Material Testing: What Can Be Specified

Testing is very often carried out as a block; however, more testing does not mean greater assurance. Each test may close one specific gap; however, as a whole, it says very little about the others, and some simply cannot be repeated. A chemistry report will never prove low-temperature capability; a hardness reading on a heavy forging will not tell you what the core is doing; HIC resistance is developed at the steel mill, not in a testing lab. This page sets out what eachpipe material testing scope proves, and when it has to be ordered.

Standard Testing, Included by the Specification

Test	What it proves
Chemical analysis	Composition against the specification range
Tensile test	Tensile strength, yield strength and elongation
Hydrostatic test	That the item holds its test pressure without leaking
Dimensional check	Size and tolerance against the dimensional standard
Visual examination	Surface condition and marking

These come with the material under the governing standard. Everything below is supplementary and has to be ordered.

Supplementary Testing, Ordered Separately

Impact Testing, Charpy

Proves notch toughness at a stated test temperature, and it is the only evidence of low temperature capability. Chemistry does not show it and positive material identification cannot find it:A106 Grade B and A333 Grade 6 are close enough in chemistry that only the impact report distinguishes them, and the same applies toA234 WPB and A420 WPL6.

Specify the test temperature and the acceptance energy from the project specification rather than relying on the ASTM default. And remember the items usually left out:bolting, valve bodies and small bore fittings. A193 B7 is not a low temperature grade.

Hardness Testing

Proves the hardness limit for sour service under NACE MR0175 and ISO 15156 Part 2, where the general ceiling is 22 HRC. Two cautions:

On a heavy section such as a flange hub, a surface reading can pass while the core sits outside the tempering window. Where the specification requires it, testing is item by item rather than by heat
The weld and heat affected zone are not covered by the material certificate. A welding procedure hardness survey covers those

HIC Testing, NACE TM0284

Proves resistance to hydrogen induced cracking, which is blistering and stepwise cracking without applied stress. The critical point: HIC resistance comes from sulphur level and inclusion shape control at the steelmaking stage, so it determines where the material is made. It cannot be added to steel that has already been rolled, which makes it a sourcing requirement rather than a testing requirement. It belongs in the enquiry.

SSC Testing, NACE TM0177

Proves resistance to sulphide stress cracking, which is cracking under applied or residual stress. Unlike HIC, this is driven by hardness and strength, so it can be specified on a finished component. State the method and the acceptance criteria.

Corrosion Testing

Test	Applies to
ASTM G48	Pitting and crevice resistance, routinely paired with a PREN requirement onsuper duplex
ASTM A262	Intergranular attack susceptibility on austenitic stainless
ASTM A923	Detrimental intermetallic phase in duplex, which is the sigma phase question

A PREN figure is a calculation, not a measurement, which is why specifications that require PREN 40 normally require a corrosion test with it. See theduplex vs super duplex guide.

Non-Destructive Examination

Method	Finds
Radiography	Volumetric defects in welds. Not practical on socket weld fillets
Ultrasonic	Volumetric defects and wall thickness
Magnetic particle	Surface and near surface defects in ferromagnetic material
Liquid penetrant	Surface defects, including in austenitic material that magnetic particle cannot examine
Eddy current	Tube examination

State the method, the extent as a percentage, and the acceptance standard. "NDE required" is not a scope.

Positive Material Identification

Confirms alloy composition on the item. Its limits should be stated rather than assumed:

It cannot separate grades whose difference is a mechanical property, so it will not distinguish A106 Gr B from A333 Gr 6
It cannot separateGrade 91 from Grade 92 with standard portable equipment, because the difference is tungsten
Where it cannot discriminate, segregation and marking carry the control

Specify the stage at which PMI is applied, because on a project it is often required again at site.

Ferrite and Phase Balance

Onduplex and super duplex, hot forming and welding move the ferrite and austenite balance, and the balance rather than the chemistry is what carries the properties. On formed and forged items this is the acceptance item.

What Each Test Cannot Tell You

You need to know	The test that answers it	The test that does not
Low temperature capability	Impact test at the specified temperature	Chemistry, PMI, tensile
Sour suitability of the base material	Hardness, plus HIC and SSC where specified	Chemistry alone
Sour suitability of the joint	Welding procedure hardness survey	The material certificate
Which of two lookalike alloys this is	Marking and traceability, sometimes PMI	PMI alone, for Grade 91 and 92
Whether duplex kept its properties after forming	Phase balance and A923	Chemistry
Core condition of a heavy forging	Testing at the required location	A surface hardness reading

Testing That Cannot Be Added Later

Worth separating out, because the cost of missing these is not money but a re-order:

HIC resistance. Created at the steelmaking stage
EN 10204 3.2 certification. Requires witnessed testing, so it has to be arranged before the tests happen. See theMTC guide
Impact testing on a heat already shipped. Possible only if material from the same heat is still available
Any test requiring a hold point already passed

What to State on the Enquiry

Each test required, with the method, the extent and the acceptance standard
Test temperature and acceptance energy for impact testing
Whether hardness testing is by heat or item by item
Whether HIC and SSC are required, which affects sourcing
PMI requirement and the stage at which it applies
Certification type, and the nominated agency for a 3.2
The standard edition the project is qualified against

Testing FAQ

What testing comes as standard?

Chemical analysis, tensile testing, hydrostatic testing, dimensional check and visual examination, as required by the governing standard. Everything else is supplementary and must be ordered.

What is the only proof of low temperature capability?

The impact test report at the specified test temperature. Chemistry and positive material identification cannot distinguish A106 Grade B from A333 Grade 6.

Why is HIC a sourcing requirement rather than a test requirement?

Because HIC resistance comes from sulphur level and inclusion shape control at the steelmaking stage, so it determines where the material is made and cannot be added afterwards.

What is the difference between SSC and HIC testing?

SSC to TM0177 tests cracking under stress and is hardness driven, so it can be specified on a finished component. HIC to TM0284 depends on steelmaking cleanliness.

Why is a PREN requirement paired with a corrosion test?

Because PREN is a calculated index rather than a measurement, so ASTM G48 or similar is used to verify actual pitting resistance.

Is 'NDE required' a sufficient instruction?

No. The method, the extent as a percentage and the acceptance standard all have to be stated.

Specify Your Testing Scope

List each test with its method, extent and acceptance standard rather than asking for full testing. And flag HIC and 3.2 certification first, because those two are the ones that cannot be added once production has started.

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Testing: What Can Be Specified and What It Proves