07 PPP TTE Heat Exchanger Inspection

8/13/2019 07 PPP TTE Heat Exchanger Inspection

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Matthews Engineering Training Ltd

INSPECTING HEAT

EXCHANGERS


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INSPECTING HEAT EXCHANGERS

Shell-and-tube type Plate type

We will look mainly at these (most are

statutory equipment as they contain

relevant fluids)


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Some heat exchanger technical standards

TEMA 8thEd :Standards for design and

construction of heat exchangers

API 662 :Plate heat exchanger specifications

API 660 :Shell and tube heat exchangers forgeneral refinery service

ASME PTC 39 : Air cooled heat exchangers



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The TEMA regulations

(Tubular Equipment Manufacturers

Association

A USA technical standard ( but also used for guidance

in most other countries)


TEMA is the main design document of interest to

inspectors


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TEMA sections

1.Nomenclature (names of heat exchanger components)

2.Manufacturing tolerances

3.General fabrication information

4.Performance and operation

5.Design information

6.Flowinduced vibration7.Thermodynamics

8.Properties of fluids

9/10: Recommended good practice

Most useful

parts for

inspectors



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TEMA classes : R, C and B

R: Severe applications : Petrochemical industry

C: Moderate applications:General process uses

B: Chemical process service

High risk

Low risk

R C B = Differences in : Minimum corrosion allowanceTube pitch,shell thickness and other design parameters

INSPECTING HEAT

EXCHANGERS


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TEMA

EXCHANGERS

ARECLASSIFIED

BY TYPE

:USING A 3-

LETTERACRONYM

First letter

:Front end

arrangement

Second letter

:Shell flow path

Third letter

:Back end

arrangement



Exchanger type AESA E

S

TEMA EXCHANGER TYPES



Kettle reboiler type AKT

A: Channel and removable cover

K: Reboiler configuration

T:Pull-through floatinghead

TEMA TYPES: ANOTHER

EXAMPLE



CONTACT TYPE EXCHANGER

9% Cr alloy for

high

temperature

steam

attemporator



ASME V111 Div 1

TEMA TECHNICAL CRITERIA

TEMA covers

predominantly

the tubesheetand tube

components

The pressure

envelope is more

often covered by

pressure vessel

code e.g ASME VIII-I



G max

TEMA EXAMPLE:NOZZLE

TOLERANCES

Major cause ofoverstressing of

nozzle welds



IN-SERVICE INSPECTION OF HEAT

EXCHANGERS

Common corrosion and erosionmechanisms

Failure assessment to pressure

envelope code requirements

Failure assessment to TEMA

requirements

3 major areas of interest



Water jet cleaning before inspection

Steamcleaning can

cause

distortions

IN-SERVICE INSPECTION

Light

distillate is

sometimesused

BUT



Corrosionproducts

should be

sampled

BEFOREwater

washing





Example of scale before water

washing




In-service checks can be divided into 3 parts

Shell Tube bundle Nozzles and fittings



SHELL INSPECTION

OVERALL wall

thinning (internal orexternal)

LOCALISED wall

thinning (internal orexternal)

Remember: isolated pi t t ingis

often ignored (according to

API 510)

???

Which is the

mostdangerous?



SHELL INSPECTION

COMMON MECHANISMSARE:

External CUI

Internal wastage

(impingement/erosion/corrosion)

Creep damage (>400

degC)

SCC in stainless steel

components

Flange face

imperfections (often SCC)

Require a

Code

assessment.

(See

inspection

exercise)



External CUI

Internal wastage

(impingement/erosion/corrosion)

Creep damage (>400

degC)

SCC in stainless steel

components

Flange face

imperfections (often SCC)

SHELL INSPECTION

SOME EXAMPLES:


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SHELL INSPECTION

MORE FLANGE FACEPROBLEMS:


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TEMA gives limits on RF flange face imperfections

Measurement

in radialdirection

SHELL INSPECTION


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Limits of imperfections in RF flange faces

SHELL INSPECTION


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Tubeplate ligament

erosion/cracking

Leaking tube-to-tubesheetjoints

Tubesheet distortion

Scaling/corrosion of tubes

Cracking/erosion of flow

baffles

TUBE BUNDLE INSPECTION

SOME EXAMPLES:

Some of

these require

a Code

assessment.

(See

inspectionexercise)


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Tube pitch may be square or triangular

(different TEMA rules for each)

More difficult to

mechanically clean

outside

Ligament

Erosion


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CuNi tubes can suffer from

galvanic corrosion caused by

graphite

Graphite is used as

a mandrel lubricant

during

manufacture of thetube


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Some types suffer from intergranular

corrosion

Ti tubes can

suffer fromproblems due to

incomplete

annealing


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Expanded (rolled)into tubesheet:some are seam welded

Rules of thumb for inspections


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The internal joint is rarely seal welded (poor

access)

Note threaded tie bar


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Tubeplate bore measurement using a 3-point device




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Tube-to-tubesheet joints can suffer crevice

corrosion



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Common internal pitting


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NDT of heat exchanger tubes

1. Borescope (90 head)

2. Eddy current testing


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ECT INSPECTION OF TUBES

ECTcan locate:Wall thinning (loss of material due to

corrosion)

Surface breaking cracks (only)

Principle:

1. A probe induces eddy currents into the

material

2.Cracks or lack of material affects the

response and is measured by an electric

circuit


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Probe traversed through each tube


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Note defect categorisation


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FITTINGS:BAFFLE IMPINGEMENT

Maximum clearance (TEMA)

between baffles and shellapprox 5mm

Impingement

wear

Wear is worst around inlet nozzle

area


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1. Heat exchangers are PRESSURE EQUIPMENT

2. Hundreds of different designs(TEMA categories)

3. Specialised NDT techniques (ECT)

4. Heat exchangers are often (statutory) coded

equipment

5. Corrosion/damage requires an assessment againstcode

KEY POINT SUMMARY

WHAT IS THE RELATIONSHIP BETWEEN

THESE?

Documents

07 PPP TTE Heat Exchanger Inspection