1

[L2.1.6]

R&D on Diagnostic Technology for Coking

in Heating Furnace Pipes

(Coking Diagnostics Group)

Sendai 402 Laboratory �Hirotada Mitsuhashi, Kazuhiro Somaki,

Koichi Nakada

1. R&D Objectives

In the petroleum refining industry of recent years, demand has arisen for augmentation of an

equipment control system so as to promote voluntary maintenance of security, secure safe plant

operations and facilitate continuous, long-term, stable operations. From this standpoint, the

equipment control status of heating furnace pipes is reviewed, and in designing component

materials to be used under high temperature and high pressure, attention is given to securing

safety by such means as examining materials and monitoring application temperatures. But with

changes in operating conditions, cases will arise in which there is creep damage to materials

and/or inner surface corrosion because of tube wall temperature increases, bringing about rapid

adhesion of coke (that is, coking). And in light of past maintenance experience, it can be

confidently forecasted that the worst of such cases can lead to accidents.

With the equipment in question, therefore, accurate determination of the status of inner surface

coking is extremely important in equipment control, and this status is checked periodically. Yet

with current methods of investigation, adequate information is not always obtained. Against this

backdrop, the purpose of the present R&D is to develop a small, lightweight, coking diagnosis

unit that can diagnose coking conditions quickly and accurately, employing a sound wave

method, and thus contribute to safe plant operations.

In JFY1999, preliminary tests were conducted for construction of a trial-produced circuit for

coking diagnosis unit, and the trial-produced circuit was laid out. In JFY2000, data were

collected on practical equipment piping and on heating furnace piping in the field, and by

comparing results with those obtained by other methods, detection performance was evaluated.

For this purpose, an ultrasonic wave input/detection probe that can withstand applications in the

field was trial produced, and it was applied in field tests. Furthermore, based on the results of

preliminary tests and field tests, a small-scale, lightweight trial-produced system, the

development target, was designed and fabricated, and tests were conducted to verify its

functions. In JFY2001, data were collected with practical unit heating furnace in refineries at

three locations, and by comparing the results with those obtained by RT (scale checker*) or by

radiographing, the detection performance of the trial-produced coking diagnosis unit was

evaluated. In order to investigate the limits of detection with the trial-produced coking diagnosis

unit, model coking pipe was used in conducting detection tests.

*NOTE：Scale checker is a kind of radioactive test. Radioisotope and detector move across from one side

of pipe to the other side, then it estimate clogging rate by counting the amount of passed

radioactivity.

2002

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2. R&D Contents

Table 2-1 presents the overall plan of the R&D.

Table 2-1: Overall Plan of R&D

Year Month

JFY1999 JFY2000 JFY2001

Item

April to

June

July to

Sept.

Oct. to

Dec.

Jan. to

March

April to

June

July to

Sept.

Oct. to

Dec.

Jan. to

March

April to

June

July to

Sept.

Oct. to

Dec.

Jan. to

March

1) Collection of basic data, construction of trial-produced circuit, and verification by test piece

2) Fabrication of trial-produced probe, and verification by test piece and field testing

3) Fabrication of practical unit, evaluation by field testing, and verification of sensitivity by test piece

2.1 R&D in JFY1999

As a preliminary test for construction of trial-produced circuit for coking diagnosis unit, an extant

AE analysis system (hereinafter, C-AEAS: Figure 2.1-1) was employed, and the following

preliminary tests were conducted in order to investigate the feasibility of the method in question.

(1) Identification of the presence/absence of full-surface coking and tests for detection of

coking thickness, implemented by comparing the results of analysis of new steel pipe and

of test steel pipe in which the full inner surface was coated with rubber.

(2) Identification of the presence/absence of partial coking and tests for detection of coking

locations, implemented with test steel pipe in which partial coking is mimicked, using

coking materials closely resembling practical coking ingredients.

(3) Construction of a trial-produced circuit and verification of trial-produced circuit feasibility.

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Figure 2.1-1: Outline Drawing of Test System

2.2 R&D in JFY2000

In the development of a trial-produced coking diagnosis unit, the following developments, tests

and evaluations were completed in order to evaluate the trial-produced circuit fabricated in

JFY1999.

