99 MMaatteerriiaallss

LID 1757.00 edition: 13.04.2012 9.10-1

9.10 Specific Material Requirements

9.10.1 Carbon Equivalent and Weldability

The Carbon Equivalent (CE) is used for rating of weld-ability of ferritic low alloy steels. It takes into account the equivalent additive effects of carbon and other alloying elements on a particular characteristic of steel. A commonly used formula to calculate the Carbon Equivalent is based on a publication of the International Institute of Welding (IIW) [Technical Report 1967, IIW Doc. IX-535-67]: CE = C + Mn/6 + (Cr + Mo + V)/5 + (Cu + Ni)/15 For this equation the weldability based on a range of CE values can be defined as follows: Carbon equivalent (CE) Weldability Up to 0.35 Excellent 0.36–0.40 Very good 0.41–0.45 Good 0.46–0.50 Fair Over 0.50 Poor [Ginzburg, Vladimir B.; Ballas, Robert (2000), Flat rolling fundamentals] [SA-6/SA-6M - Specification For General Requirements For Rolled Structural Steel Bars, Plates, Shapes, And Sheet Piling. ASME BPVC Section II] 9.10.2 Killed Carbon Steel or Killed Steel

The definition of "killed steel" is given in ASTM A 941: "A steel deoxidized to such level that essentially no reaction occurred between carbon and oxygen during solidification." The purpose of the deoxidation is to avoid gas bubbles in the material in order to fulfill the quality requirements given in material standards like ASME SA 216. However there is no material standard like ASME SA 216 , ASME SA 352 or ASME SA 703 that actually requires the process of deoxidation as part of the manufacturing process. Deoxidation of steel casting materials is an industry standard and is performed for every material supplied by LESER. "Killed steel" is not related to a specific material grade like LCB, it also applies to other grades like WCB

9.10.3 Corrosion Allowance

Other than for pressure vessels or pipelines (see e.g. ASME Code Sec. VIII Div. 1 UG-25) it is not common practice to increase the material thickness of safety valve bodies or nozzle and disc to allow for a certain corrosion. Material selection, especially of nozzle and disc should be such that corrosion does not occur, because it may lead to untightness or malfunction of the safety valve.