construction materials for pressure vesel

8/12/2019 Construction Materials for Pressure Vesel

1/35

CONSTRUCTION

MATERIALS FOR

PRESSURE VESSELS

Prepared by:

Rahul S Vora (LEMF)

N Velliyangiri (LEMF)


2/35


3/35

General Considerations

Corrosion resistance

Strength requirements

Cost

Fabricability

Quality of future maintenanceAvailability


4/35

Materials Classification

Based on service environment

Corrosive Service

NonCorrosive Service


5/35


6/35

Cryogenic Temperatures

It ranges from -250 C to -101 C

In this range CS and LAS are brittle

Austenitic stainless steelsor nonferrous

metals like aluminum alloyscan be employed

here as they exhibit no loss in the impact

strength

Materials such as SA240 TP 304, 304L, 316,

316L, 347


7/35

Low Temperatures

It ranges from -100C to 0 C

Here Low Alloy Steelsand fine grainCarbon Steelsare employed

Materials like SA203 Gr. A, B, D, E,

SA516 All Grades


8/35


9/35

Elevated TemperaturesAbove 425 C

The steels begin to exhibit a drop in UTS & YS

and cease its elastic nature and starts becoming

plastic in nature so here the main requirement is

high creep-rupture strength

At higher temps. number of changes in the steel

microstructure occurs, to a large extent both in

grain structure and in chemical composition,which affect the mechanical properties

So here a coarse grained structureis preferred.

Materials like SA387 Gr. 11, 12, 22, SA240 TP

304, 316, 321, 347


10/35

Non-Corrosive Service - Summary

Carbon Steels

C-Mo steels, Low and intermediate Cr-Mo alloy

steels

Resistance to graphitization and hydrogen attack

High creep-rupture strength at high temperatures

Over 345C it is economical

Ferritic SS Austenitic SS

Special high temperature resisting alloys

SA240 TP310 and Incoloy


11/35


12/35

CS-High Temperature Vessels

Most of them are fabricated at low cost

by using low alloy CS with an internal

refractory lining (insulation)

Not for small dia. Piping or in Heat

Exchangers


13/35

Corrosive Service

Here corrosion resistant materialhas to be

employed else protective lininghas to be

done on the base material

For up to 10mm thick vessel shells SS plate is

economical to use and above that CS or LAS

shells with applied corrosion resistant layer(of SS) are used i.e. Cladding

3 methods are employed for attaching the

protective layer:


14/35

1. Integrally Applied Cladding

Fabricated in steel mills by hot rollingof

assemblies of CS or LAS plates

(backing) & corrosion resistant sheet

(liner)

At high temp. the pressure creates asolid-phase weldbetween the backing

and cladding metals


15/35

2. Strip or Sheet Lining

In strip lining, strips of 3-5 ft. long and

3-6 in. width are attached to the shell

by continuous weld around edgesIn sheet type lining, sheets of several ft

in width and length is tightly attached

to the shell wall by resistance spot or

seam weldson a standard square

spacing


16/35

3. Weld Overlay Cladding

Welding process in which a material

with desired properties is deposited on

the surface of base material i.e.continuous bonded layerof corrosion

resistance

Here SAW and ESSC processes are used

for overlay cladding after plate rolling /

bending operation


17/35

Stainless Steel


18/35

Stainless Steel

Alloy of Cr and Fe (Cr: 11-30%)

Advantages

Corrosion ResistanceIncrease the life and safety

Strength at elevated Temp.

Oxidation Resistance at elevated Temp.

High Impact strength at Cryogenic Temp.