(1) Fabrication of an ultrasonic wave input/detection probe that can accurately detect

measurement data

Preliminary tests conducted in JFY1999 disclosed that the state of contact at contact

points between the ultrasonic input/detection probe waveguide and measurement pipe

surface has a major impact on test results. Accordingly, an ultrasonic input/detection

probe was trial produced in which the level of stability in contact status was elevated by

spring-induced pressure.

(2) Application to sample piping, and evaluation

With the trail-produced ultrasonic input/detection probe, detection of partial dummy coking

on sample piping, using 10B pipe, was tested (Figure 2.2-1).

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Dummy coking Pipe support

Piping specification: STPG370-S 10B

SCH80

Elbow: PT370 10B

SCH80 90LR

Pipe shoe : 400L

Dummy coking

Pipe support

Figure 2.2-1: Sample Pipe Drawings (Measurement points)

(3) Application to practical equipment and heating furnace tube and piping, and evaluation

Tests were conducted on detection of coking in practical equipment piping and in heating

furnace piping at petroleum plants during routine servicing, using the analysis system

developed in 1999 and the ultrasonic wave probe developed in 2000.

· Target piping

Unit name : Residual oil fluid catalytic cracker Main fractionator bottom oil effluent line

Dimensions : 12B

SCH80 and 10B SCH80 Material : 5Cr-0.5Mo Steel

· Target heating furnace tube

Unit name : Residual oil direct desulfurization unit (Reactor Feed Furnace)

Dimensions : 6B SCH120 Material : SUS347TF

(4) Fabrication of trial-produced system and evaluation, analysis of its functions

Based on the results of preliminary tests and field tests, a trial-produced system (including

ultrasonic wave probe and small computer for analysis) was fabricated. The system

consists of three major components: probe, signal processor and control computer. Its

circuit composition is depicted in Figure 2.2-2. An overview of the system appears in

Figure 2.2-3.

Figure 2.2-2: Circuit Composition

of Trial-Produced

Coking Diagnosis

System

Figure 2.2-3: Overview of

Trial-Produced

Coking Diagnosis

System

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(5) Test application of trial-produced system to sample piping

Functions of the trial-produced system were verified by using the system to test its

detection of partial dummy coking in two types of sample piping: U-shaped pipe comprised

of 10B steel pipe and 4

B straight steel pipe.

2.3 R&D in JFY2001

Using the trial-produced coking diagnosis system developed in JFY2000, data were collected

with practical unit heating furnace in refineries undergoing routine maintenance at three

locations (A, B, C), and by comparing the results with those obtained by RT (scale checker) or

by radiographing, the detection performance of the trial-produced coking diagnosis system was

evaluated. In order to investigate the limits of detection with the trial-produced coking diagnosis

unit, model coking pipe in which half the pipe inner surface was coated with rubber was used to

conduct tests.

(1) Collection of data on practical unit heating furnace pipe (Measurement method for refinery

A is shown as a typical example.)

· Target pipe

Unit name : REACTOR FEED HEATER FU-01A/B

Dimensions: 7B Sch120

Material: A271TP321 (SUS 29)

· Measurement location and method

Figure 2.3-1 is a drawing of the measurement positions of the target pipe. At a height of

1500 mm from the furnace floor, measurements were taken over 5 intervals, at positions

1, 5, 10, 15 and 20, from the linear pipe inlet. At the outlet side, where the rate of

clogging due to coking is believed to be high, measurements were taken at positions 24,

25 and 26, more closely arranged than on the inlet side. In this way, measurements were

taken at a total of 8 locations per pass. In response to the 4 passes of FU-01A (2

passes) and FU-01B (2 passes), measurements were taken at a total of 32 locations.

Figure 2.3-1: Drawing of FU-01A/B Measurement Locations

(2) Half-face rubber coating test

The following two types of test pipe were used, each being 6B,

Sch40JISG3459SUS321TP pipe 500 mm in length (outer diameter: 165.20 mm; inner

diameter: 151.00 mm; thickness: 7.10 mm; material: SUS321).

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· TP0 pipe ... Elemental pipe (no inner surface coating)

· TP1 pipe ... Pipe with about 0.3 mm of rubber coating on inner surface half face

Acrylic synthetic rubber was used for coating TP1 pipe uniformly at a layer thickness of

approximately 0.3 mm. The pipe was then left to dry for 24 hours at room temperature

before being used.

