Application of Risk-Based Inspection in Safety Assessment of Pressure

Proceedings of PVP2006-ICPVT-11 2006 ASME Pressure Vessels and Piping Division Conference July 23-27, 2006, Vancoucer, BC, Canada

PVP2006-ICPVT-11-94044

CHEN Xuedong, YANG Tiecheng, WANG Bing, AI Zhibin, CHENG Chuanqing

Hefei General Machinery Research Institute, Hefei 230031, China

Application of Risk-based Inspection in Safety Assessment of Pressure

Equipment of Chinese Petrochemical Plants

Abstract

carried out by the authors in recent years on ten sets of

In this paper the effect of quantitative RBI work

plants of six SINOPEC and PetroChina system using BV’large-scale petrochemical enterprises in ®

software and database is introduced, several outstanding

s RB.eye

problems about application of RBI in Chinese

petrochemical plants are discussed and suggestions

about further development of RBI works in the future

are proposed.

Keywords

Pressure Equipment; Safeguard

Rise-based Inspection (RBI); Petrochemical Plant,

1. Introduction optimization of inspection strategy established based on Risk-based inspection (RBI) is a methodology for the concept that seeks unity between system safety and economy, its essence is to analyze and prioritize the occurrence possibility and consequence of hazardous events so as to find out principal problems and weak links, ensure intrinsic safety as well as reduce running cost.

American developed countries took the lead to apply risk After middle 1990s last century, European and analysis methods to inspection and service of pressure-bearing equipments of petrochemical enterprises, especially oil refinery plants and obtained favorable effect [1]~[3]API successively published two documents API BRD . In the first two years this century, 581[4]platform for various countries to develop RBI works of and API RP 580[5], which provide a unified base petrochemical plants.

1equipment bureau of the State Administration of Quality Since 2003, under the concern of the special Supervision, Inspection and Quarantine under the support of the two big petrochemical (AQSIQ) and groups—inspection station of Hefei General Machinery Research SINOPEC and PetroChina, the pressure vessel Institute (GMRI) has conducted quantitative RBI works on tens of petrochemical plants in China in cooperation with Bureau Veritas (BV), we have discussed such matters as the relationship between acceptable risk and statutory regulations, fitness to Chinese national conditions and software improvement, etc.[6][7]RBI practice of ten plants already finished in 2004, In this paper based on summary on the quantitative . several problems about development of RBI in China are further discussed and suggestions about future development of RBI are proposed.

2. Outline of RBI Implementation Effect

inspection strategies are all formed through risk RBI process is not complicated, optimized calculation and failure modes, analysis of failure mechanisms and prioritization, determination of major positions and inspection procedures, specific methods have been introduced in relevant API documents and literature[6][8]herein.

, therefore, description of them is omitted RBI works of ten petrochemical plants, for specific By the year 2004, we have completed quantitative plants, see Table 1. Hereafter we implementation effect respectively in terms of risk will discuss RBI distribution, failure mode, damage mechanism, position, inspection strategy and inspection cycle etc. of damage equipments and pipes. in the plants.

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Table 1

Plant

SINOPEC Maoming branch

Plant name

Dalian west Pacific Petrochemical Co., Ltd.

Fujian Refining and Chemical Co., Ltd.

system of heavy oil catalytic unit

(Unit) 84 Remarks

(Pcs) Finished in 2003 Completed in 2004

391

Completed in 2004

2.1 Analysis of risk distribution results

5×5 matrix is adopted as the output format for risk prioritization, for risk distribution of stationary

equipments and pipelines for the ten units of plants, see Table 2 and Fig. 1~3.

When viewing from the statistical results of risk distribution of stationary equipments and pipelines, the stationary equipments with "medium and high" risk or "high" risk in the ten oil refinery and chemical plants whose inspections have already been completed account for about 44%, and pipelines with "medium and high" risk or "high" risk account for about 11%. Whereas the equipments with "medium and high" risk or "high" risk in the petrochemical plants in developed countries in

Europe and America etc. roughly account for about 20% of total equipments (i.e. meets the 20%/80% split theory). When viewing from the present RBI risk analysis results, the risk level of Chinese petrochemical plants is higher than that of foreign similar plants as a whole.

As plants are concerned, equipments with "high" risk have a relatively high proportion in the hydrogenation plants, catalytic cracking units take second place, and following it are atmospheric and

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vacuum distillation units and hydrogen production plants, whereas ethylene cracking units have no high-risk equipments in the process system.

2.2 Failure modes and analysis of damage mechanism

RBI analysis results show that the main failure modes of stationary equipments and pipelines for ethylene cracking units are as follows: corrosion thinning, external corrosion; the main failure modes of stationary

equipments and pipelines for catalytic cracking units are: corrosion thinning, SCC, external corrosion; and main failure modes of stationary equipments and pipelines for hydrogen production plants are: corrosion thinning, external corrosion and high temperature hydrogen attack.

For the distribution of damage mechanisms of stationary equipments and pipelines of the ten plants, see Fig. 4~8.

