Hairline cracks in stellite 6 coating (HF) - A216 WCB

[Materials & Welding]

Is it true that stellite 6 HF will leave hairline cracks on the
surfece?, one of the reputed valve vendor is quoitng that

"Seat overlay made of Stellite 6 is possible but not recommended by
us. We clearly mention that it is not possible to perform a Stellite 6
completely free of hair cracks. Probably after final machining the
surface will show hair cracks which is normal in case of using
Stellite 6 and this do not affect the sealing function. We normally do
not use Stellite 6 because of this fine cracks and because of much
better experience with Stellite 21. If you insist on Stellite 6
seating surface showing hair cracks will not be a reason not to accept
the valves if seat tightness test is ok"

[Pieper QSI]

Dear Sir,

It's true that this alloy sometimes has small crack in its surface, it is
mostly used for wear resistance and in such cases this won't be a problem.
The alloy Stellite 6 has less tendency to crack than for example Stellite
12, but only when multi-layer technique is used. In single layer
applications you probably will have small cracks.
So it is possible to apply the material without cracks but in cases where
the hard facing also is used for corrosion resistance or for a perfect
sealing you perhaps better can choose another wear resistance alloy in order
to avoid cracks.

Met vriendelijke groeten / Best Regards

Herman Pieper

Pieper Quality Support & Inspection
Phone: +31 (0)521 380083
Fax: +31 (0)84 7539225
Cell: +31 (0)6 51691215
www.pieper-qsi.nl

-----Oorspronkelijk bericht-----
Van: material...@googlegroups.com
[mailto:material...@googlegroups.com]
Verzonden: vrijdag 12 augustus 2011 10:01
Aan: Materials & Welding
Onderwerp: [MW:12201] Hairline cracks in stellite 6 coating (HF) - A216 WCB

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[M S R K S Prasad]

Dear members,
I am thinking of changing MOC of one of the exchanger channel cover bolts from B7 to B16 as the exchanger channel cover is leaking very frequently. Whenever it leaks we tighten it manually the leak minimizes after few days it resurfaces.In each tightening  the nuts are moving by about 10 to 15 deg.

I request members to suggest whether the choice of B16 is OK are any other bolting material is better than B16 is available.
with regards

[tong tong]

Same with my situation. During our last TA, the stellite 6 was overlaid on jet nozzle of regen. standpipe after minor repair on it. After the weldment was cooling down, DPT was carried on that particular area and revealed a hair line crack.

On Fri, Aug 12, 2011 at 4:00 PM, Materials & Welding <material...@googlegroups.com> wrote:

Is it true that stellite 6 HF will leave hairline cracks on the
surfece?, one of the reputed valve vendor is quoitng that

"Seat overlay made of Stellite 6 is possible but not recommended by
us. We clearly mention that it is not possible to perform a Stellite 6
completely free of hair cracks. Probably after final machining the
surface will show hair cracks which is normal in case of using

Stellite 6 and this do not affect the sealing functiont We normally do

not use Stellite 6 because of this fine cracks and because of much
better experience with Stellite 21. If you insist on Stellite 6
seating surface showing hair cracks will not be a reason not to accept
the valves if seat tightness test is ok"

[deepak Patil]

Dear Mr. Prasad,
the situation described by you indicated following

1. There is leakage of joint (through gasket) suggests that the bolts
are not able to exert necessary force Wm1 ( of appendix 2)
Wm1 is in the operating condition scenario in which bolt shall
resist the hydrostatic end force H and additional force Hp to maintain
the joint (gasket) contact surface under required compression to avoid
leak.

Wm1 = H + Hp
= 0.785 G2 P + (2b x 3.14 G m P)

This force Hp is specified as multiple m of internal pressure and
gasket contact width.

2. Look at the flange design calculation and you should find the
operating condition govering.

here check if correct value of m is used. There is a possibility
of using lesser value of m which has resulted into smaller force Hp
hence resulting the leak.

3. If the calculations (and the m factor of gasket ) are ok then there
is possibilty of actulal value of gasket m factor being different than
those used in calculation ( the actual value will be higher); here try
replacing the gaskets.

5. i wont advice you to go for higher strength bolts until flange is
analysed for this higher bolt strength.

Deepak

On Aug 12, 5:39 pm, M S R K S Prasad <MSRKSPra...@nagarjunagroup.com>
wrote:

[Ashok Raman B Kutty (MNT/PPTSB)]

The yield strength of both B7 and B16 is 105,000psi at ambient temp. Changing the bolts will probably not solve the problem. You will need to look at the joint as a whole and check the following -

 

1.       Flatness of gasket faces

2.       Gasket type – jacketed/spiral wound/camprofile/flat metal versus joint type. An example of a poor combination would be a male/female joint with a jacketed gasket.

