Pipe Inspection Methods & Tests

Inspection Categories

Pipe inspection verifies compliance with standards (ASTM, API, ASME) across five areas: visual (surface defects), dimensional (OD, ID, WT, length), metallurgical (chemical composition, microstructure), mechanical (tensile, impact, hardness), and pressure (hydrostatic testing). Results are documented in Mill Test Certificates.

Pipe Inspections

Pipes Inspection

Pipe inspection verifies that newly manufactured pipes are fit for their intended purpose, capable of safely handling operational demands and compliant with applicable standards and specifications. Every pipe entering an oil and gas facility, power plant, or chemical processing plant must pass a defined set of tests before acceptance.

Why Inspection Matters

Reason	Benefit
Safety assurance	Detects hazards before catastrophic failures
Regulatory compliance	Meets industry codes; avoids fines and shutdowns
System reliability	Identifies issues before they escalate
Performance verification	Confirms design flow rates and pressure ratings
Lifecycle extension	Early defect detection reduces maintenance costs
Contractual obligation	Satisfies purchase order and project specification requirements

Standard Inspections per ASME/API

Category	Tests	What’s Checked
Visual	Surface inspection	Dents, scratches, laminations, weld seam integrity, straightness, roundness
Dimensional	OD, ID, WT, length	Compliance with ASME B36.10/B36.19 tolerances
NDT	RT, UT, MPI, DPI	Internal flaws, weld defects, surface cracks
Mechanical	Tensile, Charpy, hardness	Strength, toughness, wear resistance
Metallurgical	Chemical analysis, microstructure	Alloy composition, grain size
Pressure	Hydrostatic test	Leak-tightness at design pressure
Marking	Stencil/stamp verification	Manufacturer, grade, size, heat number
Documentation	MTC review	EN 10204 certification with all test results

Inspection Scope: Full vs. Sample

Approach	Tests	Frequency
100% inspection	Visual, dimensional, UT for wall thickness, hydrostatic	Every pipe
Sample inspection	Tensile, Charpy impact, chemical analysis, microstructure	Per heat/batch

Sampling rates are defined by applicable standards (API, ASTM, ASME). For critical applications or high-spec orders, sample testing frequency may increase, or every pipe may be tested. Sampling rates can be negotiated with the client.

Pipe inspection verifies compliance with standards across five areas: visual (surface defects), dimensional (OD, ID, WT, length), metallurgical (chemical composition, microstructure), mechanical (tensile, impact, hardness), and pressure (hydrostatic testing). For critical applications, define witness and hold points in the Inspection Test Plan before the order is placed; not after.

Mill Inspection vs Third-Party vs Site Inspection

Pipe inspection occurs at three distinct locations, each with a different scope and purpose.

Mill Inspection (Manufacturer QC)

Mill inspection is performed by the pipe manufacturer’s own quality control department as part of the standard production process. The mill’s QC team follows internal procedures based on the applicable product standard (API 5L, ASTM A106, ASTM A312, etc.) and the customer purchase order.

Mill inspection covers:

• Raw material verification (incoming steel plate, billet, or coil)
• In-process checks during forming and welding
• Heat treatment verification (temperature, soak time, cooling rate)
• All required mechanical and chemical testing
• Final visual and dimensional inspection
• Hydrostatic testing
• Marking and documentation

EN 10204 Type 3.1

Standard mill inspection results in an EN 10204 Type 3.1 certificate (test results validated by the manufacturer’s authorized representative). This is the default certification level for most industrial pipe orders.

Third-Party Inspection (TPI)

Independent inspection agencies (Lloyd’s, SGS, DNV, Bureau Veritas, Cotecna, TUV) provide impartial verification for critical applications. The third-party inspector works on behalf of the buyer, witnessing tests and reviewing documentation at the manufacturer’s facility.

Scenario	Why Third-Party
High-stakes applications	Oil & gas, nuclear, where failure consequences are severe
Regulatory requirements	Some jurisdictions mandate independent verification
Contract specifications	Client or project manager stipulates third-party witness
Certification	ASME, API stamps require independent verification
International trade	Builds trust across borders; facilitates customs clearance
Specialized expertise	Testing capabilities manufacturer lacks in-house

MTC 3.2

When third-party inspection is performed, an EN 10204 Type 3.2 certificate is issued, the highest assurance level, with test results validated by both manufacturer and independent inspector.

