JPH06136516A - Reducing valve for urea synthesis plant - Google Patents
Reducing valve for urea synthesis plantInfo
- Publication number
- JPH06136516A JPH06136516A JP5034962A JP3496293A JPH06136516A JP H06136516 A JPH06136516 A JP H06136516A JP 5034962 A JP5034962 A JP 5034962A JP 3496293 A JP3496293 A JP 3496293A JP H06136516 A JPH06136516 A JP H06136516A
- Authority
- JP
- Japan
- Prior art keywords
- reducing valve
- chromium
- chromium nitride
- pressure reducing
- urea synthesis
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P20/00—Technologies relating to chemical industry
- Y02P20/141—Feedstock
Landscapes
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
- Physical Vapour Deposition (AREA)
- Control Of Fluid Pressure (AREA)
Abstract
Description
【０００１】[0001]
【産業上の利用分野】本発明は尿素合成プロセスにおい
て腐食およびキャビテーションエロージョンを受けやす
い部位である減圧弁の新規な構成に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel construction of a pressure reducing valve which is a site susceptible to corrosion and cavitation erosion in a urea synthesis process.
【０００２】[0002]
【従来の技術】尿素合成プロセスは高温高圧の腐食性の
高いプロセス流体を取扱うものであり、使用される構造
材料の腐食が従来より問題にされてきた。特に、尿素合
成後の未反応のアンモニアおよび炭酸ガスを分離するた
め、温度150 〜230 ℃のプロセス流体の圧力を150 〜28
0 気圧から数10気圧に低減させる減圧弁や、反応中間体
であるカーバメイト流体を循環させるラインに用いられ
ている減圧弁では、従来より、ステンレス鋼またはジル
コニウムおよびジルコニウム合金が使用されているが、
これらの材料では、キャビテーションエロージョンが腐
食に重畳し、減圧弁材料の損傷を加速し、短期間にその
機能を失わさせている。その結果、尿素合成プラントの
長期安定運転を困難にしている。図１は、尿素合成プラ
ント用減圧弁の断面図で、図中符号１は減圧弁本体であ
る。この減圧弁は、減圧弁本体１と、プラグ３と、シー
トリング５から構成され、入口２より入った高温高圧の
プロセス流体が、プラグ３の先端部４とシートリング５
により囲まれた狭部６を通過することによって減圧され
る仕組みである。そしてこの減圧の際、先端部４及びシ
ートリング５の内面は高速のプロセス流体にさらされる
ことにより、腐食に加えて、キャビテーションエロージ
ョンを受け、通常図中斜線で示した箇所において著しい
減肉を生じる。2. Description of the Related Art The urea synthesis process deals with a highly corrosive process fluid at high temperature and high pressure, and the corrosion of structural materials used has been a problem in the past. In particular, in order to separate unreacted ammonia and carbon dioxide gas after the urea synthesis, the pressure of the process fluid at a temperature of 150 to 230 ° C is adjusted to 150 to 28 ° C.
A pressure reducing valve for reducing the pressure from 0 atm to several tens of atm, and a pressure reducing valve used in a line for circulating a reaction intermediate, a carbamate fluid, have conventionally used stainless steel or zirconium and zirconium alloys.
In these materials, cavitation erosion overlaps with corrosion, accelerating damage to the pressure reducing valve material and causing it to lose its function in a short period of time. As a result, long-term stable operation of the urea synthesis plant is difficult. FIG. 1 is a cross-sectional view of a pressure reducing valve for a urea synthesis plant, in which reference numeral 1 is a pressure reducing valve body. This pressure reducing valve is composed of a pressure reducing valve body 1, a plug 3 and a seat ring 5, and a high temperature and high pressure process fluid introduced from an inlet 2 is applied to a tip portion 4 of the plug 3 and a seat ring 5.
The pressure is reduced by passing through the narrow portion 6 surrounded by. At the time of this pressure reduction, the inner surfaces of the tip portion 4 and the seat ring 5 are exposed to a high-speed process fluid, so that in addition to corrosion, cavitation erosion is caused, and a remarkable thinning is usually generated at a portion shown by a diagonal line in the drawing. .
