Introduction To The Field Of The Invention.
This invention relates to a method of making fuel gas pipeline and improved fuel gas pipeline prepared therefrom
Prior Art and Drawbacks:
It is already known to prepare fuel gas pipelines and uptill now fuel gas pipelines are, generally, fabricated/ spirally welded from 6-10 mm mild steel cods/ plates with chemistry and properties conforming to IS 2062 Indian Specification and IS 5504 (1969) pipeline specification respectively. Frequent repair and replacement of damaged sections require shutdowns, adversely affecting the plant productivity Presently the pipelines are fabricated from commercially available cotls/ plates of mild steel conforming to IS' 2062 which has carbon upto 0.23 % and Mn upto 1 5% as principal alloying elements
Objects of the invention:
It is an object of the invention to propose a method for the manufacture of corrosion resistant steel for fuel gas pipelines and pipelines prepared therefrom which will have increased service life
Another object is to propose such a method, which will provide gas pipelines requiring less maintenance
A further object is to propose such fuel gas pipelines, which will not require frequent repair, and / or replacement of damaged sections
A still further object of this invention is to propose such improved fuel gas pipelines, which will reduce the number of shutdowns based by the use of the presently available fuel gas pipelines These and other objects of this invention will be apparent from the following paragraphs-
BACKGROUND OF INVESTIGATION:
The internal surfaces of fuel gas pipelines transporting Blast Furnace (BF) Coke Oven (CO), Converter and mixed gases, in integrated steel plants, suffer corrosive attack due to aggressive chemical constituents such as chlorides (CI"), sulphates (SO42~) sulphites (SO32*)', ammonium
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radical (NH4+)t cyanides (HCN'.CN), hydroxides (OH'), hydrogen sulphide (H2S) and carbon dioxide (CO2). The average service life of these pipelines is 4-7 years. Lower life is, particularly, reported in certain critical sections in CO and By-product plant (BPP) before the stage of ammonia separators.
In order to increase the service life of fuel gas pipelines, steel chemistry was modified and redesigned to improve its corrosion resistance in fuel gas environment The carbon (C) content in the steel was lowered from 0.15 - 0 23% to 0 06 - 0 12% and minor alloying additions of copper, Cu (0 20-0.35%) and phosphorus, P (0.03-0 08%) were incorporated in the steel chemistry with the aim of achieving improved corrosion resistance properties. For retaining the mechanical properties as stipulated in IS.5504 for fuel gas pipelines, the manganese content was kept in the range of 0 65-0 85%,
BRIEF STATEMENT OF THE INVENTION.
1 According to the invention there is provided A method of making corrosion resistant fuel gas pipelines characterized by having the following alloy elements based on weight percent.
a) An alloy steel having the carbon content between 0.06 to 0.12%.
b) Copper content between 0 20 to 0 35%
c) Phosphorus content between 0 03 to 0 08%
d) Manganese content between 0.65 to 0 85%, and the steel having additionally the following
elements:
$S Si 0 25%-0.35%
If) Sulphur maximum of 0.01% Ity) Aluminium between 002 to 004%
casting the same in to slabs in a continuous caster, rolling slabs into coils of in conventional Hot Strip Mill and thereafter preparing spirally welded pipes from the said coils in a known manner
1. There is also provided a corrosion resistant fuel gas pipeline made from a steel composition having the following compositions
a) An alloy steel having the carbon content between 0 06 to 0 12%
b) Copper content between 0.20 to 0 35%.
c) Phosphorus content between 0 03 to 0.08%
d) Manganese content between 0 65 to 0 85% and the steel having additionally the following
elements
i) Si 0.25 %- 0 35%
fr) Sulphur maximum of 0.01% W/) Aluminium between 0.02 to 0 04% Whenever prepared by the method of Claim 1
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Detailed Description of the Invention
The improved steel was made in 8 separate heats in Steel Melting Shops through basic Oxygen furnace (BOF) and was cast to slabs in a continuous caster (CC) 750 tonnes of slabs were rolled into 10 mm thick coils in Hot Strip Mill (HSM), Thereafter, spirally welded pipes of 36, 54 and 64 inch diameter were made in Spirally Welded Pipe Plant (SWPP). 800 meters of steel pipes were installed for transportation of mixed gas to Cold Rolling Mill for evaluation proposes.
