Structural and Fracture Methods as Means of Predicting the Lifetime of HDPE Pipes [PE]
Nezbedova, Zahradnickova, Salajka
# 2001 Munich
High-density polyethylene (HDPE) is being used more and more in critical long-term
application, such as in pipes for the distribution of water and gas. For this reason it is
important to have a strong understanding of those parameters which control the fracture
behaviour of HDPE. The main parameters are :
i. Chain structure
iii. Processing conditions.
The structure is characterised by SIS/DSC method (SIS-Stepwise Isothermal Segregation),
DSC and “rapid” SIS/DSC. For evaluation the failure mode (long term brittle failure),
which limits the lifetime of HDPE pipes accelerated PENT (Pennsylvania Notch Test) and
FNCT (Full Notch Creep Test) tests have been applied. A correlation between fracture and
structure parameters has been found.
Please note that the whole article content is available on PPCA website only
Author(s) : Pavel Hutař, Jan Poduška, Jaroslav Kučera, Eva Nezbedová, Andreas Frank, Jiří Sadílek, Gerald Pinter
Residual stresses can significantly influence the lifetime of polymer pipes. Therefore, realistic estimation of residual hoop stress can contribute to accurate lifetime estimations. The previously used “accurate method” is quite time consuming and needs a lot of specimens to be prepared and treated. A simplified...
Author(s) : Andreas Frank, Gerald Pinter, Mridula Kapur, E. Nezbedová
Results from cracked round bar tests (CRB) and pennsylvania notch tests (PENT) for several polyethylene (PE) pipe grades are compared. The CRB tests were conducted at 23 °C and 80 °C, the PENT tests only at 80 °C. A material ranking based on the CRB tests was in good accordance to PENT failure times, although a slight...
The service life for HDPE (PE 80, PE 100) materials used in plastic pipes application covers a
time span of up 50 years. The new type of PE 100 (PE 100 RC) should achieve the life time
over 100 years. Conventional hydrostatic pressure test to qualify a new resin must last 104
hours (ISO 1167). In the last twenty years...
A multilayer pipe consisting of two different layers, namely of PE and PPH, was analysed.
The relevant numerical model based on the Finite Element Method (FEM) was used to
calculate the stress and strain distribution and to estimate the fracture characteristics. As
variables the thickness of the material layers and...
The influence of processing conditions on molecular structure and microstructure of highdensity polyethylene pipe material has been studied. By modifying the segment arrangement
and package of additives, conditions during pelletising in the extruder have been changed.
Structural analyses obtained by gel permeation...
Full Notch Creep Test (FNCT) is widely used to characterize the slow crack growth behavior of particularly pipe and blow moulding PE materials, especially in Europe. However, the validity of the FNCT data is not satisfactory, as the results show large variability so far. Among other SCG tests, which exist and are used...
Author(s) : Eva Nezbedová, Pavel Šindelář and Petr Bohatý
Changing the catalyst composition, it allowed us to alter placement of comonomer from lower
to higher polymer molecular weight fractions together with a certain reduction of molecular
weight distribution (MWD). Using this catalyst several polymer samples differing in level of
branching, in comonomer unit placement and...
Structural and morphological parameters together with processing conditions determine the type of fracture behaviour of polyethylenes. Long time brittle failure which occurs under low stresses and at room temperature limits the lifetime of polyethylens used as pipes for water and gas distribution. In order to optimise...