How can I tell if regrind was used in my pipe?

Not by looking at it. Melt flow rate and oxidation induction time together will show a heat history that virgin resin does not have, and both should be reported per batch with values. Neither means much without traceability to the resin lot, so ask for the resin supplier's certificate alongside the test results.

What is the difference between the 20 °C and 80 °C hydrostatic tests?

The 20 °C test runs about 100 hours and shows the batch holds its rated pressure now. The 80 °C test runs at elevated temperature as an accelerated proof of the 50-year design assumption. The second is the one that stands behind a design life claim, and the one more often missing from a certificate.

Should I use a third-party inspection agency?

They are useful for presence and photographs, and their generic checklists cover packaging, counts and labels well. The PE-specific checks — regrind indicators, minimum wall at multiple points, which hydrostatic test was run — usually have to be written into the inspection brief, because a general checklist will not include them.

When is the best time to inspect?

Before loading rather than at the door. It costs the same, and it is the last moment where rejecting a batch is merely inconvenient instead of a programme delay. Inspection at the container has almost no remedy left except refusing to load.

What if pipe arrives oval?

Small ovality can be corrected with re-rounding clamps at the joint, and coiled pipe is expected to need it. Significant ovality from a badly built stack is a loading defect and is very hard to recover commercially once the container has sailed — which is why loading photographs at three stages belong in the payment terms.

Technical articles

Inspecting HDPE Pipe Before You Pay For It

Third-party inspection agencies publish generic checklists — count the cartons, check the labels, photograph the loading. They are written to cover any product, so they miss everything specific to polyethylene pipe. Here is what we would look for if we were buying from us.

There is an obvious objection to a factory writing this. Take it as an argument in our favour if you like, but the substance stands on its own: every check below is one a competent buyer can insist on, and any supplier who resists them is telling you something.

Regrind: the one that matters most and shows up last

The most common corner cut in this industry is adding reprocessed material to pressure pipe. It saves real money, it is invisible in a finished pipe, and it does not fail immediately — it fails as slow crack growth, five to ten years in, long after the retention is released.

You cannot see it. You can catch it three ways, and a serious inspection uses all three.

How regrind is detected
Check	What it shows	Where it happens
Melt flow rate (MFR)	Reprocessed material has been through heat before; MFR drifts from the virgin resin's declared value	Laboratory, per batch
Oxidation induction time (OIT)	Antioxidant is consumed by every heat history; a low OIT means the material has less life left	Laboratory, per batch
Resin lot traceability	Whether the batch can be tied to a specific delivery of virgin resin, with the supplier's own certificate	Documentation

MFR and OIT together are the practical test. Traceability is what makes them meaningful — a good MFR on a batch that cannot be tied to a resin lot proves only that one sample was fine.

The same inspection costs the same at any of these four moments. What differs is what you can still do about what it finds.

Dimensions: measure the minimum, not the average

Wall thickness is where SDR is either real or not. The trap is that an average wall can be comfortably in tolerance while one point on the circumference is thin — and the thin point is the one that governs the pressure rating.

1
Outside diameter at two axes
Measured at the same cross-section, ninety degrees apart. The difference is the ovality, which matters for jointing as much as for pressure.
2
Wall thickness at six points around the circumference
Not two, not four. The minimum of the six is the figure to compare against the standard, and the spread tells you how well centred the die was.
3
Length and squareness of the cut
An out-of-square end costs facing time at every butt weld, and on a long run that is hours.
4
Ovality on coiled pipe specifically
Coils go oval in storage. Check it on delivery rather than at the trench, where re-rounding equipment may not be to hand.

Six points, one cut ring, two minutes. This is the check most often reduced to a single measurement, and a single measurement cannot find the thin spot.

Hydrostatic testing: which one was actually run

"Hydrostatically tested" on a certificate can mean two very different things, and the gap between them is the difference between a leak check and a proof of design life.

The two tests, and what each proves
Test	Duration	What it demonstrates
Short-term at 20 °C	100 hours	The batch holds its rated pressure now
Long-term at 80 °C	165 hours at elevated temperature	Accelerated proof of the 50-year design assumption
Quick pressure check	Minutes	Nothing about design life — this is a leak test

The 80 °C test is the one that stands behind the 50-year claim, and it is the one most often absent. Ask which was run, at what temperature and for how long.

