NACE TM0177-2024 Standard

Revision History

The standard has been revised repeatedly since the 1980s, each revision tightening procedure and reporting. The table shows the published lineage.

The 2024 revision clarified general information and revised the test solution definitions to accommodate expanded industry needs, including deaeration and saturation procedures. Reporting requirements for all four methods were revised and qualification provisions updated.

4 NACE TM0177 Test Methods: A, B, C and D

Four methods sit in the standard, and each measures a different thing. Methods A and C produce a cracking or no-cracking result at a stress level, Method B produces a statistically derived critical stress factor (S_c), and Method D produces a numerical fracture-mechanics value. Choosing the wrong one gives a valid test that answers the wrong question.

Method A: NACE Standard Tensile Test

Method A evaluates metals for EAC resistance under uniaxial tensile loading. It offers a simple unnotched specimen with a well-defined stress state, and susceptibility is usually determined by time to fracture. Specimens loaded to a particular stress level give a cracking or no-cracking result; testing several at varying stress levels produces an apparent threshold stress.

The standard tensile specimen has a reduced section of 6.35 ± 0.13 mm (0.250 ± 0.005 in) diameter by 25.4 ± 0.13 mm (1.00 ± 0.005 in) long. A subsize specimen at 3.81 ± 0.05 mm (0.150 ± 0.002 in) diameter by the same length is acceptable. Reduced section diameter and length must both be reported, and specimen orientation affects results so it is reported too.

The test terminates at specimen fracture or after 720 hours, whichever comes first. Method A is the test ISO 15156-2 names for Cr-Mo low-alloy tubulars at the 690 to 760 MPa SMYS grades, where each test batch must demonstrate SSC resistance by the UT test.

Method B: NACE Standard Three-Point Bent-Beam Test

Method B tests carbon and low-alloy steels using constant-deflection fixtures that apply three-point bending. The small specimen size facilitates testing of small, localised areas and thin materials, particularly weld zones and HAZ regions.

The standard specimen is 4.57 ± 0.13 mm (0.180 ± 0.0050 in) wide, 1.52 ± 0.13 mm (0.060 ± 0.0050 in) thick and 67.3 ± 1.3 mm (2.65 ± 0.050 in) long. Generally 12 to 16 specimens are taken from a sample to determine susceptibility, because the result is a statistically derived critical stress factor rather than a single pass or fail.

Method B is listed as a product verification test in API 5CT, which is why casing and tubing mills reach for it. The test terminates after 720 hours or when all specimens have failed, whichever occurs first.

Method B uses its own test solution of 0.5 wt% glacial acetic acid in distilled or deionised water with no NaCl added, and using Test Solutions A to D with Method B has not been standardised. Because the computed stress is a pseudo-stress, Method B is not suitable for determining a threshold stress.

Method C: NACE Standard C-Ring Test

Method C uses an unnotched C-ring specimen in accordance with ASTM G38. Specimens deflected to a particular outer fibre stress level give a cracking or no-cracking result, and testing several at varying stress levels produces an apparent threshold stress.

C-rings suit tubular products because the specimen is cut directly from the pipe or tube wall and loaded circumferentially, reproducing the hoop-stress direction the material sees in service. Testing terminates after 720 hours or following cracking of all C-ring specimens, whichever occurs first.

Method D: NACE Standard Double Cantilever Beam Test

Method D measures resistance to crack propagation rather than crack initiation, expressed as a critical stress intensity factor: K_ISSC for SSC and K_EAC for the more general case of EAC. It uses a crack-arrest type of fracture mechanics test.

The advantage is reliability of outcome. Method D does not depend on the uncertainty of pitting or crack initiation, because a crack is always initiated in a valid test. It gives a direct numerical rating of crack propagation resistance rather than a cracking or no-cracking judgement.

That numerical output is also its limitation in qualification work. ISO 15156-2 Table B.1 lists DCB with acceptance criteria to be set by documented agreement, and its use as qualification is at the equipment user’s discretion with documented justification.

4 Standard Test Solutions: Solutions A, B, C and D

All four solutions are aqueous brines with an H₂S partial pressure specified by the user or purchaser. Solution A is acidified, Solution B is acidified and buffered, and Solutions C and D are acetate-containing brines whose initial pH is specified by the user or purchaser and adjusted with HCl or NaOH.

