tit bits on materials for process equipments

7/30/2019 Tit Bits on Materials for Process Equipments

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A. Design related issues:

1.

2.

3. High Alloy Steel (Part HA - Forming HT. PWHT - Optional)

4.

5.

6. RF Pad Plates can have joints.

7. Following Maximum permissible temperatures may be kept in mind:

Brass - 204C

Duplex - 316C (It is recommended to restrict to 260C due to 475C Embrittlement)

SS 304L - 649C

8. Maximum Permissible Thicknesses Sec. IID

Brass - 125 mm

9. Allowable Stress Values depend on thickness/dia in some cases (Studs, NF Plates, NF Forgings)

10. Allowable Stress depends on Type of Component

(Flanges - Note G5 of Sec. II D Table)

11. For Aluminum Bronze Weld Overlay Gasket surfaces, SPWD Gasket shall not be used.

12. Tubes Buckling due to External Pressure, especialy in Fixed Tube sheet exchangers.

TIT - BITS ON MATERIALS

FOR

PROCESS EQUIPMENTS

General requirements (UG - ASME materials only to be used, Minimum Tensile Strength, Elongation,

UTS, Impact - If applicable) - or else we have to prove the material meets a particular ASME Material).

Carbon Steel, Low Temperature CS, LAS (Part UCS - Forming Heat Treatment, PWHT, Simulation

Heat Treatment).

Dish Nominal thickness can be increased as much as we like to get the Minimum thickness after

forming. But, can not do the same in case of Bellow since the flexibility of Bellow is affected.

&&&&&

We have to check the Max permissible Design Temperature Limits as per (a) Sec. IID Table for

Internal Pressure and (b) External Pressure chart for External Pressure.

The following are some of the Code Requirements which are either overlooked or misunderstood or

oversimplified or overplayed:


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B. Fabrication and Testing related Issues:

1.

a) For Forming HT requirement - Original Plate thicknessb) For welding of components - Original Plate thickness

c)

2. Dissimilar Materials

a) As far as possible avoid dissimilar MOC

b)

c) Use higher Nickel electrodes for welding.

d) Brass Welding on CS is to be avoided. Use Nickel Aluminum Bronze Weld Overlay.e)

3.

4. Carryout UT at all surfaces of Dished Ends including SF portion after forming.

5.

6. No RT required (not even Spot), if

a) Vessel is designed for External Pressure only (or)

b) Vessel is designed with Weld Joint Efficiency E=0.7

7. No Impact Test is required if Maximum possible specimen size is < 2.5 x 10 x 55.

8. If Equipment needs to be Stress Relieved, the Dished end need not be Stress Relieved separately.

9.

10.

Normalizing of Dished Ends is not a Code Requirement. Only Stress Relieving is specified in Code,

irrespective of Thickness.

Normalizing is specified by consultants. This is derived from Clause UG-79, where it is mentioend that

the Heads shall be formed to the required shape by any process that will not unduly impair thephysical properties.

Irrespective of Thk, always carryout UT as per SA 578 Level B for Plates to be used for Dished ends.

SA 435 is less stringent and it will not deduct minor defects which will aggravate after dish forming.

Minor Laminations are permitted in Shells. That is why SA 435 is generally specified and not

SA 578.

In Dish forming, point pressing methods are employed. In such cases, the property of the material is

likely to be affected and it may not be restored with Heat treatment below the Upper Critical

Temperature ( i.e PWHT as per UCS - 56 may not do ).

If a particular component is formed with a high thick plate, welded, machined to lower thickness and

again welded as part of an equipment (e.x. Transition piece in Thick Walled Bellow), then

For welding of components

after Machining

- Machined thickness

If LAS to SS Butt welding is required, (1) Carryout buttering of LAS edge with higher alloy

electrode (2) Carryout SR (3) Then Weld the LAS with SS (4) This joint of LAS to SS need

not be Stress Relieved.

In Brass, Welded Tube to Tubesheet joint shall be avoided. If welding is inevitable, select

90:10 CuNi instead of Ad. Brass / Naval Brass.


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11.

12. Inter Granular Corrosion:

a)

b)

c)

d)

13.