Carbon black: content and dispersion are two tests

Black PE pipe is protected from ultraviolet light by carbon black, and both how much there is and how evenly it is spread matter. Content is typically specified at 2 to 2.5 percent. Dispersion is graded under a microscope, and poor dispersion leaves UV-vulnerable areas even when the content figure passes.

What a real certificate contains

The batch or production run number, and a way to tie it to the pipe you received — the same number should be in the print legend.
The resin grade and the resin lot number, not just "PE100".
Results with values, not ticks. "MFR: 0.22 g/10 min" is a result; "MFR: Pass" is a claim.
The standard each result was measured to, so the numbers can be checked against a requirement.
The date of test and the signature of whoever ran it.
Quantity and dimensions matching the packing list and the invoice.

Loading: the damage that happens after the inspection passes

Pipe leaves the factory round and arrives oval more often than anyone admits. Polyethylene creeps under sustained load, and a stack loaded badly and then left in a hot container for six weeks arrives deformed, which shows up at the first butt weld.

1
Nesting
Small diameters inside large ones saves freight and is fine — provided the inner pipe is supported and not resting its weight on the crown of the outer one.
2
Stack height and support
The bottom layer carries everything above it for the whole voyage. It should sit on timber bearers, not on the container floor, and the stack height should reflect the SDR.
3
Bundling and end caps
Bundles hold shape; end caps keep dirt and vermin out. Both should be visible in the loading photographs.
4
Photographs at three stages
Empty container with the number visible, mid-load, and sealed with the seal number readable. Ask for these as a condition of payment rather than as a favour.

How the stack is built decides what arrives. Ovality from a badly loaded container is not a shipping defect anyone will pay for later — it is caught here or not at all.

Stock held by diameter and class before loading. An inspection that happens in the yard, before the container arrives, has room to reject; one that happens at the door does not.

When to inspect

Three moments, three different powers
Moment	What you can still do	Cost of a problem
During production	Change the run	Lowest — the pipe has not been made
After production, before loading	Reject and remake	Days, and the factory absorbs it
At container loading	Refuse to load	The programme slips
On arrival at destination	Argue	You have already paid the freight

Most buyers book inspection at loading because that is what agencies sell. Booking it before loading costs the same and is the last point where rejection is cheap for both sides.

The short version, as questions

Which resin lot went into my batch, and can I see the resin supplier's certificate for it?
What were the MFR and OIT results for my batch, as numbers?
Was the hydrostatic test the 20 °C or the 80 °C one, and for how long?
What is the minimum wall thickness measured, not the average, and at how many points?
Are carbon black content and dispersion reported separately?
Can I inspect before loading rather than at the door?

Sources and standards

Frequently asked questions

How can I tell if regrind was used in my pipe?: Not by looking at it. Melt flow rate and oxidation induction time together will show a heat history that virgin resin does not have, and both should be reported per batch with values. Neither means much without traceability to the resin lot, so ask for the resin supplier's certificate alongside the test results.
What is the difference between the 20 °C and 80 °C hydrostatic tests?: The 20 °C test runs about 100 hours and shows the batch holds its rated pressure now. The 80 °C test runs at elevated temperature as an accelerated proof of the 50-year design assumption. The second is the one that stands behind a design life claim, and the one more often missing from a certificate.
Why measure wall thickness at six points instead of one?: Because the pressure rating depends on the minimum wall, not the average. A pipe can average comfortably within tolerance while one point on the circumference is thin, and that point governs. The spread across six readings also shows how well centred the extrusion die was.
Should I use a third-party inspection agency?: They are useful for presence and photographs, and their generic checklists cover packaging, counts and labels well. The PE-specific checks — regrind indicators, minimum wall at multiple points, which hydrostatic test was run — usually have to be written into the inspection brief, because a general checklist will not include them.
When is the best time to inspect?: Before loading rather than at the door. It costs the same, and it is the last moment where rejecting a batch is merely inconvenient instead of a programme delay. Inspection at the container has almost no remedy left except refusing to load.
What if pipe arrives oval?: Small ovality can be corrected with re-rounding clamps at the joint, and coiled pipe is expected to need it. Significant ovality from a badly built stack is a loading defect and is very hard to recover commercially once the container has sailed — which is why loading photographs at three stages belong in the payment terms.

Need a quote or a spec check?

Send us your drawing, tender document or bill of quantities. Our engineers reply within 12 working hours with pricing, lead time and a container loading plan.

Request a quote Email us