Test certificates according to PN-EN 10204

NORMALIZING plastic processing is a method of plastic forming with the final forming stage in a specified temperature range that corresponds with the normalization temperature. The structure of the material formed in this way is equivalent to NORMALIZATION. The condition is denoted with the letter “N”.

THERMOMECHANICAL plastic processing is a method of plastic forming with the final forming stage in a specified temperature range that makes it possible to obtain the condition of the material with specific properties which cannot be obtained through thermal processing. Subsequent heating of the material to the temperature higher than 580 ° C may result in a degradation of the properties. The condition is denoted with the letter “M”. 

Basic types of Thermal Processing:

NORMALIZING ANNEALING

It is a type of thermal processing which involves heating the steel to the temperature that is slightly above AC3 or Acm , maintaining that temperature and then cooling the steel to the ambient temperature. The purpose of this type of processing is refining the structure and making it homogeneous which improves the mechanical properties of the steel. The condition is denoted with the letter “N” (NBK, NZF)
ATTENTION! Normalization can decrease the banding of the structure, especially if no visible inclusions are present in it.

RECRYSTALLIZATION ANNEALING

It is a type of thermal processing which involves heating the steel after it is cold formed to the recrystallization temperature. The temperature is dependent on the carbon content and the degree of compression and varies from 440 to 550 ° C, maintaining the temperature and the cooling the steel to the ambient temperature. The purpose of this type of processing is restoring the original structure of the material before its cold forming. The plasticity properties of the material are improved and the mechanical properties are degraded. The condition is denoted with the letter “A”; (GBK,GZF)
ATTENTION! Recrystallization is used mainly in order to enable further cold plastic processing.

STRESS RELIEF ANNEALING

It is a type of thermal processing which involves heating the steel to the temperature that is lower than the recrystallization temperature, maintaining the temperature for a short period of time and then cooling the steel to the ambient temperature. The purpose of this type of processing is removing the stress resulting from cold forming and maintaining almost the same properties of the material. The condition is denoted with the letters “SR”
ATTENTION! This type of processing is used in the case of tubes intended e.g. for the manufacturing of hydraulic cylinders.

HARDENING

It is a type of thermal processing which involves heating the steel to the austenitization temperature, above Ac3 or Ac1, maintaining the temperature and then cooling the steel quickly to the ambient temperature. The purpose of this type of processing is obtaining the martensitic structure (the mechanical properties are considerably improved and the plasticity properties are degraded).

TEMPERING

It is a type of thermal processing which involves heating the steel to the temperature that is slightly below AC1, maintaining the temperature and then cooling the steel to the ambient temperature. In practice, three types of tempering are applied:

• low – in the range between 150 and 250 ° C in order to remove quenching stresses without compromising the high hardness and abrasion resistance properties
• medium – in the range between 250 and 500 °  C in order to increase the elasticity at the cost of considerable hardness decrease  
• high – in the range between 500 ° C to Ac1. It is applied in order to achieve the highest possible resilience properties of the steel.

ATTENTION! The Re/Rm ratio which is the value used to express the minimum material characteristics after heat treatment is also increased.

HEAT TREATMENT

Heat treatment is a type of thermal processing which involves:

• quenching
• tempering in high temperatures

This type of treatment is used in order to improve practically all the properties of steel, especially RESILIENCE.
This condition is denoted with the letter “Q”

If resilience testing is required in the Standard, the test is usually performed as Charpy V-notch test. The test and taking test samples should be performed in accordance with EN 10045-1.

As a rule, transverse sampling should be performed for the purposes of the test. The minimum diameter of the pipe from which a transverse sample can be taken is:

Dmin=(T-5) + 756,25/(T-5)               where : T stands for the wall thickness of the pipe

If it is not possible to take a transverse sample, a longitudinal sample of the maximum width possible should be taken – between 10 and 5 mm.
For pipes in the case of which it is not possible to take a 5 x 10 mm sample, resilience testing is usually not performed.

