SOUR SERVICE BOLTINGS MATERIAL 2

[gengi]

Dear All,

I have to choose the heat exchanger bolting material suitable for Sour Service.
The boltings are INTERNAL and so directly in contact with the process fluid ( completely in sour enviroment ).

The material of this exchanger is carbon steel and we are in HIGH PRESSURE SERVICE and LOW TEMPERATURE ( approx minus 30°C ).

I preliminarily used SA 320 L43 bolting (even if it would be correct to install L7M ) and I got 3.1/2" diameter.

The allowable stress of SA 320 L7 is approx. by 25% higher than L7M so using L7M I would get bigger diameters.

The ASME Code VIII Div.1 - Section II, Part D, limits the size of L7M (also B7M) to 2.1/2" diameter.
I do not understand why the reading the Section II, Part A, while for the L7M the limit is 2.1/2" diameter for the B7M in Table 2 "Mechanical Requirement" are stated also diameter up to 7" (but the allowable stress available are for 2.1/2" max.)!!

I though to provide for the L7 bolts as HOT DIP GALVANIZED per A 153 but I do not know if this will work.

I could use high strength corrosion resistance material with allowable stress close to that of SA 320 L43 but this high strength material is often not accepted by the final users.......

Could you help me please ? Do you have any syuggestion ?

Do you have experiance with high pressure internal boltings with Sour enviroment ???

Thanks in advance for you help and suggestion.

regards

GENGI

 

[SJones]

Galvanising will not help you and is a waste of time in an acidic process stream. You could look at ASTM A453 being wary of a few things:

1. Galvanically induced hydrogen stress cracking and/or galvanic corrosion issues

2. Not strictly low temperature material but engineering considerations regarding the pressure conditions leading to the -30 deg C may give rise to a favourable risk assessment.

3. Environmental and material limits of ISO 15156-3.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[metengr]

The ASME Code VIII Div.1 - Section II, Part D, limits the size of L7M (also B7M) to 2.1/2" diameter.
I do not understand why the reading the Section II, Part A, while for the L7M the limit is 2.1/2" diameter for the B7M in Table 2 "Mechanical Requirement" are stated also diameter up to 7" (but the allowable stress available are for 2.1/2" max.)!!

The reason is that for larger diameters, hardness and strength critera may not be met on a consistent basis. This is the reason why ASME Section II SC limits the allowable stresses to a maximum diameter for this material in pressure bumdary applications.

 

[gengi]

Dear SJones and Metengr,

thanks a lot for your replies!!

I would like to ask you some more things relating to your replies:

1) SJones, you suggested to take a look to ASTM A 453.
Do you mean bolting material A 453 660 Cl.B (Ni base )??

2) Metengr, about your reply, I understtod that although the ASME Section II, Part A lists, for the B7M material, sizes up to 7" the application of this material shall be limited to 2.1/2" due to the leak of allowable stresses.

In conclusion, for this matter
A) it is not possible to use size over 2.1/2" with B7M and L7M;
B) the hot dipped galvanizing does not work for this internal boltings in contact with sour enviroment;

C) if I use A 453 660 Cl.B (Ni base ) I may solve the problem but, I know that the price will rise up a lot since this material is very expensive.


I would ask to the Client to reduce the design pressure as long as the 2.1/2" boltings (in L7M or B7M) are suitable
since the operating pressure is very low and I think the Client increased the design pressure as safe measure in case of tube rupture........( we are talking about heat exchangers)..

I will be awaiting for your kind reply

thanks in advance

GENGI

 

[SJones]

1) I did not mean any specific grade or class other than one that has the desired mechanical properties; is compatible with the fluid and meets the requirements of ISO 15156-3. We do not know the specifics of the scenario that you are evaluating and, therefore, are not in a position to provide specific materials selection recommendations.



Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04