Three rules govern pH and they invalidate tests when broken. Initial pH must fall in the stated range and be reported. For the standard TM0177 solutions, altering the solution composition to adjust pH is not permitted, and an out-of-range solution is discarded, not corrected. For Solutions A and B, final pH may rise during the test but must not exceed 4.0, and a test that exceeds it is invalid.

Note: The standard notes that pH will stay inside the limit if the test-solution-volume-to-specimen-surface-area ratio is maintained and the dissolved oxygen requirements are met. A drifting pH usually points to a ratio or oxygen problem rather than the material.

Three Permitted Test Gases

The test gas is specified by the user or purchaser from three options, and after saturation the gas should be bubbled continuously at a rate that maintains saturation.

• Chemically pure H₂S, historically how Solution A was specified
• A mixture of H₂S and nitrogen, with H₂S content sufficient to produce the specified partial pressure
• A mixture of H₂S and CO₂, with H₂S content sufficient to produce the specified partial pressure

The start of the test is defined as the time that saturation is achieved, not the time the specimen entered the vessel. Saturation must be verified or validated by the procedure the standard sets out.

Test Duration and the CRA Exposure-Time Caveat

720 hours (30 days) is the standard test duration for Methods A, B and C. Each terminates at 720 hours or when the specimens have failed, whichever comes first. Method A also terminates at specimen fracture.

One note in the scope deserves more attention than its length suggests. Additional exposure time can be required when testing corrosion-resistant alloys, with further guidance in ISO 15156-3:2020 Technical Circular 2:2022.

That matters commercially. A 720-hour result on a duplex or nickel alloy may not be the full answer, and a purchaser specifying CRA testing should confirm whether the extended exposure guidance applies before the lab books the vessel.

For Method D (DCB), test duration for carbon and low-alloy steels shall be at least 14 days, or at least 17 days in Test Solutions C and D. For stainless steels and Ni-, Ni/Co-, Ti- or Zr-based alloys it should be at least 720 hours, and very high-strength steels, low temperatures or low-H₂S environments may need 21 days or longer. The duration is specified by the user or purchaser and reported with the results.

How TM0177 Connects to MR0175 and ISO 15156

TM0177 is a test method that MR0175 and ISO 15156 call on. It produces results; the material standards decide what those results permit.

The NACE MR0175 standard page explains the three-part structure and how the designations map. TM0177 sits behind all three parts as the test procedure their Annex B qualification routes depend on.

For carbon and low-alloy steels, the ISO 15156-2 standard page covers Table B.1, which sets the applied stress levels at ≥ 90 % of actual yield strength (AYS) for specific applications or SSC regions 1 and 2, and at ≥ 80 % AYS for qualification across all SSC regions.

For stainless, duplex and nickel alloys, the ISO 15156-3 standard page explains how the standard allows qualification by testing for conditions more severe than its Annex A tables give, and for metallurgical conditions different from those listed. TM0177 is how that testing is performed.

Which Materials Get Tested Under TM0177

Most material never sees a TM0177 vessel. Alloys listed in the ISO 15156 Annex A tables, used inside their stated environmental limits, are qualified without further SSC testing. Testing enters the picture in four situations.

• The alloy is not in Annex A: a grade outside the listed material types or individual alloys
• The service exceeds the Annex A envelope: higher H₂S, higher temperature, lower pH or higher chloride than the table permits
• The metallurgical condition differs: higher strength, alternative heat treatment or a cold-worked condition the table does not cover
• Weld procedure qualification: where alternative weld hardness acceptance criteria are being established from successful SSC testing of welded samples

A fifth case is commercial rather than technical. ISO 15156-2 positions its Option 2 qualification route for bulk materials such as OCTG and line pipe, where the economic incentive to use a steel outside Annex A outweighs the qualification cost.

For duplex 2205 seamless pipe? supplied solution-annealed and quenched with ferrite inside the 35 % to 65 % window, Annex A qualifies the material without TM0177 testing only when used within defined environmental limits, such as a maximum H₂S partial pressure of 10 kPa (1.5 psi) for general equipment or 2 kPa (0.3 psi) for cold-worked downhole tubulars.

The same holds further up the range. Inconel 625 seamless pipe in the annealed condition sits in a group carrying no environmental limits at all, so testing is reserved for unusual metallurgical conditions rather than routine supply.