14. Weld build up of Raw Materials is permitted.

15. Dish - Shell taper can be inside or outside or both sides.

16.

17.

18. SA 105 is for small standard Forgings - SA 266 is for large non-standard Forgings

19. SA 182 is for small Forged or Rolled LAS and SS Fittings, Flanges, Valves, etc

It also covers small and large Duplex and Super Duplex Forgings.

SA 336 is for large non-standard LAS ForgingsSA 965 is for latge non-standard SS Forgings

Stabilisation means fixing the free Carbon using elements which have stronger affinity for

Carbon than that of Chromium. Example- Ti, Nb, Cb.

Sensitisation means keeping the Steel at the Temperature ( 550 - 850 'C ) where the

Chromium Carbide precipitation will be the highest.

For SS Materials, Solution Annealing means breaking the Chromium Carbide and making the Carbon

to go into metal solution. It is not Annealing the SS material in a Solution.

For Normalizing cycle follow the parent material heat treatment cycle, as there is no cycle specified in

Code for Normalising.

As per UCS-85, this Normalising Heat treatment needs to be Simulation Heat treated and the

specimen shall be tested. Hence we have to have a Test coupon of the same Heat to be placed alongwith the Dished end.

If dish is only Stress Releived, then Test Coupon is not required as per UCS 85 ( c ).

If the Dish Blank has a weld joint, the nthe Test plate also shall have the weld.

Weld repair of Raw Material surface is permitted with the concurrence of the Inspector, and the extent

of repair permitted are specified in applicable material specs.

Hence, a Normalising Heat Treatemnt cycle( above the Upper Critical Temperature) is prefered.

If a Stabilized Grade SS Materials is used as a non welded part, then Stabilized grade need

not be stabilization Heat treated. For example SS 321 Plate material used as a Baffle need

not be stabilization heat treated.

Components not in contact with HIC fluid need not be HIC resistant. Specifying SA 193 Gr. B7M /

2HM for external studs in HIC requirements is not required. If it is specified based on Insulation

conditions, it is a different issue and it is applicable for Non HIC equipments also.

Minimum UTS during PQR Test can be lower by 5% of Base Metal Minimum UTS value, if the

Speciman has failed in Base Metal.

It is a problem associated with Carbon. If Carbon is restricted, the problem is almost

solved. Only in cases where very severe corrosive environments at high temperatures are

there, we need to go for Stabilized Grades ( SS 321, 347, 316Ti).


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20. SZC - Soft Zone Cracking

21. CS to SS contact corrosion is due to Combination of Galvanic / Crevice / Pitting corrosion.

22. Welding in Saddle permitted after PWHT.

23. External / Internal stiffening Rings - Intermittent welding permitted

24. Forging - As close to final shape As practical

- We need not fully comply as long as we ensure the

required properties

25. Grain size - ASTM Grain Size No. > 5 is Finer

- 0.05 mm Tolerance is about one Grain.

26. Roughness is always a range - 0 -125 AARH, 125 - 250 AARH

- For higher Pressures - Smoother Finish is required.

27. SS 304 - Can be used as 304L, if C < 0.03%

SS 304L - Can be used as SS 304, if UTS > 75,000 PSI &

YS > 30,000 PSI

SS 304H

SS 304

316 + Ti - 316 Ti (Something similar to SS 321 for SS 304)

- There is no equivalent for SS 347 in SS 316

410 - 410S ( SS 410 with Low Carbon. Similar to SS 304L)

28. Heat Analysis - Made for each Furnace Heat in steel Mill

Product Analysis - Made in the Product lot

- Plate - Slab, Forgings - Each Group

29. Heat - Furnace Heat

Group - Heat Treatment Lot in Forgings

Lot - A fixed number of similar items - Tubes, Fasteners.

30. Test Piece Requirements - Chemistry - Each Heat

- Mech. Test - Each Heat Treatment Lot

- IGC - Each Heat Treatment Lot

- HIC - Each Plate

(WN Flanges can be made as Rectangular cross section in

Ring Rolling and the Weld Neck can be machined to shape.

Similarly, Lipped Tubesheet can be forged as a Solid blank

and the Lip can be machined on thickness. The Tensile test

piece shall be taken in the axial direction close to the Lip)

- Can be used as 304, if C < 0.08 %

- Can be used as SS 304H, if C>0.04%, Heat Treatment &Grain Size requirement as per Spec are complied.


