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TBM vs. THT Natural Gas Odorants: Differences, Selection and Pipeline Conditioning

Jan 4
6 min read

Updated: Aug 14

TBM and THT are both used in natural gas odorization, but a factual comparison does not produce one universal winner. Tertiary-butyl mercaptan (TBM) is a mercaptan, while tetrahydrothiophene (THT) is a cyclic sulfide. Their physical properties differ, and commercial odorants may contain either compound alone or as one component of a blend.

Field results depend on the complete formulation, pipe condition, gas composition, flow history, temperature, pressure, injection method and verification plan. Those variables matter more than a simple “TBM is better” or “THT is more stable” rule.

Natural gas pipeline illustrating TBM and THT odorant selection

TBM and THT: What Can Be Compared Reliably

Factor

TBM

THT

Practical implication

Chemical family

A mercaptan (thiol), formula C4H10S.

A cyclic sulfide, formula C4H8S.

The compounds are not interchangeable labels; supplier formulation and measurement method matter.

Normal boiling point of the pure compound

About 337 K (64 °C).

About 393 K (120 °C).

Pure THT is less volatile at comparable conditions. Do not use boiling point alone to choose dose or injection method.

Commercial use

Available as a pure chemical and commonly used as a component of mercaptan or mercaptan-sulfide blends.

Used as a primary odorant in some systems and as a component of some blends.

Evaluate the complete commercial product, supplier specification and SDS—not only the named component.

Regional practice

Used in several blend families, including TBM with DMS or other mercaptans.

Used as the principal odorant in a number of European systems.

Practice varies by country, operator and gas system; regional use is not proof of universal suitability.

Field verification

A compound-specific concentration reading can support troubleshooting when the instrument and calibration are suitable.

The same limitation applies: the method must be suitable for THT and the actual formulation.

Instrument concentration and perceived odor intensity answer different questions and should not be treated as interchangeable.

The physical-property values above are for the pure compounds in the NIST Chemistry WebBook (TBM) and NIST Chemistry WebBook (THT). A commercial blend can have different volatility, freezing behavior and analytical response.

What 49 CFR 192.625 Actually Requires

The current federal rule is performance-based; it does not prescribe TBM, THT or a particular blend. 49 CFR 192.625 addresses odor detectability where the rule applies, odorant and combustion-product properties, water solubility, odorization without wide variations, and periodic sampling.

A chemical name by itself is therefore not evidence that a system meets the rule. Applicability, the selected product, injection performance and field verification must be evaluated under the operator’s procedures and other applicable requirements. BPS provides operational support and documentation, not legal advice.

For a section-by-section operational overview, read 49 CFR 192.625 Explained.

Pipeline Conditioning and Odor Fade: What the Research Supports

Laboratory and field-oriented research documents several odor-loss mechanisms, including chemical reaction with iron oxides, adsorption on porous or contaminated surfaces, absorption into liquids or materials, and masking by other gas-stream odors. The balance among those mechanisms changes with the system.

A 2015 study of TBM in steel pipe reported evidence of chemisorption, adsorption and desorption on iron oxide. In its test conditions, mercaptan removal increased with pressure, rust and temperature, and with lower flow and lower inlet odorant concentration. A 2021 steel-pipe study identified reaction with iron oxide and exposure to fine solid particles as important mechanisms in its tested scenarios. These studies support project-specific conditioning and verification; they do not establish a universal TBM-versus-THT ranking.

  • Supported conclusion: new, rusted or contaminated steel can consume mercaptan odorant under some conditions.

  • Unsupported universal conclusion: TBM always conditions a line faster or THT always requires less odorant.

  • Supported conclusion: flow, pressure, temperature, solids, liquids, surface condition and inlet concentration can affect observed loss.

  • Unsupported universal conclusion: a fixed odorant, dose or number of days works for every pipeline.

Pipeline conditioning should therefore be managed as a measured process. Establish the starting condition, document the odorant product and injection basis, measure at representative downstream locations, and use defined stabilization criteria before changing the plan or demobilizing.

Claims That Should Not Drive Odorant Selection

  • “TBM always penetrates soil better.” Soil transport and above-grade odor perception depend on soil, moisture, leak path, microbial activity, odorant formulation and weather. The reviewed sources do not support a universal field ranking.

