DE2616599B2 - Use of a high-alloy steel for the manufacture of high-strength objects that are resistant to acid gas corrosion - Google Patents

Description

The invention relates to the use of high-alloy steels known per se with that in the claim added chemical composition against Acid gas corrosion of resistant pipes, pipe connections and other objects.

So far, sour gas (· = natural gas with contents of H ₂ S and / or CO2) and sour gas products, e.g. B. sulfur compounds, unalloyed and low-alloy tubular steels are used with conventional heat treatments. What these materials have in common is inadequate corrosion resistance under the conditions of use mentioned, for example inadequate resistance to general erosive corrosion, susceptibility to pitting corrosion due to element formation and risk from hydrogen-induced stress corrosion cracking. The types of corrosion mentioned can occur individually or together. To ensure sufficient operational safety, various measures are therefore required when using unalloyed and low-alloy steels, e.g. B. drying the gas and / or adding vuii inhibitors and / or raising the pH value.

When sour gas is conveyed, the materials mentioned are preferably endangered by large-area local corrosion. These corrosion are at the Outer surface of tubings observed and are in connection with the introduction of sulfur-dissolving or to see the precipitation of sulfur-preventing agents in the annular gap between tubing and casing. The cause of this corrosion attack is probably the formation of large-area macro-elements. whose Effectiveness with increasing borehole depth and thus increasing I empcratur / takes and below one certain temperature h / w depending on the local conditions and operating conditions.

is no longer observed above a certain borehole depth.

Furthermore, corrosion damage occurs on the inner surface of the conveyor strands, which is generally caused by abrasive corrosion and erosion corrosion are caused. The most common erosive corrosion is apparently associated with the acidification of the borehole to maintain the production capacity. By Applying inhibitors can cause this type of corrosion can be reduced, but not avoided with sufficient certainty. In addition, differences in Local attacks by erosion corrosion due to the flow conditions occur. These are probably due to the fact that the top layer that arise during operation and exercise a certain protective function, do not develop in certain areas of the pipe surface or are destroyed will.

In the upper, colder tubing strand there is esp

especially when the conveyance comes to a standstill there is a risk of stress corrosion cracking caused by hydrogen. The occurrence of this type of corrosion is on it due to the fact that hydrogen formed on the surface of the material by corrosion reactions Essence of hydrogen sulfide not to water substance molecules are recombined, but diffused atomically into the structure. This can go a long way in the event of loads below the yield point lead to the formation of cracks, breaks and thus to the tearing of the pipe string. the Tendency of unalloyed and low-alloy steels to hydrogen-induced stress corrosion cracking . increases with falling temperature and thus reaches a maximum value at around room temperature explains the particular endangerment of the upper, colder and at the same time highly stressed parts of the line during the conveying operation and the increased risk in downtimes because of the further drop in temperature. As a countermeasure, higher-strength, low-alloyed ones have so far been used Quenched and tempered steels with compared to hot-rolled or hot-rolled and normalized steels improved resistance to hydrogen-induced stress corrosion cracking has been used without however, corrosion damage was completely avoided could.

Pipes for the transport of acid gas, so-called "flow-lines", are almost exclusively at risk from hydrogen-induced stress corrosion cracking because of the low temperature present here general erosive corrosion urk / other local Corrosion attacks have no practical significance in this application. Since the stress corrosion cracking caused by hydrogen absorption on a electrochemical corrosion reaction that occurs at low pH values and only in the presence of moisture can run, is bound, was previously to avoid stress corrosion cracking immediately after When the gas emerges from the borehole, the pH value is raised to pH 8 by adding alkalis then the moisture is removed in a drying system.

The same corrosion problems as in the extraction and transport also exist with Plants for the preparation and further processing of

(> ■> sour gas.

The invention has set itself the task of producing high-quality steels known per se with the claim specified chemical composition for the

To make digestion, transport and for the further processing of acid gas usable without the the objects in question are at risk of corrosion. According to the invention, this object is achieved suggested that pipes, pipe connections and apparatus parts made from such steels be used, which have been cold-formed with a degree of deformation of at least 3% during their production.

The objects according to the invention have due to their chemical composition among the Conditions for the exploration of sour gas wells, production, transport, processing and Further processing of acid gas has a high resistance to general erosive corrosion, local Corrosion such as pitting corrosion and by chlorides and especially against by hydrogen absorption caused stress corrosion. You are about it also resistant to corrosion caused by element formation.

Due to the cold deformation according to the invention Materials are the minimum yield strengths of the high-alloyed ones in the solution-annealed condition Steels substantially to the values required for contact at great depths at the same time sufficiently high values for elongation and constriction are increased. It is essential to the invention that by the Cold deformation increases the resistance to general erosive corrosion, to pitting corrosion Chlorides and penetration of atomic hydrogen * into the structure produced stress corrosion cracking and the Resistance to corrosion is not impaired by element formation. Furthermore, the previously used for safe protection of unalloyed and low-alloy steels in general however, inadequate corrosion protection measures, such as the use of inhibitors during rinsing and acidification of the borehole, alkalizing and drying the gas, are omitted or at least to a limited extent and thereby the The operational reliability of the systems is increased and an economic advantage can be achieved.

Claims (1)

Claim; Use of a high-alloy steel consisting of 0.001 to 0.12% carbon 0.2 to 1.5% silicon 0.5 to 8% manganese 12 to 30% chromium 2 to 16% nickel ) .l to 5% molybdenum 0.01 to 1.2% titanium 0.01 to 1.6% niobium 0.01 to 33% copper 0.010 to 035% nitrogen, Remainder iron and usual accompanying elements for the production of pipes and pipe connections with high strength and a yield point of at least 440 N / mm ² , which are resistant to the corrosion attacks occurring during the digestion, transport and further processing of acid gas, with the proviso that the objects during their production a cold deformation with a Be subjected to a degree of deformation of at least 3%.