3.       Tightening method – manual slogging/manual torque wrench/hydraulic torque/tension.

4.       Torque or tension value

5.       Sequence of tightening

6.       Flange rotation

7.       Surface finish of gasket face must suit the gasket type

8.       Alignment of flanges

9.       How the gasket is held in place – using tape or sealant

10.   Lubricant used and corresponding torque value calculation

 

Of particular interest in my experience were joints in a steam reboiler where steam is on the tube side with fluctuating levels of condensate in the outlet section of the bonnet. Here, in spite of addressing all of the above, we still had leaks. Finally had to use live loading washers to stop the leaks.

 

Ashok

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[Raghuram Bathula]

Any experience with barrier layer of Inconel or stellite 21 and then
with stellite 6?

[John Henning]

Stellite is a registered trade mark of Deloro Stellite

This is personal experience from the my time in the electric power
industry - Stellite 6 typically is applied only in shop and not in the
field. Stellite 6 can be successfully welded when high levels of
preheat are applied. When welding Stellite 6, the entire assembly/item
should be uniformly heated to the preheat temperature and cooled slowly
after welding. When field welding, Stellite 21 is preferred as only
modest preheat is required and because Stellite 21 is more ductile, as
deposited, than Stellite 6. Stellite 21 will work harden to develop
full hardness. Stellite 6 will be harder than Stellite 21. I have seen
many valves refurbished in the field with Stellite 21 being replaced
with Stellite 6.

I have never heard of using Stellite 21 as an interlayer before welding
Stellite 6.

John

-----Original Message-----
From: material...@googlegroups.com
[mailto:material...@googlegroups.com] On Behalf Of Raghuram
Bathula
Sent: Monday, August 15, 2011 11:35 PM
To: material...@googlegroups.com
Subject: Re: [MW:12229] Hairline cracks in stellite 6 coating (HF) -
A216 WCB

--

[Muni Andy]

Dear friends,
In valve industry,Stellite 6 is successfully overlayed in WCB material in seat rings and wedges/discs
Preheat is must and slow cooling normally in lime powder immediately after deposit is followed.
Muniyandi..

[Ramin Kondori]

Can you deposit Stellite-6 by metal spray...?
We have done that for valve parts before (balls mostly) and results were satisfactory...

What is the overlay thickness you require...?
If it is below 800 or even 1000 microns, metal spray will give you good results without any cracking...

Regards

Ramin  Kondori

   QC/Welding Engineer 

         IWE AT 0070

   

[SAMIR THAKKAR]

Mr.Prasad,

may i know what is the pressure in HE.??? AND what is the thickness of CH. cover ???

SAMIR THAKKAR
(PRABHA STEEL IND.)

From: M S R K S Prasad <MSRKS...@nagarjunagroup.com>
Sent: Sat, 13 Aug 2011 16:53:57
To: material...@googlegroups.com
Subject: [MW:12205] ASTM A 193 Gr B7 to B16
Dear members,
I am thinking of changing MOC of one of the exchanger channel cover bolts from B7 to B16 as the exchanger channel cover is leaking very frequently. Whenever it leaks we tighten it manually the leak minimizes after few days it resurfaces.In each tightening  the nuts are moving by about 10 to 15 deg.

I request members to suggest whether the choice of B16 is OK are any other bolting material is better than B16 is available.
with regards

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The views expressed/exchnaged in this group are members personel views and meant for educational purposes only, Users must take their own decisions w.r.t. applicable code/standard/contract documents.

Treat yourself at a restaurant, spa, resort and much more with Rediff Deal ho jaye!

[Suneel Gore]

Sir

With proper preheating & very slow cooling the surface hairline cracks can be definately avaoided in stellite 6 coating

We have done very successfully very large casting that to CA6NM (Very difficult to weld) stellite 6 coating on surface approx dia 36 Inches ,(Pump impeller casing)

with no cracks visible on DP 

Whole casting Pre heated to 260 0C  post weld covered with asbestos flakes with lime power & covered with glass wool & asbestoss cloth , alloed to cool to room temp after 36 Hours the bundle was opened  

Regards

Suneel Gore  

[M S R K S Prasad]

Mr Samir,
The shell side and tube side pressures are 37/39 kg/cm2
Temperature on shell side in/out: 246/120 deg C
Tube side in/out: 101/229 deg C
This exchanger is a U-tube bundle exchanger
Thickness of tube sheet is 210 mm,1290 OD, weight: 1490 kgs
Thickness of channel flange: 190mm
Thickness channel bonnet:  36/32
Weight of channel bonnet is 1820 kgs.
regards

From:	"SAMIR THAKKAR" <prabhast...@rediffmail.com>
To:	"material...@googlegroups.com" <material...@googlegroups.com>
Date:	08/17/2011 12:57 PM
Subject:	Re: [MW:12246] ASTM A 193 Gr B7 to B16

---

Treat yourself at a restaurant, spa, resort and much more with Rediff Deal ho jaye!

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