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31. Test Piece - Can be part of the Forging or

Separately forged piece if agreed by Purchaser

- Explosive Cladding separate piece permitted

32. Inspection Type - EN 10204 Type 3.1 - Mill QC certifiedType 3.2 - TPI certified

- QAP - TPI and Manufacturer

can decide on the W / H points

33. Electronic T.C.s - Accepted - No signature required.

34. Raw Material Source - Starting Ingot / Billet / Mother Hollow does not matter,

for Country of Origin.

35.

36.

37. Cladding - This word is used very loosely

- Explosive Cladding / Roll Bonding /

Weld Deposit are acceptable for Clad

- Quality as per SA 263 / SA 264 / SB 432 required

(Shear Bond & UT 578 - B)

- Lining is not cladding

38.

39. Preheat ( Minimum ) - Reduces the Temperature Gradient between

the Weld Zone and the Ambient / Adjacent parent metal.

- Hence Cooling rate will be slow. This helps to

minimise the Martensite formation during cooling,

which is the cause for hardness buildup.

- Thicker CS also preheated to avoid fast cooling

due to larger parent mass availability in Thick Shells,

especialy adjacent to the initial weld layers.

40. Interpass Temperature ( Maximum ) - When the Interpass Temperature is high,

the cooling rate of Weld metal may become too low.

- This may result in coarser grain formation in the Weld metal.

- This may affect the Impact property.

- Hence, Interpass Temperature control is required.

Electrodes are backed to drive

away moisture

SS Filler Wires are wiped with

Acetone to remove moisture

We can weld Low Nickel Steels

with High Nickel Electrodes

- Acetone has good affinity for Water.

- Vice versa is not true

- Hydrogen Inclusion, Porosity formation, etc.


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41. Post Heat - Post Heat is done to drive away Hydrogen inclusion

- Minimise the formation of Martensite

40.

- Root Gap and Land are not Essential variables

- Single V / Double V is not an Essential variable

41. Double V to Single V is an Essential - Only for Double V to Single V - WPQ to be redone.

variable for WPQ - Single V to Double V - Welder Qualification

need not be redone.

42.

43.

44.

45.

46.

47.

&&&&&&

c) If two SR is done, then the Simulation can be done by holding the Specimen for the total Holding

time of the two SR Cycles. It need not be cooled and again reheated to the Holding Temperature.

Similaly, Hubbed Tubesheet can be machined from Plate, if Tension Test Specimen is taken as per

the requirements of App.20.

Simulation Heat Treatment ( UCS - 85 ) :

a) It is applicable for all Heat treatments during fabrication exceeding 480'C

b) If a plate is Normalised, Stress relieved and again Normalised, then one normalising only need to

be simulated in the Tst Specimen ( UCS - 85(i) ).

Inspector need not witness the transfer of Marks, but shall satisfy himself that it has been correctly

done ( UG - 77 ).

Tubesheet Hub can be machined from solid blank forging, provided Tensile Test value of Test

specimen taken in the direction parral to the axis of the Exchanger.

For 90 : 10 Cu-Ni, there is no Filler Wire. We have to use 70 : 30 Cu-Ni wire only.

During Weld Overlay, barrier layers with higher Alloy content Electrodes shall be used so that the

dilution by the base metal chemistry is compensated and we get the required chemistry after the

completion of weld overlay. The top layers are done with wires which have base metal chemistry

only.

During Explosive Cladding of Tubesheets, there will be some distortion and this can be removed onlyto some extent and there will be leftout undulations to an extent of 1 to 3 mm depending upon the

Diameter. We need to machine the base metal and the clad metal judiciously so that the minimum

thickness of both clad metal and the base metal do not go down drastically at any location.

But, we shall keep in mind that since both the thicknesses are important and the undulation of 1 to 3

mm can not be avoided, the under tolerance of atleast about 1 to 2 mm can not be avoided in Clad

Metal and Base Metal in different locations.

Weld Bevel preparation is not a

Sec. IX Code requirement for

- Weld Bevel Angle is not an Essential variable

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