【０００３】[0003]
【発明が解決しようとする課題】減圧弁用材料としてス
テンレス鋼は、耐キャビテーションエロージョン特性が
良く、耐食性がかなり良好であるため、実用に供されて
きたが、尿素プラントの長期安定運転を考えた場合、後
述の比較例２に示すように耐食性が充分であるとは言え
ず、使用中の腐食により減肉し、短期間のうちに減圧弁
の機能を果たさなくなるといった問題があった。一方、
ジルコニウムおよびジルコニウム合金も、尿素合成条件
下で高い耐食性を示すため、実用に供されてきた。しか
しながら、これらジルコニウムおよびジルコニウム合金
の、JIS 2243で知られるブリネル硬度は150maxと低く、
減圧弁材料として長期間使用する場合には、後述の比較
例６に示すようにキャビテーションエロージョンにより
減肉し、短期間のうちに、減圧弁としての機能を果たさ
なくなるといった問題があった。これらの材料面の問題
点は、尿素プラントの長期連続運転を実現する上で解決
すべき必須の事柄である。また、尿素合成プロセスは、
150 〜230 ℃、150 〜280 気圧の高温高圧下で操業され
るプロセスであることから、運転条件の変動等により、
予期せざる損傷を受ける可能性があることから、安全に
操業を続ける上にも必須の事柄である。本発明の目的
は、尿素合成プロセスにおいて腐食およびキャビテーシ
ョンエロージョンを受けやすい部位、特に、減圧弁とし
て耐キャビテーションエロージョン特性、耐食性が良好
な材料を使用することにより、減圧弁の損傷を防止し、
尿素プラントの安全運転を可能にするとともに、長期に
わたる連続運転を可能にすることである。Stainless steel as a material for a pressure reducing valve has been put into practical use because it has good cavitation erosion resistance and fairly good corrosion resistance, but a long-term stable operation of a urea plant was considered. In this case, as shown in Comparative Example 2 to be described later, it cannot be said that the corrosion resistance is sufficient, and there was a problem that the thickness was reduced due to corrosion during use and the function of the pressure reducing valve was not fulfilled within a short period of time. on the other hand,
Zirconium and zirconium alloys have also been put to practical use because they exhibit high corrosion resistance under urea synthesis conditions. However, these zirconium and zirconium alloys have a low Brinell hardness of 150max, which is known by JIS 2243.
When it is used as a pressure reducing valve material for a long period of time, there is a problem that the thickness of the pressure reducing valve is reduced by cavitation erosion as shown in Comparative Example 6 and the function as the pressure reducing valve is not fulfilled within a short period of time. These material problems are essential matters to be solved in order to realize long-term continuous operation of the urea plant. Also, the urea synthesis process
Since the process is operated under high temperature and high pressure of 150 to 230 ℃ and 150 to 280 atm, it may be
It is essential for safe operation, as it can be damaged unexpectedly. The object of the present invention is to prevent corrosion and cavitation erosion in the urea synthesis process, particularly by using a material having good cavitation erosion resistance and corrosion resistance as a pressure reducing valve, thereby preventing damage to the pressure reducing valve,
This is to enable safe operation of the urea plant and continuous operation over a long period of time.
【０００４】[0004]
【課題を解決するための手段】本発明者等は、上記目的
を達成すべく、尿素合成プロセスに使用される減圧弁の
減肉を防止するために必要な高い耐食性と耐キャビテー
ションエロージョン特性を持った材料を鋭意探索した結
果、ある組成を持った窒化クロムがこの種の材料として
好適であること、そしてこの窒化クロムを基材の表面に
被覆することにより減圧弁材料として充分な性能を発揮
することを見出した。さらに、金属クロム以外の金属材
料を基材として使用する場合には窒化クロムを被覆する
前処理としてクロム拡散浸透処理をすることにより、基
材の耐食性を向上させ、このことがクロム拡散浸透処理
面に被覆した窒化クロム被膜の剥離防止に有効であるこ
とを見出し、本発明を完成するに到った。即ち本発明
は、尿素合成プロセスにおいて腐食およびキャビテーシ
ョンエロージョンを受けやすい減圧弁を窒化クロム材で
構成した尿素合成プラント用減圧弁、および金属クロム
以外の金属材料を基材として使用する場合に、クロム拡
散浸透処理した金属材を窒化クロムで被覆したものによ
り構成した尿素合成プラント用減圧弁に関する。In order to achieve the above-mentioned object, the present inventors have high corrosion resistance and cavitation erosion resistance required to prevent thinning of a pressure reducing valve used in a urea synthesis process. As a result of diligently searching for such materials, chromium nitride having a certain composition is suitable as this kind of material, and by coating the surface of the base material with this chromium nitride, sufficient performance as a pressure reducing valve material is exhibited. I found that. Furthermore, when a metal material other than metallic chromium is used as the base material, the chromium diffusion / penetration treatment is performed as a pretreatment for coating chromium nitride to improve the corrosion resistance of the base material. The inventors have found that it is effective for preventing the peeling of the chromium nitride coating film coated on, and have completed the present invention. That is, the present invention provides a pressure reducing valve for a urea synthesis plant in which a pressure reducing valve that is susceptible to corrosion and cavitation erosion in a urea synthesis process is made of a chromium nitride material, and when a metal material other than metal chromium is used as a base material, chromium diffusion The present invention relates to a pressure reducing valve for a urea synthesis plant, which is composed of a metal material subjected to permeation treatment and coated with chromium nitride.
