PWHT SS TP 347H furnace tubes 3

[0707]

Shall we PWHT SS TP 347H furnace tubes to be used in service of Hydrogen with partial pressure of 159 bar,H2S partial pressure of 1.4 x 10(-3)and vacuum gas oil?

PWHT heat up is 150/180ºC per hour, Four hour steep at 899ºC, and cool down at 150/180ºC per hour

THANK YOU

Lm

 

[stanweld]

I wouldn't.

 

[unclesyd]

The only PWHT that would really affect any properties would be to quench anneal, rarely done on stabilized grades of SS.

The stress relief aspect of the components will happen in the heatup stage. Hopefully no big surprises.

 

[0707]

The operating temperature of the heater will be around 396ºC

 

[0707]

I have eared that PWHT of TP347H reduces residual stresses from cold working and/or joint restraints, and further reduces the susceptibility to chloride stress corrosion cracking.

By the other side maximizes the rate of fine niobium carbide formation and allows for sigmatization of most remaining ferrite, often leading to substantial loss of ductility and elevated-temperature creep strength. Therefore, to prevent failure during high temperature service, heat treated stainless steel use is generally limited to uses with operating temperatures below (510° C.) to ensure immunity to sensitization.

Tubes TP347H were delivered in the solution annealed condition.

lm

 

[metengr]

0707;
I concur with the above for not performing PWHT of conventional welds UNLESS you have cold worked the 347H stainless steel during fabrication with no subsequent solution anneal. Why? This material is prone to develop strain induced carbide precipitation in elevated temperature service that results in inferior creep properties and reduced corrosion resistance.

Under no circumstances would I use 347H swaged tubes and for cold worked tubes follow the advice provided in ASME Section I, PG-19 cold forming rules.

 

[0707]

Meanwhile after performing the stabilizing PWHT heat treatment to the TP347H tubes, we found frerrite numbers in the welds above 8% which are not acceptable by the construction code. Are subsequent PWHT capable to reduce the actual ferrite number? My opinion is that the repetition of PWHT in this kind of materials is even worse inducing more carbide precipitation allowing for more sigma phase.

Is there any chance in the actual condition to lower the ferrite content, or there is nothing we can do?

The tubes we are talking about will be use in a hydro cracking unit furnace.


LM

 

[unclesyd]

The only method I've seen used to lower a Ferrite Number is quench anneal.
If I recall correctly we used the higher temperature 2150°F.

 

[stanweld]

Why are you worried about sigma at 396 C (745 F)? For that matter why is 347H specified? 347 has the same design allowable under B31.3.

Did you measure the ferrite content of the deposited weld metal prior to heat treating and was it appreciably lower than 8%?

 

[0707]

The ferrite content of deposit weld was measured after stabilising PWHT. The ferrite content in some welds is above 10%. In some welds to lower ferrite content, they performed in my opinion wrongly, more than one stabilizing PWHT. Again in my opinion wrongly the PWHT was only applied with electrical resistances in the weld and HAZ and not as it should be in all piece of pipe in a furnace.

It is LICENSOR of heater understanding that the elevated temperature heat treatment would need to be performed in the temperature range of 1065ºC to 1121ºC; and will convert the sigma phase. The higher temperature is required to ensure the carbides can be restabilized after the heat treatments. After the elevated heat treatment the tubes will then require the stabilizing heat treatment at 899ºC. During the stabilizing heat treatment there is the potential to form sigma phase again. Then during operation there is the potential to form sigma, if the tubes are exposed to temperatures above 537ºC. The basic issues are the chemistry of the welds is not correct and this has resulted in the formation of higher levels of delta ferrite, which has the potential to convert to sigma during heat treatments and operation. The only solution we are aware of to address this issue is to remove the welds.

In my opinion is that there was a mistake to specify a stabilising PWHT for TP347H in the operating conditions of this particular furnace tubes and the solution to remove the welds doesn’t solve the problem.

Thanks

LM

 

[stanweld]

It is noted that API 582 recommends a max ferrite of 11% and a minimum ferrite of 5% for 347. Ref. para. 6.3.3.

