Plastic (PPE, HDPE) welding standards
There are tests for plastic welds, below is a selection of relevant tests. EN 12814-1:1999: ‘Testing of welded joints of thermoplastics semi-finished products – Part 1: Bend test’ EN 12814-2:2000: ‘Testing of welded joints of thermoplastics semi-finished products – Part 2: Tensile test’ EN 12814-3:2000: ‘Testing of welded joints of thermoplastics semi-finished products – Part 3: Tensile creep test’ EN 12814-4:2001: ‘Testing of welded joints of thermoplastics semi-finished products – Part 4: Peel test’ EN 12814-5:2000: ‘Testing of welded joints of thermoplastics semi-finished products – Part 5: Macroscopic examination’ EN 12814-6:2000: ‘Testing of welded joints of thermoplastics semi-finished products – … Continue reading Plastic (PPE, HDPE) welding standards
Weld proximity, between two seams standard
Weld proximity is covered by a number of international standards. Extracts from these standards are shown below and summarised in the following table: Standard Applies to Minimum distance between weld toes Notes BS 2633:1987 Ferritic steel pipework 4t t= nominal thickness of the pipe See below for notes on attachment welds. BS 4515:2009 C-Mn pipelines 4t t= pipe thickness BS 2971:1991 Carbon steel pipework Agreed by parties – PD 5500:2012 Pressure vessels 4e or 100mm whichever is greater e= design thickness Refers to the staggering of longitudinal welds ASME B&PV Boilers and pressure vessels Not specified – BS 2633 ‘Class I … Continue reading Weld proximity, between two seams standard
Time delay before applying NDT in welding
The following standards stipulate delay time before inspection: BS EN 1011-2:2001 Welding – Recommendations for welding of metallic materials – Part 2: Arc welding of ferritic steels (with amendment AMD 14926 Feb 2004) Paragraph 18 states: ‘Due to the risk of delayed cracking, a period of at least 16 hours is generally required before the final inspection is made of as-welded fabrications. The minimum time may be reduced for thin materials below 500N/mm2 yield strength or increased for materials of a thickness greater than 50mm or of yield strength over 500 N/mm2 … Welds that have been heat-treated to reduce hydrogen content … Continue reading Time delay before applying NDT in welding
Austenite Stainless Steel at high-temperature (embrittlement)
The phenomenon of embrittlement in austenitic stainless steel welds exposed to high temperature is accelerated by the presence of delta ferrite. To avoid solidification cracking in austenitic stainless steel welds, the composition of the filler material must be optimized to ensure that there is some delta ferrite present in the weld metal (typically >3%). However, delta ferrite transforms into intermetallic phases, notably the sigma phase, faster than austenite either during high-temperature service or during post-weld heat treatment (PWHT). Sigma phase is an intermetallic with an approximate chemical formula FeCr and, as with most intermetallics, it is very brittle and hence … Continue reading Austenite Stainless Steel at high-temperature (embrittlement)
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
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