【０００５】本発明において、窒化クロムとは、CrN-Cr
2N-Cr 系から構成される化合物で、CrN の含有率が60％
以上100 ％以下の組成を持つものを意味する。これらの
組成含有率は、薄膜Ｘ線回折分析により得られた強度ピ
ーク比率を示したものである。また、本発明において、
減圧弁を窒化クロム材で構成するとは、構造的に減圧弁
全体を窒化クロム材で製作することを意味するが、特に
腐食およびキャビテーションエロージョンを受けやすい
減圧弁の要部、即ち前述した図１中斜線で示す、高温高
圧の腐食性の高いプロセス流体と接触する箇所のみに窒
化クロム材を適用し、プロセス流体と接触しない箇所に
は適用しない減圧弁も本発明の範疇に含まれる。また、
本発明において減圧弁を窒化クロム材により構成する場
合は、減圧弁を窒化クロム単体で形成する場合、および
窒化クロムを窒化法および物理蒸着法などの表面処理方
法によって金属およびセラミックス等の基材表面を窒化
クロム被覆された被覆材で形成する場合、および金属基
材表面をクロム拡散浸透処理により改質した後、物理蒸
着法により窒化クロム被覆された被覆材で形成する場合
をいう。本発明において、上記クロム拡散浸透処理と
は、JIS 鉄鋼熱処理用語によれば、クロマイジングと別
称され、「鉄鋼の耐食性を増加させるため、高温で鉄鋼
の表面にクロムを拡散させる操作」と定義されている手
段をいう。また、本発明に用いる窒化クロムは、物理蒸
着法では従来技術である反応性イオンプレーティング法
により、また窒化法ではイオン窒化法またはガス窒化法
にて金属クロムを窒化することにより得られる。尚、基
材が金属クロムの場合、窒化法であるイオン窒化法等に
より、減圧下、窒化温度好ましくは700 〜1000℃の条件
の下、金属クロム表面に窒化クロム層を形成させること
ができる。この場合の層の厚さは、通常50μm 以下とす
る。一方、基材がステンレス鋼、セラミックスなど、金
属クロム以外の場合には、窒化法による基材表面への窒
化クロム被覆は困難であり、この場合、物理蒸着法であ
る反応性イオンプレーティング法を用いる必要がある。
まず窒化クロム被覆の前処理として拡散浸透処理をしな
い場合について説明すると、この場合の成膜条件は、減
圧下、成膜温度350 〜550 ℃であり、皮膜の厚みは通常
10〜50μm がよい。これは、後述する実施例１および３
からも明らかなように、皮膜の厚みが10μm 以上であれ
ば、ピンホールの発生率が低下するため、皮膜の剥離を
生じないのに対し、比較例３に示す如く皮膜が10μm 未
満になると、ピンホールの発生率が高くなってアンモニ
ウムカーバメートを含む腐食性の強い尿素溶液の場合、
図２に示した概念図のように貫通したピンホール１１か
ら尿素液が侵入して、基材１３に腐食による空孔１４が
形成され、皮膜１２が基材１３の腐食によって剥離し、
基材を大きく腐食させる。また、皮膜の厚さが50μm を
越えると比較例４に示す如く、膜の内部応力で皮膜が自
己崩壊することがある。以上説明したように、窒化クロ
ム被覆の前処理としてクロム拡散浸透処理をしない場合
であっても充分課題を解決することができるが、基材が
金属クロム以外の材料では被覆した窒化クロム皮膜中で
の貫通ピンホールを無くすため、窒化クロム皮膜の厚み
を10μm 以上とするとともに、被覆部の皮膜に貫通ピン
ホールおよび割れがないことを綿密に時間をかけて検査
する必要がある。In the present invention, chromium nitride means CrN-Cr
2 N-Cr compound, 60% CrN content
It means that the composition is 100% or less. These composition contents indicate the intensity peak ratios obtained by thin film X-ray diffraction analysis. In the present invention,
The structure of the pressure reducing valve made of a chromium nitride material means that the entire pressure reducing valve is structurally made of a chromium nitride material. However, the main part of the pressure reducing valve which is particularly susceptible to corrosion and cavitation erosion, that is, in FIG. The scope of the present invention also includes a pressure reducing valve, which is shown by the diagonal lines, in which the chromium nitride material is applied only to a portion that comes into contact with the high-temperature, high-pressure corrosive process fluid and not to a portion that does not come into contact with the process fluid. Also,
In the present invention, when the pressure reducing valve is made of a chromium nitride material, when the pressure reducing valve is formed of chromium nitride alone, and when the chromium nitride is subjected to a surface treatment method such as a nitriding method and a physical vapor deposition method, the surface of a base material such as metal and ceramics Is formed with a coating material coated with chromium nitride, and is formed with a coating material coated with chromium nitride by a physical vapor deposition method after the surface of a metal