Study of samples taken from stainless steel by X-Ray microspectrographic analysis

This testing was done to define chemical composition of the material (stainless steel) in order to define areas of the equipment subject to corrosion....

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Study of the stainless steel sample chemical composition

The testing was done to prevent corrosion of metal by means of strengthening the walls while adding more resistant metals into an alloy.

Chemical analysis of stainless steel samples such as cuttings and fine pieces, taken from the following stainless vessels: “upper ring of the vessel and overflow pipe of V-80 vessel” (general view on a photo 1). Separate samples of the material taken from “upper ring of the vessel V-80” like cuttings (photo 2), “overflow pipe of V-80 vessel” such as fine pieces (photo 3) and «frame of the graphite filter» (general view on photo 4) like cuttings (photo 5).


Photo 1: Upper ring of the vessel and overflow pipe	Photo 2: Intake of the material from upper ring of the vessel like cuttings

Photo 3: Intake of the material from overflow pipe in a form of fine pieces	Photo 4: Carbon filter frame
	Photo 5: a stainless steel sample in a form of cuttings

Composition analysis of stainless steel three samples: «overflow pipe of a vessel and overflow pipe of V-80 vessel», «upper ring of a vessel and overflow pipe of vessel V-80» and «frame of the graphite filter».

Table 1 – Results obtained by X-Ray micro spectrum analysis:

Samples	Elements content in an iron-based alloy, mass%
Samples	Cr	Ni	Mo	Mn	Ti	Si
Overflow pipe V-80	16,28	11,99	2,42	1,80	0,54	0,68
Upper ring of a vessel V-80	16,39-17,12	11,02-11,06	2,11-2,57	1,69	0,40-0,39	0,44-0,42
Frame of a graphite filter	16,02-16,43	10,47-10,68	2,43-3,03	1,53-1,70	0,39-0,45	0,54-0,75

Obtained results show that all samples (“an overflow pipe of the V-80 vessel”, “upper ring of the V-80 vessel” and “frame of the graphite filter”) are close to the composition of steel AISI 316L, in accordance with ASTM A240, by their metallic properties (see Table 2).

In “frame of the graphite filter” sample the molybdenum content is on the upper height. In “overflow pipe of V-80 vessel” titanium content is on upper height. Scattering is shown based on two testing for determining content in different areas. Obviously, it, mainly, characterizes method of accuracy determining as metal (sheet) is deformed greatly and averaging of licvations by composition has occurred.

More corrosion-resistant alloy AISI 316L is differing from alloy AISI 316 by titanium presence and lower content of carbon: 0,03 instead of 0,08 mass % (see Table 2). The analysis of carbon content by chemical method showed that in all steel grades the content of carbon is ranging between 0,073-0,08 mass %. This corresponds to a maximum content of carbon in alloy AISI 316. Additional control by means of spectrum analysis confirmed presence of titanium in the alloys.

The samples correspond to alloy AISI 316. Obviously, ASTM A240 does not guarantee presence of titanium in its composition.

Table. 2 – Chemical composition of stainless steel grades type AISI 316 in accordance with ASTM A240:

Samples	C	Mn	P	S	Si	Cr	Ni	Mo	Ti
AISI 316	0.08 max	2.0 max	0.045 max	0.030 max	1.0 max	16.0 to 18.0	10.0 to 14.0	2.00 to 3.00	-
AISI 316L	0.03 max								0.5 max
AISI 316Ti	0.08 max								5X%C

AISI 316 grade – improved version 304, with molybdenum and higher content of nickel.

The given composition of AISI 316 considerably increases corrosion resistance in aggressive media. Molybdenum makes steel more protected from pitting and slotted corrosion in chlorine medium, sea water and vapors of acetic acid. AISI 316 has higher strength and has better resistance of creeping at high temperatures, than AISI 304. AISI 316 also has good mechanical and corrosion properties at negative temperatures.

When there is a risk of corrosion near welding areas, a low-carbon grade AISI 316L should be used.

AISI 316Ti version, stabilized with titanium is used to improve thermal stability within considerable period of time in a temperature range 550-800°C.