Problem overview
A pipe that cracks during cutting, handling, impact testing or installation is usually showing a fusion or toughness problem. In most cases the compound has not been fully gelled, or the formulation does not have enough toughness for the filler loading and pipe class.
Before changing additives it is important to establish whether the pipe is under-fused, over-filled, or insufficiently impact-modified — each needs a different correction.
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Use PVC Problem SolverCommon symptoms
- Pipe cracks during cutting or chamfering
- Failure in falling-weight impact test
- Brittle fracture with a rough, powdery-looking break surface
- Cracks appearing in cold weather or at the socket
- Pipe passes pressure test but fails impact
Possible causes
| What you see | Possible causes |
|---|---|
| Rough / chalky break surface | Under-fusion — temperatures too low, excess external lubricant, insufficient processing aid |
| Brittle at higher filler levels | High calcium carbonate loading for the pipe class; coarse or poor-quality filler |
| Cracks during cold handling | Low impact strength — no or insufficient impact modifier for the application |
| Brittle with discolouration | Over-fusion or degradation from excess heat |
| Variation batch to batch | Inconsistent mixing, weighing, or raw-material lot changes |
What to check
- Fusion level of the pipe (acetone immersion / methylene chloride test as per your standard)
- Barrel and die temperatures, screw RPM and motor ampere
- Filler (CaCO₃) loading and particle size
- Whether processing aid and impact modifier are part of the formulation
- External lubricant (PE wax, paraffin) quantity
- Pipe class and the test that is failing — impact, pressure, or field handling
Processing and formulation factors
Fusion
Under-fused PVC has weak boundaries between particles and breaks easily. Fusion depends on temperature, shear, lubrication and processing aid together.
Filler loading
Increasing calcium carbonate lowers cost but reduces impact strength. The acceptable level depends on the pipe class and standard.
Impact modification
Impact modifiers and CPE improve toughness, but they cannot fully compensate for poor fusion.
Cooling and stress
Fast or uneven cooling can leave residual stress, especially in thick-wall pipe.
Practical troubleshooting checklist
- Run a fusion test on the failing pipe
- Record actual zone temperatures, RPM and ampere
- Review filler level against the pipe class
- Check the external lubricant quantity
- Confirm whether processing aid / impact modifier is used
- Trial one change at a time and repeat the same test
Need help selecting a PVC additive?
Answer a few questions about your product, machine and requirements to see suitable grades.
Use Grade FinderWhen to contact a technical team
- Fusion test fails even after temperature correction
- You want to increase filler but keep impact strength
- Pipes pass in-house tests but fail at the customer site
This guide gives general starting points. Results depend on your formulation, raw materials and machine; changes should be confirmed with controlled trials.
Frequently asked questions
Why does PVC pipe become brittle after extrusion?
Most often because of under-fusion, high filler loading or insufficient impact modification. A fusion test helps tell which one applies.
Can too much wax make PVC pipe brittle?
Yes. Excess external lubricant can delay fusion, and under-fused pipe is brittle.
Does calcium carbonate reduce PVC pipe strength?
Higher loadings generally reduce impact strength. The suitable level depends on filler quality and the pipe class.
Will an impact modifier fix a brittle pipe?
It can help if toughness is the issue, but it will not correct poor fusion. Confirm fusion first.
Related Friends Chemical products
Impact Modifiers
CPE and acrylic impact modifiers for superior toughness in rigid PVC.
View productsProcessing Aids
Acrylic processing aids that promote fusion, melt strength and surface quality.
View productsCPE (Chlorinated Polyethylene)
Chlorinated polyethylene for impact modification, flexibility and flame retardance.
View productsNeed a sample or quotation?
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