 

[ijzer]

If operating temperture of these pipes is above approx. 400 °C PWHT at 900°C is recommended to avoid polythionic acid cracking during shut down.

 

[pradipgoswami]

Hi,

I saw your post quite late. As regarding PWHT of SS TP 347H furnace tubes after welding and fabrication, NACE RP-170,-Protection of Austenitic S.S against Polythionic Acid Corrosion during Refinery Shutdowns- recommneds stabilizing anneal at the above temperature for typically 2-4 hrs.

Stabilizing anneal dissolves Cr-carbide back to solution and preferentially precipitates Ti or Nb-Carbides, thus protecting the intergragular corrosion resistance of 347H S.S.
This is a very standard requirement for oil refinery design specifications.

I am not sure if those specifications could be posted at this site.But in the past I dealt with this welding and materials issue for refinery equipments.

Thanks.

Pradip

********************
If you have access to NACE,then read this paper, which explains the details about this issue-

Paper Number 98580
Title Unusual Stabilization Behavior in Type 347H SS Tubulars for a Refinery Heater
Authors Steven R. Bolinger, Shell Norco Refinery Co.; L.E. Kolp, and William C. Fort, Shell Oil Products Co.
Source CORROSION 98, March 22 - 27, 1998 , San Diego Ca.
Preview ABSTRACT
Type 347H SS was specified for the tubulars in a Refinery Lube Oil Vacuum Flasher Heater. The heater was designed for tube metal temperatures of 565°C ( 1050°F), and the tubes were specified to be stabilized annealed in order to resist polythionic acid stress corrosion cracking (PTA-SCC). Testing was performed to determine if resistance to PTA-SCC had been compromised during fabrication of the heater. The test protocol was based on ASTM A-262 Practice C, the 65% nitric acid (Huey) test. All return bends failed the tests, while most of the straight tubes sections passed the tests. The columbium carbide phase was present in very large particles instead of being evenly dispersed as fine particles throughout the matrix. This compromised the effectiveness of the stabilizing anneal and reduced the resistance to PTA-SCC.

INTRODUCTION
A Lube Oil Vacuum Flasher unit was designed to process a high sulfur pitch into lube oil products and residue. The unit receives the pitch from an atmospheric distillation column and heats the pitch under deep vacuum conditions to separate the different lube oil components. At the heart of the unit is the Vacuum Flasher heater. The heater was designed with a tube metal temperature of 565°C (1050?F). Tube materials were specified as Type 347H SS stainless steel in order to prevent sulfidation and resist potential polythionic acid stress corrosion cracking (PTA-SCC). Tubulars were purchased to appropriate ASTM specifications, with a supplemental requirement to stabilize anneal at 899°C (1650?F) for four hours.

In the current business climate many refinery heaters are ordered on a turnkey basis. The owner/operator works with an engineering company who specifies and purchases a heater from a heater supplier. The heater supplier in turn orders the tubes from a distributor or directly from a manufacturer of the tubulars. Conveying very detailed materials information directly to the manufacturer can be difficult with these types of business relations. Such is the case with relaying detailed specifications meant to avoid sensitization and PTA-SCC of the tubulars in this heater.

Polythionic Stress Corrosion Cracking

Austenitic stainless steels and other austenitic alloys may become sensitized, a condition that makes the alloy susceptible to rapid intergranular corrosion, as a result of adverse thermal treatment which causes precipitation of chromium carbides at the grain boundaries. This depletes the matrix adjacent to the grain boundary of the chromium necessary to maintain the overall corrosion resistance of the alloy. Sensitization may occur during weld fabrication, hot processing or operation in the sensitizing range from approximately 426?C (8OO?F) to 816°C (1500?F). The sensitization range varies somewhat for different alloys. In order to prevent sensitization during processing of the material, all of the commonly used ASTM specifications for the various product forms of austenitic stainless steel and other austenitic alloys require a solution anneal heat treatment after manufacture. Chemically stabilized grades may also be procured with a stabilizing heat treatment which further prevents sensitization and increases resistance to PTA-SCC. The stabilizing heat treatment may be invoked at the time of purchase (per Supplemen