrinsically self-lubricating, anti-adhesion, low temperature resistance and excellent chemical resistance.

 

Role of Molecular Weight

 

  • UHMWPE denotes Ultra High Molecular Weight Polyethylene which is a polyethylene polymer with an average molecular weight is greater than 3,100,000 as defined by ASTM D4020 – Standard specification for UHMWPE polymers.  This molecular weight is well above the molecular weight of most typical polymers which are between 1,000,000 and 400,000 thus earning the title Ultra-High Molecular Weight Polyethylene. Polyethylenes with molecular weight in the 3.1 -4.5 Million range have been found to exhibit the best combination of impact strength and abrasion resistance. For Polyethylene molecular weight classification the following guidelines can be used:
  • HDPE (High Density Polyethylene):    100,000 – 400,000 MW
  • HMWHDPE (High Molecular Weight High Density Polyethylene)    500,000 – 1,999,999
  • VHMWHDPE (Very High Molecular Weight High Density Polyethylene)    2,000,000 – 3,100,000
  • UHMWPE (Ultra High Molecular Weight Polyethylene)    > 3,100,000 + MW

 

Attributes of UHMWPE Pipes

 

  • Abrasion resistance – UHMWPE pipes have excellent abrasion resistance providing long life in abrasive slurry applications.
  • Chemical resistance – outstanding resistance to a wide range of chemical reagents allows the use of UHMWPE systems in tailings pipelines and chemical treatment applications used in mining operations.
  • Flexibility – UHMWPE pipes can be bent to a minimum of 30 times the pipe’s outside diameter for HDPE. This flexibility and resiliency allows the pipe to absorb surge pressures, vibration and stresses caused by soil movement. This makes the pipes particularly useful in submarine pipe lines, mine subsidence and earthquake prone areas.
  • High flow capacity – low friction compared with materials such as fibre reinforced cement and resistance to material deposit buildup give UHMWPE pipes long lived high flow capacity.
  • Lower pumping cost due to greater hydraulic capacity as compared with steel and HDPE pipes.
  • Ease of installation – UHMWPE is easy to install with light weights and flanged couplings.

 

Benefits of Ultra High MW

 

  • UHMWPE by virtue of its extremely high molecular weight yields several unique properties, including the highest abrasion resistance and highest impact strength of any plastic. Beware of competitive products claiming to be UHMWPE as some techniques for processability of UHMWPE are not without an attendant disadvantage since effective amounts of intermediate molecular weight polyethylene causes a marked decrease in some of the most desirable properties of the UHMWPE, such as impact strength and abrasion resistance. The high molecular weight is what gives UHMW-PE a unique combination of high impact strength, low coefficient of friction and abrasion resistance that outwears carbon steel 10 to 1 making it more suitable for many applications where lower molecular weight grades fail. UHMWPE pipes can be used in a broad range of mining and industrial slurry applications due to its three main characteristics: high impact strength, outstanding abrasion resistance and extremely low coefficient of friction. Ultra-high molecular weight polyethylene (UHMW) is a tough, abrasion-resistant thermoplastic with a molecular weight of greater than 3 million. UHMWPE pipes have reduced coefficient of friction, improved abrasion resistance, lower wear rates over conventional HDPE pipes such as PE100.

 

Exceptionally High Wear

 

  • Ultrahigh molecular weight polyethylene (UHMWPE) shows unusually high wear resistance compared to most materials.  This is due to a combination of very high molecular weight and the resulting entanglements and relative surface softness with a slippery waxy surface.

 


 

Bowl of Spaghetti

 

  • An easy way to envisage UHMWPE is to think of a plate of cooked spaghetti with the long strands all intertwined. If the spaghetti is cut up, it would closely approximate the molecular appearance of regular HDPE. Since very long strands of spaghetti approximating the chains of UHMWPE are completely intertwined it would be very difficult to pull them apart. This simplification explains the outstanding abrasion resistance (the difficulty in pulling out particles of the polymer).

 

Pressure Rating

 

  • The nominal diameter of the UHMWPE pipes is from 65mm to 800mm, and the wall thickness if from 8mm to 38mm usually.   The nominal pressure rating of UHMWPE pipes etc. is from 0.6 MPa to 2.0 MPa and UHMWPE composite pipe can reach 6.4 MPa.