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sulfur/naphthenic acid corrosion on inner wall overlay. It can be seen from statistical results of damage

The damage mechanisms of stationary equipments mechanism distribution that the main damage

and pipelines for atmospheric and vacuum distillation mechanisms of stationary equipments and pipelines for

units are mainly SSCC, HIC/SOHIC, sour water ethylene cracking units are mainly corrosion under

corrosion, high temperature sulfur/naphthenic acid insulation, SSCC, HIC/SOHIC, sour water corrosion and

corrosion and corrosion under insulation etc. Compared carbonate cracking, etc. Corrosion under insulation

to other plants, the high temperature sulfur/naphthenic mainly occurs on cold insulation equipments and

acid corrosion of equipments and pipelines in this plant pipelines of low temperature separation system. Because

appears more remarkable. the raw material (mainly naphtha) used by ethylene

The corrosion damage of stationary equipments in cracking unit is relatively clean, the corrosion damage

catalytic cracking unit is more severe than pipelines, the (especially damage under wet H2S environment) of

damage mechanisms of stationary equipments are SSCC, equipments and pipelines during the operation is

HIC/SOHIC sour water corrosion, carbonate cracking relatively light compared to oil refining plant.

and corrosion under insulation etc., whereas damage The damage mechanisms of stationary equipments

mechanisms of pipelines are mainly SSCC, HIC/SOHIC, and pipelines in the hydrogenation plant (including

sour water corrosion etc. In addition, in catalytic hydrocracking and hydrofining units) are SSCC,

regeneration system there is nitrate SCC mechanism and HIC/SOHIC, sour water corrosion, corrosion under

in flue gas ducts there may be the phenomenon of flue insulation, high temperature sulfur/naphthenic acid

gas dust erosion. corrosion etc. Among them SSCC and HIC/SOHIC may

The damage mechanisms of stationary equipments occur in all types of equipments (columns, reactors, heat

and pipelines in hydrogen production plant are mainly exchangers, air coolers, storage vessels, etc.), sour water

corrosion under insulation, high temperature corrosion mainly occurs on heat exchangers, air coolers

sulfur/naphthenic acid corrosion and high temperature and part of vessels, whereas high temperature

hydrogen corrosion, etc., there are less damage sulfur/naphthenic acid corrosion mainly appears on heat

mechanisms of equipments and pipelines in this plant, exchangers and reactors and related pipelines.

especially there are basically no typical SSCC, Meanwhile, the RBI analysis results of hydrogenation

HIC/SOHIC damages in other plants. The main reason plants also show that the damage mechanisms existing on

lies in that the hydrogen production plant adopts clean overlay welded hydrogenation reactors under normal

light hydrocarbons as the raw stock, and no other operating conditions are mainly high temperature

stronger corrosive substances will be charged or formed hydrogen sulfide/hydrogen attack, high temperature

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through reaction in the process.

2.3 Development of inspection strategies

The so-called RBI inspection strategy is to solve the four questions during equipment inspection as what, where, how and how long. The first three questions have been discussed [6], therefore this paper mainly introduces

the determination of inspection cycle.

Reasonable determination of equipment inspection cycle is an important aspect which embodies scientificalness of RBI inspection strategy, Fig. 9 shows the division of inspection cycle of stationary equipments in the ten plants.

and one hydrogen production plant, the rest all belong to We observe the following general rules according

the equipments with high failure consequence and low to years experience of Hefei General Machinery

failure probability, as long as management is carried out Research Institute when we determine the inspection

during the normal operation and service (inspection), cycle of equipments for the ten plants: First, we usually

these equipments will have a low probability for failure determine the inspection cycle as 2~3 years of the

occurrence. In China, in the past the inspection items of equipments with "medium and high" risk or "high" risk

hydrogenation reactors were too comprehensive and and failure probability level bigger than 3. Such

inspection cycle was on short side, they belong to the equipments account for about 4% of total equipments;

equipments of "excessive inspection". Second, we determine equipment inspection cycle as 6

years of the equipments with "medium" risk and failure

probability level bigger than 3, or with "high" risk and

3. Discussion about Several Problems

failure probability level of 3, but one online inspection

3.1 Relationship between RBI techniques and Chinese law should be added during this period. Such equipments

regulations and technical standards account for about 17% of total equipments; Third, we

The risk control using API 580 or API 581 needs a determine inspection cycle as 6 years of the equipments

series of supports of inspection codes and fit-to-use with failure probability level of 3 and "low" risk, or

integrity assessment standards, these supports are various failure probability level not bigger than 3 and "medium"

specific requirements for inspection, examination and and "medium and high" risk or failure probability level

maintenance technology such as API 750, API 510, API not bigger than 2 and "high" risk. Such equipments

570, etc. account for about 68% of total equipments; Fourth, we

API 581 and API 580, when practiced in China, also determine the inspection cycle as properly extended 7~9

need a series of technical supports. "Periodical inspection years of the equipments with "low" or "medium" risk and

regulations for in-service pressure vessels" and failure probability level less than 3, but one online

"Periodical inspection regulations for in-service inspection should be added during this period. Such

industrial pipelines" promulgated by the State equipments account for about 11% of total equipments

Administration of Quality Supervision, Inspection and (which are mainly vessels storing medium as dry

Quarantine are the mandatory technical specifications, compressed gas).

and also the specific methods for inspection and It needs to be pointed out that except for two

maintenance technology that are consistent with China's reactors which have been in service for more than 30

realities. In RBI activities, they and codes on integrity years in a total of 20 hydrogenation reactors in the four

assessment of defect-containing equipments, for example, hydrogenation (including cracking and refining) plants

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