substrate is modified by chromium diffusion and penetration treatment. In the present invention, the chromium diffusion and permeation treatment is, according to JIS steel heat treatment terms, also called chromizing, and is defined as "an operation of diffusing chromium on the surface of steel at high temperature in order to increase the corrosion resistance of steel". It means the means. Further, the chromium nitride used in the present invention can be obtained by nitriding metal chromium by a reactive ion plating method which is a conventional technique in the physical vapor deposition method, and by ion nitriding method or gas nitriding method in the nitriding method. When the base material is metallic chromium, a chromium nitride layer can be formed on the surface of metallic chromium under reduced pressure at a nitriding temperature of preferably 700 to 1000 ° C. by an ion nitriding method which is a nitriding method. In this case, the layer thickness is usually 50 μm or less. On the other hand, when the base material is other than metallic chromium such as stainless steel and ceramics, it is difficult to coat the surface of the base material with chromium nitride by the nitriding method. In this case, the reactive ion plating method which is a physical vapor deposition method is used. Must be used.
First, the case where no diffusion and penetration treatment is performed as a pretreatment for chromium nitride coating will be explained.In this case, the film forming conditions are a reduced pressure and a film forming temperature of 350 to 550 ° C, and the film thickness is usually
10 to 50 μm is preferable. This is described in Examples 1 and 3 below.
As is clear from the above, when the thickness of the coating is 10 μm or more, the rate of pinholes decreases, so that the coating does not peel, whereas as shown in Comparative Example 3, when the coating becomes less than 10 μm, In the case of highly corrosive urea solution containing ammonium carbamate with high pinhole generation rate,
As shown in the conceptual diagram shown in FIG. 2, the urea solution enters from the pinhole 11 penetrating therethrough to form the pores 14 in the base material 13 due to corrosion, and the film 12 is peeled off due to the corrosion of the base material 13.
Corrodes the base material significantly. Further, when the thickness of the coating exceeds 50 μm, as shown in Comparative Example 4, the coating may self-disintegrate due to the internal stress of the coating. As described above, the problem can be sufficiently solved even when the chromium diffusion / infiltration treatment is not performed as a pretreatment for the chromium nitride coating, but in the chromium nitride coating coated with a material other than metallic chromium as the base material. In order to eliminate the through pinholes, it is necessary to set the thickness of the chromium nitride film to 10 μm or more and carefully inspect the coating film for through pinholes and cracks over time.