Site (Receiving) Inspection

Site inspection is performed when pipes arrive at the fabrication yard, construction site, or warehouse. It serves as the final quality gate before pipes enter the piping system.

Check	Purpose
Visual inspection	Detect transport damage (dents, scratches, bent ends, coating damage)
Dimensional spot-check	Verify OD, WT, and length against PO
Marking verification	Confirm stencils match MTC and purchase order
MTC review	Verify all test results meet specification requirements
PMI (if required)	Positive Material Identification confirms alloy composition
Quantity count	Reconcile delivered quantity against packing list

Transport Damage

Pipes frequently arrive with end damage, dents from improper stacking, or coating defects from rough handling. Reject damaged pipes immediately and document with photographs. Do not install pipes with unresolved NCRs (non-conformance reports).

Inspection Stages: Pre-Production to Shipping

Pipe manufacturing inspection follows four stages, each with defined activities and checkpoints.

Stage 1: Pre-Production

Activity	Details
ITP review and approval	Agree on inspection and test plan with all parties
Raw material certificates	Verify incoming steel (plate, billet, coil) MTCs
Chemical analysis	Confirm heat analysis meets grade requirements
Welding procedure review	Approve WPS/PQR for welded pipe production
Calibration records	Verify all testing equipment is calibrated and current

Stage 2: In-Process

Activity	Details
Forming verification	Monitor pipe forming (piercing, rolling, or plate bending)
Welding monitoring	Verify weld parameters match approved WPS
Heat treatment witness	Confirm temperature, hold time, and cooling method
In-process NDT	UT of weld seam, lamination check on plate
Dimensional spot-checks	OD, WT at intervals during production run

Stage 3: Final Inspection

Activity	Details
Visual inspection (100%)	Every pipe checked for surface defects
Dimensional inspection (100%)	OD, WT, length, straightness, end prep on every pipe
NDT (as required)	Full-body UT, weld seam RT/UT per specification
Hydrostatic test (100%)	Every pipe pressure-tested
Mechanical testing (per heat)	Tensile, impact, hardness on sample pipes
Marking verification	Stencils match specification and PO requirements
MTC preparation	Compile all test results into certificate

Stage 4: Shipping Inspection

Activity	Details
Coating/protection	Verify end caps, coating, corrosion inhibitor applied
Bundle/crate inspection	Proper stacking, dunnage, and securing
Packing list verification	Quantity, sizes, heat numbers match documentation
Loading supervision	Prevent handling damage during truck/vessel loading

Pro Tip

Define your witness and hold points in the ITP (Inspection Test Plan) before the order is placed, not after. A “witness point” means you may attend but production continues regardless; a “hold point” means work stops until you release it. For critical materials, place hold points at heat treatment and final inspection.

Types of Pipe Inspections

Visual Inspection (VI)

HFW Pipes

Visual inspection is the first step in any inspection regime: quick, cost-effective, and often sufficient to identify obvious defects requiring further investigation.

Aspect	What’s Checked
Surface condition	Cracks, dents, scratches, laminations, tears
Weld quality	Uniformity, porosity, undercut, incomplete penetration
Coating/insulation	Integrity of protective coatings
Markings	Grade, size, manufacturer, heat number
Deformation	Bends, bulges, ovality

Tools: Flashlights, mirrors, magnifying glasses, borescopes/cameras for internal inspection.

Limitations: Surface defects only; VI cannot detect subsurface or internal flaws. ASME/API/ASTM define acceptable defect criteria.

Dimensional Inspection

Dimensional inspection verifies pipe geometry against ASME B36.10/B36.19 or API 5L tolerances.

Dimension	Why It Matters	Tolerance Source
OD	Fit with fittings, flanges, equipment	ASME B36.10/B36.19, API 5L
ID	Flow capacity and resistance	Calculated from OD and WT
Wall thickness	Pressure rating, mechanical strength	ASME B36.10/B36.19, API 5L
Length	Logistics, installation planning	Per order specification
Straightness	Alignment and connection integrity	~1 mm/m typical; ASTM A312M: 3.2 mm/3 m for SS
Ovality	Connection sealing, flow characteristics	Per applicable standard
End preparation	Weld bevel angle and root face dimensions	ASME B16.25 (37.5 deg standard bevel)
End squareness	Proper fit-up during field welding	Per applicable standard

Measurement tools: Calipers, micrometers, UT (wall thickness), laser scanning (roundness/straightness), tape measures (length), bevel gauges (end prep), pi tapes (circumferential OD).

