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PD ISO/TR 19686 — Petroleum Products Test Method Equivalency Standard Series
Petroleum Products — Equivalency of Test Method Determining the Same Property — Technical Report Series Overview
⛽ PD ISO/TR 19686 is a BSI Published Document series adopting ISO technical reports on petroleum product testing, focused on evaluating the “equivalency” of different test methods that determine the same property. The series was prepared by BSI technical committees PTI/13 (Petroleum testing and terminology) and PTI/2 (Liquid fuels) and carries ICS 75.080 (petroleum products). Using atmospheric distillation of petroleum products as an example, it explains how to compare two test methods measuring the same property, how to judge equivalency, and the background and principles of equivalency evaluation, supporting harmonisation of petroleum test methods and mutual recognition of interlaboratory results.
💡 The same property is often covered by multiple standard test methods (e.g., different distillation methods). If methods are not equivalent, results from different laboratories using different methods become incomparable, affecting product acceptance and trade settlement — precisely what this series addresses.
1. Series Structure and Scope 📌
This batch comprises two technical reports, one giving the atmospheric distillation example and one the general equivalency principles:
| Part | Document | Subject | Main Content |
|---|---|---|---|
| Atmospheric distillation example | PD ISO/TR 19686-1:2014 (ISO/TR 19686-1:2014) | Atmospheric distillation of petroleum products | Comparison, reasons for divergence, meaning of equivalency, questionnaire for checking similarities, conclusion |
| Evaluation principles | PD ISO/TR 19686-100:2016 (ISO/TR 19686-100:2016) | Background and principle of comparison and equivalency evaluation | Scope, terms, comparison, equivalency evaluation principles, applicability |
⚠️ The technical reports do not impose fixed equivalency limits; they provide an evaluation methodology. Actual judgment typically combines statistical tests, method precision data and product specification requirements.
2. Method Comparison and Reasons for Divergence 🔍
Part 1 uses atmospheric distillation of petroleum products as an example and analyses the key issues when comparing two test methods:
- Reasons for divergence: instrument construction, operating conditions, temperature sensor position, distillation rate control and atmospheric pressure correction can cause inter-method differences.
- Meaning of equivalency: two methods are equivalent if, in a statistical sense, they give acceptably consistent results for the same property.
- Method similarity check: use a structured questionnaire to compare instrument, conditions and operational details item by item and identify potential difference sources.
- Conclusion: give the equivalency conclusion and scope, providing a basis for method adoption.
✅ A structured questionnaire is a practical tool for method comparison: it breaks a complex distillation into checkable elements, helping analysts quickly locate “where might it differ and how much does it matter”.
3. Background and Principles of Equivalency Evaluation 📚
Part 100 (background and principles) generalises the distillation example into a common methodology:
- Background: why equivalency is needed — the common needs of method standardisation, laboratory accreditation, trade settlement and regulatory compliance.
- Starting point: first confirm the premise of “determining the same property”, then check whether the methods’ scope and measurement object are consistent.
- Evaluation principles: compare the bias and precision of the two methods statistically and judge whether differences fall within an acceptable range.
- Applicability: note that equivalency conclusions depend on sample type, concentration range and conditions, and define the applicable scope.
⚠️ Equivalency does not mean identical. Two methods may still be equivalent if results agree statistically and in precision despite minor differences; conversely, even similar steps cannot be deemed equivalent if systematic bias is significant.
4. Key Elements of Equivalency Evaluation 📊
| Element | Content | Evaluation Focus | Typical Method |
|---|---|---|---|
| Method bias | Average difference of results for the same sample | Whether the difference is significant and varies with concentration | Paired t-test, regression analysis |
| Method precision | Repeatability and reproducibility | Whether the two methods have comparable precision | Precision data comparison |
| Sample coverage | Different grades/boiling ranges | Whether conclusions cover the target product range | Representative sample matrix |
| Statistical judgement | Equivalency decision at a set confidence level | Whether the acceptance limit is reasonable | Equivalency test, confidence interval |
5. Engineering Practice Essentials 🛠️
- 🔍 Method selection and adoption: before adopting a new or alternative method, perform method comparison and equivalency evaluation per this series.
- 🔧 Interlaboratory comparison: assess the consistency of different methods in actual laboratories through interlaboratory comparisons and proficiency testing.
- 📊 Data sharing: build a method-equivalency database to support reasonable method clauses in product specifications and trade contracts.
- 📋 Reporting: equivalency reports should include method descriptions, sample information, statistical results, judgement conclusions and applicable scope.
6. Frequently Asked Questions ❓
❓ Q: Why evaluate the equivalency of different test methods?
A: Different bodies may prescribe different test methods; if methods are not equivalent, results for the same product from different laboratories using different methods are incomparable, affecting acceptance, trade and regulatory consistency.
A: Different bodies may prescribe different test methods; if methods are not equivalent, results for the same product from different laboratories using different methods are incomparable, affecting acceptance, trade and regulatory consistency.
❓ Q: Which differences matter in atmospheric distillation comparison?
A: Instrument construction, temperature sensor position, distillation rate, atmospheric pressure correction and operating conditions; these can cause systematic bias at different boiling points.
A: Instrument construction, temperature sensor position, distillation rate, atmospheric pressure correction and operating conditions; these can cause systematic bias at different boiling points.
❓ Q: Does equivalency evaluation always need statistical analysis?
A: Typically yes. Statistical tests and confidence intervals judge whether inter-method differences are significant, combined with precision data for reliable conclusions, avoiding arbitrary judgement on isolated points.
A: Typically yes. Statistical tests and confidence intervals judge whether inter-method differences are significant, combined with precision data for reliable conclusions, avoiding arbitrary judgement on isolated points.
🔍 Q: Does the series give a unified equivalency acceptance limit?
A: No fixed limit. It provides the evaluation method and principles; concrete limits should be set by method precision, product specifications and industry practice.
A: No fixed limit. It provides the evaluation method and principles; concrete limits should be set by method precision, product specifications and industry practice.