【０００６】次に、被覆部の皮膜に貫通ピンホールおよ
び割れがないことを綿密に時間をかけて検査する必要の
ない窒化クロム被覆の前処理としてクロム拡散浸透処理
をした場合について説明する。前述のように、基材とし
て金属クロム以外の金属を使用し、クロム拡散浸透処理
をしない場合には、基材の腐食によって被覆された窒化
クロム皮膜が剥離することがあることは、前述の通りで
ある。このような皮膜剥離は、基材の耐食性が充分でな
いために、皮膜の微小な貫通欠陥を通して基材が腐食さ
れることが直接の原因となっており、従って、基材の耐
食性をさらに向上させることが皮膜剥離の防止に有効で
ある。尿素合成環境中において、材料の耐食性を向上さ
せる因子の一つとして材料中に含まれるクロム濃度があ
り、クロム濃度の増加とともに材料の耐食性が向上する
ことが知られているが、クロム濃度の上昇とともに、材
料の加工性、靭性が悪くなることも事実であり、ある一
定量を超えたクロム含有設計はできなくなるのが現状で
ある。そこで本発明者らは、図３に示したように基材１
３の表面にクロム拡散浸透処理を施して高クロム合金層
１６を形成することにより基材１３表面の耐食性を高
め、さらにその上に窒化クロムを被覆することにより窒
化クロム皮膜１２中に微小な貫通欠陥１１があっても容
易に皮膜剥離を生じない高耐食性、高耐キャビテーショ
ン性の減圧弁を製作することができた。その結果、被覆
材を使用する前のピンホール検査は簡素化でき、製品の
歩留まりは飛躍的に向上することも可能となった。この
場合、クロム拡散浸透処理による高クロム合金層および
反応性イオンプレーティング法による窒化クロムの最小
厚さは、後述する実施例４より明らかなように、それぞ
れ５および３μm 以上が好ましく、最大厚さは高クロム
合金層の割れ、および窒化クロム皮膜の自己崩壊を考慮
して、いずれの場合も50μm 以下が好ましい（実施例５
参照）。Next, the case where the chromium diffusion coating is carried out as a pretreatment for the chromium nitride coating, which does not require a thorough inspection for the through-holes and cracks in the coating film, will be described. As mentioned above, when a metal other than chromium metal is used as the base material and the chromium diffusion / infiltration treatment is not carried out, the chromium nitride coating film may be peeled off due to corrosion of the base material. Is. Such film peeling is directly caused by corrosion of the substrate through minute penetration defects in the film due to insufficient corrosion resistance of the substrate, thus further improving the corrosion resistance of the substrate. It is effective to prevent the film peeling. In the urea synthesis environment, the chromium concentration contained in the material is one of the factors that improve the corrosion resistance of the material, and it is known that the corrosion resistance of the material improves as the chromium concentration increases. At the same time, it is a fact that the workability and toughness of the material are deteriorated, and under the present circumstances, it is impossible to design a chromium content exceeding a certain amount. Therefore, the inventors of the present invention, as shown in FIG.
The surface of No. 3 is subjected to a chromium diffusion and infiltration treatment to form a high chromium alloy layer 16 to enhance the corrosion resistance of the surface of the base material 13, and a chromium nitride film 12 is further coated thereon to form a fine penetration into the chromium nitride film 12. It was possible to manufacture a pressure-reducing valve having high corrosion resistance and high cavitation resistance that does not easily cause film peeling even if there is a defect 11. As a result, the pinhole inspection before using the covering material can be simplified and the product yield can be dramatically improved. In this case, the minimum thickness of the high chromium alloy layer by the chromium diffusion and infiltration treatment and the minimum thickness of the chromium nitride by the reactive ion plating method are preferably 5 and 3 μm or more, respectively, as will be apparent from Example 4 which will be described later. In consideration of cracking of the high chromium alloy layer and self-disintegration of the chromium nitride film, is preferably 50 μm or less (Example 5).
reference).
【０００７】[0007]
【発明の効果】本発明の尿素合成プラント用減圧弁は、
窒化クロム材で構成されているので、耐食性および耐キ
ャビテーションエロージョン性が極めて高いものとな
る。その結果、減圧弁の寿命が延び、尿素プラントの安
全な長期連続運転が可能となり、運転効率も著しく向上
した。また、本発明の尿素合成プラント用減圧弁のう
ち、クロム拡散浸透処理後の金属基材に窒化クロム材を
被覆したものは、初期貫通欠陥に起因する皮膜剥離を防
止することが可能となり、その結果、被覆材を使用する
前のピンホール検査が簡素化され、製品の歩留まりを飛
躍的に向上することも可能となった。即ち、上記本発明
の効果は、アンモニアと炭酸ガスを原料とする尿素合成
プラントの、高温高圧の高腐食性プロセス流体と接触す
る減圧弁表面に、窒化クロムを適用することにより得ら
れるものである。The pressure reducing valve for the urea synthesis plant of the present invention is
Since it is made of a chromium nitride material, it has extremely high corrosion resistance and cavitation erosion resistance. As a result, the life of the pressure reducing valve was extended, the safe long-term continuous operation of the urea plant became possible, and the operating efficiency was significantly improved. Further, among the pressure reducing valves for the urea synthesis plant of the present invention, those in which the chromium nitride material is coated on the metal base material after the chromium diffusion permeation treatment makes it possible to prevent the film peeling due to the initial penetration defect. As a result, it became possible to simplify the pinhole inspection before using the covering material and dramatically improve the product yield. That is, the effect of the present invention is obtained by applying chromium nitride to the pressure reducing valve surface of a urea synthesis plant using ammonia and carbon dioxide as raw materials, which comes into contact with a high-temperature, high-pressure highly corrosive process fluid. .