Field Note

When checking wall thickness with UT, take multiple readings around the circumference and along the length, because seamless pipes can have eccentricity up to the tolerance limit. I’ve seen pipes pass OD and nominal WT checks but fail minimum WT at one spot. Always verify the thinnest point, not just the average.

Custom Tolerances

End-users may negotiate tighter tolerances than ASME/API standards. These special requirements override standard tolerances when accepted by the manufacturer.

Mechanical Testing

Mechanical testing permanently alters samples to determine material behavior under extreme conditions. Results are documented in Mill Test Certificates.

Test	What’s Measured	Application
Tensile	Yield strength, tensile strength, elongation, reduction of area	All pipes
Hardness (Rockwell, Brinell, Vickers)	Resistance to indentation	All pipes; max 22 HRC for sour service (NACE MR0175)
Impact (Charpy V-notch)	Toughness at specified temperature	Low-temp service, API 5L PSL2, critical applications
Bend	Ductility, weld quality	Welded pipes (transverse guided bend)
Flattening	Ductility, soundness of weld and base metal	Seamless and welded pipes
Drop weight tear (DWTT)	Fracture propagation resistance	Large-diameter pipeline (API 5L, high grades)

Tensile Testing

Tensile testing is the most fundamental mechanical test. A machined specimen is pulled to failure to measure:

• Yield strength (Rt0.5 or Fy): Stress at which permanent deformation begins
• Ultimate tensile strength (Rm or Fu): Maximum stress before necking
• Elongation (A%): Ductility measure, expressed as percentage of original length at fracture
• Reduction of area (Z%): Cross-section reduction at fracture point

Specimens are taken longitudinally (body) and transversely (weld) per the applicable standard. API 5L PSL2 requires both body and weld transverse tensile tests.

Impact Testing (Charpy V-Notch)

Charpy testing measures the energy a material absorbs before fracturing at a specific temperature. A notched specimen is struck by a pendulum, and the absorbed energy (Joules) is recorded.

Standard	Typical Test Temperature	Minimum Energy
API 5L PSL2	Per supplementary requirement or 0 deg C default	Grade-dependent (e.g., 27 J min for body, 20 J min for weld)
ASTM A333 Gr.6	-46 deg C	18 J average
ASTM A106	Not mandatory (unless specified)	Per PO requirement
NACE MR0175	Service temperature	Per applicable part of ISO 15156

Low-Temperature Service

For cryogenic and low-temperature applications, impact testing at the minimum design metal temperature (MDMT) is mandatory. Failing to specify the correct test temperature in the purchase order is one of the most common procurement errors, and one of the most expensive to correct after manufacturing.

Hardness Testing

Hardness is measured using Vickers (HV), Brinell (HBW), or Rockwell (HRC) methods. Hardness values verify that heat treatment achieved the correct microstructure and are critical for sour service compliance.

Material	Max Hardness	Standard
Carbon steel (sour service)	22 HRC / 248 HBW / 250 HV10	NACE MR0175 / ISO 15156
API 5L PSL2 (most grades)	250 HV10	API 5L Table 6
Duplex SS	36 HRC (typical)	ASTM A789/A790
Austenitic SS	22 HRC (sour) / no limit (sweet)	NACE MR0175 / ASTM A312

Chemical Analysis

Chemical analysis verifies that the steel composition matches the specified grade. Two levels of analysis exist:

Type	Sample Source	When
Heat (ladle) analysis	Molten steel during casting	Steel mill provides with MTC
Product analysis	Finished pipe specimen	Mandatory for API 5L PSL2; optional for PSL1

Key elements checked include carbon (C), manganese (Mn), phosphorus (P), sulfur (S), silicon (Si), chromium (Cr), nickel (Ni), molybdenum (Mo), vanadium (V), niobium (Nb), titanium (Ti), copper (Cu), nitrogen (N), and boron (B). The carbon equivalent (CE) is calculated to predict weldability.

