TITANIUM ALLOYS IN OIL, GAS, & PETROCHEMICAL INDUSTRY

A presentation held in the 1st Ti & Ti Alloys seminar in Iran

Presented by: A.R. Aminian

HISTORY OF TITANIUM

The element titanium was discovered by an English priest (W. Gregor) in 1791 though it was not extracted as pure titanium until 1901.

Titanium is one of the commonest metallic elements on earth and titanium ore is found in sands distributed throughout the world.

Despite its widespread occurrence, the extraction of titanium and production of ingots is an expensive process and the product is much more expensive per ton than carbon steel.

PROPERTIES OF TITANIUM

Titanium is recognized for its high strength-to-weight ratio.

It is a light, strong metal with low density;

It is quite ductile when pure (especially in an oxygen-free environment),lustrous, and metallic-white in color;

The relatively high melting point makes it useful as a refractory metal;

Melting point = 1668

PROPERTIES OF TITANIUM-2

Pure titanium melts at 1670°C and has a density of 4.51 g cm-3. It should therefore be ideal for use in components which operate at elevated temperatures, especially where large strength to weight ratios are required;

Pure titanium has low tensile strength (216 MPa ) and high ductility (50% elongation at break). However, commercially pure titanium contains controlled amounts of interstitial elements, principally oxygen, which increase the strength and lower the ductility.

PROPERTIES OF TITANIUM-3

UTS = 375 MPa upto 1.4 GPa for Beta alloys;

Hard and difficult to machine;

Looses strength above 430°C;

Burns in oxygen and nitrogen;

Low electrical and thermal conductivity

TYPES OF TITANIUM

α+β and β-phase alloys are harder, stronger and less ductile than the a-phase but can still easily be forged;

α-phase alloys are generally used where corrosion resistance is of paramount importance, in such applications as tubing and heat exchangers in chemical plant

α+β and β-phase alloys are used for structural applications where strength is important

TYPES OF TITANIUM-2

alloys close to the a-phase are used for their high temperature creep strength in applications such as gas turbines

α+β-phase alloys are the main structural alloys of titanium, of which Ti-6A1-4V is the most common

β -phase alloys have high strength whilst retaining reasonable ductility making them a good choice for high strength bolting, pressure vessels, high pressure thin wall piping and other highly loaded applications

TITANIUM ALLOYS

There are over 35 commercially available titanium alloys, though many of them havebeen developed for aerospace and defense use and their properties are eitherunsuitable or exceed those required in the oil and gas industries;

Commercially pure titanium is available in four grades (ASTM Grades 1 to 4). The higher grade numbers are stronger but at the expense of ductility;

Typical proof stress for Grade 1 is 220 Mpa rising to 550 MPa for Grade 4;

Of the pure titanium grades, Grade 2 is the most commonly used

TITANIUM ALLOYS-2

TITANIUM ALLOYS-3

TITANIUM ALLOYS-4

All titanium is highly corrosion resistant but the resistance to crevice corrosion in hot chlorides is improved with the addition of palladium (Pd);

Grades 11 and 7 are equivalent to Grades 1 and 2 in mechanical properties but 0.2% Pd gives what are known as corrosion resistant grades;

Reducing palladium to 0.05% gives Grades 17 and 16 respectively;

A recent development has been the use of ruthenium in place of palladium. Ruthenium gives similar corrosion resistance but at a much reduced price.

TITANIUM ALLOYS-5

Introducing β-phase alloy into the matrix produces an alloy that can be heat treated to give higher strength;

The basic structural alloy of the aerospace industry is Grade 5 which has the addition of 6% aluminum and 4% vanadium;

Grade 5 is more prone to stress corrosion cracking in seawater than other grades and there is still some question mark over its hydrogen absorption in well fluids at temperatures above 80°C.

TITANIUM ALLOYS-6

The toughness and resistance to stress corrosion cracking has been improved to an extent by limiting the interstitial content, mainly oxygen, to produce the 'Extra Low Interstitial' (ELI) Grade 23;

Grade 24 is basically Grade 23 with 0.05% Pd to eliminate crevice corrosion at temperatures above 85°C;

By halving the aluminum and vanadium content, a more formable, weldable and tougher alloy than Grade 5 has been produced;

This alloy (Grade 9) has about a 30% lower strength than Grade 5;

Again, its corrosion resistance can be improved further by the addition of 0.05% Pd, to produce Grade 18.