【０００８】[0008]
実施例１ 50mm×50mm×厚み４mmの形状を持つステンレス鋼材を用
い、その表面にクロム拡散浸透処理を施さず、直接、反
応性イオンプレーティング法により窒化クロム（CrN ：
100 ％）を10μm の膜厚で被覆して試験片とした。次に
この試験片を、温度150 〜230 ℃、圧力150 〜280 気圧
の条件下で、尿素、アンモニア、炭酸ガスおよびアンモ
ニアカーバメートなどからなるプロセス流体が存在する
運転中の尿素合成塔内に１年間挿入し、窒化クロムの耐
食性を調べた。結果を表１に示す。 実施例２ 窒化クロムの種類を、CrN ：60％、（Cr2N＋Cr）：40％
のものに変えた他は実施例１と同様の試験片仕様であ
り、実施例１と同様にして耐食性を調べた。結果を表１
に示す。 実施例３ 窒化クロムの被覆膜厚を50μm とした他は実施例１と同
様の試験片仕様であり、実施例１と同様にして耐食性を
調べた。結果を表１に示す。 比較例１ 窒化クロムの種類を、CrN ：30％、（Cr2N＋Cr）：70％
のものに変えた他は実施例１と同様の試験片仕様であ
り、実施例１と同様にして耐食性を調べた。結果を表１
に示す。 比較例２ 実施例１で用いたのと同様のステンレス鋼材を窒化クロ
ム皮膜を被覆することなくそのまま用いて試験片とし、
実施例１と同様にして耐食性を調べた。結果を表１に示
す。 比較例３ 窒化クロムの被覆膜厚を３μm とした他は実施例１と同
様の試験片仕様であり、実施例１と同様にして耐食性を
調べた。結果を表１に示す。 比較例４ 窒化クロムの被覆膜厚を60μm とした他は実施例１と同
様の試験片仕様であり、実施例１と同様にして耐食性を
調べようとしたが、皮膜に割れが認められ、その後の評
価は行わなかった。 実施例４ 実施例１で用いたのと同様のステンレス鋼材に、前処理
として厚さ５μm となるクロム拡散浸透処理を施した
後、反応性イオンプレーティング法により窒化クロム
（CrN ：100 ％）を３μm の膜厚で被覆して試験片と
し、実施例１と同様にして耐食性を調べた。結果を表１
に示す。 実施例５ 実施例１で用いたのと同様のステンレス鋼材に、前処理
として厚さ50μm となるクロム拡散浸透処理を施した
後、反応性イオンプレーティング法により窒化クロム
（CrN ：100 ％）を50μm の膜厚で被覆して試験片と
し、実施例１と同様にして耐食性を調べた。結果を表１
に示す。Example 1 A stainless steel material having a shape of 50 mm × 50 mm × 4 mm in thickness was used, and its surface was not subjected to a chromium diffusion / infiltration treatment, and was directly subjected to a reactive ion plating method to form chromium nitride (CrN:
100%) was coated with a film thickness of 10 μm to obtain a test piece. This test piece is then placed in a urea synthesis tower under operation for 1 year under the conditions of a temperature of 150 to 230 ° C and a pressure of 150 to 280 atm, in the presence of a process fluid consisting of urea, ammonia, carbon dioxide and ammonia carbamate. It was inserted and the corrosion resistance of chromium nitride was investigated. The results are shown in Table 1. Example 2 CrN: 60%, (Cr 2 N + Cr): 40%
The specifications of the test piece were the same as those of Example 1 except that the corrosion resistance was changed. The results are shown in Table 1.
