1
General
One of the duties of the Visual/Welding Inspector is to carry out materials
inspection. There are a number of situations where the inspector will be
required to carry out materials inspection:
At the plate or pipe mill,
Of material during fabrication or construction
Of material after installation, usually during a planned maintenance
programme, outage or shutdown.
A wide range of materials are available, that can be used in fabrication and
welding. These include, but are not limited to:
Steels
Stainless steels
Aluminium and its alloys
Nickel and its alloys
Copper and its alloys
Titanium and its alloys
Cast iron
These materials are all widely used in fabrication, welding and construction
to meet the requirements of a diverse range of applications and industry
sectors.
There are three essential aspects to materials inspection that the Inspector
should consider:
Material type and weldability
Material traceability
Material condition and dimensions.
Material Types and Weldability
A Welding Inspector must be able to understand and interpret the material
designation in order to check compliance with relevant normative
documents. For example materials standards such as BS EN, API, ASTM,
the welding procedure specification (WPS), the purchase order, fabrication
drawings, the quality plan/the contract specification and client requirements.
A commonly used material standard for steel designation is BS EN 10025
Hot rolled products of non-alloy structural steels.
Rev 1 January 2010
Materials Inspection
Copyright TWI Ltd 2010
A typical steel designation to this standard, S355J2G3, would be classified
as follows:
S
355
J2
G3
Structural steel
Minimum yield strength: N/mm at t 16mm
Longitudinal Charpy, 27Joules 6-20C
Normalised or normalised rolled
In terms of material type and weldability, commonly used materials and
most alloys of these materials can be fusion welded using various welding
processes, in a wide range of thickness, and, where applicable, diameters.
Reference to other standards such as ISO 15608 Welding - Guidelines for a
metallic material grouping system, steel producers and welding consumable
data books can also provide the Inspector with guidance on the suitability of
a material and consumable type for a given application.
Alloying Elements and Their Effects
Iron
Fe
Carbon
C
For strength
Manganese
Mn For toughness
Silicon
Si
< 0.3% deoxidiser
Aluminium
Al
Grain refiner, <0.008% deoxidiser + toughness
Chromium
Cr
Corrosion resistance
Molybdenum
Mo 1% is for creep resistance
Vanadium
V
Strength
Nickel
Ni
Low temperature applications
Copper
Cu
Used for weathering steels (Corten)
Sulphur
S
Residual element (can cause hot shortness)
Phosphorus
P
Residual element
Titanium
Ti
Grain refiner, used as a micro alloying element (S&T)
Niobium
Nb
Grain refiner, used as a micro alloying element (S&T)
(S&T) = strength and toughness
Rev 1 January 2010
Materials Inspection
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Material Traceability
Traceability is defined as the ability to trace the history, application or
location of that which is under consideration. In the case of a welded
product, traceability may require the Inspector to consider:
Origin of the materials both parent and filler material
Processing history for example before or after PWHT
Location of the product this would usually refer to a specific part or subassembly
To trace the history of the material, reference to the inspection documents
must be made. BS EN 10204 Metallic products Types of inspection
documents is the standard, which provides guidance on these types of
document. Under BS EN 10204 inspection documents fall into two types:
a) Non-specific inspection
Inspection carried out by the manufacturer in accordance with his own
procedures to assess whether products defined by the same product
specification and made by the same manufacturing process, are in
compliance with the requirements of the order or not.
Type 2.1 are documents in which the manufacturer declares that the
products supplied are in compliance with the requirements of the order
without inclusion of test results.
Type 2.2 are documents in which the manufacturer declares that the
products supplied are in compliance with the requirements of the order and
in which test results based on non-specific inspection are supplied.
b) Specific inspection
Inspection carried out, before delivery, according to the product
specification, on the products to be supplied or on test units of which the
products supplied are part, in order to verify that these products are in
compliance with the requirements of the order.
Type 3.1 are documents in which the manufacturer declares that the
products supplied are in compliance with the requirements of the order and
in which test results are supplied.
Type 3.2 are documents prepared by both the manufacturers authorised
inspection representative independent of the manufacturing department,
and either the purchasers authorised representative or the inspector
designated by the official regulations, and in which they declare that the
products supplied are in compliance with the requirements of the order
and in which test results are supplied.