NOTE Samples taken for the purpose of resilience testing should not be flattened before the test is performed
 
If resilience testing is performed on samples with the width of less than 10 mm, the following calculation formula should be used in order to compare the fracture work value with the table

KV=(8 x 10 x KVp)/Sp               where :      KVp – the measured work value needed to fracture the sample

Sp – the cross section area of the sample at the notch

or
 
KV=(10 x KVp)/W                 w – sample width

Tightness is basically tested in two ways: by means of a water pressure test or by means of equivalent eddy current testing in accordance with EN 10246-1

It is usually assumed that if no specific method of testing the tightness of the pipes is selected by the Client, the manufacturer can perform the equivalent eddy current testing instead of the water pressure method if the nominal pressure is <= 7Mpa and the pipe diameter is lower than 500 mm

In order to calculate the pressure value for which the pipes should be tested, the following formula is used:

P=(20 x S x T)/D

where:

p – hydrostatic pressure of the water  /bar/
D – outside diameter of the pipe
S – stress corresponding with a percentage of the minimum Re value /N/mm2/

Depending on the type of pipes tested, that is the Standard according to which they are to be manufactured, the appropriate S values are applied.

S values are always provided in the appropriate Standard.

The time period in which the water pressure test is conducted is as follows:

• 5 seconds for pipes with the outside diameter <= 457 mm
• 10 seconds for pipes with the outside diameter of more than 457 mm

In order to determine the weldability of a material, the so- called CEV factor is determined

Exceeding its value for a given steel grade can result in stresses during the welding and cooling process that lead to microcracks in the cross section of the weld and of the parent material.

The full formula used to calculate the CEV factor is as follows:

Cev=C+Mn/6 + (Cr+Mo+V)/5 + (Cu+Ni)/15
where :C,Mn,Cr,Mo,V,Cu,Ni % content of elements in the steel

Calculating this factor is particularly important for structural steels and for steels used to construct pipelines that transport combustible fluids.

The galvanization properties are basically determined by the amount of silicon (Si) in the chemical composition.

Two silicon percentage ranges for which the silicon coating is correct are distinguished:

• below 0,03 % Si
• from 0,15 to 0,20 % Si

According to some publications, the maximum Si amount in the second case can amount even to  0,25 %
Also, the following dependency that can be used to determine whether the silicon coating is correct is provided in the literature:

•  C + Si <= 0,50 %

The ovalness of the circular section expressed in % is calculated according to the formula:

O=100 X (Dmax – Dmin)/D
Where:     Dmax – maximum measured diameter
Dmin – minimum measured diameter
D – nominal diameter

The concentricity tolerance of the circular opening expressed in % is calculated according to the formula:

100 x [(Tmax - Tmin)/(Tmax + Tmin)] = WS
Where :     Tmax – maximum measured wall thickness of the pipe
Tmin – minimum measured wall thickness of the pipe
WS – Concentricity factor.

The orthogonal tolerance for the square section and for the rectangular section is calculated according to the formula:

90 – θ <= 1 degree

Where θ – the angle between the horizontal plane and the side of the profile

Fine grain steel is steel in which the austenite grain size after austenitization conducted in accordance with PN corresponds with master no 5 or higher (higher master number = smaller grain size).
PN-84/H-04507/01

Example:

Grain size number G: 5
Average size of the cross section area a [mm²]: 0,0039
Number of grains per 1 mm²: 256
Average number of grains in 1 mm³ [N]: 4096
Average grain diameter d [mm]: 0,062

Fine grain steels display much higher resilience values and yield limit values in comparison to coarse grained steels.

The standards applied in ultrasonic testing are divided into 6 acceptance classes (U1 ….U6) depending on the depth of the test notch constituting % of the nominal wall thickness (3, 5, 10, 12,5, 15, 20%). The most rigorous requirements are defined for Class U1.

Apart from the acceptance class, also 4 sub-classes are distinguished (A, B, C, D) depending on the minimum notch depth ( 0,1 ; 0,2 ; 0,3 ; 0,4 mm).

The most frequently applied acceptance classes for seamless pipes are: U2C and U2B

Eddy current test standards in accordance with EN10246-3

A few test methods are used in eddy current testing:

• The encircling coil technique
• The contactor-segment coil technique
• The eddy pipe / contactor coil technique

 
The most frequently used method is the encircling coil technique. Four Acceptance Levels are distinguished here (E1H – E4H) depending on the pipe diameter and the diameter of the hole drilled.

While testing the pipes with the use of this method, it is important to remember that the maximum sensitivity can be observed on the surface of the pipe and it decreases proportionally to the increase of the wall thickness. The possibility to penetrate the pipe wall depends on the wall thickness and on the frequency. The lower the frequency, the deeper the penetration into the pipe wall.