The project requires Killed Steel treatment on Pipe, Plate MTC.

Fully killed is the term to describe de-oxidized steel. After the steel is made, it is then poured into the continuous caster to make a long slab of steel. Think of a sausage maker – molten steel goes in at the top and rectangular slab comes out the bottom. This is called casting. During casting, small carbon monoxide bubbles can form between the steel grains if the oxygen is not removed. If you’ve ever painted a door and seen bubbles in the paint once you apply it you’ll recognize the similarities. To stop these bubbles appearing you paint slower, but … Continue reading The project requires Killed Steel treatment on Pipe, Plate MTC.

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

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

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