  • “THT does not fade.” THT may behave differently from mercaptans, but no odorant is exempt from losses, liquids, masking, poor injection, sampling errors or system-specific interactions.

  • “Both products automatically meet regulation.” The rule evaluates the odorized gas and odorization process where applicable, not a product name in isolation.

  • “Adding THT to a blend automatically improves stability or cold-weather behavior.” Use the exact supplier specification and SDS for the complete blend; component names alone do not establish blend properties.

  • “One chemistry always costs less.” Compare quoted product price, target basis, actual consumption, storage, refill logistics, monitoring, conditioning time and downstream compatibility for the specific job.

Odorant Selection Inputs for a Real System

A defensible selection record should capture the following before procurement, mobilization or commissioning:

  • Applicable operator procedures, tariff or interconnection requirements, and current federal, state and local requirements.

  • Exact supplier product name, composition or allowable composition range, sales specification, SDS and certificate-of-analysis requirements.

  • Gas sources and composition, including changes among supply points and any downstream process, catalyst, turbine, fuel-cell or customer constraints.

  • Pipe material, internal coating, age, rust or mill-scale condition, construction debris, liquids, filtration and prior odorization history.

  • Minimum, normal, maximum, zero and intermittent flow; pressure and temperature ranges; restarts, source switching and expected transients.

  • Injection method, flow signal, turndown, power, communications, storage volume, refill access, containment and contingency arrangements.

  • Representative sampling locations and the intended evidence: compound concentration, perceived odor intensity, injection records, inventory reconciliation or a combination.

  • Analyzer suitability for the target compound or blend, calibration basis, cross-sensitivity review, sample conditioning and data-quality checks.

Commissioning and Verification Plan

Odorant selection is only one part of commissioning. The turnover record should connect the chosen formulation to what was actually delivered and what was observed downstream.

  1. Record the approved odorant product, blend basis, target injection basis and responsible operator approvals.

  2. Document starting tank inventory, instrument status, calibration or functional checks, valve alignment and the applicable gas-flow configuration.

  3. Compare the commanded injection rate with independent evidence of actual delivery, including tank-level or mass change, refill records and equipment totals where available.

  4. Measure at representative downstream points and record time, flow, pressure, source configuration, sample conditioning and method limitations.

  5. Keep concentration measurement separate from perceived odor-intensity testing. A concentration result can support troubleshooting, but it is not automatically equivalent to the detectability test described in the federal rule.

  6. Define stabilization, alarm-response, change-control and demobilization criteria before startup rather than choosing an arbitrary duration.

See Odorant Concentration vs. Odor Intensity for the distinction between the two measurement questions.

So, Is TBM or THT Better?

Neither is universally better. TBM and THT have different chemistry and volatility, and operating practices vary by region and system. The better choice is the specific commercial formulation that fits the operator’s requirements, gas and pipe conditions, injection and storage arrangement, downstream constraints, supplier data and verification method.

If the evidence is incomplete, the defensible next step is not a blanket chemistry claim. It is a documented field plan with defined measurements, representative locations and acceptance criteria.

Project Support

Burgess Pipeline Services can support project-data review, temporary odorization, pipeline conditioning, field concentration measurement and turnover documentation. The operator and odorant supplier should approve the formulation, compliance basis and acceptance criteria. Review pipeline pickling and conditioning support or call (323) 609-5009.

Frequently Asked Questions

Does U.S. federal regulation require TBM or THT?

No. The current text of 49 CFR 192.625 sets performance and property requirements where it applies; it does not name TBM or THT as the required chemistry.

Does THT always experience less odor fade than TBM?

No universal conclusion is supported. Results depend on the exact product or blend, pipe surfaces, solids, liquids, gas composition, operating history and measurement method.

Can a concentration analyzer alone establish odor detectability?

Not automatically. A compound-specific concentration reading and a perceived odor-intensity test answer different questions. Use the method required by the operator’s procedures and applicable requirements, and document the limitations of each result.

Should pure-compound boiling point decide the odorant?

No. Boiling point helps describe volatility, but selection also requires the complete blend specification, operating envelope, injection method, storage, downstream compatibility and verification plan.

Sources Reviewed

Technical review completed August 14, 2026. Sources are paraphrased; standards and supplier documents should be checked in their current versions before use.

 
 
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