Shown in. Example 3 The test piece specifications were the same as in Example 1 except that the coating thickness of chromium nitride was 50 μm, and corrosion resistance was examined in the same manner as in Example 1. The results are shown in Table 1. Comparative Example 1 CrN: 30%, (Cr 2 N + Cr): 70%
The specifications of the test piece were the same as those of Example 1 except that the corrosion resistance was changed. The results are shown in Table 1.
Shown in. Comparative Example 2 A stainless steel material similar to that used in Example 1 was used as it was without being coated with a chromium nitride film to give a test piece.
The corrosion resistance was examined in the same manner as in Example 1. The results are shown in Table 1. Comparative Example 3 The test piece specifications were the same as in Example 1 except that the coating thickness of chromium nitride was 3 μm, and corrosion resistance was examined in the same manner as in Example 1. The results are shown in Table 1. Comparative Example 4 The test piece specifications were the same as in Example 1 except that the coating thickness of chromium nitride was 60 μm, and it was attempted to examine the corrosion resistance in the same manner as in Example 1, but cracks were found in the film, No further evaluation was done. Example 4 The same stainless steel material as that used in Example 1 was subjected to a chromium diffusion infiltration treatment to a thickness of 5 μm as a pretreatment, and then chromium nitride (CrN: 100%) was applied by a reactive ion plating method. Corrosion resistance was examined in the same manner as in Example 1 by coating a test piece with a film thickness of 3 μm. The results are shown in Table 1.
Shown in. Example 5 The same stainless steel material as used in Example 1 was subjected to a chromium diffusion / infiltration treatment to a thickness of 50 μm as a pretreatment, and then chromium nitride (CrN: 100%) was applied by a reactive ion plating method. Corrosion resistance was examined in the same manner as in Example 1 by coating a test piece with a film thickness of 50 μm. The results are shown in Table 1.
Shown in.
【０００９】[0009]
【表１】 [Table 1]
【００１０】〔耐キャビテーションエロージョン性の評
価〕 実施例６ 上述した実施例１〜５の窒化クロム被覆ステンレス鋼に
ついて、耐キャビテーションエロージョン性を調べるた
め、ASTM規格（G32-77）に準じた対向型のキャビテーシ
ョンエロージョン加速試験を行ったところ、いずれの試
験片も同様の結果を示し、図４のグラフに示すように、
重量減はほとんど見られなかった。 比較例５ 比較例２で用いたステンレス鋼について実施例４と同様
の試験を行った結果、図４のグラフに示すように、実施
例４の場合に比し重量減が見られた。 比較例６ ステンレス鋼に変えてジルコニウムを用いた以外は比較
例５と同様の試験を行った結果、図４のグラフに示すよ
うに、顕著に重量減が見られた。[Evaluation of Cavitation Erosion Resistance] Example 6 With respect to the chromium nitride-coated stainless steels of Examples 1 to 5 described above, in order to investigate the cavitation erosion resistance, a facing type according to ASTM standard (G32-77) was used. When a cavitation erosion acceleration test was performed, all the test pieces showed similar results, and as shown in the graph of FIG.
Little weight loss was seen. Comparative Example 5 As a result of performing the same test as in Example 4 on the stainless steel used in Comparative Example 2, as shown in the graph of FIG. 4, a weight reduction was observed as compared with the case of Example 4. Comparative Example 6 The same test as in Comparative Example 5 was carried out except that zirconium was used instead of stainless steel, and as a result, as shown in the graph of FIG. 4, a significant weight reduction was observed.
【図１】 尿素合成プラント用減圧弁の断面図である。FIG. 1 is a cross-sectional view of a pressure reducing valve for a urea synthesis plant.
【図２】 (a) 〜(c) は、貫通欠陥（ピンホール）から
の腐食過程を説明するための概念図である。2A to 2C are conceptual diagrams for explaining a corrosion process from a penetration defect (pinhole).
【図３】 基材に前処理としてクロム拡散浸透処理を施
した後、窒化クロム被覆を施した場合の本発明に係る減
圧弁の状態を示す概念図である。FIG. 3 is a conceptual diagram showing a state of a pressure reducing valve according to the present invention when a chromium diffusion coating is applied to a substrate as a pretreatment and then a chromium nitride coating is applied.
【図４】 窒化クロムの耐キャビテーションエロージョ
ン性を示すグラフである。FIG. 4 is a graph showing cavitation erosion resistance of chromium nitride.