· Measurement method

Figure 2.3-2: Measurement Method for Half-Face Rubber Coated Pipe

TPO pipe and TP1 pipe were measured, using the coking diagnosis system developed

last year, and the detection limits of the trial-produced coking diagnosis system were

investigated through comparative studies. Measurements were taken of TP1 pipe, which

underwent rubber coating over half its inner surface, at the location where the ultrasonic

wave probe of the coking diagnosis tester was attached, directly opposite to the rubber

coating side, as shown in Figure 2.3-2.

3. R&D Results

3.1 R&D Results in JFY1999

As a preliminary test for development of a heating furnace pipe coking diagnosis system,

ultrasonic wave analysis tests were conducted on rubber coated pipe, using the AE analysis

system (C-AEAS). It was demonstrated that differences in coking condition of pipe inner surface

can be detected quickly and accurately by using AE parameters as assessment standards. In

addition, the trial-produced circuit was laid out and its feasibility was studied. The results

obtained are presented below.

(1) In an analysis of elemental 6B, Sch40 pipe and of pipe in which the entire inner surface

was coated with rubber to approximately 0.3 mm, it was demonstrated that distinctions

could be clearly made by using an amplitude and continuation time period correlation filter.

The time period for such distinctions, including frequency analysis, was approximately 45

seconds.

(2) In a comparison of the results of ultrasonic wave analysis of three types of model coking

pipe, in which the entire inner surface was coated with rubber to 0.3 mm, 0.6 mm or 0.9

mm, it was demonstrated that even slight differences in coating thickness of only 0.3 mm

could be detected by using the correlation between amplitude and continuation time

period.

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(3) In ultrasonic wave analysis of elemental 6B, Sch40 pipe and of pipe which underwent two

types of coking process, with practical coking material mimicked over an area of 100 mm

� 100 mm on the inner wall, it was demonstrated that in either case, the presence of

partial coking could be clearly distinguished by using energy and continuation time period,

the AE parameters (Figure 3.1-1). It was also suggested that the approximate positions of

coking can be estimated. And these analysis time periods were no more than about 3

seconds.

Figure 3.1-1: Comparison of Correlations between Energy and

Continuation Period for TPO, TP2-C3, and TP1-C3

(TPO: elementary pipe, TP1: a 1:1 mixture of oil paint and

fine coal, TP2: a 1:1 mixture of paste and fine coal, C3:

partial coking at surface 180° opposite)

(4) The basic concept of the practical equipment coking diagnosis unit was presented and a

trial-produced circuit was established based upon the same. Equipment currently

available was used in part, and it was by combining these that the trial-produced circuit

was established. Feasibility could be confirmed because verification test results were

similar to results obtained in (1), (2) and (3) above. The handy-type input/detection unit

was also investigated and presentations were made of specific development concepts.

What is more, there were no sounds or vibrations in these tests that could be detected by

human senses.

3.2 R&D Results in JFY2000

Data were collected with practical equipment piping and heating furnace piping at the local plant,

and the coking detection performance of this newly developed system was evaluated by making

comparisons with results obtained by other methods. At first, an ultrasonic input/detection probe

for local plant was trial produced, then tests were done on detection of partial coking in sample

piping. Feasibility of the trial-produced probe was investigated, and detection tests were done

on clogging rate due to coking of practical equipment piping and heating furnace piping

available for joint use at a petroleum plant. Next, the trial-produced system (including ultrasonic

wave probe and small computer for analysis) was fabricated, and functioning was verified by

conducting detection tests of partial coking in two types of sample piping, using the

trial-produced system. The results obtained are presented below.

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(1) Using trial-produced ultrasonic wave probe, tests were done on detection of partial coking

of 10B, Sch80 sample pipe. As a result, it was discovered that detection of partial coking

and to some extent, determination of its location are possible (Figure 3.2-1). Tests took

place within the plant compound and favorable results were obtained, with no impact from

noise or vibration.

Continuation Period

Correlation

Energ

y

Figure 3.2-1: Correlation between Continuation Period and Energy

Count (Figure 2.2-1 points 6 to 10)

(2) From detection tests of clogging rate due to coking of 12B, Sch80 pipe and 10

B, Sch80

pipe used jointly at a practical petroleum plant, it was learned that differences in clogging

rates of 0, 7, 12, 23 and 29% could be distinguished (Figure 3.2-2). In addition,

measurements could be taken by one worker and the time required for distinction was

about 5 seconds.

