July 31, 2019

Stress Analysis of HDPE, PE-RT, PP-H, PP-R, PVC-C, PVDF Piping

By Alex Matveev

Features of HDPE, PE-RT, PP-H, PP-R, PVC-C, PVDF

The main features of HDPE piping and other plastic piping related to steel piping is:

  • The allowable stress of plastic piping is dependent on service life and temperature. The equation is. The A, B, G, J factors are stored in Start-Prof material database
  • In some cases, the swelling elongation due to chemical reaction with the product should be considered. The swelling strain should be specified in pipe properties
  • Linear expansion for plastic piping is much greater than for steel piping and caused by Bourdon effect, thermal expansion, and swelling elongation
  • Pressure elongation of plastic piping is significant (Bourdon effect), and thermal expansion is also great.
  • Unlike steel piping, Young’s modulus (creep modulus) for plastic piping depends on service life. For higher service life – the lower creep modulus is used. The support loads, displacements, etc. calculated at 100 minutes creep modulus. The seismic analysis performed using a 0.1-hour creep modulus.
  • In operating condition, the average creep modulus is used (average between installation and operating temperature)
  • Allowable stress for plastic piping depends on chemical resistance factor, laying condition factor, safety factor and joint strength factor
  • The wall thickness check is performed only for straight pipes and not performed for fittings

Modeling of HDPE pipe in Start-Prof

To model HDPE or other plastic piping choose GOST 32388 code:

Choosing the Piping Code
Choosing the Piping Code

Then create a pipe and choose appropriate material from the database:

Selecting the Pipe Material
Selecting the Pipe Material

In additional pipe properties specify the chemical resistance factor (usually 1.0), Joint strength factor (0.4-1.0), Laying conditions factor (0.8 for buried piping, 0.9 for underground piping in concrete channels, 1.0 for above ground piping). The temperature range is multiplied by this factor. It considers the nonlinear distribution of temperature across the wall thickness. For plastic piping recommended value is 1.0 and for fiberglass piping 0.85 for fluid and 0.8 for gas if no other information is available.

The swelling strain used for a chemical swelling elongation. It is the same as temperature elongation but caused by the chemical reaction between pipe material and product.

Allowable Stress Values
Allowable Stress Values

That’s all. All other job is the same as for steel piping.

The Database contains all material properties. If there’s no material you need in the database, you can add it’s properties manually.

Adding the properties in Material Database
Adding the properties in Material Database

All load cases for analysis will be created automatically. After analysis, you get results according to code.

Analysis Results
Analysis Results

Videos for HDPE Piping Stress Analysis in START-PROF

Part 1 of of HDPE Piping Stress Analysis video:

Part 2 of HDPE Piping Stress Analysis Video:

Download the HDPE piping example file. See how to open the piping model file