１：減圧弁本体 ２：流体入口 ３：プラグ ４：プラグ先端部 ５：シートリング ６：プラグ先端部とシートリングに囲まれた狭部 ７：流体出口 11：ピンホール 12：皮膜 13：基材 14：腐食による空孔 15：剥離した皮膜 16：高クロム合金層 1: Main body of pressure reducing valve 2: Fluid inlet 3: Plug 4: Plug tip part 5: Seat ring 6: Narrow part surrounded by plug tip part and seat ring 7: Fluid outlet 11: Pinhole 12: Film 13: Base material 14: Voids due to corrosion 15: Exfoliated film 16: High chromium alloy layer
Claims (2)
ャビテーションエロージョンを受けやすい減圧弁を窒化
クロム材で構成したことを特徴とする尿素合成プラント
用減圧弁。1. A pressure reducing valve for a urea synthesis plant, characterized in that the pressure reducing valve which is susceptible to corrosion and cavitation erosion in the urea synthesis process is made of a chromium nitride material.
基材を窒化クロムで被覆したものにより構成されている
ことを特徴とする請求項１記載の尿素合成プラント用減
圧弁。2. The pressure reducing valve for a urea synthesis plant according to claim 1, wherein the pressure reducing valve is composed of a metal base material subjected to a chromium diffusion and infiltration treatment and coated with chromium nitride.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP5034962A JP2608234B2 (en) | 1992-02-26 | 1993-02-24 | Pressure reducing valve for urea synthesis plant |
Applications Claiming Priority (5)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP3930092 | 1992-02-26 | ||
| JP4-39300 | 1992-09-11 | ||
| JP24315992 | 1992-09-11 | ||
| JP4-243159 | 1992-09-11 | ||
| JP5034962A JP2608234B2 (en) | 1992-02-26 | 1993-02-24 | Pressure reducing valve for urea synthesis plant |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH06136516A true JPH06136516A (en) | 1994-05-17 |
| JP2608234B2 JP2608234B2 (en) | 1997-05-07 |
Family
ID=27288591
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP5034962A Expired - Lifetime JP2608234B2 (en) | 1992-02-26 | 1993-02-24 | Pressure reducing valve for urea synthesis plant |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP2608234B2 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2008223907A (en) * | 2007-03-13 | 2008-09-25 | National Institute Of Advanced Industrial & Technology | Back pressure regulating valve |
Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5219123A (en) * | 1975-08-06 | 1977-02-14 | Nakano Hagane Kk | Chromizing by previously heated agents |
| JPS56147756A (en) * | 1980-04-15 | 1981-11-16 | Toyo Eng Corp | Synthetic method of urea using silicon carbide material in apparatus |
| JPS59205469A (en) * | 1983-05-02 | 1984-11-21 | Mitsubishi Heavy Ind Ltd | Chromium diffuse permeation treatment method |
| JPS61257466A (en) * | 1985-05-09 | 1986-11-14 | Mitsubishi Heavy Ind Ltd | Erosion-resisting film |
| JPH02129360A (en) * | 1988-11-07 | 1990-05-17 | Sumitomo Metal Mining Co Ltd | Corrosion-resistant and wear-resistant coated steel and its manufacture |
-
1993
- 1993-02-24 JP JP5034962A patent/JP2608234B2/en not_active Expired - Lifetime
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5219123A (en) * | 1975-08-06 | 1977-02-14 | Nakano Hagane Kk | Chromizing by previously heated agents |
| JPS56147756A (en) * | 1980-04-15 | 1981-11-16 | Toyo Eng Corp | Synthetic method of urea using silicon carbide material in apparatus |
| JPS59205469A (en) * | 1983-05-02 | 1984-11-21 | Mitsubishi Heavy Ind Ltd | Chromium diffuse permeation treatment method |
| JPS61257466A (en) * | 1985-05-09 | 1986-11-14 | Mitsubishi Heavy Ind Ltd | Erosion-resisting film |
| JPH02129360A (en) * | 1988-11-07 | 1990-05-17 | Sumitomo Metal Mining Co Ltd | Corrosion-resistant and wear-resistant coated steel and its manufacture |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2008223907A (en) * | 2007-03-13 | 2008-09-25 | National Institute Of Advanced Industrial & Technology | Back pressure regulating valve |
Also Published As
| Publication number | Publication date |
|---|---|
| JP2608234B2 (en) | 1997-05-07 |
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