The basic tundish cover powder is added on the molten steel in tundish of continuous casting. Due to heat transfer from molten steel, it melts and forms a thin layer of basic molten slag. The slag has got high affinity to absorb inclusion particularly alumina (AI2O3) present in low carbon aluminium killed steel.
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5. Salient Features of Innovation:
The designed chemistry of new steel for fuel gas pipelines is as under
C Mn n Si S P Cu Al
0.06-0 10 0.65-0.85 0 25-0 35 0.01 max 0.03-0.08 0.20-0.35 0 02-0 04

The mechanical properties specified and achieved are tabulated below.
Mechanical Property Specified (min) Achieved (Range)
Yield Strength (MPa) 240 290-354 o""
Ultimate Tensile Strength (MPa) 410 420-456
% Elongation 20 30-34
The new steel. SAILCOR steel, existing pipeline steel from RSP, Russian steel from BSP and IS 2062+Cu steel were evaluated for their corrosion rates and passivation characteristics in synthetic CO gas condensate media using potentiodynamic polarization technique The composition of the synthetic gas condensate is as given below.
NaCI (wt%) Na2SO4 Na2SO3 (wt%) Free NH3 {wt%) [NH4SCNJwt%^
0 017 0 04 0 06 04 f 1 45
pH- 9.45
The corrosion rates of pipeline steels in CO gas condensate as determined by
Potentiodynamic Method and the passivation characteristics in ammoniacal CO
gas condensate are given in the following two tables
Steel Corrosion Rate (mpy)
New steel 2 05
SAILCOR steel 2 21
Existing pipeline steel from RSP 12 3
Russian pipeline steel from BSP 2 41
IS 2062+Cu 3 32

Steel Passivation Range (mV) Passivation Current (x10'* A|__
New steel 1725 1 00
Existing pipeline steel from RSP 1500 1 50
Russian pipeline steel from BSP 1300 1 35
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WE CLAIM:
1. A method of making corrosion resistant fuel gas pipelines characterized by having the following alloy elements based on weight percent
a) An alloy steel having the carbon content between 0 06 to 0 12%.
b) Copper content between 0.20 to 0.35%
c) Phosphorus content between 0 03 to 0 08%
d) Manganese content between 0.65 to 0 85%, and the steel having additionally the following
elements
i) Si 0.25 %- 0 35%
ii) Sulphur maximum of 0 01 %
HI) Aluminium between 0.02 to 0.04%
casting the same in to slabs in a continuous caster, rolling slabs into coils of in conventional Hot Strip Mill and thereafter preparing spirally welded pipes from the said coils in a known manner.
2 A corrosion resistant fuel gas pipeline made from a steel composition having the following
compositions
a) An alloy steel having the carbon content between 0.06 to 0 12%
b) Copper content between 0 20 to 0.35%.
c) Phosphorus content between 0 03 to 0.08%.
d) Manganese content between 0.65 to 0 85% and the steel having additionally the following
elements
lj Si 0 25%-0.35%
Vih Sulphur maximum of 0.01% \'\'i) Aluminium between 0 02 to 0 04% Whenever prepared by the method of Claim 1
3 A method of making corrosion resistant fuel gas pipelines substantially as herein described with
reference to the examples.
4 A corrosion resistant fuel gas pipelines substantially as herein described with reference to the
examples.
There is provided an improved fuel gas pipeline having improved corrosion resistance and made from a steel composition having the following chemistry
a) An alloy steel having the carbon content between 0.06 to 0 12%
b) Copper content between 0.20 to 0.35%
c) Phosphorus content between 0 03 to 0 08%
d) Manganese content between 0 65 to 0 85%