A pipe inlet

Correlation

Energ

y

Continuation Period

C pipe outlet

C pipe inlet

A pipe outlet

B pipe outlet

Figure 3.2-2: Correlation between Pipe Continuation Period and Energy

Count

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(3) From detection tests of clogging rate due to coking of 6B, Sch120 heating furnace pipe

(total length about 120m) available at a practical petroleum plant, differences of 5 to 10%

in clogging rate could be distinguished, but it was very difficult to distinguish differences of

1 to 2%.

(4) Using trial-produced ultrasonic wave probe, tests were done on detection of partial coking

of 10B, Sch80, U-shaped, sample pipe. As a result, it was discovered that detection of

partial coking and to some extent, determination of its location are possible. From a

comparison with measurements taken by general-purpose AE analysis system (C-AEAS)

it was learned that roughly similar results can be obtained, and thus the functions and

performance of the trial-produced system were confirmed.

(5) Using trial-produced system, tests were done on detection of partial coking of 4B linear

sample pipe with weld seam. As a result, it was discovered that detection of partial coking,

even thin coking of 1 to 2 mm, and to some extent, determination of its location are

possible. It was also found that with this method, there was virtually no impact from weld

seam.

3.3 R&D Results in JFY2001

Using the trial-produced coking diagnosis unit developed in JFY2000, data on practical

equipment heating furnace piping was obtained at three oil refineries. Coking detection by this

trial-produced system was evaluated by making comparisons with inspection results obtained by

RT (scale checker) and by radiographing. The results are presented below.

(1) Using the trial-produced coking diagnosis unit at refinery plant A, currently undergoing

routine maintenance, REACTOR FEED HEATER FU-01A/B heating furnace pipe

(dimensions: 7B Sch120, material: A271TP321 (SUS 29)) was measured before and after

de-coking. Generally, at the heating furnace piping, experience disclosed that although

coking is also dependent upon the reaction system, because the pipe outlet temperature

is higher than the inlet temperature, coking increases as you go from pipe inlet to outlet

and clogging rate increases. In this analysis method, which uses the correlation between

AE continuation period and energy count, the clogging rate diminishes as you go farther

to the upper right of the correlation drawing and increases as you go farther to the lower

left. From these measurements it was recognized that in every pass correlation drawing,

the values tend to go from the upper right to the lower left as you get closer to the outlet

from the inlet. It was also learned that these results match well with findings obtained from

experience. In addition, by making a comparison of data before and after decoking, it was

found that for all passes, coking can be removed by decoking, that measurement data

moves to the upper right, and that results reflecting the effects of proper decoking are

obtained (Figure 3.3-1).

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Continuation Period

Correlation

En

erg

y

Figure 3.3-1: FU-01AS Correlation Diagram before (blue) and after (red)

Decoking (Continuation Period vs Energy) (In the figure,

numbers to the left denote measurement point No. and to

the right, clogging rate.)

On the other hand, no clear relationship could be noted between clogging rate by RT and

measurement data obtained with the trial-produced system. One reason for this may be

that structurally, the RT meter measures the local, cross-sectional clogging rate of the

measurement site and does not measure average internal surface clogging property, as

does the trial-produced system.

Accordingly, verification of correlation was made by means of a graph in which clogging

rate was plotted on the vertical axis and AE energy or continuation period was plotted on

the horizontal axis. Although disparities were large, a rough correlation was recognized in

which energy or continuation period tends to become large as the clogging rate grows

smaller (Figure 3.3-2).

Continuation period (µ sec)

Clo

ggin

g r

ate

(S

cale

checker:

%)

Energy (counts)

Error

+/- about 5%

Clo

ggin

g r

ate

(S

cale

checker:

%)

Error

+/- about 5%

Figure 3.3-2: Clogging Rate vs Energy and Clogging Rate vs

Continuation Period (Refinery A: FU-01AS)

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(2) Using the trial-produced coking diagnosis system at refinery plant B, currently undergoing

routine maintenance, REACTOR FEED FURNACE RDS-FU-01A/B heating furnace pipe

(dimensions: 6B Sch120, material: SUS347TF) was measured. From the correlation

drawings of every pass, it was confirmed that the values tend to go from the upper right to

the lower left as you get closer to the outlet from the inlet. It was also learned that these

results match well with findings obtained from experience. On the other hand, no clear

relationship could be noted between clogging rate by RT and measurement data, but a

reason similar to that given in (1) above can be given to explain the situation.

