Stainless steel 347H and PWHT
”In the welded condition many stainless steels are susceptible to rapid intergranular corrosion or stress corrosion cracking. This is because the heat from welding sensitizes the base metal heat affected zone (HAZ) and the weld. Sensitization is the condition where chromium carbide precipitation at the grain boundaries (from a heating process, e.g., welding, hot forming, hot bending, service temperature, etc.) reduces the amount of chromium in solution in the stainless steel. The temperature range for sensitization to occur for austenitic stainless steels is approximately 700 °F to 1500 °F. Since the carbides precipitate in the HAZ or weld deposit at … Continue reading Stainless steel 347H and PWHT
Hardness requirement in Sour service for (Duplex) Stainless steel
Section 7, Table 7-11 of DNV Standard OS-F101 October 2010 – Submarine pipeline systems – provides HV10 limits for weldments in 22Cr and 25Cr duplex stainless steels for line pipes. For 22Cr and 25Cr duplex, the hardness in the weld and HAZ shall not exceed 350HV10 and the base material shall not exceed 290HV10 for 22Cr, and 330HV10 for 25Cr. Section 6, paragraph B201 of DNV Standard OS-F101 October 2010 states that materials shall be selected for compliance with ISO 15156. NORSOK Standard M-630 Rev.4 January 2004 – Material data sheets for piping – included material requirements in the form … Continue reading Hardness requirement in Sour service for (Duplex) Stainless steel
What is Engineering Critical Assessment (ECA)?
What is an ECA? Most welding fabrication codes specify maximum tolerable flaw sizes and minimum tolerable Charpy energy, based on good workmanship, i.e. what can reasonably be expected within normal working practices. These requirements tend to be somewhat arbitrary, and failure to achieve them does not necessarily mean that the structure is at risk of failure. An Engineering Critical Assessment (ECA) is an analysis, based on fracture mechanics principles, of whether or not a given flaw is safe from brittle fracture, fatigue, creep or plastic collapse under specified loading conditions. An ECA can, therefore, be used: During design, to assist … Continue reading What is Engineering Critical Assessment (ECA)?
Change electrode manufacture, vendor in welding WPS.
If welding is to be performed according to a welding procedure specification, it is possible that changing the electrode manufacturer will invalidate the approval of the procedure to the code/standard on which it was based. The manufacturer or ‘trade name’ of the electrode can be classed as an essential variable in a given weld procedure. The extent to which re-qualification is necessary will vary from code to code. For example, in EN ISO 15614-1[1] and in the UK standard BS 4515:2004[2], approval is only restricted to the specific make of electrode if impact testing is required as part of the procedure qualification. On the … Continue reading Change electrode manufacture, vendor in welding WPS.
Portable hardness test tools
There are several portable hardness testers available, with some more appropriate to certain situations than others. The particular hardness tester for the job would depend on what you needed to find out and why. For example, a Barcol hardness tester for use on Al alloys is generally used as a comparative tool; to indicate a loss in strength in damaged regions of a structure compared with undamaged regions or virgin material. Barcol hardness testers are very portable and are good for this type of comparative work, but the conversion to more widely recognized hardness scales is only approximate. Telebrineller testers. … Continue reading Portable hardness test tools
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)
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