A neat-looking weld can still fail acceptance when the destructive seam coupon is pulled in the wrong direction or read without its failure mode.
Peel and shear are complementary tests for thermo-fusion geomembrane seams under ASTM D6392. Peel challenges the bonded interface; shear loads the joined specimen across the seam. Buyers need the specified acceptance values, specimen orientation, failure description and sampling plan together. One attractive peak load cannot substitute for the complete seam record.
For landfill, pond and mining buyers, the practical issue is how test results become a defensible release decision on site.
Send your project drawings, technical specifications, quantities and destination for material-fit review before quotation.
Send drawings and specificationsWhy Are Two Mechanical Results Reported?
Peel tends to reveal whether the two sheets separate at the interface; shear measures resistance when the joined specimen is pulled across the seam. The loads and failure locations mean different things. A report that gives only a headline number may conceal whether material tore outside the weld, the bond separated, or the sample failed in a way that needs interpretation under the project specification. ASTM D6392 defines the laboratory method. It does not choose your project's minimum acceptance values or sampling frequency. Those belong in the approved technical specification before field welding starts. [1]
What Changes Between a Dual-Track Weld and an Extrusion Detail?
A dual-track hot-wedge seam creates an air channel that may allow non-destructive pressure testing between the tracks. An extrusion weld is often used for repairs or complex details and needs a different inspection sequence. Do not treat an air-channel pass as a substitute for every destructive test, and do not apply a dual-track procedure to a single extrusion bead. Identify the seam type on the as-built drawing. Where a repair crosses an existing seam, document the weld geometry and the retest method rather than copying the main production seam checklist. [2]
| Check | What it tells you | What it does not prove |
|---|---|---|
| Peel | Bond-interface behavior | Not a complete leak test |
| Shear | Joint load across seam | Does not locate every void |
| Air-channel pressure | Continuity of dual-track channel | Not applicable to every detail |
The comparison is a procurement screen, not a replacement for the approved engineering design. A test method defines how a property is measured; acceptance thresholds and the site detail must come from the project specification.
How Should a Failed Sample Be Investigated?
First check sample identification, test direction, specimen preparation and instrument records. Then determine whether the problem is isolated or points to a welding window: temperature, speed, pressure, surface contamination or weather change. The repair extent and additional sampling should follow the approved CQA plan, not a hurried decision at the test bench. ASTM D7700 helps select seam test methods, but it does not override the project acceptance specification. When a coupon is borderline, record the actual failure mode and ask the quality team to decide; do not round a result into compliance. [2] [3]
What Should Be Sent With the Liner RFQ?
Give the supplier the resin type, nominal thickness, surface texture, required sheet standard and expected welding method. Ask for a data sheet and roll traceability so site coupons can be tied to the material actually delivered. Include the project seam specification, inspection authority, testing laboratory and any trial-weld requirements. A quote for sheet alone will not price the field testing, repairs or weather downtime. Procurement should keep those commercial scopes separate while checking that the proposed sheet can be welded with the planned equipment. [3]
What Should the Site Team Verify Before Work Starts?
Before production, run a trial weld using delivered sheet, the actual equipment and current weather conditions. Keep the trial separate from production acceptance, and define what change in ambient temperature, wind or machine settings triggers another trial. Mark the coupon so both peel and shear results can be traced to a seam number and time. Where test reports arrive after the cover crew, set a hold point that prevents burial until acceptance is recorded. If a weld fails, map the potentially affected interval instead of repairing only the coupon hole. A retest plan should identify the endpoints of that interval and the authority who releases it. This workflow is slower than simply filing a number, but much faster than unearthing an undocumented seam.
What Should Be in the RFQ?
Request the liner data sheet, target thickness and surface, roll width, resin and batch identification, project acceptance thresholds, sampling frequency, test laboratory and method statement. Ask whether the contractor’s quotation includes trial welds, destructive coupons, non-destructive checks, repair materials and retesting. MJY can review HDPE liner sheet specifications against the RFQ, but the engineer of record should approve seam criteria.
For the connected design check, review our geomembrane welding quality checks guide before approving a material substitution.
For a fair quotation, ask each supplier to state the proposed grade, tested properties, test edition, usable roll dimensions, packaging, batch identification, lead time and exclusions. Put the drawing revision and destination on the inquiry. If a proposed substitute changes an engineered detail, request written design approval rather than treating it as a price-only decision.
Factory Tip and Buyer Check
QC Check: Keep a simple weld log that links roll IDs, machine settings, weather, seam number, sample number and repair location. Without that chain, even a legitimate passing coupon may be hard to connect to the area that will be covered tomorrow.
Before bulk production, compare the labelled sample or approved data sheet against the purchase specification. At goods receipt, keep roll IDs and packaging photographs. These small controls make a later site question traceable instead of turning it into an argument about what was ordered.
FAQs
Is higher shear strength enough to approve a seam?
No. Review peel, shear, failure mode and the specified acceptance criteria together.
Can an air-channel test replace coupons?
Not automatically. It is a different check and depends on the seam geometry and project plan.
Who sets pass/fail limits?
The approved project specification and quality plan, interpreted by the responsible project team.
Conclusion
Seam acceptance is a chain of evidence, not one number. Send project drawings and weld specifications to MJY for a material review, and require the installer to document the exact seam and test sequence before production welding.