CE Formula	Application	Max CE (typical)
CE(IIW) = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15	API 5L (C > 0.12%)	0.43 for X65 PSL2
CE(Pcm) = C + Si/30 + (Mn+Cu+Cr)/20 + Ni/60 + Mo/15 + V/10 + 5B	API 5L (C <= 0.12%)	0.25 for X65 PSL2

PMI Verification

For alloy and stainless steel pipes, Positive Material Identification (PMI) using handheld XRF or OES analyzers provides rapid field verification of alloy composition. PMI catches material mix-ups that documentation alone cannot prevent.

Metallurgical Inspection

Metallurgical inspection evaluates material properties and microstructure to verify compliance with specifications and detect defects that could cause in-service failures.

Micro-Metallurgical Tests

Test	Purpose	Application
Chemical composition (OES, XRF)	Verify alloy matches specified grade	All materials
Ferrite content	Balance of phases for strength/corrosion resistance	Duplex, austenitic SS
HIC testing	Resistance to hydrogen-induced cracking	Sour service (H2S environments)
SSC testing	Resistance to sulfide stress corrosion cracking	Sour service
Grain size	Affects strength, toughness, creep resistance	All steels
IGC testing (ASTM A262)	Resistance to intergranular corrosion	Stainless steels

Sour Service

Materials for H2S-containing environments (sour service) require HIC and SSC testing per NACE MR0175/ISO 15156. Failure to test can result in catastrophic in-service cracking.

Common Mistake

Ordering HIC/SSC tested material at the last minute when you discover sour service requirements late in the project. HIC testing takes time and not all mills have the capability; plan for this during material requisition, not after. Expediting sour-service materials is expensive and often unsuccessful.

Macro-Metallurgical Analysis

Macro examination uses low magnification (up to 100x) or naked eye to assess:

Aspect	What’s Examined
Weld quality	Discontinuities, misalignment, incomplete penetration
Heat treatment	Uniformity of grain structure across treated zones
Grain structure	Size and distribution (affects mechanical properties)
Defects	Cracks, porosity, slag inclusions, laminations
Corrosion	External/internal attack patterns (service pipes)

Techniques: Visual inspection, stereomicroscopy, chemical etching (reveals weld zones, HAZ, grain boundaries), photographic documentation.

Surface Condition and Defect Acceptance Criteria

Pipe surface quality is governed by the applicable product standard. Defects that exceed acceptance criteria must be repaired (by grinding) or the pipe must be rejected.

Defect Type	Acceptance Criteria (Typical)
Dents	Depth <= 6.35 mm and length <= 50% of OD (API 5L)
Scratches / gouges	Remaining WT above minimum; no sharp-bottomed defects
Laminations	Not acceptable at pipe ends (within 100 mm); body laminations per standard
Cracks	Not acceptable; any crack is cause for rejection
Hard spots	Not acceptable per API 5L (PSL2: max 35 HRC)
Weld defects	Per applicable NDT acceptance criteria (ASME, API)
Arc strikes	Not acceptable on pressure-containing surfaces; must be ground and NDE verified

Grinding Repairs

Defects may be removed by grinding provided the remaining wall thickness is within tolerance (typically 87.5% of nominal WT for API 5L). Ground areas must be smooth-contoured with no sharp transitions. After grinding, the area must be re-inspected by UT (wall thickness) and surface NDE (MT or PT).

Destructive Testing

Destructive testing permanently alters samples to determine material behavior under extreme conditions. Results are documented in Mill Test Certificates.

Test	What’s Measured	Application
Tensile	Yield strength, tensile strength, elongation, reduction of area	All pipes
Hardness (Rockwell, Brinell, Vickers)	Resistance to indentation	All pipes
Impact (Charpy, Izod)	Toughness at specified temperature	Low-temp service, critical applications
Bend	Ductility, weld quality	Welded pipes
Flattening	Ductility, soundness	Seamless and welded pipes
Burst	Ultimate pressure resistance	Design verification
Chemical analysis	Alloy composition	All pipes

Non-Destructive Testing (NDT)

NDT evaluates pipe properties without causing damage. See Non-Destructive Testing Types for detailed coverage of VI, LP, MP, UT, RT, and EC methods.

Hydrostatic Testing

Pressure testing pump for hydrostatic tests

The hydrostatic test fills pipes with water and pressurizes above design pressure to verify strength and leak-tightness. See Hydrostatic Test for complete procedures and standards.