Rev 1 January 2010
Materials Inspection
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Application or location of a particular material can be carried out through a
review of the welding procedure specification (WPS), the fabrication
drawings, the quality plan or by physical inspection of the material at the
point of use.
In certain circumstances the Inspector may have to witness the transfer of
cast numbers from the original plate to pieces to be used in production.
On pipeline work it is a requirement that the inspector records all the
relevant information for each piece of line pipe. On large diameter pipes this
information is usually stencilled on the inside of the pipe. On smaller
diameter pipes the information may be stencilled along the outside of the
pipe.
Rev 1 January 2010
Materials Inspection
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BS EN 10204: Metallic materials
Types of inspection documents summary
a) NONSPECIFIC INSPECTION *
Inspection document type 2.1
Declaration of compliance with the order
Statement of compliance with the order.
Validated by the manufacturer.
a)
Inspection document type 2.2
Test report
Statement of compliance with the order,
with indication of results of non-specific
inspection.
Validated by the manufacturer
Non-specific inspection may be replaced by specific inspection if specified in the
material standard or the order.
b) SPECIFIC INSPECTION *
Inspection certificate type 3.1
Inspection certificate type 3.2
Statement of compliance with the
order, with indication of results of
specific inspection
Validated by the manufacturers
authorised inspection representative
independent of the manufacturing
department.
Statement of compliance with the order,
with indication of results of specific
inspection.
Validated by the manufacturers authorised
inspection representative independent of
the manufacturing department and either
the purchasers authorised inspection
representative or the inspector designated
by the official regulations.
b)
Quality management system of the material manufacturer certified by a
competent body established within the community and having undergone a
specific assessment for materials
Rev 1 January 2010
Materials Inspection
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Material Condition and Dimensions
The condition of the material could have an adverse effect on the service life
of the component; it is therefore an important inspection point. The points for
inspection must include:
General inspection, visible imperfections, dimensions and surface condition.
General inspection
This type of inspection takes account of storage conditions, methods of
handling, the number of plates or pipes and distortion tolerances.
Visible imperfections
Typical visible imperfections are usually attributable to the manufacturing
process and would include cold laps, which break the surface or laminations
if they appear at the edge of the plate. For laminations, which may be
present in the body of the material, ultrasonic testing using a compression
probe may be required.
Cold lap
Plate lamination
Dimensions
For plates this would include length, width and thickness.
For pipes, this would not only include length and wall thickness, but also
inspection of diameter and ovality. At this stage of the inspection the
material cast or heat number may also be recorded for validation against the
material certificate.
Surface condition
The surface condition of the material is important, it must not show
excessive mill scale and rust, must not be badly pitted, or have
unacceptable mechanical damage.
Rev 1 January 2010
Materials Inspection
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There are four grades of rusting which the inspector may have to consider:
Rust Grade A Steel surface largely covered with adherent mill scale with
little or no rust
Rust Grade B Steel surface, which has begun to rust, and from which mill
scale has begun to flake.
Rust Grade C Steel surface on which the mill scale has rusted away or from
which it can be scraped. Slight pitting visible under normal
vision.
Rust Grade D Steel surface on which mill scale has rusted away. General
pitting visible under normal vision.
Rev 1 January 2010
Materials Inspection
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Summary
Material inspection is an important part of the Inspectors duties and an
understanding of the documentation involved is the key to success.
Material inspection must be approached in a logical and precise manner if
material verification and traceability are to be achieved. This can be difficult
if the material is not readily accessible, access may have to be provided,
safety precautions observed and authorisation obtained before material
inspection can be carried out. Reference to the quality plan should identify
the level of inspection required and the point at which inspection takes
place. Reference to a fabrication drawing should provide information on the
type and location of the material.
If material type cannot be determined from the inspection documents
available, or if the inspection document is missing, other methods of
identifying the material may need to be used.
These methods may include but are not limited to: spark test, spectroscopic
analysis, chemical analysis, scleroscope hardness test etc. These types of
tests are normally conducted by an approved test house, but sometimes on
site, and the Inspector may be required to witness these tests in order to
verify compliance with the purchase order or appropriate standard(s).
*EN ISO 9000 Quality management systems Fundamentals and vocabulary
Rev 1 January 2010
Materials Inspection
Copyright TWI Ltd 2010
