No replies to this topic

[Karthikram]

Rupture disk (RD) is provided on the compressor aftercooler on the cooling medium side (outlet line) for the protection against tube rupture scenario.

 

Required relief flowrate has been calculated considering upstream pressure PAHH and downstream as relieving pressure and relief flow is estimated based on assumption of two orifice during tube rupture as a conservative approach.

 

RD size follows the inlet pipe size as a common approach. Outlet piping has been designed based on required relief flowrate (verified Mach and Rho.v2) as per API 521, Jan 2007, section  7.2, table 12. The same has been specified in the Client specification to follow required relief rate for sizing.

 

Vendor has designed the RD based on required relief rate. Nominal size follows the inlet pipe size (general design approach) and provided free flowing area after rupture & other dimensions. Also, vendor has provided maximum flow through the rupture disk (rated flow/peak flow) based on free flowing area in vendor calculation sheet.

 

Client has requested to verify integrity of downstream piping based on peak flow based on Vendor data. Client knows that it is out of process/ piping design scope as per contract, however they insist to verify even though peak flow is expected for only few seconds & discuss the commercial issues later. They extend this comment for all compressor aftercoolers.

 

We performed FIV/AIV check for downstream piping and both fails.

FIV LOF > 1, need a piping support arrangement with natural frequency of 14 Hz to qualify the FIV LOF limit., which is difficult to achieve as per piping. FEA  study is recommended by third party.

AIV PWL is higher and LOF >1 which requires additional mitigation for the piping support.

Reaction force (provided by RD vendor) considering peak flow is almost double, current piping geometry and support structure is not designed for this load.

 

I don't have any queries reg. FIV/AIV calculation method.

 

Can you clarify the points below,

 

- Is it mandatory to design the RD downstream piping considering short term peak flow. Any technical justification to avoid such requirement.

(Evidence/confirmation from API 521, Client Process Design Criteria & Vibratec (FIV/AIV third party) is provided but client needs additional justification)

 

- Can someone clarify the following statement as per  API 521, Section 7.2.2 (highlighted in red).

 

"For rupture-disk or buckling-pin devices installed as a stand-alone device (i.e., not upstream of a pressure-relief valve), the required relieving rate is typically used to size the piping and the relief device. The design of downstream equipment, particularly scrubbers and thermal oxidizers, should consider the higher load that can be encountered based on the upstream pressure at which the relief device opens. The piping mechanical design should also consider this higher initial capacity."

 

As per my understanding, higher initial capacity/higher load refers to required relief flowrate considering Upstream PAHH condition (same as relief flow estimation mentioned above) and this is not the peak flow corresponds to free flowing area. Correct if am wrong

 

- Any previous experience on the similar subject. Any recommendations are provided in ASME/other design codes (SHELL DEP etc)

 

Appreciate your valuable inputs on this subject.

 

Thank you