Marking and Traceability

Api pipes multiple marking

Marking inspection verifies that pipe stencils/stamps match specifications and enable full traceability from heat of steel to installed location.

Required Marking Elements

Marking Element	Purpose	Example
Manufacturer	Source identification	Mill name or logo
Material grade	ASTM/API specification compliance	API 5L Gr. X65 PSL2
Size	NPS x Schedule or OD x WT	12” x SCH 40 or 323.8 x 9.53
Heat number	Traceability to MTC and batch	A7823
Standard	Applicable specification	API 5L, ASTM A106, ASTM A312
Pipe type	Manufacturing process	S (seamless), E (ERW), L (LSAW)
Test pressure	Hydrostatic test pressure applied	250 bar
TPI stamp	Third-party inspector verification	Agency logo/stamp

Marking Methods

Method	Application	Notes
Stenciling (paint)	Standard for most pipe	White or yellow paint; must remain legible
Die stamping	Pipe ends, thick wall pipe	Low-stress stamps only; not permitted on thin wall (< 4 mm)
Color coding	Grade identification bands	Supplementary to stenciling
Labels/tags	Bundled small-bore pipe	Must be securely attached

Verification process: Visual inspection of markings, comparison against PO/MR specs, cross-reference with MTC, documentation of findings, and rectification of discrepancies.

Die Stamping Restrictions

Die stamping is not permitted on thin-wall pipes (typically < 4 mm WT) or on certain alloy grades where stress concentration from stamps could initiate cracking. Some client specifications prohibit die stamping entirely for sour service materials. Always check the purchase order requirements.

Third-Party Inspection (TPI) and the Inspection Test Plan (ITP)

The Role of the Third-Party Inspector

The third-party inspector (TPI) acts as the buyer’s representative at the manufacturer’s facility. The TPI does not perform tests; the manufacturer’s lab performs testing while the TPI witnesses the process, verifies procedures, reviews results, and signs off on compliance.

Key TPI responsibilities:

• Review and approve the Inspection Test Plan (ITP) before production
• Witness tests at agreed hold and witness points
• Verify calibration of testing equipment
• Review MTCs and test reports for compliance
• Issue inspection release notes (IRN) for shipment
• Report non-conformances and verify corrective actions

Inspection Test Plan (ITP) Structure

The ITP is the master document governing all inspection activities. It is prepared by the manufacturer, reviewed by the TPI agency, and approved by the buyer before production begins.

ITP Column	Description
Activity	Description of the inspection/test step
Reference standard	Applicable code or specification
Acceptance criteria	Pass/fail limits
Manufacturer	QC activity level (Perform, Record, Certify)
TPI	Hold (H), Witness (W), Review (R), Monitor (M)
Client	Hold (H), Witness (W), Review (R), Monitor (M)
Frequency	100%, per heat, per lot, per shift

Hold, Witness, Review, and Monitor Points

Code	Meaning	Production Impact
H (Hold)	Inspector must be present; work stops until released	Production halted until sign-off
W (Witness)	Inspector invited; production continues if absent after notice	24-48 hour notification typical
R (Review)	Inspector reviews documentation after the fact	No production delay
M (Monitor)	Inspector monitors activity periodically	No production delay

ITP Tip

Place hold points only on truly critical activities (final inspection, hydrostatic test, MTC review). Excessive hold points slow production and increase TPI costs without proportional quality benefit. Use witness points for important but non-critical steps like heat treatment and in-process dimensional checks.

Comparison of Tests by Pipe Specification

Test	API 5L PSL1	API 5L PSL2	ASTM A106	ASTM A312 (SS)	ASTM A333 (Low-Temp)
Chemical (heat)	Required	Required	Required	Required	Required
Chemical (product)	Optional	Required	Not required	Not required	Not required
Tensile	Required	Required	Required	Required	Required
Charpy impact	Not required	Required	Not required (unless specified)	Not required (unless specified)	Required
Hardness	Not required	Required	Not required	Not required	Not required (unless sour)
Flattening	Required (welded)	Required (welded)	Required	Required (welded)	Required
Bend	Alternative to flattening	Alternative to flattening	Required	Not required	Required
Hydrostatic	Required	Required	Required	Required (or eddy current)	Required
NDT (full body)	Not required	Required (UT or EMI)	Not required (unless specified)	Not required (unless specified)	Not required
NDT (weld seam)	Required (welded)	Required (welded)	N/A (seamless)	Required (welded)	N/A (seamless)
DWTT	Not required	Per supplementary req.	N/A	N/A	N/A

PSL1 vs PSL2

The difference between API 5L PSL1 and PSL2 is significant: PSL2 mandates product analysis, Charpy impact testing, hardness limits, full-body NDT, and tighter chemical composition limits. For oil and gas pipeline service, PSL2 is the standard requirement. PSL1 is used for lower-criticality applications such as water lines and low-pressure utilities.

