Yes you can, but for the piggable sections they are not recommended as it restricts the type and size of pig you can use and can also lead to high stress concentrations.
Why do you ask?
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
Unsure of what location this is in but if it's in the US there's language in CFR 49:192.150 and CFR 49:195.120 outlining requirements for the passage of pigs. One of them references NACE SP0102-2010, Section 7. I'm not familiar with this document but I'm assuming it covers elbows and such for pigging.
