Duplex piping and seawater
22%Cr duplex stainless steels are not suitable for elevated temperature unprotected seawater applications because they suffer from the crevice and pitting corrosion at even moderate temperatures. Super duplex stainless steels present superior corrosion resistance to duplex stainless steels in seawater applications, and provided weld quality is maintained, pitting should not occur in seawater up to about 40°C. The operational limit stipulated in the Norsok Standard (M-001, Rev.2, November 1997) is one of the most conservative for unprotected super duplex service and is more restrictive than most operators’ own requirements. The maximum operating temperature is set at 15°C and the maximum … Continue reading Duplex piping and seawater
Make temporary flange for Hydro-test or Blind as ASTM A 694.
A specification for steel forgings such as ASTM A694 covers a wide range of strength grades from F42, with a minimum specified yield strength of 290 MPa, to F70, with a minimum specified yield strength of 485 MPa. The compositional limits are given in ASTM A694 (product analysis) are ≤0.3% carbon 0.13-0.37% silicon and ≤1.50% manganese. Additionally, the steel may contain micro-alloying elements, i.e. it may be a micro-alloyed (or high strength low alloy) steel; alternatively, Cr-Ni-Mo-V low alloy steel, ASTM A707 Grade L5, may be used. Particularly for small valves and thin section sizes, it may be expected that … Continue reading Make temporary flange for Hydro-test or Blind as ASTM A 694.
Stainless steel and PWHT – Post weld heat treatment
Most austenitic stainless steel weldments do not require post-weld heat treatment. For those that do, the heat treatment temperature should reflect the particular concern that is being addressed. The necessity for any type of heat treatment of austenitic chromium-nickel steel weldments depends largely on the service conditions encountered. For some applications, heat treatment is used to impart the greatest degree of corrosion resistance possible, eg by solution treating to homogenize the composition or stabilizing, to minimize the risk of sensitization during subsequent elevated temperature exposure. In other applications, heat treatment may be used for stress relieving. This may give more … Continue reading Stainless steel and PWHT – Post weld heat treatment
Blue colour when welding Stainless steel
Oxidation of the root bead and adjacent HAZ during welding of stainless steels is commonly called heat-tint. A chromium-rich scale is formed, which is typically not very protective, and the stainless steel surface becomes chromium-depleted: these effects may impair the corrosion resistance of stainless steel welds. Tests performed in various corrosive environments have shown that susceptibility to pitting and crevice corrosion is greater when the surface is heat-tinted, and the colour of the heat-tint is an indicator of the degree of susceptibility to corrosion. For example, purple-blue oxides are generally the most susceptible to corrosion attack. The critical pitting temperature, … Continue reading Blue colour when welding Stainless steel
Hardness test for Duplex, Super duplex
It is sometimes necessary to meet hardness limits for duplex and super duplex stainless steels, and it is convenient to be able to convert between the Rockwell C (HRC) and Vickers (HV) hardness scales. A conversion exists for carbon steel in ASTM E140 but there is no standard conversion for duplex and super duplex grades and the carbon steel conversion has been shown to be inappropriate for these high alloy steels. A correlation between the two hardness scales for duplex and super duplex grades has been developed at TWI from a compilation of data supplied by various organizations. There was … Continue reading Hardness test for Duplex, Super duplex
Stainless steel become Magnetic (304, 316, 321, 347 series)
Austenitic stainless steels with around 10-12% nickel (e.g. grades 304, 316, 321 and 347) are predominantly non-magnetic due to the face centered cubic (fcc) crystal structure of the austenite phase, which imparts so-called ‘paramagnetic’ (i.e. non-magnetic) behavior. Although a number of second phases, e.g. inclusions or ferrite stringers, may exist in wrought austenitic stainless steel products, the structure is almost exclusively made up of the austenite phase and hence they are essentially non-magnetic. However, weld metals made with filler metal compositions matching the 300 series austenitic steels (e.g. 308, 309, 316 and 347 types) are designed to have a small … Continue reading Stainless steel become Magnetic (304, 316, 321, 347 series)
BS 7448 vs ASTM E1820 CTOD fracture test
Both BSI and ASTM have published standards for ‘combined’ fracture toughness test methods, allowing measurement of critical values of stress intensity (K), J and CTOD. The standards cover both ‘single-point’ values of fracture toughness and tearing resistance curves. BS 7448: Fracture mechanics toughness tests, is published in four parts: Part 1: ‘Method for determination of KIc, critical CTOD and critical J values of metallic materials’. Part 2: ‘Method for determination of KIc, critical CTOD and critical J values of welds in metallic materials’ – superseded by BS EN ISO 15653. Part 3: ‘Method for determination of fracture toughness of metallic materials … Continue reading BS 7448 vs ASTM E1820 CTOD fracture test
Heat input vs Arc energy in welding
In arc welding processes, heat input (HI) and arc energy (AE) are both measures of how much energy has been supplied to the workpiece to form a weld. They are both measured in units of energy per unit length. In Europe, this tends to be in kJ/mm, whereas in America it tends to be kJ/in. Arc energy Arc energy is the energy supplied by the welding arc to the workpiece before the efficiency of the process is considered. It is calculated by the following equation: where: V is the voltage used, in volts I is the current used, in amperes … Continue reading Heat input vs Arc energy in welding
EN 287 vs EN ISO 9606
The current status of BS 287-1 and ISO 9606-1 are explained in What is the current status of EN 287-1 and BS EN ISO 9606-1 for welder qualification? Due to this complex situation, it is possible that fabricators will be moving from EN 287 Part 1 to ISO 9606 Part 1, or using the two in parallel, depending on the type of product being manufactured. This means it is necessary to fully understand each standard and the variations between the two. This Job article will provide some insight into the differences between the standards. There are some differences between the two … Continue reading EN 287 vs EN ISO 9606
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