Standards Reference

Standard	Scope
API 5L	Line pipe for oil and gas pipelines; covers grades, testing, tolerances
ASTM A530	General requirements for carbon and alloy steel pipe, including supplementary requirements common to all ASTM pipe specifications
ASME B36.10	Welded and seamless wrought steel pipe: standard dimensions and wall thicknesses
ASME B36.19	Stainless steel pipe: dimensions and wall thicknesses
ASME B16.25	Buttwelding ends; bevel dimensions for pipe and fittings
EN 10204	Metallic products: types of inspection documents (MTC 2.1, 2.2, 3.1, 3.2)
ASME B31.3	Process piping: inspection and examination requirements for installed piping
ASTM A370	Standard test methods for mechanical testing of steel products
ASTM E23	Standard test methods for notched bar impact testing (Charpy)
ISO 6892-1	Metallic materials: tensile testing at ambient temperature
NACE MR0175 / ISO 15156	Materials for use in H2S-containing environments (sour service)

Special End-User Requirements

End-users may specify requirements beyond standard ASME/API specifications. When present in a purchase order, these require tailored inspection procedures.

Requirement	Purpose
Carbon equivalent (CE) limit	Confirms weldability without preheat or PWHT
Low-temperature tensile	Verifies strength at service temperature
Transverse tensile	Confirms weld zone properties
Low-temperature impact	Charpy testing at design minimum temperature
HIC/SSC resistance	Sour service qualification (NACE MR0175)
Enhanced corrosion resistance	Higher Cr/Mo/Ni than standard grades
Ultra-low sulfur	Improved toughness and weldability
Fine grain practice	Microstructure control for toughness

Frequently Asked Questions

What is the difference between mill inspection and third-party inspection?

Mill inspection is performed by the manufacturer using in-house QC staff as part of standard production. Third-party inspection (TPI) is conducted by an independent agency (such as Lloyd's, SGS, DNV, or Bureau Veritas) hired by the buyer to witness and verify testing at the mill. TPI provides impartial confirmation that pipes meet purchase order specifications and results in an EN 10204 Type 3.2 certificate, the highest assurance level.

What tests are required for API 5L PSL2 pipe?

API 5L PSL2 requires: chemical analysis (product analysis mandatory), tensile testing (yield, UTS, elongation), Charpy V-notch impact testing at specified temperature, hardness testing (max 250 HV10 for most grades), hydrostatic test, full-body NDT (UT or EMI), dimensional inspection, and visual inspection. PSL2 has stricter limits on chemical composition, mandatory impact toughness, and carbon equivalent restrictions compared to PSL1.

What is an Inspection and Test Plan (ITP)?

An Inspection and Test Plan (ITP) is a document that lists every inspection and test activity for a manufacturing order. It specifies what is tested, the applicable standard, acceptance criteria, sampling frequency, and whether the activity is a Hold point (H), Witness point (W), Review point (R), or Monitor point (M). The ITP is agreed between buyer, manufacturer, and third-party inspector before production begins.

What are hold points and witness points in pipe inspection?

A Hold point (H) means production stops until the inspector is present, inspects, and formally releases the hold. Work cannot proceed without sign-off. A Witness point (W) means the inspector is invited to attend but production may continue if the inspector does not show up after reasonable notice. Hold points are used for critical activities like final inspection and hydrostatic testing; witness points for activities like heat treatment and in-process dimensional checks.

What pipe marking information is required by API 5L?

API 5L requires marking to include: manufacturer name or logo, specification (API 5L), PSL level (PSL1 or PSL2), grade (e.g. X65), pipe body type (S for seamless, E for ERW, L for LSAW), size (OD x WT), heat or lot number, and length. Additional markings may include test pressure, supplementary requirements, and third-party inspection stamps. Marking may be stenciled (paint) or die-stamped depending on wall thickness and client specification.