(3) Using the trial-produced coking diagnosis unit at refinery plant C, currently undergoing

routine maintenance, test was performed to detect coking in 4 pipes laid out horizontally

inside a VACUUM TOWER CHARGE HEATER 9AF-1. In using this analysis method, pipe

was analyzed by three pipe sizes (5B, 8

B, 10

B) because measurement results vary by pipe

outer diameter. Trial-produced equipment was evaluated with measurements both by RT

(scale checker) and radiographing.

Generally, at the heating furnace piping, experience disclosed that although coking is also

dependent upon the reaction system, because the pipe outlet temperature is higher than

the inlet temperature, coking increases as you go from pipe inlet to outlet and clogging

rate increases. In this analysis method, which uses the correlation between AE

continuation period and energy count, the clogging rate diminishes as you go farther to the

upper right of the correlation drawing and increases as you go farther to the lower left.

With the four pipes subject to these measurements, it could be confirmed that if attention

focuses on the number of stages installed from furnace floor, irrespective of pipe size, as

the number of stages diminishes, the cluster of measurements in the correlation drawing,

from inlet side to outlet, goes from upper right to lower left, and although differences arise

between pipe stages, the results in general match with extant findings. In piping laid out

on the same stage from the furnace floor, there are cases in which a correlation cannot be

noted between the sequence from inlet side and the cluster formation position. But the

latest measurements suggest that for pipe at the same stage, a cluster forms more easily

at the lower left if the pipe tip is a header rather than a U-bend.

In general, measurements of clogging rate by RT scale checker, used for evaluating the

trial-produced equipment, and of coking thickness by radiographing correctly supported

the results of analysis by the trial-produced system.

(4) In order to investigate the detection limit of the trial-produced coking diagnosis unit,

comparisons were made of measurement data from test pipe (Sch40JISG3459

SUS321TP of 500 mm length) on which half the inner surface was coated with rubber at

approximately 0.3 mm thickness and from elementary pipe not coated with rubber. The

cluster of measurement data from the rubber-coated test pipe clearly appeared more to

the lower left than did the cluster of elementary pipe data. What this means is that when

the trial-produced system is used, dummy coking equivalent to rubber coating of about

half the pipe’s inner surface can be detected with no problems. In this way, the level of

sensitivity in detection by the trial-produced system was confirmed (Figure 3.3-3).

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Continuation period

Energ

y

Figure 3.3-3: Diagram of Correlation between Elementary Pipe (TPO)

and Half Face Rubber Coated Pipe (TP1) (Continuation

Period vs Energy)

4. Synopsis

In JFY1999, basic data were collected by means of preliminary tests aimed at the development

of a coking diagnosis unit. By taking AE parameters as assessment criteria, it was

demonstrated that the presence/absence of coking in steel pipe inner surface, and differences

in conditions thereof, could be detected quickly and accurately. Based on preliminary test data,

a trial circuit of a coking diagnosis unit was constructed and verified. Its feasibility could be

confirmed because results similar to those from preliminary tests were obtained.

In JFY2000, an ultrasonic input/detection probe and trial-produced system were trial-produced

based on the trial circuit fabricated in JFY1999, and these were applied to sample piping,

practical equipment piping and heating furnace piping. It was confirmed that the trial-produced

system has a data detection capacity equivalent to that of a general-purpose AE analysis

system device. And in completing the trial-produced system, the objectives of smaller size and

reduced weight for the coking diagnosis unit were achieved.

In JFY2001, using the trial coking diagnosis system developed in JFY2000, data on practical

equipment heating furnace piping were retrieved at three oil refineries undergoing routine

maintenance, and comparisons were made of inspection results obtained by RT (scale checker)

and by radiographing. Generally, at the heating furnace piping, experience disclosed that coking

increases as you go from pipe inlet to outlet and clogging rate increases. But research in

JFY2001 revealed that the presence/absence of coking, and coking magnitude, can be detected

constantly by using the trial-produced system. What is more, comparisons of measurement data

before and after decoking clearly supported the fact that coking can be detected. From

verifications of correlations between clogging rate and AE energy or continuation period, it was

recognized that there are correlations in general, although disparities were large. Tests using

model coking pipe, with half the pipe’s inner surface coated with rubber, confirmed that the

trial-produced system’s level of sensitivity in detection of coking is high.

Copyright 2002 Petroleum Energy Center. All rights reserved.