TITANIUM ALLOYS-7

A near a alloy is Grade 12 which contains small amounts of molybdenum and nickel as alloying elements;

This grade has only about half the strength of Grade 5 but has excellent resistance to hot chloride stress corrosion cracking at temperatures above 90°C and is approved by NACE for sour service;

Ruthenium bearing versions of Grade 23 and 9 have now been given the ASTM designations 29 and 28 respectively;

TITANIUM ALLOYS-8

NACE MR-01-75 identifies Grades 2, 12, 19 and Ti-6A1-2Sn-4Zr-6Mo as acceptable for sour service;

However, NACE is being revised and more grades will be added to the list, particularly Grades 21, 23 and 24;

This alloy has a typical proof stress of 1100 MPa and excellent resistance to hot chloride crevice corrosion;

Like Grade 12 it is also approved by NACE for sour service and is now available as ASTM Grade 19

TITANIUM USE IN OIL & GAS-CORROSION

a-phase alloys are classed as corrosion resistant but all types of titanium are resistant to attack by many fluids and are noble in seawater;

Titanium’s corrosion resistance and nobility arise from its strong and stable oxide layer;

However, when the oxide layer is removed there is sufficient cathodic potential between the titanium oxide layer and the base material to electrolyze the surrounding water, liberating sufficient oxygen to regenerate the oxide layer almost instantaneously.

TITANIUM USE IN OIL & GAS-HYDROGEN ABSORPTION

Pure titanium has excellent resistance to corrosion and is used widely in thechemical industries. There is a passive oxide film which makes it particularlyresistant to corrosion in oxidizing solutions. The corrosion resistance can befurther improved by adding palladium (0.15 wt%), which makes hydrogenevolution easier at cathodic sites so that the anodic and cathodic reactionsbalance in the passive region;

Titanium is capable of absorbing up to 60% of hydrogen, which can also be removed by annealing in a vacuum.

the solubility actually decreases with temperature. This contrasts with iron which shows the opposite trend;

TITANIUM USE IN OIL & GAS-HYDROGEN ABSORPTION 2

Because of this characteristic, titanium is a candidate material for the first wall of magnetically confined fusion reactors;

The hydrogen based plasma is not detrimental since at 500°C and 1Pa pressure, the Ti does not pick up enough hydrogen for embrittlement;

This make the Ti very operative for Petrochemical processing plants.

Alloys have now been developed which have greater resistance to hydrogen uptake and are aimed at high temperature sour and/or highly acid wells

TITANIUM USE IN OIL & GAS-CHEMICAL ATTACK

Titanium is inert to most oilfield chemicals: the exceptions are methanol andhydrofluoric acid;

Methanol causes stress corrosion cracking of titanium when chlorides are present;

Hydrofluoric acid, which may be used for acidizing wells, attacks titanium veryquickly, in fact it is used for pickling titanium;

Alternative acids are available for wells but if hydrofluoric is required it is essential toprevent it flowing into titanium lines operationally or by system design.

TITANIUM USE IN OIL & GAS-GALLING

Galling is surface damage on moving metal parts caused by localwelding of high spots under friction;

Titanium is very prone to galling and care must be taken when it is usedin applications such as bolts where there is a combination of load andmovement;

Some anti-galling treatments and surface finishes have been developedfor titanium threads and work in this area is continuing

TITANIUM USE IN OIL & GAS-WEAR

Naturally occurring titanium oxide is hard and has good wearproperties in many situations;

However, in such applications as drilling risers, the bore is exposed towear from drill pipe and substantial damage could result;

The mechanisms of wear of titanium is quite complex: the metal canexhibit excellent wear properties in some applications and suffer verybadly in others.

TITANIUM USE IN OIL & GAS-A SUMMARY OF GRADES

THANKS FOR YOUR PATIENCE

A. R. AMINIAN-DECEMBER., 20TH, 2017