19/35

Properties

Retains Strength at elevated Temperature

(Above 600C)

Higher Stress relieving Temp and Long Holding time

Barrier Layer

Formation of un reactive Cr Oxide film

Pickling & Passivation

Removing surface contamination by Acids like HNO3

Artificial Oxide film by strong Oxidizing agent


20/35

Sensitization

At high temp Carbon molecules diffuse to the

grain boundaries

Precipitates as Cr4Cdepletion of Cr

Corrosion at grain boundaries

Intergranular Corrosion

Poor Cr envelope is anodic with respect to rest

of grain Galvanic Corrosion


21/35

Classification

Straight Cr GroupCr upto 30%400 Series

Cr - Ni GroupCr-18,Ni-8300 Series

Cr-Ni-Mn GroupPortion of Ni is replaced by Mn200 Series

Stainless SteelDepending on Alloying Elements

Austinitic StainlessSteel

Non hardenable, Non Magnetic300 Series, Ty 201

Ferritic Stainless Steel

Non hardenable, Magnetic400 Series

Martensitic Stainless Steel

Hardenable, Magnetic400 Series

Stainless Steel

Depending on Microstructure


22/35

Austenitic Stainless Steel

Formation:

Solution Annealing above 1000C

Austenite is a powerful Solvent

Cr, Ni, C dissolved in Austenite matrix

To retain microstructure Cooled rapidly to 425C

Corrosion Resistance, Ductility, Strength are Max

425870C - Sensitization 3-6 mm Band away from and parallel to weld


23/35

Austenitic Stainless Steel-

Classification

Gr ICan be Affected

Can be cured

304, 316, 309,310

Gr IIImmunated

321,347

Gr IIIRoot is Eliminated

304L, 316L

Austinitic Stainless SteelDepending on the Possibility of Sensitization


24/35

Austenitic Stainless Steel- Group I

Sensitization may be encountered by

Welding/Flame cutting

Cure (Desensitization) Full Solution Annealing

Heating above 870C to dissolve carbide

Rapid cooling- Introduce Residual Stresses

Stress Relieving at 425C

Operating Temperature stay below 425 C


25/35

Austenitic Stainless Steel- Group II

Alloying elements like Ti, Cbhave higher

affinity to carbon than Cr

They form carbides in preference to Cr

These carbides dispersed through metal

Can be sensitized by special heat treatment

(Carburized)Knife edge attack

Operating temperature above 425C

347(Cb) is superior than 321(Ti)


26/35

Austenitic Stainless Steel- Group III

Extra low carbon grades (


27/35


No general transformation from austenitic to

martensite Non hardenable

Brittle in heat affected zone because of Rapid

grain growth

Sensitizedby heating above 930C and cooling

in air. Desensitizedby heating to 790C

(Allows Cr to diffuse)


28/35


The composition of electrode is so chosen to

produce austenitic or air- non hardanable

high alloy weld metal

885F Embrittlement

Toughness is reduced when heated to 750

900F due to

the precipitation of Cr rich ferrite

Exhibits lower ductility at lower temperature


29/35


Seldom used for construction of Pr. Vessel

except as a cladding (405, 410S)

They are Magnetic


30/35

Martensitic Stainless Steel

Straight Cr steels

Hardenable by heat treatment

Magnetic

Rarely used for construction of Pr. Vessel

Least corrosion resistance among SS


31/35

Hydrogen Attack

Mono atomic hydrogen diffuses in to the

metal.

At voids and slag inclusions they combine

each other and form molecular hydrogen

As the time grows pressure also grows


32/35

Hydrogen Attack

Effects

Near surfaceCrack

At depthBlistering

At high temp (>315C) Fe3C decompose and

hydrogen combine with C and forms CH4.Pressure builds up and leads to Intergranular

crack


33/35

Hydrogen Attack Suitable

Materials

Cs and LAS at low temp and high Pr or high

temp and low Pr.

Austenitic Stainless Steel

Under hydrogen service both clad and base

material should be a hydrogen attackresistance


34/35

Overview of common Materials

SA 203 Ni SA302 Cr-Mo SA515 SA612

SA204 C-Mo SA353 Ni SA516 SA724/737

SA240 SA387 Cr-Mo SA517 SA738

SA263 Cr-Clad SA533 SA812

SA264 Cr-Ni Clad SA537

SA265 Ni- Clad SA542SA283 SA553 Ni

SA285

SA299

CS LAS SS

InC


35/35

construction materials for pressure vesel

Documents